Testing of enclosed electromagnetic relays

An apparatus for testing enclosed electromagnetic relays includes a probe displaceable into the relay enclosure to engage the movable contact thereof. The probe is associated with a force transducer and a displacement transducer which provide inputs to a circuit including microprocessor unit which operates to detect the probe force required to break contact between the movable contact and the normally closed contact and to detect the position of the probe when such break occurs and when the normally open contact is made and to calculate the contact travel from the position signals it receives. Contact over travel is also measured by applying current to the relay winding and measuring probe displacement required to re-engage the contact.

BRIEF SUMMARY OF THE INVENTION 
This invention relates to the testing of enclosed electromagnetic relays. 
During the manufacture of enclosed electromagnetic relays, the mechanical 
processes involved in enclosing the functional parts of the relay in a 
cover or housing sometimes result in the functional parts of the relays 
being deformed or damaged. While it is a relatively simple matter to test 
the proper functioning of a relay before the cover or housing is affixed, 
such testing is inadequate because of the possibility of the relay ceasing 
to function correctly when the cover or housing is affixed. 
Accordingly it is one object of the present invention to provide a 
convenient method of testing an enclosed relay after its enclosure is 
complete. 
Basically the invention arises from the appreciation that a relay can be 
tested by means of a fine probe inserted through an opening in the 
enclosure, which opening can be subsequently blocked without creating 
mechanical stresses in the enclosure. 
A method in accordance with the invention comprises inserting a measuring 
probe through an opening in the relay enclosure into engagement with a 
movable contact of the relay, displacing said probe so as to move the 
movable contact and measuring the force exerted by the probe to break 
electrical contact between said movable contact and a first fixed contact 
of the relay and the distance moved by the probe between such breaking of 
electrical contact and the making of electrical contact between the 
movable contact and a second fixed contact of the relay. 
Preferably, when the movable contact makes electrical contact with said 
second fixed contact, the coil of the relay is caused to be energised and 
the same probe is then displaced further until it again engages the 
movable contact and this further displacement is measured. 
The invention also resides in apparatus for testing enclosed 
electromagnetic relays comprising means for mounting a relay to be tested, 
a probe for insertion into an opening in the relay enclosure, means for 
displacing the probe into engagement with a movable contact of the relay, 
a displacement transducer sensitive to displacement of the probe, a force 
transducer sensitive to the force applied to the probe to displace the 
movable contact, and measuring means connected to said transducers and 
also connected to fixed contacts of the relay for measuring the force 
required to break electrical contact between the movable contact and a 
first one of said fixed contacts and the distance through which the probe 
is displaced between such breaking of electrical contact and the making of 
electrical contact between the movable contact and a second one of said 
fixed contacts. 
Preferably means controlled by said making of electrical contact are 
provided for energising the relay coil and the measuring means is also 
used to measure the distance through which said probe is moved between 
initial making of said electrical contact and re-engagement of the probe 
with the movable contact.

Referring firstly to FIGS. 1 and 2 the apparatus shown includes a stand 10 
on which a slide member 11 is slidably mounted. A fixedly mounted bracket 
12 carries a jig 13 for receiving the relay 14 to be tested. Slidably 
mounted on the bracket 12 is a carrier 15 on which there is mounted a 
force transducer 16 having a probe 17. The carrier 15 abuts the slide 11 
so that movement of the slide 11 causes the carrier 15 to move relative to 
the bracket 12. The probe 17 extends through an opening on the base 14a of 
the relay and into engagement with the movable contact 14b thereof. The 
jig 13 incorporates spring loaded contact elements 18, which make 
electrical contact with the terminals 19 on the base of the relay. 
The bracket 12 also carries a displacement transducer 20 which has a 
movable element 21 connected to the carrier 15. 
In the example shown the side 11 is movable by means of a screw 22 driven 
by a handwheel 23, although it will be appreciated that a servo-motor 
could readily be used instead of a handwheel. 
The electrical block diagram of the apparatus shown in FIG. 3 shows a 
micro-processor based control unit 25 which receives and processes signals 
from the transducers 16 and 20 and also controls the sequence of 
operation. A detailed description of the unit 25 is not given herein since 
a man skilled in the art could readily construct a suitable unit in the 
light of the information given hereinafter. 
Certain of the input-output ports 26A to 26G of the control unit 25 receive 
a 7-bit digital input from an analog-to-digital converter 27 which serves 
for both the force transducer 16 and the displacement transducer 20. A 
switch circuit 28 receives the analog signals from the two transducers and 
selects which to pass to the converter 27 in accordance with the output of 
another of the input/output ports 26H. The transducers produce analog 
signals varying linearly with the force applied to probe 17 and the 
displacement of carrier 15 respectively, the force transducer being a full 
bridge inductive transducer and the displacement transducer being a linear 
variable differential transducer and each including well known circuits 
for providing a d.c. output. 
Two further ports 26I and 26J are connected to receive signals via 
opto-isolators O.I.1 and 0.I.2 from the normally closed and normal open 
fixed contacts NC and NO of the relay, the movable contact 14b being 
earthed. A further port 26K provides a signal to control a drive circuit 
29 for energising the relay coil 30. Yet another port 26L receives a START 
signal from an operator actuated switch 31 via a further opto isolator 
0.I.3. Finally there are three ports 26M, 26N and 260 which provide output 
signals. These signals are routed to three separate lamp driver circuits 
32, 33 and 34 and also to a NAND gate 35 controlling a further driver 
circuit 36 which energises an ACCEPT light 37 and an actuator 38 which 
determines the route taken by the relay when it is unloaded from the 
testing aparatus. 
When a relay has been loaded into the jig 13, the operator actuates the 
START switch which puts an input into the unit 25 via port 26L. The unit 
25 then causes lamp drivers 32, 33 and 34 to be energised and switch 28 to 
be put into the state in which the output of displacement transducer 20 is 
connected to the converter 27. The operator then turns the handwheel 23 to 
cause the probe to enter into the relay and engage the movable contact 
14b. When the contact 14b loses contact with the normally closed contact 
NC, the signal entering the unit 25 via port 26I causes the output of the 
converter 27 to be transferred into a data store in the unit 25. A signal 
at port 26H then causes switch 28 to change-over so that the force analog 
signal is applied to converter 27 and after a suitable short delay, the 
output of the converter is transferred into another part of the data store 
of unit 25. This digital signal is compared in unit 25 with tolerance 
limits held in the read-only memory of the unit 25 and if it is within 
these limits an output is produced at port 260 to extinguish lamp 32. If 
the digital signal is outside the set limits lamp 32 remains lit and the 
sequence of operations is discontinued. 
If the force transducer output is within the set limits, the switch 28 is 
changed back to the displacement transducer output and, when contact 14b 
touches contact NO, the output of the converter 27 is again transferred 
into yet another part of the data store of unit 25. This displacement 
signal and that stored when the contact NC opened are now processed to 
produce a digital signal representing the contact gap or free travel and 
this gap digital signal is stored and compared with limit data drawn from 
the ROM. If the gap digital signal is outside the set limits the test is 
stopped so that lamp driver 33 remains energised. 
If the gap digital signal is within the set limits driver 33 is 
de-energised, driver 29 is energised and switch 28 is operated to switch 
the converter 27 to the force transducer 16. As a result of energisation 
of the coil 30, the movable contact 14b is caused to overtravel so that 
the probe 17 ceases to engage it. When the probe has travelled far enough 
to re-engage the movable contact again this is signalled by a rise in the 
output of the force transducer and as a result of the increase in the 
input to unit 25, the switch 28 is switched back to the displacement 
transducer and another displacement reading is transferred into the memory 
store of unit 25. This displacement signal and that stored at the time 
when contact NO closed are now processed to produce an overtravel digital 
signal which is transferred into the store and is also compared with set 
limits data drawn from the ROM. If the overtravel digital signal is 
outside the set limits lamp driver 34 remains energised. If it is within 
the limits, the lamp driver 34 is de-energised, and driver 36 is energised 
to light the ACCEPT lamp 37 and also operate the actuator 38 to direct the 
relay onto a route for accepted relays after it has been unloaded from the 
test equipment. 
The test sequence now being completed, the unit 25 now calls up the contact 
force digital signal, gap digital signal and overtravel digital signal 
from its memory store in turn and transmits these via a teleprinter 
interface circuit 40 to a printer 41 and/or via a cassette interface 
circuit 42 to a cassette recorder 43. The unit is then ready for a new 
test cycle to commence. 
In the manual apparatus described the operator now rewinds the slide 11 
back to its starting point and unloads the test relay. 
Where a servo-motor is used to drive the slide 11, this can be controlled 
by the microprocessor unit to start, step and reverse at the appropriate 
times in accordance with the signals received from the various contacts, 
switches and transducers. 
It will be appreciated that the test apparatus described above may be 
incorporated in a larger automatic apparatus in which other tests, e.g. 
insulation tests, are made on the relays, in which case, the same 
microprocessor control unit 25 may also control the other tests. The 
apparatus may also include a mechanism for assembling and crimping the 
covers of the relays on the bases thereof immediately before testing.