SU1775745A1 - Electromagnetic relay rejection method - Google Patents

Description

The invention relates to a technique for rejecting potentially unreliable electromagnetic relays and can be used at enterprises that manufacture and use these relays.

A known method of monitoring the quality of contacts of electromagnetic relays by fixing the current through its closed contacts.

When testing according to this method, the test contacts are connected to a voltage source that exceeds the breakdown voltage of the films of tarnishing of the material of the contacts formed during the manufacture of the relay, but does not exceed the breakdown voltage of the total films formed on the surface of the contacts during manufacture, storage and operation of the relay. The absence of current on the contacts indicates the presence of insulating films on the surface of the contacts.

The accuracy of the method is insufficient, since it does not reveal films with semiconducting properties and films with a resistance significantly greater than the resistance of the contact material, and therefore the effectiveness of the method is also insufficient.

There is a known method for assessing the quality and reliability of contacts, including contacts of electromagnetic relays, based on measuring the voltage drop across closed contacts when passing through them a series of short current pulses of large amplitude (30 ... 500 A) with its sequential increase.

According to this method, a sequence of 1775745 A1 short current pulses is passed through the closed contacts and at the same time the voltage drop across them is measured, and at the moment when it begins to decrease, the transition resistance (Rnep) is determined by the formula:

R ln ⁼ t ~~ '

I cr where C is a constant characterizing the materials from which the investigated contacts are made;

Ικρ is the current value at which the voltage drop across the contacts begins to decrease, by the value of which the quality of the contact connection is judged.

This method reveals contamination and other contact defects, but a large pulse current and the need to regulate it by increasing it cause low productivity of the method and subject the contact zone to influences that are not characteristic of their actual operation. In addition, checking only the relay contacts in this way determines its insufficient effectiveness for assessing the quality of the relay as a whole.

Known methods of rejection of electromagnetic relays, based on quality control of their contacts by measuring the voltage drop across closed contacts in the mode of switching low currents and voltages.

According to these methods, a small current (units of microamperes) is passed through the closed contacts and the voltage drop across the closing contacts is measured once or repeatedly, manipulating the number of relay operations, the direction and nature of the current through the contacts, the voltage on the opening contacts, and each time the resistance of the contact circuit is determined (Rkts) according to the formula where Uk is the voltage drop of the closing contacts;

Ικ is the current through the contacts.

by the size of which the quality of contacts is judged.

These methods are distinguished by their accuracy, productivity, they identify and reject relays, the contacts of which contain contact defects such as contamination, oxidation, and partially the regulation of the electromechanical system.

However, these methods have insufficient accuracy and efficiency, since in the area of microampere currents at which the same parameter Uk is measured once or repeatedly, its measurement is significantly affected by the resistance of the circuit between the meter and the relay contacts to which it is connected, and the transition resistance between the relay contacts and the connecting device. This influence is such that when these methods are used to check the resistance Rku of the contacts of the same relay at different workplaces and especially those located at different enterprises, the information obtained about the value of Rku may be contradictory.

To reduce this influence in order to improve the accuracy of these methods, gilding of the contacts of the connecting devices, special care for them, their regular replacement after a certain number of connections, as well as work to ensure the assembly, assembly, etc. are required. identity of jobs, including those located at different enterprises, which is associated with material, technical and other costs and difficulties.

These methods also have insufficient efficiency due to the fact that they check the quality of all relay components, but only its contacts, and in the mode of one-time operation, which, in terms of the physical process, is not a complete analogy to the mode of its dynamic functioning, and therefore the information obtained by these methods about as a relay is not sufficiently reliable and complete for the purpose of predicting its reliability and reliability during operation.

The closest in technical essence to the invention is a method of non-destructive quality control and predicting the reliability of electromagnetic relays, according to which voltage pulses are supplied to the winding of the relay under study, in amplitude equal to the operating voltage, and the nature of the transient process in the electromagnetic system is recorded on the oscilloscope screen by removing the voltage drop across a resistor of a small value, connected in series with the winding of the relay under study and the deviation of the observed characteristics from the reference ones, the quality of its electromagnetic system is judged, and a sequence of short current pulses is passed through the closed contacts and at the same time the voltage drop across the contacts under test is measured and at the moment when it begins to decrease , determine the contact resistance according to the above form 1775745 le (R nep

, by the value of which the quality of the contact connection of the controlled relay is judged.

This method detects defects in the winding, electromagnetic and electromechanical systems, foreign particles in the armature gap, oxidation and contamination of contacts.

However, it has insufficient efficiency, 10 accuracy and productivity, since checking the quality of the relay components separately when it is switched on separately, it does not check the quality of the relay as a whole due to the lack of the possibility of obtaining a complex relay characteristic from one connection in the 15th method, necessary for this purpose.

In addition, measurement on the oscilloscope screen is associated with the influence of a subjective factor and makes it difficult to apply the method for mass control, and the one-time relay operation mode used in the method is not fully equivalent to its dynamic 25 operation mode. Therefore, the information obtained is not sufficiently complete and reliable for the purpose of predicting the reliability of the relay during operation. It is also insensitive to semiconductor films on contacts, has an inaccuracy in identifying defects in the adjustment of the contact mechanism, namely: a small joint stroke and weak contact pressure, and the spread of controlled characteristics of the transient process can be caused not only by defects in the electromagnetic system, but also the spread of the winding resistance allowed by the technical conditions on the relay. 40

The aim of the invention is to expand the range of diagnostic capabilities, to obtain from one connection a complex characteristics of the relay and to increase the efficiency of monitoring. 45

This goal is achieved by the fact that according to the method of rejecting electromagnetic relays, based on fixing the nature of the transient process in the electromagnetic system of the relay by removing the voltage drop across a small resistor connected in series with the winding of the relay under study, in accordance with that connected in series with the winding of the relay under study, according to 55 of the invention, include in series with the winding and a small resistor a circuit of series-connected break contacts of all contact groups, connect separately in each group fixed contacts to each other, supply the entire circuit with positive rectangular voltage pulses with an amplitude equal to the maximum operating voltage on the winding relay, with a pulse duration equal to 2/3 of the period, and with a period equal to approximately half the duration of the inertia closure of a switching contact with a closing contact, which occurs when the voltage is disconnected from the winding at the moment when the relay starts to operate, the oscillator is recorded ograph with memorization on a resistor of a small value of at least one period of the complex characteristic of the relay and the absence of pulses of a shorter duration on it or the presence of bounce on any of its sections rejects the relay.

Figure 1 shows a relay test diagram; figure 2 is a timing diagram explaining the method.

The relay test circuit contains: 1.2 - terminals; 3 - button for closing; 4 - small resistor; 5 - winding of the tested relay; 6, 7 and 8, 9 - its break contacts, 10, 11 - normally open contact; 12 - storage oscilloscope; 13 - parasitic capacitance of the winding,

The timing diagrams in figure 2 contain: a time sequence of input rectangular pulses; timing diagram of the voltage on the relay coil; the timing diagram of the pulses Ur of the voltage drop across the small resistor.

Testing the relay by the proposed control method is divided into two stages:

the first is the determination of the parameters of the electrical control mode of the relay being tested and the second is the actual test of this type of relay in the selected mode, which remains constant for further tests of all relays of this type in this way.

This method is checked as follows.

To terminals 1, 2 in the scheme of the workplace according to Fig. 1, to which an electric circuit is connected, consisting of a series-connected button 3, a resistor 4 of a small value, a winding 5 of the relay under investigation, its disconnecting contacts 6, 7 and 8.9, in each a group of which fixed contacts 9, 10 and 11, 7 are connected to each other, serve a sequence of positive rectangular pulses with an amplitude equal to the maximum operating voltage of the relay, with a frequency of 40 ... 80 kHz. with a duration equal to 2/3 of the period, press and immediately release button 3, while on the screen of the storage oscilloscope 1 ... 2 periods of the voltage drop characteristic across the resistor 4 should be reproduced, which should correspond to the form shown in Fig. 2c and in order to determine mode parameters measure the duration of a shorter pulse of this characteristic t3, as shown in Fig. 2c.

Measure data is carried out on 5 ... 10 pieces. a relay of the type under study, and if there are relays in the characteristic of which there are no pulses of shorter duration, as shown in Fig. 4, then such relays are not taken into account.

According to the measured values, the average value of the duration (t3cp) of a shorter pulse of the characteristic is determined and, in order to reject a relay of this type, by the proposed method, positive rectangular pulses with an amplitude equal to the maximum operating voltage of the relay are supplied to terminals 1, 2 with a period determined by the formula

T ~ 0.5t3cp ..

(which is const for this type of relay) and duration equal to 2/3 of the period, connect the tested relay in the test circuit, press and immediately release button 3, while on the screen of the storage oscilloscope 12, 1 .., 2 periods of the specified characteristic should be reproduced. If this characteristic has at least two pulses in at least one period, then such a relay is recognized as corresponding to the proposed test method, and if there are no pulses of shorter duration in its characteristic in all periods, or there is bounce in any of its sections, then such relays are recognized as not corresponding to this method control and rejected.

Below is a description of the physical processes occurring when checking the relay in this way and the rationale for its reliability and effectiveness.

The most effective methods for checking the quality of multicomponent products, which include relays, are methods based on checking the effect of the properties of their components on the complex characteristics of the dynamic functioning of the product as a whole.

... The maximum detectability of these influences and the reliability of control are ensured when checking the product in a mode that promotes the manifestation of its components with the greatest influence on the complex nature of the product's operation. This mode includes a mode of operation in which the internal energy states of the components will not be suppressed and neutralized as much as possible by external force influences, as a result of which they will have the greatest influence on the nature of the product's operation and the formation of its characteristics, jointly creating signs and criteria about the internal predisposition to this. or other nature of the product. In practice, this means that this method checks the compatibility of the properties of the components of the product to fulfill their functional purpose.

• The functional purpose of electromagnetic relays is to switch their moving contact under electromagnetic influence on its winding. Therefore, in order to ensure the greatest reliability and efficiency of the method for controlling their quality, it should be based on the use of a mode with a minimum external energy impact during the entire period of switching of the movable contact. This is ensured by the accumulation of voltage on the winding before the start of the relay operation according to the increasing law, in order not to inform the winding of excess energy, and at the moment the relay starts to operate, when its normally closed contacts begin to open, disconnect the external voltage from the relay elements for the entire further period his work, until returning to its original state.

These conditions are most favorable for providing its components with the opportunity to maximize their individual properties in the joint formation of a complex characteristic of the relay, the information of which can be used to predict its quality and reliability.

As follows from the analogs and the prototype, the most informational parameters of electromagnetic relays are the contact current and the winding current, which, according to the indicated methods, are checked separately.

In order to increase the effectiveness of the check in the proposed method, one complex informative parameter is used: the current of the relay winding passing through its closed contacts with minimal external electrical impact.

For this, the winding of the relay under investigation and its normally closed contacts are connected in series into a single circuit, together with a small resistor, from which the monitored information is read, as shown in Fig. 1.

Another important feature of the method is the form and type of applied external energy impact. These can be single or low-frequency, sawtooth or rectangular pulses that meet the requirements of TU. But such influences ensure the operation of the relay and do not contribute to the formation in its integral characteristic of the criteria necessary for effective prediction of its quality and reliability.

This is due to the fact that in statics or at a low frequency, such defects of relay components as microcracks, micropores, inhomogeneities, oxide films, etc., are weakly manifested, as well as by the fact that when a quantity already formed and sufficient for the relay to operate is supplied to the winding, voltage, by its force effect on the individual energy properties of the components, it suppresses and neutralizes the features introduced by them into the process of forming the general characteristics of the functioning of the relay and generally excludes the process of forming and accumulating voltage on the winding, which makes this test mode uninformative and not sufficiently effective.

Therefore, in the proposed method, high-frequency pulses are used as an input energy effect, which the relay will not be able to track by operating on each of them, but their effect on the winding (in the workplace diagram according to Fig. 1) is such that charging processes are formed in it (at the moment of the pulse) and discharge (in pause). And if the charge prevails over the discharge, then the voltages Uo6m and, accordingly, on the winding and a small resistor will abruptly increase until after a time ti, as shown in Fig. 2, the voltage on the winding reaches the value and _O bm.srab. relay actuation.

To ensure the prevalence of charge over discharge in the same circuit, it is necessary that the duration of the acting impulses exceed their pause. Therefore, in the proposed method, the duration of the input pulses is chosen equal to 2/3 of their period, and the pause is 1/3 of the same period. And so that the voltage on the winding, accumulated during its charging, could reach any value of its operation voltage that meets the requirements of TU, the amplitude of the input pulses is chosen equal to the maximum operating voltage of the relay.

In the proposed method, the voltage Uo6m is not rigidly set. on the winding, it is formed by the components of the tested relay to the value necessary for its operation and obm.shrab, including up to the maximum operating value and _About bm.mah. permissible according to TU, if the relay under investigation is capable of operating only at a given voltage.

The nature of the processes of charging and discharging in the winding is influenced by such parameters and components of the relay as parasitic capacitance 13 and inductance 5 of the winding, according to FIG. 1, its active resistance, pollution and films on the contacts, resistance R _Kl . contact circuit, the mechanical moment of the moving contact, i.e. relay adjustment, quality of the magnetic system, etc.

After a time and after the input pulse sequence is applied to terminals 1, 2, the voltage across the winding reaches the pickup voltage and _O bm pickup, from which its break contacts 6. 7 and 8, 9 according to FIG. 1 _? open and the movement of its movable contacts 6, 8 begins towards the corresponding fixed closing contacts 11. 10. During this, ·> time t ₂ . as shown in FIG. 2, the input pulses do not affect the components of the relay, and its coil is quickly discharged. But during the time t _{2 the} winding does not have time to completely discharge, and by the end of this time the voltage Uo6m.mhh remains on it, as shown in Fig. 2, equal to

2 ... 5 V. It is much less than not only the pick-up voltage, but also the drop-out voltage, which provides, according to the requirement of the method, a minimum of external energy power effect on the relay components at a given time.

When the movable contacts 6.8 by inertia reach the closing contacts 11.10 and close with them by inertia, the voltage Iobm.min remaining on the winding is used as an energy source to set the current through these contacts in order to diagnose their quality.

The duration of the inertial closure of moving contacts with closing contacts is determined by the time t3. With the beginning of their closure in the relay winding, the processes of its charge and discharge are restored. And here it is important that during this time tj the voltage on the winding would not reach one of the values capable of exerting an energetic effect on it: this either the actuation voltage or the release voltage.To meet this requirement, the frequency of the input pulses is chosen such that during the time t3 the number of periods of input pulses would be no more than 2 ,,. 3 pcs, i.e. so that the condition

where Tech is the period of the input pulses.

And since the time t3, depending on the relay samples, has a scatter of its values, then to ensure the fulfillment of the specified requirement, when determining Tech, the average value of the time rs is used, according to experimental data obtained on 5..10 pieces of relays containing pulses of shorter duration Ur, as this is shown in Fig. 2c.

If the relay tested by the proposed method has a technological predisposition to high-quality functioning, then under the influence of pulses of a given frequency with the above parameters, its movable contacts open with opening contacts, by inertia move towards the closing contacts, by inertia they close with them for a time ta. which is determined by the joint action of the properties of such parameters as the quality of the magnetic core, wire, winding, contact holders, adjustment, and if the closing contacts do not contain contamination and films, then in the circuit of its contacts 10, 8, 11, 6.winding 5 and resistor 4, according to figure 1, a current arises at time 19, which causes a voltage drop across the resistor 4 in the form of a pulse Ur of a shorter duration, the presence of which is used in the proposed method as an informative parameter about the compliance of the quality of the tested relay with the requirements of the method, and its absence classified as non-compliance of this relay with the proposed method.

Physically, the operation of the relay in this method is due to the joint action of its mechanical MB and magnetic M ^ moments.

In the initial state of the relay, its disconnecting contacts 7.9 are connected to the corresponding movable contacts 6, 8 due to mechanical forces acting on the movable contacts introduced during adjustment and characterized by the moment M <r.

When testing the relay by the proposed method, its magnetic moment M increases during the time ti and during the time to. according to figure 2 is compared with the mechanical moment.

Mg- = / to

Due to the inertia of the movable contacts from opening with opening starts after this equality is fulfilled after the time Δti Ati at the time ti, as shown in Fig. 2. During this time, the magnetic moment acting on the armature will increase by ΔΜ ^ χ and at the moment the relay is triggered, the following condition will be met:

Mju> Μρ / ti

In the interval t ₂ during the flight of the moving contacts, the magnetic moment decreases in proportion to the voltage on the winding, according to Fig. 2b, to an insignificant value Mj, ', therefore, at time t3, the condition m _e > mu

From the beginning of time t3, charge-discharge processes are restored in the winding and the magnetic moment of the armature increases from the value of Mu. But the rate of its growth due to the selected frequency and duty cycle of the pulses is such that it does not have time to increase during the inertial closure of the moving contacts with the closing ones to a value that can affect the behavior of the relay armature. Therefore, under the action of a mechanical moment, the stage of restoring the initial state of the relay begins, which lasts for a time k, as shown in Fig. 2c.

The switching characteristic of the electromagnetic relay obtained by the proposed method from one connection, shown in Fig. 2c, is used to control its quality based on the presence or absence of pulses of a shorter duration Ur!

If this impulse is present, then the tested relay corresponds to this method, and if it is absent, then the relay is rejected.

This characteristic also contains other parameters and criteria that can be used as informative parameters of the quality of the relay to tighten its testing and expand the diagnostic capabilities of the control method, namely:

Time duration ti

Depending on the samples of the relay of the same type, the spread of ti ranges up to 2 ... 3 times values.

The time ti determines the rate at which the voltage builds up on the winding up to the value at which the relay picks up. In this case, if ti is increased, then this is due to a large discharge of the winding in pauses, which is a consequence of a decrease in the active resistance of the winding, and, consequently, increased losses. Therefore, relays with a significant increase in ti have more winding losses, will heat up more under the influence of the supply voltage and, for this reason, will be more prone to failure due to defects in the winding than relays with a lower ti value.

Maximum pulse amplitude Ur at time ti.

This amplitude correlates with the standard parameter of the relay - trip current, according to which, the smaller it is, the lower the relay trip current and the more economical and reliable it is.

Linearity of pulse growth U R.

The coil current of the relay as an inductance current should increase linearly. Its linearity is violated under the influence of current conductivity in micropores, microcracks in the magnetic circuit, capacitive couplings. Therefore, the more linear the increasing section of the pulse U'r, the fewer hidden defects the electromagnetic relay system contains.

Duration of saturation (flat top) of the pulse U'r.

The cessation of the growth of the pulse amplitude U ^r R is due to the cessation of the growth of the magnetizing current, i.e. its saturation, this is due, on the one hand, to the inertia of the moving contact when the voltage on the winding reaches the trigger level, and on the other hand, to the quality of the magnetic conductor.

Variations of the pulse saturation area _x U'r, depending on the relay samples, are 2 ... 3-fold spread. The shorter the duration of the flat top of the pulse u'r, the less the inertial relay, the less heat losses in it, the better it is and can work at higher frequencies.

Duration of times t ₂ , N

These times characterize the quality of the contact group, its adjustment and design. The smaller they are, the more high-frequency the relay is, but equality is the optimal criterion.

t ₂ = t4 ₍

The duration of the time rz (pulse u ^). Depending on the samples of the tested relays of the same type, the spread of this parameter reaches 3 times the values. This parameter characterizes the technological inheritance of the relay as a whole and its components to the closing of the closing contacts, i.e. to fulfill the functional purpose of the relay. The longer the duration Гз of the impulse U'r, the greater the propensity of the relay to fulfill its functional purpose, i.e. reliable switching.

Pulse amplitude U'r.

The spread of this parameter is the largest of all parameters of the considered characteristic. Depending on the relay samples of the tested type, the pulse amplitude ranges from zero to the maximum value of the pulse amplitude U'r. The impulse U'r is due to the actuation current of relay 15 (having a certain spread), passing through the make contacts, which, with their resistance Vkts, affect its value. The greater the resistance Rku, the lower the amplitude of the pulse ur and 20 the lower the quality of the relay.

Period T characteristics

The shorter this period, the more qualitative and high-frequency the relay under investigation.

Thus, the claimed method, in comparison with the prototype, provided a complex characteristics of the relay from one connection, expanded the range of diagnostic capabilities and increased 30 the effectiveness of control.

The method has been tested and positive results have been obtained.

The most effective method can be used by the manufacturer of the relay at the 35th stage of adjustment in order to obtain a 100% output of the relay with the maximum identity of the functional characteristics, which also corresponds to their best quality or at the input control of the consumer for 40 rejection of relays prone to failure.

Claims (1)

Claim A method for rejecting electromagnetic relays, based on fixing the nature of the 45 transient process in the electromagnetic system of the relay by removing the voltage drop across a small resistor connected in series with the relay coil, characterized in that. that, in order to expand the range of diagnostic capabilities by obtaining a complex characteristic of the relay from one connection and increasing the efficiency of monitoring, include in series with the winding and a small resistor a circuit of series-connected break contacts of all contact groups, connect separately in each group the fixed contacts to each the other, positive rectangular voltage pulses are applied to the entire circuit with an amplitude equal to the maximum operating voltage on the relay winding, a pulse duration equal to 2/3 of the period, and a period equal to 5 approximately half the duration of the inertia closure of a switching contact with a closing contact occurring during deviation voltage from the winding at the moment the relay starts to operate, is recorded by an oscilloscope with memorizing on a resistor of a small value at least one period of the complex characteristic of the relay and by the absence of pulses of a shorter duration on it or by the presence of bounce on any part of the rejection relays.