US 3678344 A
A monitoring circuit is disclosed that is connected to the driving conductor to the relay by a transformer having one winding in series with the drive line from a fast operating, electronic, common control sequencing circuit. The monitor circuit includes a transistor, connected to another winding of the transformer and normally biased to be nonconductive. The transistor is brought into its conductive state by the dip in the operating current flowing in the drive conductor as sensed by the transistor to set a bistable device to record the operation of the relay.
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Description (OCR text may contain errors)
United States Patent Wedmore 1 July 18, 1972 54] ELECTROMAGNETIC RELAY 3,275,899 9/1966 Wolf ..317/DIG. 6
OPERATION MONITOR Primary Examiner-L. T. Hix  Inventor William wedmore Glen Ellyn Attorney-K. Mullerheim, B. E. Franz and Theodore C. Jay,  Assignee: GTE Automatic Electric Laboratories ln-' corporated, Northlake, Ill. 22 Filed: Feb. 25, 1971  ABSHMCT ] Appl No: 118,717 monitoring circuit is disclosed that is connected to the drivmg conductor to the relay by a transformer having one winding in series with the drive line from a fast operating, elec- Cl ..3l7/l37, 340/248 R, 3 5 tronic, common control sequencing circuit. The monitor cir-  Int. Cl. ..H0lh 47/00 cuit indudes a transistor, connected to another winding f the  Field ot'Search ..317/l37, 148.5 R, DIG. 4, DIG. 6; transformer and normally i d to be nonconductive The 340/248 R transistor is brought into its conductive state by the dip in the I operating current flowing in the drive conductor as sensed by  References Cited the transistor to set a bistable device to record the operation UNITED STATES PATENTS of the y- 2,994,07l 7/1961 Olson et al. ..317/DIG. 6 1 Claim, 2 Drawing Figures RELAY MATRIX rl siesta 2; ssiiiccifis J5 E |7 L l2 t r|8 PATENTEU JUL] 81972 3,678,344
RELAY MATRIX GATING 3O SIGNAL 22 CONTROL CLEAR R 0gb 2O CIRCUIT 7 FIG.
32 9,15 L F/G. 20
RELAY ARMATURE MOTION F/G. 2c
0 A F/G. 2d
INVENTOR WILLIAM R, WEDMORE ATTORNEY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to circuits for monitoring the operation of electromagnetic relays.
2. Description of the Prior Art In electronically controlled circuits for operating relays in a switching system, commands for operating relays are to be given successively as rapidly as possible in order to provide the most economical use of the system. To complete a sequence of interdependent relay operations, where it is necessary that a certain relay or relays be operated before the command for a subsequent relay to operate be given, it is essential that the sequencing control provide ample time for the operation of the preconditioning relays prior to applying the subsequent operating command. When a fixed time interval is provided, it must be sufficient for the slowest operating relay of its type to operate completely. This interval must be sufficient for even the most adverse condition. An interval longer than required would of course slow down the system, while a shorter interval would obviously not insure that every relay could operate within the allotted time. Further, this time interval that must be provided for the relay operations while small, is cumulative in a system where many relays may be required to operate in sequence.
SUMIVIARY OF THE INVENTION Accordingly it is an object of this invention to provide an improved circuit for determining when a relay has operated.
This is accomplished by sensing the change in current in a drive line to the relay. Use is made of a characteristic possessed by relays employing moving armatures, that is, as the armature moves toward the relay pole piece it generates a counter electromotive force that causes a sharp reduction in the current flowing in the relay winding. This effect persists for as long as the armature is in motion, typically more than 1 millisecond. It is also evident during the time that a relay is releasing as the armature is moving away from the relay pole piece.
By using the usual windings of the relays for the critical timing purposes, a minimal number of additional circuitry and parts are required. The time interval allotted for the operation of a particular relay is variable and determined by the relay itself. The circuit automatically adjusts the interval to the differences in the characteristics of different relays that may be connected to this circuit and for the different rates of operation or release that may be caused by external parameters.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a generalized black and line diagram of a circuit embodying the principles of this invention;
FIG. 2 shows a series of waveforms at various points in the diagram of FIG. 1 to assist in an understanding of the operation of the circuit.
DESCRIPTION OF THE PREFERRED EMBODINIENT In FIG. 1 relays l1, 12, 13 and 14 represent a number of relays in a relay matrix group that are selectively operated as required by the closing of their operate paths at the select switches l5, l6, l7 and 18 from a source of positive potential at terminal 19 to a negative potential at terminal 20. A transformer 21 has a winding 22 located in series in the drive line to the relay coils. The other winding 23 of this transformer is connected between the negative potential 20 and the base of transistor 25 via resistor 24. Transistor 25 has its emitter connected to the negative potential source 20, and its collector to a positive potential source 19' via resistor 26. In this configuration the transistor is normally non-conductive, and remains so during the time that the current flows through winding 22 to energize the selected relay, since winding 23 is polarized to cause a negative bias upon the base of transistor 25 during the current build up interval. This invention makes use of a characteristic possessed by relays employing moving armatures, that is, as the armature moves toward the relay pole piece it generates a counter electromotive-force that causes a sharp reduction in the current rising in the relay winding. This effect persists for as long as the armature is in motion and is illustrated in FIG. 2( b). The voltage to the base of transistor 25 varies as shown by FIG. 2(0), where the increase of negative bias can be seen up to the point that the relay armature starts to move. At this time the voltage swings in the positive direction, and reaches a value sufficient to cause a current flow from terminal 19' through resistor 26 through the collector to emitter path of transistor 25 to the negative source terminal 20 as shown by FIG. 2(d). The voltage at terminal 30 swings from the nominal value at source 19' into the negative direction as shown by FIG. 2(e).
The switches 15, I6, 17 and 18 are controlled by a common control circuit 29 which also serves to sequence other operations within the system of which relays 11 through 14 are a part of. This control circuit 29 prior to the time of operation of the selected switches, rests bistable register 28 and immediately after operation of the selected switches applies a gate signal to AND gate 27. As can be seen from FIG. 2(a), the duration of the gate signal is for an interval suflicient for the selected relay to fully operate under worse case conditions. Gate 27 is now primed and upon detection of the pulse from transistor 25, indicating the operation of the relay, a set pulse will be passed to the input of the bistable register 28. The set output at the l terminal now serves to trigger the control circuit 29 to proceed with any following steps of the sequence without waiting the fully interval of the gate signal pulse.
What is claimed is:-
I. In a system having a plurality of electromagnetic relays with respective inductive coils and armatures, a control circuit common to all of said relays, a source of energizing potential, a plurality of current paths from said source of potential through said relay coils, and switching means in said current path controlled by said control circuit for selectively completing said current paths for controlling selected ones of said relays; the improvement comprising a monitor circuit for providing an indication of the operation of said selected relays to said control circuit comprising: a transformer having a first and a second winding, said transformer first winding connected in said current path, a transistor having a base, emitter and collector, said collector and emitter operatively connected to said source of energizing potential, said transformer second winding connected to said transistor base and emitter, said transformer windings poled to bias said transistor into a non-conducting direction upon said switching means controlling said relay to operate it, a two input AND gate having a first input connected to said transistor collector and a second input connected to said control circuit, said second input energized by said control circuit upon said control circuit controlling said selecting means to complete a circuit path to a selected one of said relays, bistable register means having a set input connected to said gate output and a set output connected to said control circuit, said transformer and said transistor responsive to the induced voltage pulse appearing across said relay coil while said relay armature is in motion for generating a pulse at said transistor collector terminal, said gate operated responsive to said pulse to set said register, whereby said register output is sent to said control circuit to trigger a following operation.