US2075869A - Power circuit - Google Patents

Description

1 K In wen fora. //o r Lws April 1937- P. SHERRICK ET AL 2,075,869

POWER CIRCUIT Filed May 6, 1935 .Pczal Sherrie/t ai 25 tronic tube and having zero grid bias with openrect and alternating current.

Patented Apr. 6, i937 g UNITED" (STATES PATENT worries ism ralllsherriakmdmlmllenchic'agmm,

ailgnontoEEShrientlrOo.,Chicago,llL, aotlflinoia Application Kay 6, 1935, Serial No. 20,058 I cums; (on. sis-20p This invention relates to power circuits used The mercury in the regulator I is electrically imder control of a thermostatic contact device. connected by the lead Iii-to the grid of the elec- The precision which can be obtained in the elec- V tronic tube ii. The filament oi the tube ii is trical control (if temperature or other loads by connected by leads l2 and I! to selectedpoints 5 automatic regulators of various types is largely on the potential divider l, and a high resistance 5 limited by the progressive deterioration of congrid leak I4 is connected between the lead Hi and tacts which are required to carry any appreciable the lead ii. The plate of the tube I l is connected current. Mercury is frequently used as a conby lead ii to a high resistance first stage relay tasting element but unless employed in a vacuum l1 and thence by lead I8 to the main lin I. A

or inert gas is subject to oxidation and consecondenser I9 is connected by leads 2!! and l in 10 (went deterioration as a contactor. parallel relation with the relay H. The arms.-

The main objects of this invention are to proture 22 of the relay is connected to close a convide an improvedjorm oi thermostatic control tact with the lead 23 thence through the second circuit in which there is almost no appreciable stage relay 24 and lead to the main line 2. The

flow of current through the thermally actuated armature 26 oi'the second stage relay is arranged '15 contact and consequently no arcing and no oxito close the circuit through the heating element dation of the mercury; to provide a circuit par- Tl through leads 28 and 29 which are connected ticular1y adapted to give precision in automatic to the main line. control of temperatures in thermal-bath appa- In the form of heating circuit shown, we employ ratus; toprovide an improved circuit giving prea potential divider 3 of the resistance type for else thermal control independent of line voltage supplying filament, plate and grid bias voltages, variations and uneven frequency characteristics; which make easy the conversion ior operation on to provide a power tube circuit sibstantially indirect current circuits. This is true because the dependent of the operatingeiiiciency oi the elecaction of the potential divider is the same on di contacts and excessive grid bias with closed con- In operation the electronic tube acts as a valve tents to provide a regulator circuit having such operating with high plate circuit resistance at a small current flow through the contacts that zero grid potential with the theme-regulator substantially a potential contact rather than-a contacts in the grid circuit applying a sufiicient 30 current contact'is obtained andto provide a power negative bias when the contacts are closed to re- 30 circuit for thermal bath control which can be duce the plate current substantially below the adaptedtooperate onanycommercial service line. operating requirements of the first stage relay A specific embodiment of this invention is ilcoil. lustrated in the accompanyin drawing, which is A three-element tube is satisfactory, but a vaa diagram showing the power circuit as it might riety of tubes may be applied in this application, 35 be employed for heating a thermal bath under the selection being determined by the periormthe control of a thermostat in which the temperance characteristics at zero grid potential. Curature responsive element ismercury. rent drain in the plate circuit is held at a sum- In our improved power circuit the main source ciently low figure by first stage relay coil resis- 40 of current is represented by the lines designated tance to represent only,a small fraction of the 40 l and 2 and may be the usual 110 volt A. C. service rated tube capacity and the tube therefore may lines. The line wires l and I are directly conbe operated at lower voltages than those emnectedtoahigh resistancecoil or potential divider ployed in audio circuits, thus providing a long I in which the fall of potential is substantially lite for the tube. The plate currentoperates the proportional to the length employed. One end first stage relay whose contacts control the coil 45 ot the potential divider I is connected by the lead current in the second stage relay the contacts of I to a condenser 5 and thence by lead i to the which, if desired, may be of the mercury switch contact I of the theme-regulator device 8 which type. This circuit permits the use of alternating is located in the medium whose temperature is to current as plate, filament and coil'voltages, and

5 be controlled, as for example, a thermal bath a eliminates any requirement for rectification of of the type which is described in our copending' alternating current. The first stage relay may be applications for patents, Serial No. 18,698, filed either D. C. or A. C. design, provided only that its April 27, 1935, on Thermo-regulator's, and Serial coll current be held well below the desirable con- 110,113,699, filed April 27, 1935, on Heater and tinuous plate current calculated on a D. C. basis.

5 circulator for thermostatic baths. Such relays have an armature response suiii- 1 such half cycle would be of a. value corresponding cientlyfast to open between the successive half waves delivered from an electronic tube to which alternating current is applied. In order to prevent relay chatter the condenser i 9 is connected in parallel vn'th the relay coil. The capacity of this condenser is determined by calculating the quantity in coulombs necessary to maintain the rated current through the relay coil for a period of one-half cycle. This quantity is then increased by a sufilcient amount to compensate for the progressive voltage reduction between the condenser plates during discharge, this reduction resulting in a mean applied voltage of roughly one-half the line voltage measured across the coil terminal's.

The efiect of this condenser I9 is to fill in the half phase periods during which the tube plate is made negative with respect to the filament, the condenser being recharged at each reverse phase. This arrangement results in smooth and positive relay action regardless of whether D. C. or A. C. power is applied to the circuit.

In the application of the electronic tube, alternate phases of reversal when the thermoregulator contacts are closed, closing' the grid circuit, introduce the possibility of large grid currents. Half of each phase represents a difierence in which the cathode is from 10 to 15 volts negative to thegrid and the current flowing thrqugh the regulator contacts during to 15 volts divided by a resistance figure representing internal cathode togrid resistance plus the resistance of the circuit through the regulator contacts which ampere range.

with the regulator contacts, a. condenser of small capacity. By the use of this condenserth'e cur-Z, rent flowing from the cathode to the grid in the half cycles referred to is limited by the capacity of thecondenser. Theoretically, the correct ca-' pacity of this condenser would be one of the same order of magnitude as the capacity of the grid in which circumstance the grid would be freely charged and discharged to the limit of its capacity at impressed biased voltage and yet, excess current values originated by the fiow of electrons from the cathode to the grid during the reverse phase would be held to the lowest possible quantity. i

Assuming that such a condenser based upon the probable capacity of the grid were or a ca pacity one-ten thousandth of a microfarad, the grid biasfiiteen volts and the frequency sixty cycles, it will be seen that charge, discharge and recharge of the grid circuit condenser would allow maximum currents in the grid circuit through the regulator contact points of no greater order of magnitude will thus be seen that the amounts of current required to fiow across the regulator contacts are minute and only in order of magnitude of grid capacity and it is only such current that is necessary to transfer a charge to and from the grid with the result that in a descriptive, rather than a quantitative sense, the thermoregulator or grid circuit closer makes'a potential contact between its elements rather than a current contact. 3

A grid leakof high resistance value, such as approidmately 10,000 megohms, has proved very satisfactory when used with a 12-A tube and a grid condenser of approximately 0.002 microiaralternating current to circuit would be essentially Zem'." Thiscurrent would rise to values lnthe mllliw than 0.05 to 0.10 microampere. It

ad, to draw the accumulated electrons from the grid when the regulator contacts are opened.

With zero grid bias existing when the regulator contacts are open the plate current is limited only by the impedance of the first stage relay winding and therefore represents the full relay power requirement. When the regulator contacts close an excessive grid bias is applied producing an infinite tube resistance, thus reducing the plate circuit current to a practically zero value.

The excessive grid bias is permitted by the grid condenser 5 which prevents flow of current in the grid circuit in the phases which make the grid positive with respect to the cathode.

By the selection of adequate parallel condenser capacity and the imposition of an excessive grid bias, special adjustments are not necessary because the critical values for relay operation are not approached. With the grid circuit closed, the plate current is infinitesimally small, and with the grid circuit open the plate current is limited only by the impedance of the first stage relay winding which automatically fixes a more than adequate operating power rot-the relay.

The condenser l9 functions as a potential source for supplying'current to the relay winding during the half phases in which no current is supplied through the electronic valve II.

To employ this circuit for direct current, it is only necessary to eliminate the grid condenser 5 and to provide the corresponding coil windings in the second stage relay.

Although but one specific embodiment of this invention is herein shown and described, it will .be-understood that Such currents are entirelyj'elin i. inated by placing in the grid circuit, in series details of the construction shown may be altered or omitted without depart- -ing from the spirit of this invention as defined '-by the following -We claim:

claims.

1. In an electric control circuit, a circuit closer, acondensenan electronic tube having its grid connected to said circuit closer in series with said condenser, and a potential divider having a pair of taps connected to the filament of said electronic tube and one of said taps connected to the grid through a grid leak, whereby open contacts of said circuit closer give zero grid bias and closed. contacts excessive grid bias.

2. In an electric control circuit, a thermal regulator havinga pair of cooperating contacts, a condenser, an electronic tube having its grid connected to said re lator in series with said condenser, and'a potential divider having a pair of taps connected to the filament of said electronic tube and one of said taps connected to the grid through a grid leak, whereby open contacts of said thermal regulator give zero grid bias and closed contacts excessive rigid bias.

3. An electric power circuit comprising a potential divider, a contacting element connected through a condenser to. one end of said potential divider, an electronic tube having a grid connected to a second contacting element, said contact elements being arrangedto cooperate with each other in a temperature responsive device, a filament in said tube connected to selected points on sid potential divider, a. grid leak connecting said grid to one of said filament leads, a first stage relay, 8. plate in said electronic tube connected through said first stage relay to the opposite end of said potential divider, a. oondener shunting said first stage relay, electrical heating means positioned to influence said temperature responsive device, and a. circuit for said heating means controlled by said relay.

4. An electric power circuit comprising a circuit closer, an electronic tube, a grid circuit having a condenser in series with said circuit closer, a plate circuit including a relay, and a potential divider having a pair of tapsconnected to the filament of said tube and arranged to give through a grid leak zero grid bias on an open grid circuit and excessive grid bias on a closed grid cir cuit, all arranged whereby said circuit closer controls said relay and makes substantially a potential contact rather than current contact.

5. Apparatus of the class described, comprising a thermostatic circuit closer, an electronic tube,

a grid circuit having a condenser in series with said circuit closer, a plate circuit including a relay, a potential divider having a pair of taps connected to the filament of said tube and arranged to give through a grid leak zero gridbias on an open circuit and excessive grid bias on a closed grid circuit, whereby said circuit closer controls said relay and makes substantially a potential contact rather than a current contact,.e1ectrical heating means positioned to influence said circuit closer, and a power circuit for said heating means controlled by said relay.

- PAUL SI-IERRICK.

CHARLES H. NHLIER.

CERTIFICATE OF CORRECTION.

Patent No. 2,075,869.

April 6, 1937.

PAUL SHERRICK, ET AL.

It is hereby certified that error appears in the printed specificaticr of. the above numbered patent requiring correction as follows:

Page 2,

second column, line 59, claim 2, for "rigid" read grid; and page 5,

second column, line 6, claim 5, after the word 'open" insert the word grid; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Seal) Henry Van Arsdale Acting Commissioner of Patent:

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