US3457464A - Electronic timer circuits providing switching at multiple intervals - Google Patents

Description

July 22, 1969 K. D. wALLEN'rowlTz 3,457,464

ELECTRONIC TIMER CIRCUITS PROVIDING SWI'ICUNG AT MULTIPLE INTERVALS Filed Feb. 15. 1967 l/UYACA 51 smnr Na'krn Ware 8a Daw/s Hrrokmsys.

United States Patent O 3,457,464 ELECTRONIC TIMER CIRCUITS PROVIDING SWITCHIN G AT MULTIPLE INTERVALS Klaus D. Wallentowitz, Waterbury, Conn., assignor to General Time Corporation, Stamford, Conn., a corporation of Delaware Filed Feb. 15, 1967, Ser. No. 616,370 Int. Cl. Htllh 47/18 U.S. Cl. 317-142 5 VClaims ABSTRACT F THE DISCLOSURE energization of the second relay, connect the lter capacitor into a circuit providing a predetermined discharge time. The rst relay is connected across the lter capacitor and thus drops out a predetermined second time interval subsequent to the energization of the second relay.

The first timed interval is detected by a unijunction transistor. The energization of the second relay is controlled by a silicon controlled rectifier. A resistor is connected across the second relay coil to provide an initial current path for initially turning on lthe silicon controlled rectifier. A capacitor is connected across the bases of the unijunction transistor to stabilize the base 1 to base 2 voltage of the unijunction transistor against transients. A resistor is connected between the output of the unijunction transistor and the gate of the SCR which in combination with another resistor connected in circuit with the gate and cathode of the SCR lengthens the pulse provided by the unijunction transistor so that the relay SCR circuit may be operated from half-wave rectified alternating current.

Related applications The timer disclosed in the present application utilizes the bridge circuit timer invention disclosed and claimed in my co-pending application, Ser. No. 405,503, tiled Oct. 21, 1964, entitled Electronic Timer Circuit (now Patent No. 3,355,632 issued Nov. 28, 1967). That application is assigned to the same assignee as the present invention and is incorporated herein by reference.

The present invention was made during a program of electronic timer development at applicants assignees Industrial Controls Division Engineering Department and the following United States patent applications resulting from said development exemplify the prior art: The United States patent applications of Robert S. Lundin, Ser. No. 472,844, filed July 19, 1965, entitled Condition Responsive Input Controllers; Ser. No. 479,553, filed Aug. 13, 1965, entitled Condition Responsive Process Timer; 4(now Patent No. 3,393,604 issued July 23, 1968) Ser. No. 589,335, -filed Oct. 25, 1966, entitled Relay Circuit for Half-Wave Alternating Current Energization and Electronic Timer Employing the Same, Ser. No. 590,- 707, filed Oct. 31, 1966, entitled Electronic Timer Circuits; my United States patent applications, Ser. No.

589,336, filed Oct. 25, 1966 (now Patent No. 3,417,296 issued Dec. 17, 1968); Ser. No. 591,016, filed Oct. 31, 1966 (now Patent No. 3,417,297 issued Dec. 17, 1968); Ser. No. 615,527, all entitled Electronic Timer Circuit(s); the United States patent application of George I. Yagusic, entitled .Delay on De-energzation Electrical Timers, Ser No. 595,993, filed Nov 21, 1966; and the United States patent applications of Edward T. Bosman entitled Electronic Timer Circuits, Ser. No. 595,955, filed Nov. 21, 1966, and Ser. No. 601,780, filed Dec. 14, 1966s All of the above-identified applications are assigned to the same assignee as the present application and are incorporated herein by reference.

Background of the invention This invention relates to electronic timer circuits providing switching at multiple intervals. More particularly, it relates to such an electronic timer for connection to a Source of alternating current wherein a single capacitor performs the dual functions of acting as the filter, capacitor in the rectifying network for supplying direct current to a first interval timing network; and, upon completion of the first timing interval, of providing the time base for a second timing interval. To this end, transfer contacts on a relay operated at the end of the first timing interval alternately connect the dual function capacitor into appropriate circuits.

Such timers are employed in original manufacturers equipment and are utilized to provide successively timed load circuit controlling switching functions.

It would be obvious, according to the prior art, to provide a timed succession of relay contact transfers by connecting a second interval or delay timer energized upon the conclusion of the timing operation of a first interval or delay timer. Such a circuit would be relatively expensive; however, in that two time interval bases, such as the resistance-capacitor bridge charging circuits disclosed in my above-identified application, Ser. No. 405,503, would have to be provided along with separate detection circuits therefor and separate load relay controlling circuits. Thus, such timers, according to the prior art, might include a pair of timing capacitors, a pair of detector semiconductor devices, and a pair of silicon controlled rectifiers or other load controlling switching devices.

It is known, according to the above-identified applications, to operate a relay from half-wave rectified alternating current by connecting a diode in parallel across the energization coil of the relay. For example, such a circuit is disclosed and claimed in the above-identified application of Robert S. Lundin, Ser. No. 589,335, wherein the energization of the relay is under control of a silicon controlled rectifier (SCR). One diiculty I have discovered with this circuit is that the relay may not always energize during the first positive half of the AC cycle subsequent to the timed interval because transients developed when initially energizing the relay coil may prevent enough current from being supplied to the cathode of the SCR to switch it to its conducting state.

In my above-identified application, Ser. No. 589,336, I disclose and claim a circuit utilizing a unijunction transistor for detecting the completion of a timing interval measured in a RC timing circuit. The load relay is controlled by a silicon controlled rectifier and in order to provide transient protection therefor, I connect a resistor and a capacitor in parallel across the gate and cathode terminals of the SCR. I also provide a diode connected between the base 1 of the unijunction transistor and the gate terminal of the SCR. As described in that application, this circuit stretches out the short pulse supplied by the unijunction transistor at the completion of the timing 1nterval so that it is longer than one-half of the altern-atlng current cycle time in order to insure that the SCR turns on, since it is operated from pulsating half-wave alternating current. I have discovered that this action may be greatly improved at less expense by substituting a resistor for the diode connected between the base of the uni]unc tion transistor and the gate of the SCR.

I have further discovered that the unijunction transistor is very sensitive to transients, especially near the end of the timing interval when the timing capacitor is nearly fully charged; and that this sensitivity can be greatly reduced by connecting a capacitor in circuit across the bases of the unijunction transistor.

Summary of the invention It is, therefore, an object of the present invention to provide an electronic timer circuit providing switching at Imultiple intervals.

A further object of the invention is to provide a timer circuit of the above character in which said switching functions are provided by independent relays.

Still another object of the invention is to provide a timer circuit of the above character in which the timing determining elements are capacitors.

A further object of the invention is to provide a timer circuti of the above character in which the switching functions `are controlled by semiconductor devices.

A still further object of the invention is to provide a timer circuit of the above character utilizing a unijunction transistor as a timing detector device.

A yet further object of the invention is to provide a timer circuit of the above character utilizing a load circult comprising a silicon controlled rectifier controlling a relay operated from half-wave rectified alternating current under control of the unijunction transistor.

Another object of the invention is to provide a timer circuit of the above character providing inherently more secure initial energization of said load circuit than according to the prior art.

Yet another object of the invention is to provide a timer circuit of the above character providing inherently greater protection against transients for said unijunction transistor.

. Still another object of the invention is to provide an electronic timer circuit of the above character providing an advantageous pulse stretching circuit connected between the unijunction transistor and the SCR.

A further object of the invention is to provide an electronic timer circuit of the -above character utilizing a minimum number of inexpensive components.

A still further object of the invention is to provide an electronic timer circuit of the above character of increased reliability.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of electrical elements, and electrical circuit arrangements which will be exemplified in the electronic timer circuit herein disclosed. The scope of the invention is indicated in the claims.

The present invention is exemplified in the electronic timer shown in FIGURE 1 of the drawing. Momentary contact closure initiation is provided by depressing start switch S1. This quickly energizes relay RY1 through switch S4 since capacitor C1 quickly charges. Relay RYls contacts S2 then transfer to complete a holding circuit keeping relay RY1 energized and supplying power to the remainder of the timer circuit 10. Capacitor C1 acts as a filter capacitor providing direct current between busses 16 and 18. Timing capacitor C2 is charged through variable resistor RS. Unijunction transistor UT fires after a predetermined interval; and the pulse provided thereby is stretched by resistors R10, R11 and R8 to provide a triggering pulse to the gate of the silicon controlled rectiier SCR.

Relay RYZ then energizes, transferring contacts S4. Because of the charge on capacitor C1, relay RY1 remains energized. Capacitor C1 then discharges through variable resistor R2, resistor R3, and relay RY1. When the voltage across relay RY1 falls to its dropout level, relay RY1 deenergizes, transferring contacts S2 thereof, de-energizing the timer circuit. Relay RYZ de-energizes and timing capacitor C2 discharges through resistor R6 to provide a quick reset feature. The relays RY1 and RYZ are thus operated, as shown in FIGURE 2, for the intervals 26 and 28, respectively.

The unijunction transistor UT is protected against transients by a capacitor C3 connected between its base 2 terminal 20 and the negative bus 18, thus forming with resistor R8 a circuit between base 1 terminal 22 and base 2 of the unijunction transistor.

Resistor R13 connected across the coil of relay RYZ provides an initial path for current to the SCR to insure that it turns on in spite of any transients caused by the initial energization of relay RY2.

Resistor R10, connected in circuit with resistor R11, stretches the pulse supplied by the unijunction transistor UT so that it is long enough to insure that the SCR will turn on during the next succeeding positive portion of the pulsating alternating current on load conductor 24.

The drawing For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawing, in which:

FIGURE 1 is a schematic electrical circuit diagram of a preferred embodiment of my invention; and,

FIGURE 2 is a timing diagram illustrating the operation of the embodiment of FIGURE 1.

Specific description Now referring to FIGURE 2 of the drawing, the customer specifications for the timer 10, shown in FIGURE 1, are that upon depressing the start switch S1, relay RY1 will be energized for 700 milliseconds as shown at 26 in FIGURE 2, and that relay RYZ will be energized for 100 milliseconds just before relay RY1 de-energizes as shown at 28 in FIGURE 2. These functions are effected as follows:

Depressing the start switch S1 connects the timer circuit 10 to a source of 110 vo-lt alternating current connected across terminals 12 and 14. The current passes through dropping and surge resistor R1, is rectified at diode D1, passes through contacts S4 and quickly charges capacitor C1. Enough current then iiows through resistor R3 and relay RY1 to energize relay RY1. Upon energization, relay RY1 transfers its contacts S2 to furnish a holding circuit to keep the timer 10 connected in circuit with terminals 12 and 14.

In combination with resistor R4, capacitor C1 now acts as a filter so that direct current is supplied Ibetween positive buses 16 and 18. This current charges timing capacitor C2 at a rate determined by the setting of variable resistor R5. Unijunction transistor UT has its bases 20 and 22 connected in circuit with a biasing network formed by potentiometer P3, resistor R9, and base resistors R7 and R8. When the charge on capacitor C2 reaches a predetermined value, unijunction transistor UT fires, that is, its emitter terminal 30 becomes essentially shorted to its base 1 terminal 22, so that capacitor C2 discharges into a network formed of resistors R8, R10, and R11. The time constant of this output pulse is equal to the resistance provided by resistor R8 connected in parallel with-resistors R10 and R11, multiplied by the capacitance of the timing capacitor C2. By choosing R10 appropriately this can be conveniently made longer than the half cycle period of the line frequency, e.g., 19 milliseconds, so that the gate 32 of the SCR will remain conditioned for turning the SCR on until the next positive half of the A.C. cycle.

Power for the load circuit is supplied through dropping and surge resistor R1 and is rectified by diode D2. The resulting pulsating half-wave rectified alternating current is supplied on line 24 to the parallel connected relay RY2, diode D3 and resistor R13. Resistor R13 insures that current will iiow to the anode of the SCR and that it will turn on during the next succeeding positive half cycle when the gate 32 is conditioned by discharge of capacitor C2. Diode D3 insures that the relay RY2 remains energized during the negative half cycles, as more fully explained in the above-identified application of Robert S. Lundin, Ser. No. 589,335. Diode D4 biased by resistor R12 biases the SCR against transients, as explained in my above-identified applications, Ser. Nos. 589,336 and 591,- 016. Capacitor C4 and resistor R11 also protect the SCR against transients and noise, as also explained in those applications.

Upon energization, relay RY2 closes contacts S3 thereof to form a holding path so that the SCR does not have to be maintained in its conducting condition. Relay RY2 will remain energized until removal of power by the transfer of contacts S2 of relay RY1. Upon the energization of relay RY2, its contacts S4 transfer disconnecting capacitor C1 from the timing circuit and connecting it in circuit with variable resistor R2. Capacitor C1 then discharges through variable resistor R2 and resistor R3 and relay RY1, maintaining relay RY1 energized for a predetermined period of time which is adjusted by adjusting variable resistor R2. When the voltage on the relay RY1 reaches its dropout value, relay RY1 de-energizes and its contacts S2 transfer, removing the timer 10 from circuit connection to the ll() volts AC across terminals 12 and 14- Relay RY2 thereupon substantially immediately drops out as illustrated in FIGURE 2. Furthermore, contacts S2 connect resistor R6 across capacitor C2 to quickly discharge it, quickly resetting the timer 10 `for the next possible energization through closure of start switch S1.

By providing potentiometer P3, I am able to adjust the time range of the initial timing interval. Connecting capacitor C3, as shown in FIGURE 1, is very effective in keeping the voltage between base 1 (22) and base 2 (20) of unijunction transistor UT isolated from fiuctuations in the D C. voltage between buses 16 and 18 either introduced by line transients or by high frequency radiation.

The values of components that may be used inthe timer 10 of FIGURE 1 to provide for 700 millisecond energization of relay RY1 and 100 millisecond energization of relay RY2, as shown in FIGURE 2, are as follows:

The unijunction transistor UT may be a type TIS43, supplied by Texas Instruments; the SCR a type C106B, supplied by the General Electric Company; diode D1 may 'be a type DE300; diodes D2 and D3, types DE200; and diode D4, type DE50, all supplied -by Semiconductor Products. Capacitor C1 may be an 8O microfarad, 200 volt capacitor; capacitor C2 a 50 microfarad, 50 volt capacitor; capacitor C3 a .001 microfarad, 20 volt capacitor; and capacitor C4 a .l microfarad, 10 Volt capacitor. Resistor R1 is then a l() ohm, 1/2 watt resistor; resistor R2 takes the form of a 4.7 kilohm, 1/2 watt fixed resistor, and a 10 kilohm potentiometer connected in series; resistor R3 is a 6 kilohm, 5 watt resistor; resistor R4, 33 kilohms, l watt; and variable resistor R5 takes the form of a fixed 33 kilohm, 1/2 watt resistor connected in series with a l() kilohm potentiometer. Resistor R6 is 22 ohms; resistor R7, l0() ohms; resistor R8, 470 ohms; resistor R9, 4.7 kilohms; resistor R10, l kilohm; resistor R11, l kilohm; resistor R12, 47 kilohms, all 1/2 watt resistors; and resistor R13 is a 10 kilohm, one

watt, resistor. Potentiometer P3 is a 5 kilohm potentiom- 75 6 eter. Relay RY1 has a resistance of 2.5 kilohms and relay RY2 is a 48 volt DC relay.

Those skilled in the art will realize that many variations are possible according to my invention of using capacitor C1 as both a filter capacitor and a second time interval determining capacitor; that the capacitor C3 connected in circuit lwith the bases of the unijunction transistor UT is of general utility when utilizing a unijunction transistor as a detector in electronic timers; that the pulse stretching effect of resistor R10 is of general utility in timers utilizing half-wave energization of semiconductor ycontrolled rectifier controlled load circuits; that the connection of a resistor R13 across relay RY2 to insure enough current to properly fire a SCR connected in series therewith is also of general utility in timers wherein a relay is energized through a SCR.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description are efficiently attained, and since certain changes may be made in the above circuit without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An electronic timer circuit providing switching at multiple intervals comprising:

(A) a first relay (a) connected for energization at the beginning of a first timing interval;

'(B) a second relay (a) connected for changing its state upon the completion of said first timing interval,

(b) contacts upon said second relay connected in circuit with the energization terminals of said first relay and arranged to disconnect said first relay from its source of energization;

(C) energy storage means connected in circuit with said first relay for maintaining its energization for a predetermined interval subsequent to the energization of second relay, said energy storage means cornprising a capacitor connected in circuit across the energization terminals of said first relay.

(D) a direct current energized timing circuit controlling said second relay; and

(E) a direct current supply for said timing circuit (a) said capacitor being connected by said contacts on said second relay during said first timing interval such as to act as the filter capacitor of said direct current supply.

2. An electronic timer circuit as defined in claim 1 and a variable resistor connected in circuit with said capacitor by said second relay at the completion of said first timing interval.

3. An electronic timer circuit providing switching at multiple intervals comprising:

(A) a first relay (a) connected for energization at the beginning of a first timing interval;

(B) a second relay (a) connected for changing its state upon thecompletion of said first timing interval,

(b) contacts upon said second relay connected in circuit with the energization terminals of said first relay and arranged to disconnect said first relay from its source of energization;

(C) energy storage means connected in circuit with said first relay for maintaining its energization for a predetermined interval subsequent to the energization of second relay, and

(D) contacts on said first relay for, when said first relay is energized, connecting it and said second relay in circuit with a source of electrical energy.

4. An electronic timer circuit as defined in claim 3 and 7 f y s 1 (E) a momentary contact switch connected in parallel 3,286,135 11/1966 Haver et al S17-142 across the contacts of said rst relay. 3,320,440 5/ 1967 Reed. 5. An electronic timer circuit as defined in claim 4 3,406,295 10/ 1968 Corey 307-141 XR wherein said second relay is normally de-energized.

JOHN F. COUCH, Primary Examiner 5 Refefences Cted W. M. SHOOP, J R., Assistant Examiner UNITED STATES PATENTS 2,497,656 2/1950 Clarke 317-139 XR 'Us' Cl- X'R' 2,902,707 9/1959 Bearer 317139 XR 307-141; B17-148.5, 154

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