US2453486A - Electronic timer - Google Patents

Description

Nov. 9, 1948. J. BALL ELECTRONIC TIMER Filed Jan. 1, 1945 g x 2/ 28 L I 300 INVENTOR. FE. 5.- JACK BALL.

Patented Nov. 9, 1948 ELECTRONIC TIMER Jack Ball, Cleveland, Ohio, assignor to Picker X-Ray Corporation Waite Manufacturing Division, Inc., Cleveland, Ohio, a corporation of Ohio Application January 1, 1945, Serial No. 570,977

5 Claims. 1

This invention relates to improvements in a timer of the electronic type and adapted to cause the closing and opening of a power circuit.

An object of the present invention is to provide novel means for very accurately timing periods of short duration.

Another object of the present invention is to provide a circuit wherein the time period depends upon a space-discharge device to which voltage is applied only for the very short duration of the operation timed.

Another object of the present invention is to provide timing means controlled by the time period necessary to build up a predetermined charge on a condenser which is short circuited except during the short period when a timing operation is being performed.

Another object of the present invention is to provide novel means for insuring that the controlled circuit will be opened at the end of a selected time period or very shortly thereafter under all circumstances.

Other objects of the invention comprise the provision of safety devices insuring the proper operation of all parts at all times and the novel arrangement of circuits as disclosed in the accompanying drawings and specification, and the essential features of my invention will be set forth in the appended claims.

In the drawings,

Fig. 1 is a view showing one embodiment of my invention utilizing rectified A, C. current in the timing circuit;

Fig. 2 is similar to Fig. 1 but illustrates a number of safety features added to the circuit of Fig. 1 to insure the proper operation under all circumstances; while Fig. 3 is a circuit similar to Fig. 1 but utilizing A. C. current in the timing circuit.

Referring to Fig. 1, the circuit Ill represents the controlled circuit in which the electrical energy is to be applied for a predetermined period. In one form of my device, it is utilized for controlling the exposure of an X-ray tube. Referring to United States Letters Patent Number 2,267,908, granted December 30, 1941, to Edwin R. Goldfield et al., my circuit Ill of the present application might well be used to energize the relay I! of the said Goldfield et al. patent so as to hold the X-ray tube circuit in energized condition so long as the relay is energized by my controlled circuit, and when my control circuit is de-energized, then the relay I! would be deenergized and the contact member 16 of the Goldfield et a1. patent would automaticallyopenand,

de-energize the X-ray tube circuit. This application of my invention is illustrative only and in no sense a limitation upon my invention.

Referring back to Fig. 1 of the drawings, in series in the circuit I0 is a pair of normally open contacts H (which are closed at the beginning of a timed period) and a set of normally closed contacts l2 (which are opened to terminate a timed period). To a suitable low voltage source L1, L2, are connected lines 13 and M. In one of these lines is placed the manually controlled push-button [5 whose associated contacts l6 are normally opened, and closed only so long as the button I5 is held down. Connected between lines l3 and i4 is a relay coil I! which controls the contacts II. A second relay coil ii! is connected between lines l3 and [4 for the purpose of controlling two sets of contacts, namely [9 and 20, as will later appear.

The circuit for controlling the timing operation comprises a transformer 2| having a primary 2la energized from the source L1, L2, and two secondaries 21b and Zlcl circuit is illustrated comprising the rectifier tube 22:;-whose plates 22a and 22b are connected with opposite ends of the transformer winding 2lb and whose cathode 220 is energized from the transformer winding 2lc. Rectified current is thus supplied between line 23 and line 24, the latter having a central tap on the transformer winding 2lb. The usual condenser 25 is connected between lines 23 and 24. The resistance 25 is connected between lines 23 and 24, and a voltage regulator tube 2! is connected in parallel with this resistance to maintain a constant voltage between the tap 26a and line 24. Thus tube is shown with a cold cathode, but may be pro-. vided with a hot cathode if desired. Line 28 is connected with tap 26a and contains in series a the relay coil 29 which controls the contacts l2. Also in series in line 28 is the pair of normally open contacts 20 previously mentioned. A triode 30 is connected between lines 28 and 24. The triode has a plate 30a, a cathode 30b and a control grid 300. This tube is of the glow type which is non-conducting until the charge on the grid 30c rises to a certain threshold value.

The tube is shown with a cold cathode but might have a hot cathode if desired. One of the pair of normally closed contacts 19 is connected by I line 3| to line 24. The other of the contacts I9 is connected by line 32 to line 24 and in this line is provided the condenser 33. The voltage across condenser 33 is supplied from tap 261) on resistance- 26-throughJvariable resistance*.34.-

A known rectifier v At the time pushl9, which up to this moment have kept the con,-

denser 33 short circuited. A charge then begins to build up on condenser 33 and the. charging; rate of this condenser is determinedby (a) the potential between tap 26b and line 24-(this;is-

adjustable to give a rough time adjustment),

(b) by the capacitance of condenser-.33, and (c) by the value of the variable resistance 34 which is adjustable to give a finer time adjustment. At the moment the relay,coil i8 opened the c sla s l sed bei mallrq n c m ,,.the charge Oll -00114216115611 has risen slightly tacts ;2 ll. This placed the substantially constant potentia between tap 25 a and line 2t, across-the 1 plate 39a of the tube control of the relay winding is therelaywinding G2 which controls the norcircuit iii.-

.nectedwith line 4 and in Fig. 2 I have shown means for protecting the apparatus against such faulty operation. To this end, tube 3Q, similar to tube 3E? but having a slightly different grid, is connected in parallel with tube 3c between the upper end. of resistance 25 and line The tap 7250 for this purpose is close to 25a and is connected by line ill to the In series in line it, are the pair of normally open contacts ll under the Also in line 49 mally closed relay contacts 45; which are in the The cathode 39b of tube 35 is con- The grid Ziiic is connected .by M'tdline 3b. The tube 39 is so constructed and arranged that it becomes conducting when the charge on, grid Slicis a small amount, say

'five or ten volts, higher than the charge on grid Silc neccssaryto render the tube Bil conducting. it results from this construction, that upon fail ure of tube. til thetime periodwili continue until ,above the normally intended value so as to build tube ,30,;.-;- This is ,a trigger =tube aswmentioned aboveand is -non .-conducting .until the charge on,

the grid Silo-rises toa prcdeterminedvalue. It

will be; noted that there isnopotential across i line 4E8, tube 39, and line 2 thus energizing relay ;.windi ng' Gland opening thenormally closed. conthe tubesllun-til the moment.atimingoperaticn i begins;

(la-energize ,the, controlled circuit lil.

The oontacts lzwillremain open as long as relayfl-B; is energized which in turn is as long as the tube 3|} remains conducting. 1 ,As is :well known, the only way to recycle orto stop the,

triggeritube illl from conducting, (when D. .C.-cu.r-

to set the device; foranother exposure,

. seal) is,- t o remove-the current entirely. 1 In other words, push-buttor idmustbev -opened up a charge on grid 38c sufficient to render tube Moon ducting. Khereupon, current flows through tacts 53. This will de-energize circuit to after a time periodbut slightly longer than would. have been the case had tube 30 been functioning properly.

Preferably, but notnecessarily, I make the relay npoints iil of ,thelatched out type which I have ..indicateddiagrammatically by the latch The The above described device isvery accurate becau$e-tube and condenser leakage, in; the, timing circuit is held to a minimum. No power ,is applied ,to tube 33.;and thecondenser 33 is short circuiteduntil theinstant the timedlgperiodbemined,

The apparatus of Figt2inc1udes vall oftheparts describediin connection-with Fig. l with the. ad-.

,in placethereof The latch 45 must be mar -rcset before another operation may be operation oi-this-type of relayis well known and results in the contacts it? being latched in open -positi-on once they are opened by the energization of thareiay windingflZ. This will call the attention of the operator to the fact that tube 35! has. failed so that a new tube may be inserted and it-is assumed that before resettin this latch ,XQlflY, the operator will insert new tube 35'! so that the device is again safe against operation for an extended time periodother than that intended or expected A modification of Fig-2 which may or may not gins, and all ofthefactors, controllingthechargv be used is the insertionof the voltage regulator ing otthe condenser 33 are accuratelypredetei tube 46 between lines and 2 t. This insures a little morepositively a constant voltage at tap 26b andinsures .a little more accurately that the condenser 33 Will be charged in exactly the time interval. selected.

insureithe safe operation -.thereof.,-under all conditionsa'. All parts. :Which'are exactly like those. a

of Fig. lwand whichtoperate asthere described have been !given.:-the samereference. characters;

in Fig.2,aand further descriptionof thesefeatures will, therefore, be unnecessary To insure. against voltage failure in the. timing Fig. 3islikeFig. 1 except that it illustrates the use oi -A. C. current in the timing circuits. To

this end, the low voltage source L1, L2, is con nectedtoxthe primary Winding in as before, but

the secondary winding 2M is directly across the lines Hand 24. v The rest of the circuits are like those shown in Fig. land perform the same func- .tions,v and, therefore, have been given the same reference Characters,

cult from that shown in Fig. l is that using A. C. ourrentiacross the tube 3i, it might be possible lines 23 andizdand is so constructed.andarranged.v energizationof circuit 58. i1 the push-button l5 that when the .-voltage .is. normalin the winding maticallycand; energizationof circuit Hr under these circumstances isimpossible.

A studyofqFig. 1. will Show that iitube to shouldiail, the ener izationof circuit .ltlwould. extend past theperiodset;oaths-timing device,

One difference in this cirfor this tube to recycle and to go on. with the were held closed. This might or might not be .clisadvantageous depending upon the circum stances .To avoid this possibility, the rectified current of Fig.1 may be used.

What-I claim is: 1. Means for timing the period of energization .of a powercircuit comprising means for causing :energizatiomof said circuit including a first relay,

tube of the trigger type having a control grid controlling the conductivity condition of said tube and a source of substantially constant electric potential for said timing circuit, a condenser circuit including a condenser controlling the potential of said grid and a source of electricity for charging said condenser and a short circuit for said condenser including a pair of normally closed contacts. voltage regulator means for controlling the potential of said electrical sources for said timing circuit and for said condenser circuit, relay means for opening said normally closed contacts of said condenser circuit and for closing said normally open contacts of said timing circuit means for energizing said relay means substantially simultaneously with energization of said first relay. and said second re ay being responsive to a change in the conduc ivity condition of said tube to cause deenergization of said power circuit.

2. Means f r t ming the period of en rg z ion. of a power circuit comprising means for causing energization of said circuit including a first relay, means for causing de-energization of said circuit including a second relay, an energizing timing circuit for said second rela including in series a pair of normally open contacts and a space discharge tube of the trigger type having a control grid controlling the conductivity condit on of said tube and a source of substantially constant electric potential for said timing circuit, a condenser circuit including a condenser controlling the potential of said grid and a source of electricity for charging said condenser and a short circuit for said condenser including a pair of normally closed contacts, relay means for opening said normally closed contacts of said condenser circuit and for closing said normally open contacts of said timing circuit, means for energizing said relay means substantially simultaneously with energization of said first relay, said second relay being responsive to a change in the conductivity condition of said tube to cause de-energization of said power circuit, a second space discharge tube of the trigger type connected in parallel with said first named trigger tube, said second trigger tube having a control grid connected in parallel with said first I named control grid, said second trigger tube being adapted to change its conductivity condition at a potential of its control grid slightly higher than the threshold potential of the control grid of said first named trigger tube, a safety relay in circuit with said second trigger tube adapted on a change in conductivity condition of said second trigger tube to cause de-energization of said power circuit, and a pair of normally open contacts in series circuit with said second trigger tube and adapted to be closed by energization of said relay means.

3. Means for timing the period of energization of a power circuit comprising means for causing energization of said circuit including a first relay, means for causing de-energization of said circuit including a second relay, and energizing timing circuit for said second relay including in series a pair of normally open contacts and a space discharge tube of the trigger type having a control grid controlling the conductivity condition of said tube and a source of substantially constant electric potential for said timing circuit, a condenser circuit including a condenser controlling the potential of said grid and a source of electricity for charging said condenser and a short circuitfor said condenser including a pair of normally closed contacts, relay means for opening said normally closed contacts of said condenser circuit and for closing said normally open contacts of said timing circuit, means for energizing said relay means substantially simultaneously with energization of said first relay, said second relay being responsive to a change in the conductivity condition of said tube to cause de-energization of said power circuit, a second space discharge tube of the trigger type connected in parallel wtih said first named trigger tube, said second trigger tube having a control grid connected in parallel with said first named control grid, said second trigger tube being adapted to change its conductivity condition at a potential of its control grid slightly higher than the threshold potential of the control grid of said first named trigger tube, a safety relay in circuit with said second trigger tube adapted on a change in conductivity condition of said second trigger tube to cause de-energization of said power circu t manually resettable maintaining means for holding said safety relay in power-circuit-de-energizing position, and a pair of normally open contacts in series circuit with said second trigger tube and adapted to be closed by energization of said relay means.

4. Means for timing the period of energization of a ower circuit after initial operation thereof including a relay for initiating operation thereof, two space discharge tub-es, each of said tubes having a contro1 grid controlling the conductivity condition of its associated tube at a predetermined threshold, a condenser in circuit with said grids in parallel, electrical contact means normally short-circniiing said condenser, and electrical circuit energized by said first named relay for opening said contact means, a source of electricity for charging said condenser, an electrical circuit energized by said first named relay for connecting said source with said condenser, a relay responsive to a change in the conductivity condition of each of said tubes for causing opening of said power circuit, and the threshold of one of said tubes being slightly higher than the threshold of the other of said tubes, whereby said tube of higher threshold is normally unoperated and is available for operation upon failure of said tube of lower threshold.

5. Means for timing the period of energization of a power circuit after initial operation thereof including means for initiating operation thereof, means for causing de-energization of said circuit including a relay, an energizing timing circuit for said relay including in series a pair of normally open contacts and a space discharge tube having a control grid controlling the conductivity condition of said tube and a source of substantially constant electrical potential for said timing circuit, a condenser circuit including a condenser controlling the potential of said grid and a source of electricity for charging said condenser and a short-circuit for said condenser including a pair of normally closed contacts, voltage regulator means for controlling the potential of said electrical sources for said timing circuit and for said condenser circuit, said condenser circuit including a. variable tap on its associated electrical source for providing a rough time adjustment, said condenser circuit including other variable means for providing a fine time adjustment, relay means for opening said normally closed contacts of said condenser circuit and for closing said normally open contacts of said timing circuit, means circuit.

Number l for energizingsaid relaymeans responsive "to said first named means, and said relay being respon- 'sive to a change in theaconductivitycondition of said tube'to cause de-energization of said power 1 JACK BA-LL REFERENCES" CITED The following references are of i'e'cordrin the file of this-patent:

1 "UNITED "STATES PATENTS Name =-.Dat'e I 1,432,006 -Wo1tman Oct; 17, 1922 Number Number 8 -'Name Date Brainard Mar. 14, 1933 Blomberg May 2, 1933 Almquist July 11, 1933 Stogoff Nov. 12, 1935 Honaman Jan. 4, 1938 Sweeny Aug. 12, 1941 Weitmann May 5, 1942 Richardson Dec. 8', 1942 Schwarzschild Sept. 11, 1945 FOREIGN PATENTS Country Date Great Britain Aug. 11, 1942

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