US2515477A

US2515477A - Electronic timer

Info

Publication number: US2515477A
Application number: US709016A
Authority: US
Inventors: Bernhard F Tellkamp
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1946-11-09
Filing date: 1946-11-09
Publication date: 1950-07-18
Anticipated expiration: 1967-07-18

Description

B. F. 'I'ELLKAMP ELECTRONIC TIMER Jul 18, 1950 2 Sheets-Sheet 1 Filed Nov. 9, 1946 FIG.

BERNHARD F. TELLKAMP' INVENTOR. gymjq ATTORNEY ELECTRONIC TIMER Filed Nov. 9, 1946 2 Sheets-Sheet 2 FIGE.

TIMER DISCHARGE CURVES VOLTAGE 5 1 l3 VOLTS cl .53 FARAD$ R =IO OHMS VOLTAGE s 1. 5 VOLTS CURVE B,B| 01:55 mcRoFARADs- RI=IOGOHMS O 60 A A O MAXIMUM MINIMUM Tum-z SETTING TIME SETTING 20 TIME SECONDS BERNHARD F. TELLKAMP 1N VEN TOR.

Patented July 18, 1950 ELECTRONIC TIMER Bernhard F. Tellkamp, Whitefish Bay, Wis., as-

signor to Allen-Bradley Company, Milwaukee, Wis, a corporation of Wisconsin Application November 9, 1946, Serial No. 709,016

'7 Claims. 1

This invention relates to improvements in electronic timing devices, and in particular to electronic timing devices in which the time setting is adjustable over a range of values, or in which predetermined time intervals are obtained without the necessity of accurately matched resistance values. It is in the field of the developments contained in the pending application, Serial No. 567,721 of Lynn H. Matthias filed December 11, 1944. Both applications are assigned to the Allen-Bradley Company.

One object of my invention is an electrical timing circuit which as made in commercial production will be uniform in performance.

Another object of my invention is an electrical timing circuit that will maintain its timing range regardless of normal changes in electron tubes; variations in one tube to another; or of changes in values of adjusting resistors.

A further object of my invention is the provision of a circuit employing a variable charging voltage for the timing capacitor, and also a variable bucking voltage to which it is discharged. This feature, when used in conjunction with various appropriate values of the timing capacitor and its associated discharge resistor, allows the use of various shapes of discharge curve for the same time range, and consequently the selection of the optimum shape of discharge curve to minimize the effect of line voltage changes, and

changes in the characteristic curves of the electron tubes used in the circuit.

A further object of my invention is the use of the maximum-voltage capabilities of the grid circult of the electron tube employed and at the same time providing the maximum timing range.

Timing circuits utilizing the discharge time of a capacitor shunted by a resistor are well known in the art, however, these devices as presently made require the accurate matching of resistance values of a number of resistors to maintain their calibration and small changes in these resistance values or of the tube characteristics make large changes in the timing.

The negative grid voltages developed in present timing circuits are so high as to limit the timing capacitor voltage to a low value requiring large timing capacitors, particularly when used with gas filled Thyratron tubes.

It is desirable that an electronic timing circuit be simple and inexpensive to manufacture and that the resulting devices be uniform and permanent in their operating characteristics.

My invention fulfills these requirements and the ill accompanying diagrams and description illus- 2 trate the manner of obtaining the above desirable characteristics, in which Fig. 1 is a circuit diagram of my invention in which Fig. 2 are time gurves showing results obtainable in my inven- In the circuit arran ement in Fig. l the electronic tube is represented by E. its anode by P, its control grid by G, and its cathode by K. The cathode is heated by heater H, and an aux liary grid S is connected to the ca hode in this in stance. This tube may be of the type commonly known as a Thyratron tube, particularly the gas filled type.

The work circuit illustrated in heavy lines consists of the cathode K, transformer winding T2,

the magnet coil M of relay CR and the anode P. Variation in the control potential on the grid G prevents or allows completion of the work circuit thus operating the relay CR. Condenser C2 and resistor R4 which are connected in shunt with magnet coil M stabilize the operation of relay CR on the rectified half wave current.

. The control and timing portion of this circuit consists of grid G, resistor R5, the timing network C1R1, transfer resistor R3, transformer winding T1, the voltage dividing potentiometer R2 and cathode K. The purpose of transfer resistor R3 is to change the connection of point 3 from L1 to L2 by the closing of the single pole single throw switch SW. The switch SW changes from the reset or charging condition when open to the timing condition when closed. Potentiometer R2 adjusts the length of the timing interval. The cathode heater H is connected to transformer winding T3 as shown. Transformer windings T1, T2 and T3 are on the same core and arranged to make the grid negative when the anode is positive. Terminals L1 and L2 are used to connect the timing relay to a power supply source such as 115 volts, cycle alternating current. Capacitor C3 connected as shown bypasses high frequency surges and resistor R5 limits the grid current when capacitor C1 is being charged.

Alternatively the transformer winding T2 may be used as the primary and connected by leads L3 and L4 to a different voltage power source as 230 volts, making the device useful on either of two voltages without added windings.

In one method of operation the transformer primary T1 is connected to a source of power through connections L1 and L2 as shown. The heater H which is connected to transformer winding T3 heats the cathode K to operating temperature. With the switch SW in the open position current flows from winding T1 through re-,

sistance Rs when connection L1 is positive, and continues by way of capacitor C1 and resistance R to grid G, cathode K and adjustable connection Q to a point effectively near the opposite end of winding T1. Electron flow is in the reverse direction around this circuit and the voltage is thereby built up across condenser C1 making the grid more negative. During the grid-positive part of each succeeding cycle this voltage increases until the voltage across the capacitor C1 is nearly equal to the crest of the positive half cycle. The resistor R1 conducts a small amount of current from point 3 to point 4, namely, the connections at opposite sides of resistor R1, slightly lowering the capacitor voltage during the grid-negative half cycle. This loss is made up on each gridpositive half cycle, and the small voltage drop of the tube E and the circuit resistance while conducting the current discharged through resistor R1 is the difierence between the crest voltage and the voltage across capacitor 01. During this charging period the anode is negative when the grid is positive and no current flows through magnet coil M. When the anode is positive the grid is negative and blocks the flow of current through magnet coil M and relay CR remains in the non-operated position.

To start a timing interval the switch SW is closed connecting point -3 to terminal L2. The alternating voltage from connection Q to L2 is thus placed in series with the direct voltage stored in the capacitor C1 and when L2 is negative with respect to Q, adds to the negative voltage on the number 4 terminal of the capacitor. At this time the anode is negative and no current flows through magnet coil When L2 is positive with respect to Q the voltage from Q to L2 opposes the voltage across capacitor C1 and after the voltage across Ci has been reduced by the continued discharge through resistance R1 the net voltage on the grid is reduced to a Value too low to block the flow of current in the anode circuit, the timed interval ends and the relay GR is operated by flow of current through magnet coil M. On succeeding cycles current flows in the anode circuit each time the anode is positive and the relay CR remains operated as long as the switch SW is closed. When it is desired to energize a load during the timing interval and disconnect itat the end of the timing interval the load is connected from L1 across the contacts of the relay to terminal L5.

Thus the load is energized througha normally closed contact on CR and the switch SW during the time interval between the closin of SW and the operation of CR. This time interval is adjusted by changing the position of tap Q on resistor R2. Movingthe tap Q toward S reduces the timing interval by lowering the voltage to which the capacitor C1 is charged and simultaneouslyincreasing the bucking voltage from Q to L2 to which] the capacitor C1 discharges. When the bucking and charging. voltages are made substantially equal the grid G is at the critical voltage'immediately when SW is closed, anode current flows, and the time interval is only that required for the relay CR to close, on the order of a few one hundredths of a second.

At this minimum settin the bucking and charging voltage crests are each approximately equal to half the voltage crest from L1 to L2 and on the half cycle when L2 is negative with respect to Q with SW closed atthe start of the timing interval the maximum negative grid voltage is equal to the sum of these bucking and charging voltage crests or on the order of /2=163 volts for 115 volts from L1 to L2.

In circuits where the charging voltage is not reduced for short time intervals the bucking voltage must be increased to equal the full charging voltage to obtain minimum timing and this results in the sum of the charging and bucking voltages being on the order of 2X115 /2=326 volts negative on the grid of the tube E. This exceeds the allowable negative grid voltage on desirable types of gas filled Thyratrons, hence the chargin voltage must be lowered and capacitor C1 increased in capacity to maintain the same timing range with increased cost and bulk.

Moving the tap Q toward S3 increases the timing interval by raising the voltage to which the capacitor C1 is charged and simultaneously decreasing the bucking voltage from Q to L2 to which it discharges. With Q set at Sc the maximum time interval is obtained, and since the voltage of S3 to L2 is fixed by the transformer and does not depend upon possible changes in a resistor voltage divider it may be set at a value most desirable from the standpoint of accuracy under fluctuating line voltage conditions, and changes in tube critical grid voltage, and it will maintain this value. In Fig. 2 is shown the effect of two different values of voltage S3 to L2 on the shape of the discharge curve of timing capacitor C1.

Taps S, S1, S2 andSa may be connected to Q by a multi-position switch thus eliminating the potentiometer.

In a particular assembly of parts the following values were used; and the timing range and typical voltages are listed.

R1 =1,650,000 ohms 01:.25 microfarad R5=2000 ohms R =5000 ohms R4=200 ohms C2=8 microfarads C3=.01 microfarad R2=6850 ohms Electron tube type 502 Thyratron Voltage of T1 winding, SW closed, 115 volts R. M. S. 1

Voltage of T2 winding, SW closed, 154 volts R. M. S.

Voltage of T3 winding, SW closed, 6.1 volts R. M. S.

Voltage S3 to L2 winding, SW closed, 4.5 volts R. M. S.

Voltage across magnet windingM, SW closed,

111 volts avg.

Minimum time setting .035 second Q at S, C1

charges to 69 volts, discharges to 61 volts Maximum time setting 1.07 seconds Q at S3, C1

charges to 132 volts, discharges to 6 volts Supply voltage 115 volts, L1 to In The exact components described and the particular circuit shown are one embodiment of my invention and not to be considered as the only means of obtaining its advantages. With appro priate circuit constants vacuum type electronic tubes may be used as well as the Thyratron type used in the foregoing illustrative case.

What I claim as my invention is as follows:

1. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a power source connected in series with said anode and cathode; a capacitor bridged by a resistor with one terminal of the capacitor connected to said grid; the other terminal of the capacitor connected through a resistance to a second power source phased to make the grid of said tube negative when its anode is positive; a switch arranged to connect said second terminal of the capacitor to the other terminal of said second power source when closed; in combination therewith a potential divider connected to said second source of power with its adjustable contact connected to said cathode.

2. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a transformer winding connected in series with said anode and cathode; a capacitor bridged b a resistor with one terminal of the capacitor connected to said grid; a second transformer winding connected to the second terminal of said capacitor and phased to make the grid of said tube negative when its anode is positive; a switch arranged to connect a transfer resistor across said second transformer winding; in combination therewith a potential divider connected across said second transformer winding and having its adjustable contact connected to said cathode, and means including said switch to charge said capacitor to a predetermined voltage when said switch is open and discharge said capacitor to a second predetermined voltage when said switch is closed to effect operation of the current responsive device.

3. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a transformer winding connected in series with said anode and cathode; a capacitor bridged by a resistor with one terminal of the capacitor connected to said grid; the second terminal Of the capacitor connected through a resistance to a second transformer winding phased to make the grid of said tube negative when its anode is positive; a switch arranged to connect said second terminal of the capacitor to the other terminal of said second transformer Winding when closed; in combination therewith a potential divider connected to said second transformer windin withv its adjustable contact connected to said cathode.

4. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a power source connected in series with said anode and cathode; a capacitor bridged by a, resistor with one terminal of the capacitor connected to said grid; a second power source connected through a transfer resistor to the second terminal of said capacitor and phased to make th grid of said tube negative when its anode is positive; a switch arranged to connect said transfer resistor across said second power source; in combination therewith a potential divider with its ends connected to said second power source and its movable contact connected to said cathode, and means including said switch and transfer resistor for connecting the said second terminal of said capacitor to one end of said second power source when said switch is open and to the other end of said second power source when said switch is closed.

5. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a power source connected in series with said anode and cathode; a capacitor bridged by a resistor with one terminal of the capacitor connected to said grid; a second power source connected through a transfer resistor to the second terminal of said capacitor and phased to make the grid of said tube negative when its anode is positive; a switch arranged to connect said transfer resistor across said second power source; in combination therewith a potential divider with its ends connected to said second power source and its movable contact connected to said cathode and means including said switch and transfer resistor for charging said capacitor to an adjustable fraction of the supply voltage crest when the switch is open and allowing the capacitor to discharge to the remaining fraction of the supply voltage crest when the switch is closed, to elfect operation of the current responsive device.

6. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a power source connected in series with said anode and cathode; a capacitor bridged by a resistor with one terminal of the capacitor connected to said grid; a second power source connected through. a transfer resistor to the second terminal of said capacitor and phased to make the grid of said tube negative when its anode is positive; a switch arranged to connect said transfer resistor across said second power source; in combination therewith a potential divider having its ends connected to said second source of power and its movable contact connected to said cathode; and means including said switch and transfer resistor for connecting the second terminal of said capacitor to one end of said second power source to charge the capacitor when said switch is open and allow the capacitor to discharge when said switch is closed to effect operation of the current responsive device.

7. In an apparatus for producing a time delay, having an electron tube with anode, cathode and grid; a current responsive device and a power source connected in series with said anode and cathode; a capacitor bridged b a resistor with one terminal of the capacitor connected to said grid; a second power source connected through a transfer resistor to the second terminal of said capacitor and phased to make the grid of said tube negative when its anode is positive; a switch arranged to connect said transfer resistor across said second power source; in combination therewith a potential divider connected across said second source of power and having its adjustable contact connected to said cathode, and means including said switch to charge said capacitor to a predetermined voltage when said switch is open and discharge said capacitor to a second predetermined voltage when said switch is closed to effect operation of the current responsive device.

BERNI-IARD F. TELLKAMP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,171,347 Schneider Aug. 29, 1939 2,292,846 Pritchard Aug. 11, 1942 2,296,580 Smiley Sept. 22, 1942 2,371,981 Few Mar. 20, 194.5