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Methods for determining the reliability of rea and p. Methods for improving the reliability of rea

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lec06.doc

DESIGN OF RADIO-ELECTRONIC GEOPHYSICAL INSTRUMENTS

Development and creation of geophysical instruments. Protection of the equipment from mechanical influence

Topic 6: HARDWARE PROTECTION

FROM MECHANICAL IMPACT AND INTERFERENCE

We are all smart when it comes to giving advice, but when it comes to avoiding mistakes, we are nothing more than children.

Menander. Greek poet and comedian. 4th century BC.

Because the advice is based on generalizations, and a miss is always specific.

Valery Samoilin. Ural geophysicist and radio engineer. 20th century

Under strength design is understood as the ability of the equipment to perform functions and save parameters after the application of mechanical influences. Sustainability design - the ability of REA to maintain functions and parameters in the process of mechanical influences.

The response, or the reaction of the structure to mechanical influences, is the transformation and transformation of the energy of mechanical excitation. These include mechanical stresses in structural elements, displacement of structural elements and their collisions, deformation and destruction of structural elements, changes in the properties and parameters of the structure.

Mechanical effects can lead to mutual movements of parts and assemblies, deformation of fasteners, load-bearing and other structural elements, and their collision. With insignificant mechanical influences, elastic deformations occur in structural elements that do not affect the performance of the equipment. An increase in load leads to the appearance of permanent deformation and, under certain conditions, to the destruction of the structure. Destruction can also occur at loads that are much lower than the limiting values of the static strength of materials, if the structure is subject to alternating loads.

Equipment failures are recoverable after removing or weakening the mechanical impact (changing the parameters of the components, the occurrence of electrical noise) and irrecoverable(breaks and short circuits of electrical connections, peeling of conductors of printed circuit boards, violation of fastening elements and destruction of supporting structures).

The transported electronic equipment during its operation is affected by vibrations, shock loads and linear accelerations. ^ Harmonic vibrations characterized by frequency, amplitude, acceleration. Impact loads are characterized by the number of single blows or their series (the maximum number of blows is usually specified), the duration of the shock impulse and its shape, the instantaneous speed upon impact, and the movement of the colliding bodies. Linear accelerations characterized by acceleration, duration, sign of the impact of acceleration.

The overloads arising from vibrations, shocks and accelerations are evaluated by the corresponding coefficients. To reduce the impact of vibrations and shocks, the equipment is mounted on shock absorbers or damping materials are used.

The impact of linear accelerations is equivalent to an increase in the mass of the equipment and, with a significant duration of exposure, requires an increase in the strength of the structure. Shock absorbers practically do not protect against linear overloads.

As the operating experience of the transported electronic equipment shows, vibrations have the greatest destructive effect on the structure. As a rule, the design of the apparatus, which has withstood the impact of vibration loads in a certain frequency range, withstands shock loads and linear accelerations with large values of the corresponding parameters.

The concept of vibration resistance and vibration strength. With regard to the design of REA, two concepts are distinguished: vibration stability and vibration strength.

^ Vibration resistance - the property of an object with a given vibration to perform the specified functions and keep the values of its parameters within the normal range. Vibration strength- strength at a given vibration and after its termination.

The impact of transport shaking consists of shocks and vibrations. The introduction of shock absorbers between the electronic equipment and the object as a medium that reduces the amplitude of the transmitted vibrations and shocks reduces the mechanical forces acting on the electronic equipment, but does not completely destroy them. In some cases, the resonant system formed with the introduction of shock absorbers entails the occurrence of low-frequency mechanical resonance, which leads to an increase in the amplitude of CEA oscillations.

The concept of rigidity and mechanical strength of the structure. When developing the REA design, it is necessary to ensure the required rigidity and mechanical strength of its elements.

^ Structural rigidity is the ratio of the acting force to the deformation of the structure caused by this force. Under structural strength understand the load that a structure can withstand without permanent deformation or failure. Increasing the strength of the REA design is associated with strengthening its structural basis, the use of stiffeners, locking of bolted joints, etc. Of particular importance is the increase in the strength of supporting structures and their components by pouring and enveloping methods. Filling with foam allows you to make the assembly monolithic with a slight increase in mass.

Design as an oscillatory system. In all cases, the formation of a mechanical oscillatory system should not be allowed. This applies to the fastening of mounting wires, microcircuits, screens and other parts included in the electronic equipment.

The main parameters of any design in terms of response to mechanical impacts are mass, stiffness and mechanical resistance (damping). When analyzing the effect of vibrations on the design of modules, the latter are represented as a system with lumped parameters, in which the mass of the product m, the stiffness element in the form of a spring, and the element of mechanical resistance in the form of a damper are specified, characterized by the parameters k and r, respectively.

If it is necessary to build more complex models, for example, a plate with modules installed on it, you can use the model shown in fig. 6.1.1, and with a sufficiently large number of cells, obtain a system model with distributed parameters.

Rice. 6.1.1.
The most important indicator of a mechanical system is the number of degrees of freedom that determine the position of the system in space at any time. The considered number of degrees of freedom of the design depends on the degree of its simplification, i.e., the model must to a certain extent reflect the real design and be simple enough for research.

In a system with one degree of freedom, the external force F(t) at each moment of time will be counteracted by the inertial forces of the mass F m , stiffness F k and damping Fr:

F(t) = F m + F r + F k . (6.1.1)

F m = m d 2 /dt 2 , F r = r d/dt, F k = k .

Where  is the displacement of the system from the equilibrium position under the influence of the force F(t).

Linear differential equation describing the state of the system at any time:

M d 2 /dt 2 + r d/dt + k F(t). (6.1.2)

The equation of natural oscillations of the system can be obtained by equating F(t) to zero, and we obtain (ignoring the initial phase):

  exp(-t) sin  o t

Where  o - initial oscillation amplitude;  \u003d g / (2m) - damping coefficient; o =
= 2f o - natural oscillation frequency of the system with damping.

In real mechanical systems, in each cycle of oscillations, energy losses occur - damping of oscillations.

The solution of the differential equation of forced oscillations of the system (at F(t) = F m sin t) has the form:

  exp(-r o t) sin  o t + A to sin t.

The first term describes natural oscillations of the system with a frequency, the second describes forced oscillations, where   and A в are the amplitudes of natural and forced oscillations, respectively. When the frequency of natural oscillations of the system is close to the frequency of the forced ones, the phenomenon of mechanical resonance occurs in the oscillatory system, which can lead to damage to the structure.

Depreciation designs CEA . One of the effective methods of increasing the stability of a structure, both transportable and stationary, to the effects of vibrations, as well as shock and linear loads, is the use of shock absorbers. The action of shock absorbers is based on the damping of resonant frequencies, i.e., the absorption of part of the vibrational energy. Equipment mounted on shock absorbers, in the general case, can be represented as a mechanical oscillatory system with six degrees of freedom: a set of coupled oscillations consisting of linear displacements and rotational oscillations along each of the three coordinate axes.

The damping efficiency is characterized by a dynamic or transmission coefficient, the numerical value of which depends on the ratio of the frequency of the active vibrations f to the frequency of the shock-absorbed system f o .

When developing a damping scheme, it is necessary to strive to ensure that the system has a minimum number of natural frequencies and that they are 2-3 times lower than the lowest frequency of the disturbing force.

For depreciated equipment, the natural frequency should be reduced as much as possible, and for non-depreciated equipment, on the contrary, it should be increased, bringing it closer to the upper limit of disturbing influences or exceeding it.

Shock absorber layouts. The design of a REA damping system usually begins with the choice of the type of shock absorbers and their layout. The choice of shock absorbers is made on the basis of the permissible load and the limiting values of the parameters characterizing the operating conditions. These parameters include: ambient temperature, humidity, mechanical stress, the presence of oil vapor in the atmosphere, diesel fuel etc.

Rice. 6.1.2.
The choice of the arrangement of shock absorbers depends mainly on the location of the equipment on the carrier and the conditions of dynamic action. On fig. 6.1.2 shows the main shock absorber layouts. Option " a " is quite often used for damping relatively small blocks. Such an arrangement of shock absorbers is convenient from the standpoint of the overall layout of the blocks at the facility. However, with this arrangement of shock absorbers, it is fundamentally impossible to get the center of gravity (CG) to coincide with the center of mass (CM) and not to get a rational system. The same can be said about the accommodation option " b ". Accommodation option " v " allows you to get a rational system, however, such an arrangement of shock absorbers is not always convenient when placed on an object. Placement type " G " and " d "is a kind of variant" v " and is used if the front panel of the unit is placed near the shock absorber located below. Placement of shock absorbers of the " e "is used in rack-mount equipment, when the height of the REA is much greater than the depth and width of the rack. To dampen rack vibrations around the x and y axes, two additional shock absorbers are placed on top of the rack.

Strength of structural elements. The mechanical strength of structural elements is checked by the methods of resistance of materials and the theory of elasticity for the simplest structures with a distributed and mixed load. In most practical cases, the designs of CEA parts have a more complex configuration, which makes it difficult to determine the stresses in them. In calculations, a complex part is replaced by its simplified model: a beam, a plate, a frame.

Beams include bodies of a prismatic shape, the lengths of which significantly exceed all other geometric dimensions of the structure. The ends of the beams are pinched (by welding, soldering), hingedly supported (installed in guides) or hingedly fixed (single screw connection). Plates are rectangular bodies, the thickness of which is small compared to the dimensions of the base. Such structures include printed circuit boards, walls of instrument casings, racks, panels and other similar structures. Rigid fastening of the edge of the plates is carried out by soldering, welding, clamping, screw connection; hinged fastening - by installing plates in guides, a female connector. Frame structures model multi-output components: microcircuits, relays, etc.

When designing a structure, perform:

Verification calculations, when the shape and dimensions of the part are known (revealed during design);

Design calculations, when the dimensions of dangerous sections are unknown and they are determined on the basis of the selected allowable stresses;

Calculations of allowable loads for known dangerous sections and allowable stresses.

When carrying out verification calculations for elastic vibrations, taking into account the direction of impact of vibrations, parts and assemblies with the greatest deformations are selected, calculation models are selected, natural frequencies are calculated, loads are determined and the obtained values are compared with the tensile strengths of the selected materials, if necessary, take decision to increase the strength of the structure.

To increase vibration strength, additional fastenings, ribs and stiffening reliefs, flanges, extrusions are introduced into the design of individual elements, materials with high damping properties, damping coatings are used.

External vibrational influences are often specified by a rather narrow frequency range. In properly designed equipment, the natural frequency f o of the structure should not be in the frequency spectrum of external influences. Although any structure has several values of natural frequencies, however, the calculation is performed only for the lowest values of f o , since the deformations of structures in this case will be maximum. If the lowest value of the natural frequency is included in the range of external influences, then the design is finalized in order to increase f o and exit from the frequency spectrum of external influences.

Structural rigidity is understood as the ability of a system (element, part) to withstand the action of external loads with deformations that do not allow a violation of its performance. Quantitatively, the stiffness is estimated by the stiffness coefficient  = P / , where P is the acting force;  maximum deformation. The design can be represented as a set of elements (parts), each of which works like a beam of a certain length and section, fixed at one or both ends. It is known that the stiffness of a beam clamped at one end, which is under the influence of a concentrated load, is calculated by the expression EF / l when the beam is in tension or compression and by the expression 3EJ / 1 3 when the beam is in bending (E is the modulus of elasticity of the beam material ; F - cross-sectional area; J - axial moment of inertia; l - beam length). The greater the modulus of elasticity of the material, the higher the rigidity of the beam. The rigidity of the structure depends on the length, shape and dimensions of the cross section of the beam.

The table shows the parameters of materials used for REA designs. The specific strength and stiffness of materials is calculated using the following expressions:

For metals:  p beats = [] p / ,  and beats = [] and 2/3 /  , E beats = E/

For non-metals:  p beats = [] p /,  and beats = [] and 2/3 / ,

Where p is the density of the substance.

Structural material parameters

Material	Brand	 r, MPa	E, GPa	 g/cm2	Specific strength and stiffness
Material	Brand	 r, MPa	E, GPa	 g/cm2	 ud 	 and beat	E beat
Carbon steel	St10	334	203	7,85	42,5	12	26
Carbon steel	St45	600	200	7,85	76,5	18	25,5
Alloy steel	39HGSA	490	198	7,85	62	,7	25,3
Aluminum alloys	AD-1	58	69	2,7	21	7,7	26
Aluminum alloys	B-95	275	69	2,8	96	21	24
magnesium alloys	MA2-1	255	40	1,8	142	27	23
magnesium alloys	MA2-8	275	40	1,8	154	29	22
copper alloys	L-63	294	103	8	35	11	12
copper alloys	Br-B2	392	115	8	48	13	14
titanium alloys	VT1-0	687	113	4,5	152	28	25
titanium alloys	VTZ-1	1176	113	4,5	218	41	25
Phenoplast	K-21-22	64	8,6	1,4	38	46	6,2
press material	AG-4S	245	34	1,8	273	136	19
Getinaks	II	98	21	1,4	49	70	15
Textolite	PTK	157	10	1,4	70	112	7
Fiberglass	VFT-S	245	-	1,85	180	132	-
Fluoroplast	4A	14	0,44	2,2	10	6,2	0,2
fiberglass	SWAM-ER	687	21	2	221	343	10,3
Styrofoam	PS-1	-	0,15	0,35	14	-	0,45

Vibrations directed orthogonally to the plane printed circuit board, alternately bend it and affect the mechanical strength of the microcircuits and components installed on it. If the components are considered rigid, then their conclusions will bend. Most component failures are due to broken solder connections between pins and the board. The most severe impacts take place in the center of the board, and for rectangular boards also when the element body is oriented along the short side of the board. Bonding components to the board greatly improves the reliability of solder joints. A protective lacquer coating 0.1...0.25 mm thick firmly fixes the components and increases the reliability of electronic equipment.

Mechanical stresses on soldered joints from the impact of vibrations can be reduced by: increasing the resonant frequencies, which makes it possible to reduce board deflection; an increase in the diameter of the contact pads, which increases the adhesion strength of the contact pad to the board; bending and laying the leads of the elements on the contact pad,
which increases the length and adhesion strength of the solder joint; by reducing the quality factor of the board at resonance by damping it with a multilayer varnish coating.

Experimental data on natural frequencies of printed circuit boards

PP dimensions, mm	35	70	140	PP thickness, mm
PP dimensions, mm	Natural frequency, Hz			PP thickness, mm
25	2780	2070	2260	1,0
25	5100	3800	3640	1,5
50	1400	690	520	1,0
50	2600	1270	955	1,5
75	1120	450	265	1,0
75	2030	830	490	1,5

The table above shows the experimental data on the natural frequencies of the PP depending on their linear dimensions. The material of the boards is fiberglass, the mounting of the elements is two-sided, the fixation of the board is around the entire perimeter. In order for natural frequencies to exceed the limits of the upper frequency range of external influences, it is necessary to increase the thickness or decrease the width (length) of the board.

Fixing fasteners. When exposed to vibrations, it is possible to unscrew the fasteners, to prevent which fixators are introduced, friction forces are increased, fasteners are installed on the paint, etc. When choosing methods for fixing fasteners, the following considerations should be taken into account: impacts; the speed of the connection, its cost; the consequences of a connection failure; life time.

The possibility of replacing worn or damaged parts should be taken into account, instead of screw pairs, quick-coupling elements should be used: hinges, latches, pawls, etc. The bolts should be oriented head up so that when unscrewing the nut, the bolts are in the installation place. It is recommended to use several large fasteners instead of a large number of small ones. The number of turns required to tighten or loosen the screw must be at least 10.

Service life of the structure. Vibrations in structures cause alternating stresses and structures can collapse under loads that are much lower than the ultimate static strength of materials due to the appearance of microcracks, the growth of which is influenced by the features of the crystal structure of materials, stress concentration at the corners of microcracks, and environmental conditions. As microcracks develop cross section parts are weakened and at some point reaches a critical value - the structure is destroyed.

If the mass of the product is not a critical factor, then the structure is strengthened, using materials with a margin, avoiding the introduction of holes, overcuts, welds, carry out calculations of structures by the worst case method.

The structural integrity of the equipment and protection against mechanical influences is provided by the structural material, which must satisfy the specified mechanical and physical properties, have ease of processing, corrosion resistance, low cost, have a maximum strength-to-weight ratio, etc. Depending on the complexity, the supporting structure is made in the form of a single part or a composite one, including several parts combined into a single structure by detachable or one-piece connections. In modern equipment with the use of microcircuits, the mass of supporting structures reaches 70% of the total mass of REA. The main way to reduce the weight of products is to lighten the load-bearing structures while simultaneously meeting the requirements of strength and rigidity.

The service life of a structure under vibration exposure is determined by the number of cycles to destruction that the structure can withstand at a given level of mechanical load. The fatigue characteristics of materials are revealed on a group of specimens under an alternating repetitive load.

^ 6.2. Protecting EQUIPMENT from interference

The reliability and reliability of the operation of electronic equipment and systems depend on their noise immunity in relation to external and internal, random and regular interference. From right decision The tasks of ensuring the noise immunity of REE elements and assemblies depend both on the terms for the development of manufacturing and commissioning of REE, and its normal functioning during operation.

The nature of interference. Interference for the equipment is an external or internal influence that leads to the distortion of analog or discrete information in the product during its storage, conversion, processing or transmission. Interference - a signal not provided for in the design of REA, capable of disrupting its functioning. Since the signals in electronic equipment are electrical in nature, it is necessary to take into account interference of the same nature as the most likely sources of information distortion when designing. Interference can be voltages, currents, electric charges, field strength, etc. Interference sources are diverse in physical nature and are divided into internal and external.

Internal interference occurs inside the operating equipment. Sources of electrical interference are mainly power supplies and current distributing circuits. Sources of magnetic interference are transformers and chokes. In the presence of ripples in the output voltage of the secondary power sources of the power distribution circuit, clocking and synchronizing circuits should be considered as sources of electromagnetic interference. Significant interference is created by electromagnets, electric motors, relays and electromechanical devices. Internal interference is also interference from the mismatch of the wave impedances of communication lines with the input and output impedances of the modules that these lines connect, as well as interference that occurs on earth buses.

External interference is understood as interference from the power supply network, welding machines, brush motors, transmitting electronic equipment, etc., as well as interference caused by static electricity discharges and atmospheric phenomena. The effect on the equipment of external interference by physical nature is similar to the effect of internal interference.

Interference receivers are highly sensitive amplifiers, communication lines, magnetic elements. Interference penetrates the equipment directly through wires or conductors (galvanic interference), through an electrical (capacitive interference), magnetic (inductive interference) or electromagnetic field. Numerous conductors that are part of any equipment can be considered as receiving and transmitting antenna devices that receive or emit electromagnetic fields.

Galvanic coupling occurs as a result of the flow of currents and voltage drops on electrical connections common in power circuits. Therefore, the conductors that combine the modules into single system, should be as short as possible, and their cross sections as large as possible, which leads to a decrease in the active resistance and inductance of the wires. A radical way to eliminate galvanic interference is to eliminate the circuits through which the combined supply and ground currents pass, both noise-sensitive circuits and relatively powerful circuits.

The fight against interference is becoming increasingly important for the following reasons.

1. The energy level of information signals tends to decrease, and the energy level of external interference is continuously increasing.

2. An increase in the mutual influence of the elements due to a decrease in the overall dimensions of the active elements and communication lines between them, as well as an increase in the density of their placement.

3. An increase in the level of interference due to the complication of systems and the expansion of the use of external devices with a large number of electromechanical components.

4. Implementation of REA in all spheres of human activity.

Rice. 6.2.1. Classification of interference in REA
Interference classification. Interference can be classified according to pointing reason, the nature of the manifestation and distribution pathways(Fig. 6.2.1).

The main reasons causing distortions of signals during their passage through the REA circuits are as follows:

A) reflections from unmatched loads and from various inhomogeneities in communication lines;

B) edge deterioration and delays that occur when loads with reactive components are turned on;

C) delays in the line caused by the finite speed of signal propagation;

D) crosstalk;

E) interference from external electromagnetic fields.

The degree of influence of each listed factors on signal distortion depends on the characteristics of communication lines, logical elements and signals, as well as on the design of the entire system of elements and connections.

Ways to reduce interference. The electrical combination of logical and other elements of REA is carried out by connections of two types:signal and food chains. Information is transmitted via signal connections in the form of voltage and current pulses. Power rails are used to supply energy to the elements from low-voltage direct voltage sources.

Interference in signal conductors. Connections between REE elements are performed in various ways: for relatively slow devices - in the form of printed or hanging conductors; in devices with increased operating speeds - in the form of printed strip lines, "twisted pairs" (bifilars).

When grouping elements into nodes and blocks, a large number of electrically " short"and electrically" long» connections.

Electrically "short" is called a communication line, the propagation time of the signal in which is much less than the leading edge of the pulse transmitted along the line. The signal reflected from unmatched loads in this communication line reaches the source before the input pulse has time to change. The properties of such a line can be described by lumped resistances, capacitance and inductance.

An electrically "long" communication line is characterized by a signal propagation time that is much longer than the pulse front. In this line, the signal reflected from the end of the line arrives at its beginning after the end of the pulse front and distorts its shape. Such lines should be considered as lines with distributed parameters.

In ICs, cells and communication modules, as a rule, electrically "short" lines. The larger REA units are mostly electrically "long" lines. The share of "long" links increases with the increasing complexity of the equipment.

Interference in "short" communications. When analyzing signal transmission processes, an electrically “short” communication line can be represented as an equivalent circuit (Fig. 6.2.2) containing lumped inductance L and capacitance C (ohmic resistance is neglected), which “pull” the signal edges and thereby create response delays subsequent schemes.

Rice. 6.2.2.
Depending on the geometric dimensions of the line sections, their length, dielectric properties of insulating materials, one or another line parameter may prevail and have a greater effect on signal transmission processes than all the others. To reduce the delay in lines with an inductive nature of the coupling, it is necessary to increase the input resistance of the element E 2, with a capacitive nature - to reduce the output resistance of the element E 1.

Interference when connecting elements with "long" links. An electrically "long" communication line is considered as a homogeneous line with a distributed capacitance C o and inductance L o . Transient processes in such lines depend on the nature of the voltage drop u in at the line input and the ratio of the wave impedance of the line z 0, the output resistance z r of the pulse generator and the input resistance z n of the element loaded at the end of the line (Fig. 6.2.3).

Rice. 6.2.3.
If a line with wave resistance z 0 is loaded with resistance z n, and z 0 \u003d z n, then such a line is called agreed, if z 0 z n, the line is called inconsistent. In this case, the voltage wave, having reached the end of the line, is reflected from it. The reflected wave, having reached the beginning of the line, decays at z g =z 0 . If z g z 0 , the wave is again reflected from the beginning of the line.

The process of successive reflection of the voltage wave from both ends of the communication line goes with attenuation and continues until the amplitude of the reflected wave decreases to zero. The reflected voltage waves are superimposed on the incident ones, and as a result, the shape of the input voltage can be significantly distorted. Similar phenomena occur with the current wave. Reflections of voltage and current waves can be not only from unmatched loads at the ends of the lines, but also from various inhomogeneities in herself.

It is known that only with full matching of both lines, the induced voltage pulse has a minimum amplitude and duration. The mismatch of the receiver line at one of its ends leads to an increase in the amplitude and duration of the induced interference.

Methods for wiring "long" communication lines. In high-speed systems, in which the delay is determined only by the delays in the communication circuits, the main problem can be the way the lines are routed between individual ICs. Currently, there are three ways of wiring: radial, with intermediate taps, combined.

At radial wiring method each load IC is connected to the signal source IC by an individual connection, and the signal source IC must have an output impedance equal to z 0 /n, where n is the number of ICs loaded on it. Large n will require an IC signal source with unattainably low output impedance. Another disadvantage of the radial method is the need for a separate communication line for each load. Therefore, the radial method is only recommended for a small number of loads.

At wiring method with intermediate taps Load ICs are connected to the link-backbone and further to the signal source IC via short conductors, while the load ICs must have high input impedances, otherwise they will overload the communication lines.

^ Combined method provides coordination at any point of the communication line by wiring signals to loads placed in different directions. In this case, the number of conductors is less than with the radial method, and the output impedance of the signal source is allowed to be relatively high. If there are only two loads on the communication line, then the signal source IC can be marked at any point along it.

Pickups on food chains and methods for their reduction. When using a single voltage source, power is supplied to the elements using two conductors: forward and reverse. Often it is necessary to apply voltage to the elements from several sources with different ratings. In this case, to reduce the number of power buses, the return conductors are combined into one bus, which is connected to the product case and is called the bus " land". In a static state, stationary currents flow through the power circuits.

To reduce interference associated with the voltage drop on the power and ground buses and transients in them, use various methods.

Application of individual smoothing capacitors (ISK). The ISC is installed between the power and ground buses directly near the points of connection of electronic devices to these buses. The ISC is, as it were, an individual power source for the circuit, as close as possible to it physically. In microelectronic equipment, two types of ISCs are used, installed directly at each microcircuit and installed on a group of microcircuits within one cell, module.

The first type of ISC is designed to smooth out impulse noise at the moment of switching the microcircuit due to the localization of the circuit for the flow of current surges in the circuit of the microcircuit - ISC. Ceramic capacitors, which usually have a low self-inductance, are used as such ISCs. The capacity of the ISC is chosen based on the condition of equality of the charge accumulated by the capacitor during the switching of the microcircuit, the charge carried by the surge of current during the switching of the element.

The second type of ISC, installed on a group of microcircuits, is designed to compensate for current surges in the power supply system. These are usually high-capacity electrolytic capacitors, which ensure the exclusion of resonant phenomena in power circuits.

Rice. 6.2.4.
Noise filters. An effective circuit means of attenuating external noise on power networks is the use of noise suppression filters.

Filters are characterized by a cutoff frequency and a filtering coefficient equal to the ratio of the signal at the input and output of the filter. Knowing the frequency spectrum of the useful signal and interference, and given a certain attenuation of the interference (ideally, to zero), the corresponding filter circuits are designed.

Mains filters are designed to transmit to the output (to the device) only the frequency of the mains voltage and suppress interference from the power supply. To protect equipment from surges, gas dischargers, varistors, zener diodes, and fuses are usually introduced into the network filter circuit.

Using a metal sheet as a "ground". This method is applicable for elements of the second level of the REA constructive hierarchy (subunits, blocks, panels) and consists in installing a relatively thick metal sheet into these structural elements, to which the return wires from all fixed cells or modules are soldered.

Use of solid metal spacers as power rails. This method is applicable in the case of using multilayer printed circuit boards for ultra-fast REE devices. In such boards, individual layers are manufactured with a maximum large area metal and use them as power rails, these layers are placed inside a multilayer board. When using solid metal layers, the intrinsic inductive resistance of the power buses, the common areas of current flow of various elements are significantly reduced, and the mutual capacitance between the power buses is increased.

The use of screens in REA. When powerful signals pass through communication circuits, the latter become sources of electromagnetic fields, which, crossing other communication circuits, can induce additional interference in them. Powerful industrial installations, transport communications, motors, etc. can also be sources of electromagnetic interference. Devices that are sensitive to static magnetic fields (for example, open-circuit magnetic elements) can operate erratically even in weak fields such as the Earth's magnetic field.

Screens are included in the design to attenuate the undesirable disturbing field in a certain limited volume to an acceptable level or to localize, where possible, the action of the field source. There are two options for protection. In the first case, the shielded equipment is placed inside the shield, and the source of interference is outside it, in the second, the source of interference is shielded, and the equipment protected from interference is located outside the shield. The first option is usually used for protection against external interference, the second - internal.

In REA, the functions of screens are most often performed by casings, panels and covers of devices of blocks and racks, when choosing materials and calculating the thickness of which, in addition to considerations of shielding efficiency, it is necessary to take into account the requirements for ensuring mechanical strength, rigidity, and reliability of the connection of individual elements.

Holes and gaps in shields reduce shielding effectiveness and should be avoided or minimized. However, it is impossible to get rid of them completely. Holes are introduced into the casing for the installation of connectors, controls, indications, and ensuring normal thermal conditions. The effectiveness of the screen will not deteriorate if holes are made in its design, the maximum dimensions of which do not exceed 1/2 of the minimum wavelength of the screened signal. To prevent noise from penetrating through the ventilation holes, a metal mesh can be fixed on the inner surfaces of the casings with holes.

According to the principle of operation, electrostatic, magnetostatic and electromagnetic shielding are distinguished.

Parts of the chassis and frames, sheathing of racks, panels, subunits, cassettes, special sheet metal gaskets on the mounting side of boards, blocks, subunits, etc. can serve as screens.

In order to improve the screening of circuits that are particularly sensitive to interference (for example, for transmitting clock pulses), signal and grounded shield conductors alternate on both sides of the printed circuit boards in such a way that a grounded line on the other side of the board is always located opposite the signal line passing from one side of the board. In this case, each signal line is surrounded by three ground lines, resulting in not only effective shielding of the signal line from external interference, but also provides a waveguide-like circuit from the source to the load for the useful signal.

Shielding is also applied to the wires of the input and output lines, and in most cases it is sufficient to shield only the input circuit. To eliminate galvanic ground interference, wire shields must be grounded at one point. When printing transmission lines, shielding traces are introduced that are switched with a zero-potential bus and perform the functions of wire screens.

magnetostatic shielding. The task of shielding comes down to reducing or completely eliminating the inductive coupling between the source and receiver of interference. If the magnetic flux crosses the circuit formed by the conductor, then noise is induced in the circuit. To completely eliminate or reduce the interference voltage induced in the circuit, it is necessary:

Place the outline on the screen;

Orient it so that the magnetic field lines of the field do not cross the contour, but pass along it;

Reduce the area of the contour.

Magnetic screens are made from both ferromagnetic and non-magnetic metals. Ferromagnetic materials with high magnetic permeability have low magnetic resistance, as a result of which the magnetic field lines will be shunted by the shield material, and the space inside the shield will not be affected by the magnetic field. Magnetic shielding is the more effective, the greater the magnetic permeability of the screen and the thicker the screen. When choosing a screen material, it must be remembered that the magnetic permeability decreases with increasing field frequency, and this affects the screening efficiency. Ferromagnetic materials effectively protect equipment in the frequency range from 0 to 10 kHz.

The action of a screen made of non-magnetic metal is based on the displacement of an external magnetic field from the internal space of the device by the screen material. An external alternating magnetic field creates inductive eddy currents in the screen, the magnetic field of which is directed towards the external field inside the screen. For screens made of non-magnetic metals, the screening efficiency increases with an increase in the thickness and conductivity of the screen material. A magnetic field with a frequency above 10 MHz is shielded quite reliably if a copper or silver coating no more than 100 microns thick is applied to the dielectric casing. The thickness of a non-magnetic shield can be several times greater than the thickness of a ferromagnetic one, which provides the same attenuation at a fixed frequency. The use of ferromagnetic material can significantly reduce the weight of the screen. When shielding a magnetic field, grounding the shield is not necessary, since it does not affect the quality of the shielding.

However, before constructing a screen, it is necessary to provide for all measures in order to get rid of interference in a simpler and cheaper way. For example, a decrease in the area of the contour crossed by the magnetic field lines is obtained by laying the signal conductors directly along the grounded mounting panels of the modules.

Electromagnetic shielding covers the frequency range from 1 kHz to 1 GHz. The action of the electromagnetic screen is based on the reflection of electromagnetic energy at the dielectric-screen boundaries and its attenuation in the thickness of the screen. Attenuation in the screen is explained by thermal losses due to eddy currents in the screen material, reflection is due to a discrepancy between the wave parameters of the screen material and the environment. For the lower limit of the frequency range, reflection is of paramount importance, for the upper limit - the absorption of electromagnetic energy.

Electromagnetic shielding is performed by both non-magnetic and magnetic metals. Non-magnetic metals of high conductivity can be effectively used in the low-frequency part of the spectrum, ferromagnetic materials of high magnetic permeability and electrical conductivity - in the entire frequency range of the electromagnetic field. The thickness of the screen should be as large as possible. For frequencies below 1 MHz, copper and aluminum screens give good results, and for frequencies above 1 MHz, steel screens. However, the best results can be obtained by using multilayer screens - successively alternating layers of magnetic and non-magnetic metals. Various options for layer materials are possible: copper - permalloy - copper, permalloy - copper, copper - steel - copper, etc. The introduction of air gaps between the layers (20-40% of the total thickness of the screen) will improve the shielding efficiency. When protecting the equipment from an external field, a material with a low magnetic permeability is placed outside, with a high one - inside. If the screen protects the source of the electromagnetic field, then the material with low magnetic permeability should be the inner layer, and the high one should be the outer one.

Non-magnetic screen materials

Material	Density, kg/m 3	Resistance, Ohm mm 2 /m	Relative Price
Aluminum	2700	0,028	0,29
Brass	8700	0,06	0,85
Copper	8890	0,0175	0,6
Magnesium	1740	0,042	0,36
Silver	10500	0,018	34,0
Zinc	7140	0,059	0,17

The tables show the properties of non-magnetic and magnetic metals. Of non-magnetic materials, in terms of minimum cost and weight, magnesium has the best properties, but it easily corrodes, and the resulting oxide layer worsens the contact of the screen with the body of the product. Zinc is cheaper than copper, has a lower density, but is soft. Brass in its parameters occupies a middle position in a number of materials, but due to its excellent anti-corrosion properties and the stability of electrical contact resistance, it can be recommended for wide use as a screen material.

Ferromagnetic shield materials

In REA, screens made of steel and permalloy have become widespread. Steel screens with a low initial magnetic permeability provide small but constant screening both at low and at frequencies up to ten kilohertz. Permalloy screens with high initial permeability provide effective screening, but in a narrow frequency range from zero to several hundred hertz. With increasing frequency, screen eddy currents increase, which displace the magnetic field from the thickness of the screen and reduce its magnetic conductivity, and this affects the screening efficiency.

About noticed typos, errors and suggestions for additions: davpro@yandex.ru.

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11.5. Dust protection

Dust is a mixture of solid particles of small mass, which is suspended in the air. Distinguish between natural or natural dust, which is always present in the air, and technical dust, which is a consequence of equipment wear, material processing, fuel combustion, etc.

At relative air humidity above 75% and normal temperature, an increase in the number of dust particles, their coagulation is observed, and the probability of dust attraction to stationary surfaces increases. At low humidity, dust particles are electrically charged, non-metallic - positively, metallic - negatively. The charge of particles most often arises due to friction.

Air pollution with dust reduces the reliability of REA operation. Dust, getting into lubricants and sticking to the sliding surfaces of parts of electromechanical units, leads to their accelerated wear. Under the influence of dust, the parameters and characteristics of magnetic tapes, diskettes, magnetic heads change, the magnetic layer is scratched and becomes unusable. Dust in the contact gaps prevents the relay contacts from closing.

The dust deposited on the surface of some metals is dangerous because of its hygroscopicity, since dust significantly increases the corrosion rate even at relatively low humidity. Dust with absorbed acid solutions quickly destroys even very good paints. In tropical countries, dust is often the cause of mold growth.

Dust accumulated on the surface of the components during long-term operation reduces the insulation resistance, especially in conditions of high humidity, leads to the appearance of leakage currents between the terminals, which is very dangerous for microcircuits. The dielectric constant of dust is higher than the dielectric constant of air, which determines the overestimation of the capacitance between the terminals of the components and, as a result, an increase in capacitive noise. Settling dust reduces the cooling efficiency of the product, forms on the surfaces of printed circuit boards that are not protected by a varnish coating, conductive jumpers between the conductors.

Dust tightness of REA or its individual devices can be achieved by installing them in hermetically sealed cases. However, this increases the cost of REA and worsens temperature regime work. If the REA housing is made with perforations, dust along with air will penetrate inside the REA naturally or together with air flows from fans. It is possible to reduce the ingress of dust into the electronic equipment by installing fine-mesh nets and dust filters on the ventilation openings.

11.5.1. Equipment sealing

CEA sealing is a reliable means of protection against exposure to dust, humidity and harmful environmental substances.

The modules of the first level structure are protected by coating with varnish, pouring with epoxy resin, impregnation, especially winding products, crimping with sealing compounds based on organic (resins, bitumens) or inorganic (aluminophosphates, metal metaphosphates) substances. Sealing with compounds improves the electrical and mechanical characteristics of the module. However, the low thermal conductivity of most compounds impairs heat dissipation and makes repair impossible.

Complete sealing by enclosing the product in an airtight enclosure is the most effective way protection, but also expensive. In this case, there is a need to develop special cases, methods for sealing external electrical connectors, control and indication elements. The walls of the products to be sealed must withstand significant forces due to the difference in pressure inside and outside the product. As a result of increasing the rigidity of the structure, its mass and dimensions increase.

There is a wide variety of sealing methods. Elastic sealing gaskets are widely used for all structural elements along the perimeter of the product. The passage of air through the seals when the gasket is compressed by 25 ... 30% of its original height occurs only due to diffusion. As the material of the gaskets, rubber is used, which has high elasticity, pliability and the ability to penetrate into the smallest depressions and irregularities. Moisture will penetrate all organic materials over time, so products with organic gaskets only provide water vapor protection for a few weeks.

The constancy of relative humidity within certain limits inside the sealed apparatus can be achieved by introducing substances into the product that actively absorb moisture. Similar substances are silica gel, calcium chloride, phosphoric anhydride. They absorb moisture up to a certain limit. For example, silica gel absorbs about 10% moisture of its dry weight.

In special cases, copper is used as gasket materials and stainless steel with aluminum or indium coating. Such gaskets are most often made tubular with an outer diameter of 2-3 mm with a wall thickness of 0.1-...0.15 mm. The pressing force during sealing with metal gaskets is 20…30 kg per 1 cm of the gasket length.

With stringent requirements for the tightness of the body of the product, sealing is performed by welding or soldering around the entire perimeter of the body. The design of the body of the product must allow repeated depressurization / sealing operations. A gasket made of heat-resistant rubber is installed in the recess of the body, on which tinned steel wire is laid, which is soldered to the body, forming a seam. When the product is depressurized, the seam is heated, and the solder is removed along with the wire.

During sealing, the internal volume of the sealed equipment is filled with an inert gas (argon or nitrogen) with a slight overpressure. Gas is pumped into the housing through valves-tubes with subsequent sealing. Nitrogen purge ensures that the body cavity is free of water vapor.

Control and indication elements are sealed with rubber covers, membranes, electrical connectors are installed on gaskets, filled with compounds.

The choice of sealing method is determined by the operating conditions, the materials and coatings used, and the requirements for electrical installation. The final decision on the choice of sealing method is made after full-scale tests of REA in humidity chambers.

Control questions

1. Influence of climatic factors on the design.

2. List the types of RES protection.

3. Thermal mode of operation of the equipment.

4. Ways to protect against dust exposure.

5. What is equipment sealing used for?

Chapter 12 Protection against mechanical influences

12.1. Types of mechanical effects on REA

Mechanical impacts on REA appear under the action of external loads (vibrations, shocks, accelerations, acoustic noise) and can occur both in a working REA, if it is installed on a moving object, and during its transportation in a non-working state.

Mechanical impacts occur in a working REA if it is installed on a mobile object, or only when it is transported in a non-working state, as in the case of stationary and some types of portable REA. The amount of energy transferred determines the level and nature of the design change. Permissible levels of mechanical change in the design are determined by its strength and resistance to mechanical stress.

Under strength design is understood as the ability of the equipment to perform functions and maintain parameters after the application of mechanical influences. Sustainability design - the ability of REA to maintain functions and parameters in the process of mechanical influences.

The response, or reaction, of a structure to mechanical influences is the transformation and transformation of the energy of mechanical excitation. These include mechanical stresses in structural elements, displacement of structural elements and their collisions, deformation and destruction of structural elements, changes in properties and design parameters.

Mechanical effects can lead to mutual movements of parts and assemblies, deformation of fasteners, load-bearing and other structural elements, and their collision. With insignificant mechanical impacts, elastic deformations occur in structural elements that do not affect the performance of the equipment. An increase in load leads to the appearance of permanent deformation and, under certain conditions, to the destruction of the structure. Destruction can also occur at loads that are much lower than the ultimate values of the static strength of materials if the structure is subject to alternating loads.

CEA installed on mobile objects is affected by vibrations, shock loads and linear accelerations during its operation. Harmonic vibrations characterized by frequency, amplitude, acceleration. Impact loads are characterized by the number of single blows or their series (the maximum number of blows is usually specified), the duration of the shock impulse and its shape, the instantaneous speed upon impact, and the movement of the colliding bodies. Linear accelerations characterized by acceleration, duration, sign of the impact of acceleration. The overloads arising from vibrations, shocks and accelerations are evaluated by the corresponding coefficients. To reduce the impact of vibrations and shocks, the equipment is mounted on shock absorbers or damping materials are used.

The impact of linear accelerations is equivalent to an increase in the mass of the equipment and, with a significant duration of exposure, requires an increase in the strength of the structure.

12.2. The concept of vibration resistance and vibration strength

With regard to the design of REA, two concepts are distinguished: vibration stability and vibration strength.

Vibration resistance- the property of an object with a given vibration to perform the specified functions and keep the values of its parameters within the normal range. Vibration strength- strength at a given vibration and after its termination.

The concept of rigidity and mechanical strength of the structure. When developing the REA design, it is necessary to ensure the required rigidity and mechanical strength of its elements.

Structural rigidity is the ratio of the acting force to the deformation of the structure caused by this force. Under structural strength understand the load that a structure can withstand without permanent deformation or failure. Increasing the strength of the REA design is associated with strengthening its structural basis, the use of stiffeners, locking of bolted joints, etc. Of particular importance is the increase in the strength of supporting structures and their components by pouring and enveloping methods. Filling with foam allows you to make the assembly monolithic with a slight increase in mass.

Design as an oscillatory system. In all cases, the formation of a mechanical oscillatory system should not be allowed. This applies to the fastening of mounting wires, microcircuits, screens and other parts included in the electronic equipment.

Rice. 12. Vibrational model of a mechanical system

The main parameters of any structure in terms of response to mechanical impacts are mass, stiffness and mechanical resistance (damping). When analyzing the influence of vibrations on the design of modules, the latter are represented as a system with lumped parameters, in which the mass of the product m, the stiffness element in the form of a spring, and the element of mechanical resistance in the form of a damper are specified, characterized by the parameters k and r, respectively, .

When the frequency of natural oscillations of the system is close to the frequency of forced oscillations, the phenomenon of mechanical resonance occurs in the oscillatory system, which can lead to damage to the structure.

Depreciation of REA design. One of the effective methods for increasing the stability of a structure, both transportable and stationary, against vibrations, as well as shock and linear loads, is the use of shock absorbers. The action of shock absorbers is based on the damping of resonant frequencies, i.e., the absorption of part of the vibrational energy. Equipment mounted on shock absorbers, in the general case, can be represented as a mechanical oscillatory system with six degrees of freedom: a set of coupled oscillations consisting of linear displacements and rotational oscillations along each of the three coordinate axes.

When developing a damping scheme, it is necessary to strive to ensure that the system has a minimum number of natural frequencies and that they are 2–3 times lower than the lowest frequency of the disturbing force.

Shock absorber layouts. The design of a REA damping system usually begins with the choice of the type of shock absorbers and their layout. The choice of shock absorbers is made on the basis of the permissible load and the limiting values of the parameters characterizing the operating conditions. These parameters include: ambient temperature, humidity, mechanical loads, the presence of oil vapors, diesel fuel, etc. in the atmosphere.

Rice. 13. Shock absorber layouts

The choice of the arrangement of shock absorbers depends on the location of the equipment on the carrier and the conditions of dynamic impact. On fig. 13 shows the basic layout of shock absorbers.

Option " a " is quite often used for damping relatively small blocks. Such an arrangement of shock absorbers is convenient from the standpoint of the overall layout of the blocks at the facility. However, with this arrangement of shock absorbers, it is fundamentally impossible to get the center of gravity (CG) to coincide with the center of mass (CM) and not to get a rational system. The same can be said about the accommodation option " b ". Accommodation option " v " allows you to get a rational system, however, such an arrangement of shock absorbers is not always convenient when placed on an object. Placement type " G " and " d "is a kind of variant" v " and is used if the front panel of the unit is placed near the shock absorber located below. Placement of shock absorbers of the " e "is used in rack-mount equipment, when the height of the REA is much greater than the depth and width of the rack. To dampen rack vibrations around the x and y axes, two additional shock absorbers are placed on top of the rack.

Strength of structural elements. The mechanical strength of structural elements is checked by the methods of resistance of materials and the theory of elasticity for the simplest structures with a distributed and mixed load. In most practical cases, the designs of electronic equipment parts have a more complex configuration, which makes it difficult to determine the stresses in them. In calculations, a complex part is replaced by its simplified model: a beam, a plate, a frame.

Beams include bodies of a prismatic shape, the lengths of which significantly exceed all other geometric dimensions of the structure. The ends of the beams are pinched (by welding, soldering), hingedly supported (installed in guides) or hingedly fixed (single screw connection). Plates are rectangular bodies, the thickness of which is small compared to the dimensions of the base. Such structures include printed circuit boards, instrument enclosure walls, racks, panels, and other similar structures. Rigid fastening of the edge of the plates is carried out by soldering, welding, clamping, screw connection; hinged fastening - by installing plates in guides, female connector. Multi-output components are modeled by frame structures: microcircuits, relays, microprocessors, FPGAs.

When designing a structure, modeling is performed, in which the following are carried out:

- verification calculations, when the shape and dimensions of the part are known (revealed during design);

- design calculations, when the dimensions of dangerous sections are unknown and they are determined on the basis of the selected allowable stresses;

– calculations of allowable loads for known dangerous sections and allowable stresses.

When carrying out verification calculations for elastic vibrations, taking into account the direction of vibration exposure, parts and assemblies with the greatest deformations are selected, calculation models are selected, natural frequencies are calculated, loads are determined and the obtained values are compared with the strength limits of the selected materials, if necessary, a decision is made to increase the strength of the structure.

To increase vibration resistance, additional fastenings, ribs and stiffening reliefs, flanges, extrusions are introduced into the design of individual elements, materials with high damping properties, damping coatings are used.

where Р is the acting force; δ is the maximum deformation.

The rigidity of the structure depends on the length, shape and dimensions of the cross section of the beam.

Vibrations directed orthogonally to the plane of the printed circuit board alternately bend it and affect the mechanical strength of the microcircuits and components installed on it. If the components are considered rigid, then their terminals will bend. Most component failures are due to broken solder connections between pins and the board. The most severe impacts occur in the center of the board, and for rectangular boards also when the element body is oriented along the short side of the board. Bonding components to the board greatly improves the reliability of solder joints. A protective lacquer coating 0.1…0.25 mm thick firmly fixes the components and increases the reliability of electronic equipment.

Mechanical stresses on solder joints caused by vibrations can be reduced by: increasing the resonant frequencies, which reduces board deflection; an increase in the diameter of the contact pads, which increases the adhesion strength of the contact pad to the board; bending and laying the leads of the elements on the contact pad, which increases the length and adhesion strength of the solder joint; by reducing the quality factor of the board at resonance by damping it with a multilayer varnish coating.

Fixing fasteners. When exposed to vibrations, it is possible to unscrew the fasteners, to prevent which fixators are introduced, friction forces are increased, fasteners are installed on the paint, etc. When choosing methods for fixing fasteners, the following considerations should be taken into account: ensuring the strength of the connection under given loads and climatic influences; the speed of the connection, its cost; the consequences of a connection failure; life time.

The possibility of replacing worn or damaged parts should be taken into account, instead of screw pairs, quick-coupling elements should be used: hinges, latches, dogs, etc. The bolts should be oriented with their heads up so that when unscrewing the nut, the bolts are in the installation place. It is recommended to use a few large fasteners instead of a large number of small ones. The number of turns required to tighten or loosen the screw must be at least 10.

Service life of the structure. Vibrations in structures cause alternating stresses and structures can collapse under loads that are much lower than the ultimate static strength of materials due to the appearance of microcracks, the growth of which is influenced by the features of the crystal structure of materials, stress concentration at the corners of microcracks, and environmental conditions. As microcracks develop, the cross section of the part weakens and at some point reaches a critical value - the structure collapses.

If the mass of the product is not a critical factor, then the structure is strengthened using materials with a margin, the introduction of holes, notches, welds is avoided, and the calculations of structures are carried out using the worst case method.

Protection against mechanical impacts is provided by a structural material that must satisfy the specified mechanical and physical properties, be easy to process, corrosion resistance, low cost, have the maximum strength-to-weight ratio, etc. Depending on the complexity, the supporting structure is made in the form of a single part or a composite , which includes several parts combined into a single design by detachable or one-piece connections. The main way to reduce the mass of products is to lighten the load-bearing structures while simultaneously meeting the requirements of strength and rigidity.

The problems of increasing the mechanical strength of structures should be solved taking into account the optimization of the placement of electronic equipment in the carrier compartments.

Control questions

1. List the types of mechanical effects on REA.

2. Give the concepts of vibration resistance and vibration strength.

3. The concept of rigidity and mechanical strength of the structure.

4. Depreciation of REA design.

5. List the types of shock absorbers.

Methods of control of radio-electronic equipment in the production process

The production of modern radio-electronic equipment is unthinkable without highly qualified technical control. Such control at the plant should be subjected to both parts and blocks own production, and parts coming from enterprises of related industries.

The reliability of manufactured products depends on the means, methods and systems of product control.

The ideal control is a 100% check of all parameters of the parts in all production operations. However, in this case there are great economic and technical difficulties associated with the need to use a large number of controllers and expensive measuring equipment. Therefore, in the production process, all purchased products are checked for compliance specifications, interoperational check on technological maps and drawings and check finished products(output control).

In the production of radio-electronic equipment, the following types of control are used:

working control (RK);

preventive control (PC);

adjustment control (KN);

mode control (CR);

selective control (VC);

statistical control (Art. K).

Consider the main types of control carried out at the enterprise.

Working control provides for quality control of manufactured products directly at the workplace (machine, press, workbench). The check can be carried out both by the worker himself and by an employee of the technical control department (QCD). Control is carried out visually or with the help of tools and devices specified in technological map. Control can be 100% or selective. In the process of control, the necessary adjustment of equipment or tools can be made. Only suitable parts and assemblies, checked by the contractor himself, should be presented for acceptance by the QCD. In case of rejection of parts or assemblies, they are returned for revision.

Preventive control provides for verification of compliance with the technological process and the quality of products, as well as the prevention of mass defects. The need for preventive control and the choice of its method are determined by the result of the previous statistical analysis of the equipment manufacturing process. Statistical analysis not only helps to identify and eliminate the main causes of defects, but also allows you to identify technological factors that need to be paid special attention to during preventive control to ensure the release of high-quality products. This type of control should be carried out by qualified workers, production foremen and technologists, representatives of the QCD. The main attention of the technical staff of the workshop should be directed to checking the condition of the main equipment and tooling, as well as to checking compliance with technological regimes. Verification measurements are made with accurate universal and control instruments, control devices and devices.

All defects in products and means of production identified during the inspection of violations of the technological process are drawn up in an inspection report and analyzed. Based on the results of the inspection, appropriate decisions are made and measures are developed to eliminate defects. During repeated inspections, attention should be paid to the implementation of previously approved measures. In the event of a mass defect, as well as when major changes are made to the design documentation and technological processes, an extraordinary preventive control is carried out. The heads of workshops and the head of the quality control department of the plant are responsible for organizing and conducting preventive control.

Setup control consists in testing equipment and is carried out when using new equipment or a measuring complex in the process of manufacturing a product. After the adjustment work, the adjuster is obliged to produce a small batch of parts and present them to the Quality Control Department. Sometimes this type of control is combined with other types of control to improve the quality of products (for example, preventive control, mode control).

selective control, as well as statistical control, as a rule, they are carried out only with large-scale and mass production. With selective (or statistical) control, based on the results of checking a part of the products, they judge the suitability of all the products presented. This type of control is carried out by methods of single sampling and sequential analysis.

The single sampling method is as follows. Randomly extracted from a batch of finished products N products. The technical specifications for the product provide for a sample size N and the norm of the number of good products C in total samples. In the case when from N products turned out M defective or out of specification, if M> C batch is not accepted and rejected, and when M< C party is recognized as suitable. After testing, one of three decisions is made:

1)accept the batch;

2) continue control (take one or more samples);

3) reject the entire batch. A rejected batch can be subjected to a complete inspection or completely withdrawn and returned to the contractor for sorting and correction.

The main factors determining the reliability of sampling control are the number of products to be controlled and the control conditions on the basis of which a decision is made on the suitability of the lot. Selective control is recorded in the process flow charts as a special operation indicating the dimensions and parameters to be checked, as well as the means of control.

Selective control cannot ensure the complete exclusion of cases of missing marriage.

A complete guarantee of product quality can only be given by complete (100%) control of products. Sampling with careful and full check products increases the reliability of control.

With a well organized technological process selective control can be carried out both at intermediate and final operations (output control). The choice of the method of output control is determined by the nature of the reasons leading to marriage, the thoroughness of the measures to prevent marriage and other reasons.

The reliability of REA depends on many factors. The main ones are discussed in the previous chapter. Οʜᴎ are subdivided into constructive-production and operational.

High reliability of the facility at the design stage is ensured by:

§ choice of circuit and design solutions;

§ replacement of analog processing with digital;

§ choice of elements and materials;

§ replacement of mechanical switches and control devices with electronic ones;

§ choice of operating modes of various elements and devices;

§ development of measures for the convenience of maintenance and operation;

§ taking into account the capabilities of the operator (consumer) and the requirements of ergonomics.

When choosing circuit diagrams Preference is given to circuits with the smallest number of elements, circuits with a minimum number of control elements that operate stably in a wide range of destabilizing factors. At the same time, satisfaction of all these conditions is impossible, and the designer has to look for a compromise solution.

The main thing in the designed equipment is to use elements whose reliability meets the requirements for the reliability of the equipment itself.

Since the requirements for the reliability of equipment are constantly growing, ever higher requirements are placed on the reliability of components.

Structural solutions also affect the reliability of REA. The large-block design is technologically complex and inconvenient for repair. Design solutions should also provide the necessary thermal conditions of REA elements, failure-free operation in conditions of high humidity and under conditions of impact and vibration loads.

Significantly improves reliability right choice operating modes of the elements. It was previously stated that the optimal electrical loads of the elements should not exceed 40-60% of the rated ones.

Maintenance is a set of works to maintain the health or only the operability of an object during preparation and use for its intended purpose, during storage and transportation.

Maintenance REA includes the following components:

§ control of technical condition;

§ preventive maintenance;

§ supply;

§ collection and processing of operation results.

The technical condition control is carried out to assess the condition of the equipment, ᴛ.ᴇ. comparison of the true values of the parameters of a particular equipment with their nominal values, taking into account tolerances.

Preventive maintenance, for the implementation of which deadlines and times are set, are called scheduled maintenance.

The supply provides for the receipt of materials, equipment, instruments, tools for preventive maintenance.

The collection and processing of operating results are carried out to quantify the operational and technical indicators for a certain period of operation.

Preventive work provide:

§ external examination and cleaning of equipment;

§ control and adjustment works;

§ failure prediction;

§ seasonal, lubrication and fastening works;

§ technical inspections;

§ technical checks.

An external inspection of the equipment is performed to identify external signs of possible malfunctions, check the correct installation of controls, check the condition of the elements and installation. Cleaning equipment involves removing dust, moisture, corrosion from it.

The most time-consuming part of preventive maintenance is control and adjustment work and closely related work on predicting failures. Test papers include control of REA parameters in relation to the established tolerances.

Adjustment work is carried out to restore the properties or performance lost by the equipment. For household electronic equipment, at this stage, work is carried out to reduce the fire hazard of televisions and restore the performance of kinescopes that have lost cathode emission after long-term operation.

Failure prediction is a method for predicting failures, which is based on the assumption that the occurrence of failures is preceded by a gradual change in the parameters of an object or elements. Forecasting is carried out for gradual failures for the purpose of timely replacement (repair and adjustment) of the relevant elements, blocks.

Seasonal, lubrication, fastening work is carried out in order to prepare the electronic equipment for operation at a certain time of the year, to ensure the performance of the relevant parts. During seasonal work, measures are taken to reduce the penetration of moisture into the equipment, to insulate (in winter) and cool (in summer) equipment, use special oils for different seasons, etc. After carrying out seasonal work at the electronic equipment, control and adjustment work is carried out. It is important to note that in order to systematically control technical condition instruments carry out technical inspections and technical inspections of equipment.

The invention relates to the field information technologies and can be used in the design of complex electrical products on a computer. The technical result consists in reducing the time and computational resources spent on the design of such products, as well as in increasing the reliability of the designed products due to the early detection of design defects when analyzing the durability of radio-electronic equipment (REA) and unified electronic modules (EM) in its composition. The method for analyzing the durability of REA is based on the analysis of the stress-strain state and a detailed calculation model (RM), which includes detailed models of electrical and radio products (ERP) and structural elements. CEA durability analysis is carried out using thermal, deformation and strength RM CEA sequentially in four stages: a preparatory stage, a global analysis stage, an intermediate analysis stage, and a local analysis stage. On the preparatory stage create thermal RMs without detailing models of structural elements, deformational RMs with detailing of ERP and structural elements that affect the rigidity of the structure, and detailed strength RMs of specific elements. At the stage of global analysis, the REA temperatures are calculated when thermal RMs are used. At the stage of intermediate analysis, deformations (displacements) in REA are calculated based on the results of the REA thermal calculation of the global analysis stage, while selecting a specific REA node using deformation RM. Then, a local analysis is performed when the stress-strain state of the electronic radiation source and structural elements of the electronic equipment unit are calculated, after the calculation of the stress-strain state, the durability of the electronic equipment elements is calculated, while using strength RM. 2 w.p. f-ly, 3 ill.

Drawings to the RF patent 2573140

The invention relates to the field of information technology and can be used in the design of complex electrical products on a computer. The implementation of the invention makes it possible to reduce the time and computational resources spent on the design of such products, as well as to increase the reliability of the designed products due to the early detection of design defects when analyzing the durability of radio-electronic equipment (REE) and electronic modules (EM) in its composition.

A known method for analyzing the durability of EM. (Prediction of the reliability of nodes and blocks of radio technical devices space purpose based on the simulation of stress-strain states: monograph. / S.B. Suntsov, V.P. Alekseev, V.M. Karaban, S.V. Ponomarev. - Tomsk: Tomsk Publishing House, state. un-ta systems control. and radioelectronics, 2012. - 114 p.). The detailing of the calculation model (RM) used in this case is determined by the analysis of the stress-strain state (SSS) and, as a rule, corresponds to the detailed RM EM, which includes: detailed models of electrical and radio products (ERP), adhesive joints, sealing, soldering, printed conductors, vias and their metallization, etc. This method is taken as a prototype.

This method has significant disadvantages:

The use of a single RM EM with a high degree detailing leads to a significant increase in time and computational resources required for the calculation;

The use of several RM for each type of analysis (thermal, deformation, strength) creates significant difficulties in formalizing the boundary value problem and transferring the results from one RM to another due to the fact that there is a large discrepancy in the number of nodes and elements.

The objective of the method proposed in the invention for carrying out a durability analysis is to eliminate the above disadvantages, namely:

Reduction of time costs during calculations;

Reducing the required computing resources;

Facilitation of the formalization of the boundary value problem.

It is proposed to carry out the analysis of durability in four stages, while:

Use calculation models optimized for a specific analysis;

Use the interpolation of analysis results to facilitate the formalization of the boundary value problem and improve the accuracy of transferring results from one RM to another.

The problem is solved due to the fact that the analysis of the durability of REA, which consists in predicting the reliability of units and blocks of REA for space purposes, is carried out in stages using the created thermal, deformation and strength RM of REA, optimized for the subsequent stages of the analysis of durability, while at the preparatory stage, creation of thermal RM with ignoring the detailing of models of basic supporting structures (roundings, holes), printed circuit assembly (electro-radio products, solder joints, printed conductors, vias and their metallization), deformational RMs with detailing of specific ERI, basic supporting structures (metal frame, printed circuit assembly ), as well as other structural elements of electronic equipment (connectors, plugs, etc.), which affect the rigidity of the structure; as a strength RM, a detailed (detailed) RM of specific structural elements of the EM is used, when soldering, printed conductors, metallization of vias are taken into account; then, at the stage of global analysis, the EM temperatures are calculated as part of the REA, when thermal RMs of EMs are used, while taking into account reradiation from neighboring EM surfaces and heat transfer by thermal conduction (conduction) from neighboring EMs; then, at the stage of intermediate analysis, the calculation of deformations (displacements) in the EM is carried out according to the results of the thermal calculation of the REA of the global analysis stage, while selecting a specific EM with subsequent transfer of temperatures by interpolation using the deformation RM of the EM; then a local analysis is performed when the stress-strain state of the elements of the printed circuit assembly of the EM (ERI, soldering, printed conductors, vias) is calculated by interpolating the results of calculating the deformations (displacements) of the EM obtained at the intermediate analysis stage, after the calculation of the stress-strain state is completed carry out the calculation of the durability of the EM elements, while using the strength RM EM.

The essence of the invention is illustrated by drawings, where in Fig. 1 shows the calculation algorithm by means of interpolation, FIG. Figures 2 and 3 show images of flat linear triangular and quadrilateral elements, respectively.

In FIG. 1 shows the calculation algorithm by interpolation, where:

Stage 0. Preparatory.

Stage 1. Global analysis.

Stage 2. Interim analysis.

Stage 3. Local analysis.

The calculation can be made using the finite element method. In this case, the computational domain is approximated by a system of elements. Within an element, the function F(x,y,z) is defined by the following expression:

where N i are element shape functions, f i is the value of function F in i-th node element, f i =F(x i ,y i ,z i).

Thus, if the shape functions of the elements and the nodal values of the function are known, then it is possible to determine the value of the function F at an arbitrary point x * , y * , z * of the computational domain. If the point x * , y * , z * coincides with the node point x j , y j , z j , then:

Expression (1) is used to determine the function F(x * ,y * ,z *) of the point x * , y * , z * located inside or on the border of the element.

Consider the method of determining the function F at the point x * , y * , z * on the example of first-order elements - a flat triangular element and a flat quadrangular element.

1. Flat linear triangular element

The function F(x, y) on such an element (Fig. 2) is represented by a linear polynomial:

where i are the coefficients of the polynomial. The coefficients of the polynomial (2) are determined from the nodal values of the function F(x,y). For this, a system of linear algebraic equations is written:

According to Cramer's rule:

where ; ;

The determinants i can be expanded by the column containing the nodal values of the function:

where d ij are the corresponding determinants from (5).

When substituting (4) and (6) into polynomial (2), we get:

As a result, we arrive at expression (1), where the element shape functions have the form:

Having the form functions (8) of the element and the nodal values of the function, it is possible to calculate the value of the function at an arbitrary point inside the element.

2. Flat linear quadrangular element

A quadrangular element (Fig. 3) in X, Y space is mapped to a rectangle in , . Shape functions in space , have the form:

If for a point with coordinates x * , y * , lying inside the quadrilateral, the corresponding coordinates * , * are known, then by (1), using (9), we can determine the value of the function F(x( ,), y( ,)) in this point.

Knowing the coordinates , , one can easily find the corresponding x, y coordinates using the formulas:

where x i , y i are the coordinates of the nodes of the quadrilateral. However, the reverse transition:

does not have a simple analytical representation. Therefore, numerical methods should be used to perform this transition. It is possible to use a method similar to the method of dividing a segment in half. Its algorithm contains the following steps:

1. Among the coordinates x, y of the nodes of the quadrilateral, there are values X min , X max and Y min , Y max , between which lie the values x * and y * .

2. In space, the rectangle is divided into four rectangles. For each newly obtained rectangle, using formula (10), X min , X max and Y min , Y max are determined.

3. Using the values of X min , X max and Y min , Y max we find the rectangle in which the point with coordinates x * , y * falls.

4. If conditions:

are not met, then return to step 2. If the conditions are met, then go to step 5.

5. The coordinate * is determined as the arithmetic mean of the coordinates over all nodes of the rectangle. The * coordinate is defined in the same way.

6. According to the formula:

the value of the function is determined at the point with coordinates x * , y * .

The method for analyzing the REA durability using automatic construction of computational models in the geometric modeling system has been software developed and debugged in the design of spacecraft onboard REA. Practical use This method makes it possible to reduce the terms of designing REA, which confirms the effectiveness of the proposed method for analyzing the durability of EM REA based on computer simulation of thermal strength processes.

CLAIM

1. A method for analyzing the durability of radio electronic equipment (REA), based on the analysis of the stress-strain state and a detailed calculation model (RM), which includes detailed models of electrical and radio products (ERP) and structural elements, characterized in that the analysis of the durability of REA is carried out using thermal , deformation and strength RM REA sequentially in four stages: the preparatory stage, the global analysis stage, the intermediate analysis stage and the local analysis stage, while at the preparatory stage thermal RMs are created without detailing models of structural elements, influence on the rigidity of the structure, and detailed strength RMs of specific elements, then at the global analysis stage, the CEA temperatures are calculated, when thermal RMs are used, then at the intermediate analysis stage, deformations (displacements) in the CEA are calculated based on the results of the CEA thermal calculation of the stage global analysis, at the same time, a specific REE node is selected using deformation RM, then a local analysis is performed when the stress-strain state of the ERS and structural elements of the REE node is calculated, after the calculation of the stress-strain state, the durability of the REE elements is calculated, while using strength RM.

2. The method according to claim 1, characterized in that the CEA durability analysis is carried out using RM optimized for a specific global, intermediate, local analysis.

3. The method according to claim 1, characterized in that the analysis of the durability of CEA is carried out using the interpolation of the results of temperatures and deformations (displacements) of CEA.

Methods for determining the reliability of rea and p. Methods for improving the reliability of rea

lec06.doc

Valery Samoilin. Ural geophysicist and radio engineer. 20th century

The concept of rigidity and mechanical strength of the structure. When developing the REA design, it is necessary to ensure the required rigidity and mechanical strength of its elements.

11.5. Dust protection

11.5.1. Equipment sealing

Control questions

Chapter 12 Protection against mechanical influences

12.1. Types of mechanical effects on REA

12.2. The concept of vibration resistance and vibration strength

Control questions

Methods of control of radio-electronic equipment in the production process

Drawings to the RF patent 2573140

CLAIM

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