UNION SERVICE SPEClrlCIITION NUMBER SU- 3168 UNION' SWITCH & SIGNAL ••• •. SWISSVA~E, PA. DIVISION OF WESTINGHOUSE AIR BRAKE COMPANY PT-52 Plug-In Type Thermal Relay with Plain Back Contact. ******************** l ·11 I See Service Specification SU-3168-A for PT-52 Thermal Relay with Snap-Action Back Contact~ This service specification provides information required for the repair and adjustment of PT-52 Plug-in type thermal relays. . ' : 1. GENERAL DESIGN The PT-52 thermal relay provides an adjustable time delay and is equipped with a back contact for checking the completion of its operating cycle. Referring to the relay diagram in Figure l, the thermal contact assembly, attached to the center terminal post, consists of a driving element, heater element, front contact tip and back contact tip. The driving element consists of two bi -metallic strips fastened together end to end. The driver which carries the heater coil, has the side of higher temperature coefficient of expansion facing to the right so that when the heater element is energized the assembly moves to the right and closes the front contact. The compensator has the higher temperature coefficient side facing in the opposite direction, and the length of these two strips are so selected that with the relay de-energized the contact finger remains practically in a fixed position with the back contact closed regardless of the surrounding temperature. , The heater element on some relays is located below the contacts rather than above, but these instructions apply to both types. A lead seal is applied to the handle of the cover at the factory. Other seals are provided on the front contact adjusting post and on the shipping lock. These are furnished for the convenience of the railroad if it is desired to seal the adjusting screws after the field time adjustment has been made. The relays are arranged for wall mounting and should be timed and installed in this position; that is, with the top plate horizontal. The cover should always be in place when making timing check. 2. HEATER The heater coil may be operated from either an a-c. or d-c. source of power, and consumes approximately 10 watts. November, 1959 Al.44-200-6.39.3 u. s. & s. - 2- Service Spec. SU-3168 £XT£.RNAL ADJUSTMENT--...-... OF FRONT CONTACT MINIMUM TIME ADJUST-, MENT STOP SCREW INTERNAL BACK CONTACT ADJUSTMENT FRONT CONTACT INSULATION BACK CONTACT ---- rlG. 1 "I 3. MECHANICAL INSPECTION The flex1ble connectors should be neatly dressed so that they will not touch other metallic parts of the relay. · The silver contacts on the thermal element should touch the adjustable front and back contacts approximately in the center of the contact face, i.e., between the rivets and the end of the contact, and the contacts should line up squarely with each other. It should be noted that the back contact spring rests against the adjusting screw with enough pressure to follqw the movement of the screw when adjustments are being made. • 4. ELECTRICAL TEST Testing apparatus as shown in Figure 2 will be found convenient for the electrical tests and adjustment of PT-52 relays. Two time intervals are to be taken: "Front contact time" and "Total Operating time". "Front contact time" is the time from the instant energy is applied until the front contact closes. "Total operating time" is the time from the instant energy is applied until the back contact recloses (after the relay has made its front contact, has been deenergized and its driver has cooled to return to its original position). To obtain these operating time intervals, proceed as follows: Close the knife switch "S", at .the same time starting a stop watch, preferably one having two second hands. T.he "total time jndicator lamp" will go out when the back contact opens. When the PT-52 front contact makes, the DN-11 relay will pick up and light the "front contact time indicator lamp". One hand of the stop watch should be stopped to record this time. The other hand should be stopped when· the "total operating time indicator lamp" re-lights. After a test of the time interval has been made it is necessary to wait at least eight minutes before retesting in order to permit the relay to cool and assume normal position. ) Service Spec. SU-3168 - 3 - U.S.&S. AUXILIARY RELAY + ...-~--~~~~~~~~~ DN-11 \ .............. BATTERY(USE AT LEAST ONE MORE CELL OF STORAGE BATTERY THAN REQUIRED TO OBTAIN RATED VOLTAGE.) 110 V. A.C. OR AS REQUIRED FOR LAMPS USED. USE LOW WATTAGE LAMPS. VM ~ FRONT CONTACT TIME INDICATOR LAMP. ~ T O T A L OPERATING TIME INDICATOR LAMP. PT-5-2 RELAY__/ f'IG. 2 5. CONTACT ADJUSTMENTS Refer to Table 1. Assuming that the relay to be adjusted has an operating range of 25-35 seconds front contact time and 110-135 seconds total operating time, proceed in accordance with the following sections. A similar procedure should be followed for relays of other ranges using values as given in the table. A - PRELIMINARY BACK CONTACT ADJUSTMENT. Turn the back contact adjusting screw slowly until the back contact just touches. This represents O (zero) back contact compression. Then turn this screw clockwise one turn (1 turn = 360 degrees) as called for in the table, and bring the screw locking nut firmly, but not yet tightly, against the bracket. Be sure the back contact stop does not touch the spring. B - PRELIMINARY FRONT CONTACT ADJUSTMENT. Remove the cap nut from the left hand projecting post which contains the front contact adjusting screw. Use a small screw driver to adjust the front contact to a bridging contact opening of approximately 0. 035 inch (as called for in Table #1) with the back contact just opened. C - ADJUSTMENT AND CHECK FOR MINIMUM TIME RATING. Obtain front and back contact time, as explained in Section 4, at rated voltage as shown on the relay nameplate. If the front contact time is not 25 seconds U.S. & S. - 4- Service Spec. SU-3168 (the minimum value as called for in the first column of the table), readjust the front contact opening until 25 seconds front contact time is obtained. This is very important and must be done accurately. Next, check the total operating time. If this time is less than 110 seconds minimum value, as called for in the second column of the table, turn the back contact adjusting screw counterclockwise. If the time is more than 110 seconds, turn the screw clockwise by just a few degrees. Check front and total operating times and readjust until 25 seconds front contact time and 110 seconds total operating time are obtained. These values should not vary more than± 3%. Next bend the front stop for the back contact until it is about 0. 005 inch from the back contact spring with the relay deenergized. This is to limit the movement of back contact spring and prevent a possible short circuit between front and back contact should the back contact "freeze". Adjust and lock the minimum time adjustment stop screw (see Fig. 1) so that its tip is within 0. 002 inch from, but not touching the adjusting bracket. This setting,-0f the stop screw limits the minimum front contact time that can be obtained to slightly less than 25 seconds by making it impossible to further reduce the front contact opening. With minimum front contact time adjustment thus made, move the relay driver by hand until the back contact just opens. At that point note the front contact opening. It should be at least 0. 030 inch for all relays, regardless of time rating. When releasing the driver note thatthe back contact has appreciable compression. D - ADJUSTMENT AND CHECK FOR MAXIMUM TIME RATING Recheck the front and total operating time at the minimum setting, then increase the front contact opening until the total operating time is 135 seconds (the maximum rated value shown in the table) at rated voltage. If it is less, increase the front contact opening until 135 seconds is obtained, but do not change the back contact adjustment. The back contact adjustment should not be disturbed after the minimum time adjustment has been made. The front contact time for this maximum setting should not be more than plus 10% above its maximum rated value, or 38. 5 seconds for this relay. E - ADJUSTMENT FOR SERVICE After making the check under Section D, the relay is ready for final time setting and may be adjusted within the time ranges specified to meet service requirements. To obtain a specific adjustment of front contact time or total time, adjust the front contact only by means of the external adjustment screw until the required time is obtained. 6. SHIPPING LOCK ThePT-52relay is equippedwith a shipping lock which should be used to hold the moving element during shipment. In order to release or apply the lock the cap nut on the right hand projecting post should be removed. Grasp the pin on J - 5- U.S. & S. Service Spec. SU-3168 the top of the locking rod pushing downward to compress the spring. The rod should be turned counterclockwise to release and clockwise to apply the lock. Care should be taken that the slot in the lock rod properly engages the connector plate on the moving element when the lock is applied. The lock rod should be secure in the proper slots in the terminal post head both for locking during shipment and for release during service. TABLE #1 Time Ranges Front Total Contact Operating Time Time Sec. Sec. 10-18 45-70 10-18 60-90 10-18 ,. · 80-110 15-27 70-100 25-35 110-135 60-80 180-220 35-55 140-185 Contact Adjustments Front Cont. Full Turns on Opening Back Contact Approximate Adjusting Screw (See Note*) 1-3/4 1-1/4 1 1 1 1 0.030" 0.040" 0.050" 0.035" 0.035" 0.025" 0.030" Operating Time Corresponding to Cont. Adjust. Back Cont. Front Cont. Time Time Sec. Sec. 45 60 80 70 110 180 140 10 10 10 15 25 60 35 * This is the contact opening when the back contact is just making with the front contact adjusted to the minimum rated time. Note: - All readings of operating times must be obtained with rated voltage impressed upon the heater coils. This is given on the relay nameplate. Printed in U. S. A.
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