GB2194347A

GB2194347A - Testing relays

Info

Publication number: GB2194347A
Application number: GB08709808A
Authority: GB
Inventors: Thomas Lewis Mcdowell; John Bruce Brownwood
Original assignee: Teledyne Industries Inc
Current assignee: TDY Industries LLC
Priority date: 1986-08-27
Filing date: 1987-04-24
Publication date: 1988-03-02
Also published as: JPS6358269A; IL82638A0; FR2603419A1; GB8709808D0; DE3728676A1

Description

1 GB2194347A 1 SPECIFICATION The method includes the electrical monitor-

ing of the moving and stationary contacts Methods and apparatus for electrically when the stationary and moving contacts measuring electromechanical relay arma- touch. The relay coil current waveform as a ture overtravel 70 function of time is also monitored.

After the relay coil is energized, a first point This invention relates to electromechanical re- in time is established upon the occurrence of lay test methods and more particularly, to the contacts touching each other. When the apparatus and methods of measuring electro- armature hits the stop, an inflection occurs in mechanical relay armature overtravel. 75 the coil current waveform. The duration of A typical electromechanical relay includes a time from the first point in time until the oc- coil which, when energized, acts as a solenoid currence of the current inflection is measured.

to cause an armature to move. As the arma- The measured time duration is proportional to ture moves, it comes into contact with one or armature overtravel.

more moving contacts of the relay. The mov- 80 Other objects, features and advantages of ing contact moves with the armature until it the invention will become apparent by refer comes into contact with a relay stationary ence to the specification taken in conjunction contact. with the drawings.

Generally, the relay is designed so that the Figure 1 is a schematic diagram of a typical armature continues to move past the point at 85 electromechanical relay, showing various posi which the stationary and moving contacts tions of the armature and moving contact come together, the armature finally coming to when the relay coil is energized.

rest when it hits a mechanical stop. The dis- Figure 2 is a schematic diagram showing tance the armature travels beyond the point at the connections to the relay coil and contacts which the stationary and moving contacts 90 employed in practising the present invention; come together is known as armature overtra- Figure 3 is a graph showing the waveforms vel. The amount of armature overtravel deter- of the coil current and contact closure as a mines contact mating force and can have a function of time as measured at various points pronounced effect on relay performance. For in the circuit of Figure 2; and example, insufficient overtravel can cause un- 95 Figure 4 is a block diagram of automatic stable contact resistance, excessive contact testing circuitry employed in conjunction with bounce, and premature contact failure. the circuit of Figure 2 in practicing the inven- Generally, relay armature overtravel is ad- tion.

justed to the desired amount during the con- Referring to Figure 1, there is shown a struction of the relay by adjusting the position 100 schematic diagram of a typical electromechani of the contacts and the armature stop. Cali- cal relay 10 of the type to which the present brated shims are often employed by skilled invention is directed. The relay 10 includes a workers to measure and adjust the overtravel coil 12 and an armature 14. The armature 14 distance during relay construction. can pivot about an axis 16, and is biased to a After relay construction is completed, subde-energized position 14a by a spring 18. A sequent processing, testing and handling can set of stationary contacts is provided, includ cause misadjustment or loss of proper over- ing a normally closed contact 20 and a nor travel, which may easily go undetected. Me- mally open contact 22. A resilient moving chanical measurement of overtravel requires contact 24 pivots about an axis 26 between special tools and trained personnel, and hence 110 the contacts 20 and 22 and, in the de-ener does not lend itself to field testing. In the gized position 24a, is biased (by, for example, instance of sealed relays, there is no way to a spring or its own resilience) into physical physically check the amount of overtravel and electrical contact with the normally closed once the relay is sealed. contact 20.

Accordingly, it is an object of the present 115 The relay 10 is energized by applying a vol- invention to provide a new and improved. tage across the coil 12 at leads 28, 30.

method of measuring electromechanical relay When energized, the coil 12 acts as a sole armature overtravel. noid, producing a magnetic force which It is another object of the invention to pro- causes the armature 14 to pivot toward the vide a method of electrically measuring elec- 120 moving contact 24. An insulator 32 is pro tromechanical relay armature overtravel which vided on the armature 14 to electrically isolate does not require the need for mechanical mea- it from the contact 24.

surements or access to the interior of a relay. As the armature 14 pivots, it engages the The foregoing and other objects of the in- contact 24, which moves with it until the con- vention are accomplished by a method of 125 tact 24 touches and makes electrical contact measuring the distance of armature overtravel with the normally open contact 22. The posi to a mechanical stop from the point at which tions of the armature 14 and moving contact a designated moving contact touches a corre- 24 at this point are shown in dotted lines in sponding stationary contact when the relay Figure 1 and are labelled as 14b and 24b, coil is energized. 130 respectively.

2 GB2194347A 2 The armature 14 continues to pivot until it 34.

hits a mechanical stop 34, as shown by It has been found that the abrupt change in dotted lines labelled 14c. At this position, the the velocity of the armature 14 when it hits resilient moving contact 24 is deformed the stop 34 produces an inflection point 46 in slightly as shown by dotted lines labelled 24c. 70 the waveform of the relay coil current lc due -The distance the armature 14 travels from to the magnetic coupling between the arma- position 14b to position 14c is referred to as ture 14 and the coil 12. As shown in Figure armature overtravel. The resilience of the mov- 3, the inflection point is generally character ing contact 24 enables it to bend to accom- ized by a negative slope in the current wave modate the overtravel of the armature 14. The 75 form, followed by a relatively sharp transition amount of overtravel determines the mating to a positive slope, as the current waveform force between the contacts 22 and 24, which resumes its exponential rise. The inflection 46 directly affects relay performance character- is shown in Figure 3 as occurring at a point in istics such as contact resistance, bounce and time T2.

life. 80 It has also been found that, for a given The amount of overtravel in a particular re- relay design, a relationship may be established lay is usually established during construction between armature overtravel distance and the by adjusting the distance between the station- interval of time from point T1 to point T2 in ary contact 22 and the stop 34. Once set, the Figure 3. This is so because, for a constant overtravel distance presumably does not 85 set of environmental conditions and coil vol change. In fact, however, subsequent relay tage, the armature velocity does not vary processing, testing and handling can change appreciably among those relays of common the overtravel distance. Prior to the present design.

invention, the way to verify overtravel dis- One way in which the relationship between tance was by physical measurement, a virtual 90 the interval of time referenced above and ar impossibility in the case of sealed relays. mature overtravel may be determined for re- In the present invention, overtravel may be lays of a common design is as follows. A measured electrically in the following manner. substantial number of such relays are con Referring to Figure 2, the relay coil 12 is con- structed, and the amount of armature overtra nected in series with a current measuring re- 95 vel in each is physically measured using, for sistor 36. The series circuit is connected example, calibrated shims. Ideally, some relay f through switch 38 to a voltage source V, samples in this group will be adjusted to the which is set at the nominal coil voltage. In the minimum and some to the maximum allowable following description, all voltages are taken in limits of overtravel.

relation to the ground terminals in the Figure. 100 The measured distances are recorded so The voltage appearing across the resistor 36, that they may be correlated to each relay.

as sensed on line 39, is proportional to relay Each relay is in turn connected to the circuit coil current lc. The voltage appearing on line of Figure 2, and the desired interval of time is is approximately equal to the coil voltage measured and recorded. From a correlation of VC. 105 this data, a relationship may be established The stationary contact 22 is connected to a between the time interval and overtravel dis- voltage source V2 which is set at any conve- tance, whereby an acceptable range of time nient voltage suitable for detecting relay con- durations is arrived at which represents the tact closure. The moving contact 24 is conacceptable range of overtravel.

nected through a resistor 42 to ground. The 110 From the above description, it may be seen resister 42 in conjunction with the source V2 that the present invention provides a method establishes a nominal contact current level. of electrically measuring armature overtravel The presence of a voltage V. on lead 44 is an which may be applied to relays without the indication that the contact 24 is touching the need for access to the relay interior or for any contact 22 115 physical measurements.

Figure 3 is a graph showing waveforms of The circuit of Figure 2 may be adapted for the coil current]c as represented by the vol- automatic testing of relay overtravel by com tage appearing on line 39, and the voltage bining it with the circuity shown in block dia appearing on line 44, as a function of time gram form in Figure 4.

after closure of the switch 38 in the circuit of 120 Referring to Figures 2 and 4, the signal Figure 2. appearing on line 39 and representing coil cur- The coil current lc rises in a well known rent lc is provided as an input signal to slope exponential fashion. Eventually, sufficient magdetecting circuits 48. The purpose of the cir netic force is available to move the armature cuity 48 is to detect the inflection 46 by, for 14, which carries with it the moving contact 125 example, detecting the change in the current 24. When the contact 24 touches the contact waveform from a negative slope to a positive 22, a step change in voltage appears on the slope. Circuits of this type are well known to line 44, which event is indicated as occurring those skilled in the art.

at a point in time T1 in Figure 3. The armature An output signal from the circuit 48 is pro- 14 continues its travel until it hits the stop 130 vided to a STOP input terminal of a timer 50.

3 GB2194347A 3 The signal appearing on line 44, used to sig- be limited in scope only by the appended nify the closure of the contacts 22, 24 as claims.

described above, is provided to a START in

Claims

put terminal of the timer 50. The signal CLAIMS appearing on the line 40,

representing coil ac- 70 1. A method of measuring the distance of tuation, is provided to a momentary RESET armature overtravel to a mechanical stop from input terminal of the timer 50. the point at which a designated moving con- An output signal from the timer 50 is pro- tact touches a corresponding stationary con- vided to an input terminal of a numeric display tact upon energizing the coil of an electrome 52, such as an LED or LCD display. The timer 75 chanical relay, comprising the steps of:

output signal is also provided to an input ter- electrically monitoring the moving and sta- minal of a window comparator 54. A signal tionary contacts so as to detect when the representing an upper limit of the allowable stationary and moving contacts touch; time duration (representing maximum allowable electrically monitoring the coil current wave- overtravel distance) for the class of relay un- 80 form as a function of time; der test is provided on line 56 to an upper energizing the relay coil; limit input terminal UL of the comparator 54. establishing a first point in time upon the A signal representing a lower limit of the time occurrence of the contacts touching each duration is provided on lead 58 to a lower other; limit terminal LL of the comparator 54. 85 detecting the occurrence of an inflection in A "PASS" output signal from the compara- the coil current waveform caused by the ar- tor 54 is provided to a "PASS" indicator 60, mature contacting the stop; and and a "FAIL" output signal from the compara- measuring the duration of time from the first tor 54 is provided to a "FAIL" indicator 62. point in time until the detection of the occur The indicators 60, 62 may be visible or audi- 90 rence of the coil current inflection, whereby ble indicators. The window comparator 54 the measured time duration is related to the provides the PASS output signal when the armature overtravel.

comparator input signal falls between the up-
2. The method of claim 1 further including per and lower limits provided on leads 56, the steps of:

58, and provides a FAIL signal otherwise. 95 providing a first predetermined interval of The operation of the circuit of Figure 4 in time; conjunction with the circuit of Figure 2 is as comparing the measured interval of time to follows. Upon energizing the relay under test the first predetermined interval of time; and by closing switch 38, a signal appears on lead providing an indication if the measured inter- 40, which momentarily resets timer 50 to 100 val of time is less than the first predetermined zero. Upon the occurrence of the touching of interval.

the contacts 24 and 22, the signal appearing
3. The method of claim 1 or 2 further in- on the line 44 starts timer 50. Upon the oc- cluding the steps of:

currence of the inflection 46 in the current providing a second predetermined interval of waveform as detected by Circuitry 48, an out105 time; put signal is provided by these circuits which comparing the measured interval of time to stops timer 50. The output signal now prothe second predetermined interval of time; and vided to display 52 and comparator 54 by providing an indication if the measured inter- timer 50 represents the desired time duration val is more than the second predetermined indicative of overtravel distance, which is disinterval.

played by display 52. This same time duration
4. Apparatus for measuring the distance of signal is compared to the predetermined upper armature overtravel to a mechanical stop from and lower limits by comparator 54 which pro- the point at which a designated moving con vides either a pass or fail indication using indi- tact touches a corresponding stationary con cators 60 and 62. 115 tact upon energizing the coil of an electrome- The circuitry just described provides a mea- chanical relay, comprising:

sure of overtravel distance as well as a quick means for electrically monitoring the moving pass/fail indication. Of course, the comparator and stationary contacts so as to detect when 54 can be configured to provide a pass/fail the stationary and moving contacts touch; indication based on exceeding an upper limit 120 means for electrically monitoring the coil only, or based on failing below a lower limit current waveform as a function of time; only, as opposed to the window comparator means for energizing the relay coil; operation described above. means for establishing a first point in time While the invention is disclosed and particu- upon the occurrence of the contacts touching lar embodiments are described in detail, it is 125 each other; not intended that the invention be limited means for detecting the occurrence of an solely by these embodiments. Many modifica- inflection in the coil current waveform caused tions will occur to those skilled in the art by the armature contacting the stop; and which are within the spirit and scope of the means for measuring the duration of time invention. It is thus intended that the invention 130 from the first point in time until the detection 4 GB2194347A 4 of the occurrence of the coil current inflection, whereby the measured time duration is related to the armature overtravel.
5. The apparatus of claim 4 further includ- ing:

providing a first predetermined interval of time; means for comparing the measured interval of time to the first predetermined interval of time; and means for providing an indication if the measured interval of time is less than the first predetermined interval.
6. The method of claim 4 or 5 further in- cluding:

means for providing a second predetermined interval of time; means for comparing the measured interval of time to the second predetermined interval of time; and means for providing an indication if the measured interval is more than the second predetermined interval.
7. A method of measuring armature overtra- vel substantially as hereinbefore described.
8. Means for measuring armature overtravel -substantially as hereinbefore described with reference to Figures 2 to 4 of the accompany ing drawings.

Published 1988 at The Patent office, state House, 66/71 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.