US2379873A - Electronic control device - Google Patents

Description

July 10, 1945. F. E. LANGE ELECTRONIC CONTROL DEVICE Filed Jan. 9, 1943 Gttomeg Patented July 10, 1945 Frederick E. Lange,

Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January 9, 1943, Serial No. 471,841

6 Claims.

The present invention is concerned with an electronic control, device and more particularly with one designed to determine whether an impedance is rectifying or not.

In the co-pending application of Vilynn 0. Beam, Serial No. 450,613, filed by July 11, 1942, there is described a control device which is adapted to determine whether an impedance connected across a gap is rectifying or not and to act in one manner when the impedance is rectifying and to act in another when the gap is either open circuited or is bridged by an impedance which is non-rectifying. In this circult of the Beam application, a plurality of electronic triodes are employed, one of these triodes being employed as the main control triode and the other to function as a rectifier and to introduce certain phase shifting features. The presence of this last named triode increases the complication of the apparatu 'and adds to the number of auxiliary circuit elements which must be employed.

It is a general object ofthe present invention to provide a control device accomplishing the functions of .the device described in the aforesaid Beam application by employing a single electronic discharge device having but one anode.

A further object of the present invention is to provide a control device of the electronic type having but a single electronic amplifier, which amplifier has only one anode, the control device including a first connection between the control electrode of the amplifier and a source of power to maintain the potential of the control electrode below the value at which the amplifier is effectively conductive and a second connection between the control electrode and a different point on the source of power, thi second connection being such that it would normally also tend to maintain the control electrode potential below this value but having means associated with it which is effective upon a gap in the connection being bridged by a rectifying impedance to raise the potential of the grid above this value.

A further object of the invention is to provide a control device such as set out in the last object in which the means for raising the potential of the control electrode upon the impedance being rectifying is a condenser connected to the control electrode.

A further object of the present invention is to provide a burner control system embodying the control device of the previously named objects in which the means acting as a rectifying impedance is a means responsive to the burner lime and rectifying only when it is exposed to a burner Referring to the drawing, the control device of the present invention is shown as being located within a housing I 0. This housing may be of any suitable form. If the housing is of metal it is desirable that it be connected to ground as at l I.

Disposed within the housing I0 is a step up; step down transformer I2 having a line voltage primary l3, a high voltage secondary winding 15 and low voltage secondary windings I4 and IS. The primary winding l3is connected to terminals l1 and I8 and by conductors l9 and. 20 to line wires 3| and 32 leading to any suitable source of alternating power (not shown). The low voltage secondary winding l6 isv employed for energizing auxiliary apparatus to be controlled by the control device. The secondaries l4 and I5 are employed to energize the various elements of the control device. As faras the apparatus of the present invention is concerned, the transformer l2 constitutes the source of power and elsewhere nected to some primary source of power.

A relay 2| comprises a relay coil 22 and a switch blade 23 adapted to engage a fixed contact 24. Switch blade 23 is associated with an armature 25 which in turn is associated with the relay coil 22. Switch blade 23 is normally biased by gravity or other suitable means away from contact 24. Upon energization of relay coil 22, however, the armature 25 is drawnv to the left to move switch blade 23 into engagement with contact 24.

A condenser 21 is connected by conductors 28, 29 and 30 in parallel with relay coil 22. Condenser 2! acts as a shunt condenser to eliminate any pulsations in the relay coil 22.

The energization of relay coil 22 is controlled by an electronic discharge device 33. This device comprises a conventional envelope 34 which oncloses a cathode 35, rid 3]. The cathode 35 current flowing through an anode 33, and a control I is of the indirectly heated type and has a heater 4| associated there- 'a "negative cut off point.

atively uniform when a voltage is applied to the output circuit of such magnitude that the ampliher is effectively conductive only when the potential of the grid is positive with respect to a cut off potential substantially negative with respect to the cathode. In other words, the discharge device is of the conventional type normally operated with It is to be understood that the terms "cut oil! potential or cut oil? poin as used in the specification and claims refer to the grid potential at which the amplifier output is insuflicient to energize the relay even though there still may be an appreciable current flow through the relay. In other. words. at the "cut ofl potential, the amplifier is eflectively non conductive.

A condenser 45 and a current limiting resistor 48 are connected between the grid 31 and tap 41 of secondary I5 by conductors 48 and 49. The right hand terminal of condenser 45 is connected to ground as indicated at 50. The condenser 45 is employed to control the potential of the grid 31. as will be more fully. explained later.

The relay 2| is illustratively shown as controlling an electrically operated gas valve 54. This as valve is of the type which when energized permits a flow of gas and which upon deenergization interrupts such flow. The gas valve 54 controls the flow of gas through a pipe 55 to a main gas burner 56. Located adjacent to the main gas burner 56 is a pilot burner 51, the flame of which is indicated by the reference numeral 58.

The pilot burner 51 is connected to ground as indicated at 59. The pilot burner is supplied with gas by a pipe 60 which is connected to the gas supplv pipe 55 at a point on the upstream side of valve 54 so that the pilot burner 51 is normally constantly supplied with gas and hence normally constantly burning. A flame electrode Si is mounted so that it extends into the flame 58, when present. This flame electrode is coni nected by conductor 62; terminal 53, and conductor 54 to a resistor 65. The resistor 65 is in turn connected by conductor 66 to the; lower terminal of secondary 15.

The energization of valve 54 is not only controlled by relay 2! but also by a room thermostat 10. This room thermostat is of conventional construction and comprises a bimetallic element 1| to which is secured a contact arm 12. The contact arm 12 is adapted to be moved into and out of engagement with a fixed contact 13. As indicated by the legends C and H, the bimetallic element 1| is effective to move the contact arm 12 to the left in the direction of contact 13 upon atemperature fall and to the right away from contact 13 upon a temperature rise. A magnet 14 is associated with contact arm 12 to impart a snap action to the contact arm and to cause a suitable differential to exist between the temperature at which the contact arm 12 engages contact 13 and that at which it separates from contact 13. v

The following values are the values which can be employed in one embodiment of the invention.

The transformer i2 can be so designed that the voltage of secondary I8 is 24 volts and the voltage of each half of secondary I5, 300 volts. The tap 41 can be displaced approximately 24 volts from the center tap of secondary I5. The voltage of secondary "is dependent upon the type of heating element 4| that is employed. The resistor 46 can have a resistance of 3 to 4 megohms and the resistor a resistance oi at least 12 megohms. An 0.02 microfarad condenser can be employed for condenser 45 and an 0.5 microtarad condenser ior condenser 21. As previously indicated, however, it is to be understood that these values are merely illustrative values and that the invention is not in anyway limited to the use of elements having these particular values, except as set forth in the appended claims.

OPERATION When pilot burner is extinguished The various elements are shown in the position which they occupy when the pilot burner is extinguished and when the temperature adjacent room thermostat 10 is at or above the desired value so that the thermostat 10 is satisfied."

tap 18 of secondary l5. Due to the fact that current will only flow from the grid to the cathode, current will flow through this circuit only in the direction just traced. The eflect of the current flow in this direction is to charge condenser 45 so that a direct current potential exists across its terminals. The polarity of this potential is such that the right hand end of condenser 45 is negative and the left hand end positive. The grid 31, it wfll be noted, is connected to the right hand end of condenser 45 and the cathode 35 to the left hand end through theportions of winding [5 between taps 41 and 18. The eiiect of this charge is thus to bias grid 31 negatively with respect to cathode 35. Viewed in another light, the voltage phase of tap 41 with respect to cathode 35 is opposite to the upper terminal of secondary l5 to which the anode is connected, as will be presently explained. Thus, when the anode is positive, the tap 41 is negative with respect to the cathode 35. This connection of the grid 31 through condenser 45 to this point tends to maintain the grid at a potential displaced in phase from the anode voltage and thus tends to bias grid 31 negatively. Regardless of the manner in which the efiect of the connection including condenser 45 is explained, it is obvious that this connection acts to bias grid 31 negatively. The voltage existing between taps 41 and 18 is such that the grid is biased negatively below its out oii point,

Under these circumstances, the'amplifier 33 is not conductive so that relay coil 22 is deenergized and switch blade 23 is separated from contact 24. With the relay deenergized, it is impossible to establish a circuit to gas valve 54.

With proper flame Upon the establishment of a pilot burner flame 58, a second charging circuit can be traced through condenser 45 as follows: from the lower terminal of secondary i5 through conductor 56, resistor 65, conductor 64, terminal 63, conductor 62, flame electrode 6| flame 58, pilotburner 51, ground connection 59, ground connection 50, condenser 45, and conductor 48 to tap 41 of secondary l5. While current can flow through this circuit in either direction, the current flow is considerably greater in the direction traced than in the opposite direction due to the rectifying characteristics of the flame. As as well known, the flow of electrons through a flame is greater in the direction of propagation of the flame. Thus, the conventional current flow is greater in the direction opposite to flame propagation, which was the direction in which the last traced circuit was followed.

The effect of the current flowing through the charging circuit just traced is to tend to charge condenser 45 in a direction Opposite to that in which it was charged by the current flowing through the previously named charging circuit. Thus, the eflect of this last traced charging circuit is to tend to cause the right hand terminal or grid terminal of condenser 45 to become positive with respect to the left hand end. This positive charge raises the potential of grid 31 despite the biasing eife ct oi the alternating voltage between taps 41 and 18, to a value sufliciently above the cut off potential to render amplifier 33 conductive. As a result, current flows through relay 22 through the following circuit: from the upper terminal of secondary through conductor 30, relay coil 22, conductors 33 and 8|, anode 36. cathode 35, and conductor 11 to center tap 13 of secondary I 5. The result of this current flow through relay coil 22 is that the switch blade 23 is moved into engagement with contact 24., The

engagement of switch blade 23 with contact 24 results in the following circuit being established to gas valve 54: from the upper terminal of secondary it through conductor 33, terminal 54. conductor 85. bimetallic element ll, contact blade 12, contact 13, conductor 81, terminal 88, conductor B9, switch blade 23, contact 24, conductor 30, terminal 3|, conductor 32, gas valve 54, conductor 33, terminal 34, and conductor back to the lower end of secondary l6. As a result of the establishment of this circuit, the operating mechanism of gas valve 54 is energized with the result that the valve is moved to open position so as to permit gas to flow to the main burner 55. The gas flowing to the main burner 53 is ignited by the pilot burner 51.

Normally the burner 55 will remain ignited until the thermostat 13 becomes satisfied. When this happens, the contact arm 12 separates from contact I3, thus interrupting the energizing circuit to valve 54 and causing valve 54 to close.

If at any time during the operation of the system, the pilot burner 51 is extinguished, the control device of the present invention is effective to cause almost immediate closure of main gas valve 54. As soon as the pilot burner flame 58 is interrupted, current can no longer flow through the last traced charging. circuit for condenser 45. As a result, the only charging circuit for condenser 45 is the one flrst'traced. It will be recalled that the eifect of this charging circuit is to produce a charge across condenser 45which biases the grid 31 below the cut off potential. The time required for charging this condenser is extremely small. Thus, almost immediately after the pilot flame 58 is extinguished, the grid 31 is biased negatively below the cut off point so that the burner relay 22 is deenergized to cause an interruption of the circuit to'main gas valve 54 so as to terminate the flow of gas to the main burner 56.

When flame gap abridged may be bridged by some means having a resist flame itself. For example, carbon may deposit on the flame electrode until the point is reached where the carbon bridges the flame gap with an impedance of practically the same magnitude as a normal flame. It is very essential that the apparatus be able to distinguish between such a condition and that oi. a normal flame. The present control device i designed to distinguish between either of the types of conditions described in which the flame gap is bridged by an impedance, and a normal flame.

It will be recalled from the preceding operation that the establishment of a charge on condenser 45 of the correct polarity to raise the grid potential above the cut on value was dependent upon the rectifying action of the impedance connected between the flame electrode and the burner. As long as this gap is bridged by an impedance having no rectifying properties, the current flow through the second traced charging circuit is the same in both directions. In other words, it is an alternating current. As a result, the potential difference produced across condenser 45 as a result of this current flow is an alternating potential difference. Furthermore, since the right hand terminal of condenser 45 is connected to the lower terminal of secondary I5, the voltage phase of this terminal being displaced from the voltage phase of the upper terminal of secondary l5 to which the anode is connected, this alternating voltage will be 180 displaced in phase from the anode voltage. In other words, this alternating voltage across condenser 45 will have such a phase relation with respect to the voltage applied to anode 36 that when the anode 36 is positive with respect to the cathode 35, the right hand end of condenser 45 will be negative with respect to the cathode. Viewed in another light the control electrode 3! is connected to the lowerterminal of secondary l5 through a connection including resistor 46, the gap between burner 51 and electrode 6 l, and resistor 55. This connection would normally tend to cause the anode 31 to assume a potential considerably negative with respect to the potential of cathode 35. Due to the presence, however, of condenser 45, this connection is actually effective to cause the grid bias to be raised in potential instead of lowered. This effect of condenser 45 is present, however, only when the impedance between electrode 6| and burner 51 is rectifying. If it is not rectifying, the connection is effective to lower the potential of grid 31 as would normally be expected with any connection between the grid 31 and a point whose voltage phase with respect to the' cathode is opposite to that of the anode.

It will thus be seen from the above that upon;

tion of two legs, one of which contains condenser 45 and the other of-which contains a flame gap. In other words, one of these legs contains a capacitive impedance and the others. resistance impedance. The result is that there is considerable tendency for the grid 31 to be shifted in phase. This phase shifting effect becomes more pronounced as the resistance between the flame electrode and the burner decreases. If resistance 65 were not present, under extreme short circuited conditions, the phase displacement might be sufficiently close to 90 that the grid potential might actually be raised above the cut off point. By employing a sufliciently large resistor 65, however, it isassured that regardless of how small "the impedance of the flame gap will be, the total impedance between the lower end-of secondary i5 and ground connection 50 will still I be relatively substantial in magnitude.

Coucnnsron It will be seen that I have devised a control device particularly applicable for the control or a burner. This control device is extremely simple in construction and yet is able to distinguish between a rectifying impedance and an impedance which is not rectifying. While I have shown a flame gap as a means for providing a rectifying impedance, it is to be understood that the invention is not so limited. Even,in the burnercontrol art, other means may be employed. For example, a photo-electric cell may beemployed in lieu of the flame gap. Such a photo-electric cell, when exposed to the light of a burner flame, becomes conductive in one direction only. In other'words, the photo-electric cell acts as a rectifier. Thus, in the appended claims, where the expression means responsive to a burner flame is employed, it is to be understood that this expression is intended to be broad enough to cover both a flame gap and a photoelectric cell exposed to a burner flame. In general, while I have disclosed a specific embodiment of my invention, it is to be understood that this is for purposes of illustration only and that the invention is to be limited solely by the scope of the appended claims.

I claim as my invention:

1. In flame detecting apparatus having only one electronic amplifier, said amplifier comprising a cathode, only one anode, and a control electrode; a source of alternating power; an electrically operated device whose energization isto be controlled in accordance with the presence or absence of aflame; circuit connections'ior controlling said electrical device including said anode, said cathode, and 'a portion of said source of power and operativeto. cause said electrically operated device to be energized when the potential of said control electrode is positive with re-- spect to a predetermined cut-offvvalue which is substantially negative with respect to said cathode; a first connection between said control ofi' value; a connection between said control nee-=- trode. and a second point on said source of power such that said connection would "also normally tend to maintain the potential of saidcontrol electrode negative with respect to said cut-oi! value, said connection including a flameelectrode forming, one terminal eta-gap adapted to'be bridged by a name; and means associated with said last namedconnectionand eflective when said gap is bridged'by a flame to maintain 'said;

control element at a potential positive with respect to said cut-oil potential by reason oi the rectifyingproperties oi. "the flame.

2. In flame detecting apparatus having only one electronic amplifier, said amplifier comprising a cathode, only one anode, and a control electrode; a source of alternating power; an electrically operated devicewhose energization is to be controlled in accordance with the presence or v absence of a flame; circuit connections for controlling's'aid electrical device including said anode, said cathode, and a portion of said source of power and operative to cause said electrically operated device to be energized when the potential 01 said control electrode is positive with respect to a predetermined cut-oif value which is substantially electrode and a second point on said source of power such that said connection would also normally tend to maintainthe potential of said con-- trol electrode negative with respect to said cut-oil tive with respect to said cut-ofl potential.

potential of said control electrode is positive with respect to a predetermined cut-off value which is substantially negative with respect to said cathode; a first connection between said control elec-, trode and a point on said source or power and eflective to maintain said control electrode at a potential negative with respect to said cut-oif' value;- a connection between said control electrode and a second point on said source or power such that said connection would also normally tend to maintain the potential of said' control electrode negative with respect to said cut-oil value, saidconnection'having a portion'thereoi r responsive to a flameand acting s i ll n Y .1

impedance when exposed to flame; and means.

- associated with said last named connectionandi,

effective when said portion is rectifying to main tain said control element at a potential p with respect to said cut-oiipotentiai.

4. in name: detecting apparatus;- an electrically operated devicefwhose energizationis t'obe cone.

trolled in'ac'cordanc with thepresence or absence of aburnerflam'e'; ani'electronic am nnemom: prising a cathode, an anode, and a. control ,elec-. I i

trode :5 a' source of alternating-power: circuit con .nections for contrq in said; electrically operate deviceincluding a connection-from saidanode to Y onepointof saidsource of pow'e'rand a connection between said 7 cathode and a second point of said 5 source of power; said circuitconnections: being .3.- .eflec'tive Y to cause energizationof said electricallyx operated. device whenthezpotential of said'control I electrodefis positive with: respect to a predetermined cut oflyalue which'is substantially nega- 3. In flame detecting apparatus having only one," F electronic discharge device, said device'con prising i a cathode, only one anode, and a control' elec-. trode; an electricallyoperated device whose'energization is to be controlled in accordance with connection between said control electrode and a third point of said source of power whose voltage phase with respect to said second point is opposite to that of said first named point to which said anode is connected, said connection including said condenser; a first charging circuit for said condenser consisting solely of said last named connection, said control electrode, said cathode, and said connection between said cathode and said second point of said source of power, said first charging circuit tending to cause said condenser to become charged in such a manner that the potential of the grid is negative with respect to said cut-oil potential; and a second charging circuit for said condenser comprising a connection from said condenser to a fourth point of said source of power whose voltage phase with respect to said second point is also opposite to that of said first point, said last named connection having a portion thereof responsive to a flame and acting flame; said condenser being efiective when said portion of said connections is rectifying to assume a charge such as to cause the potential of the grid to assume a value positive with respect to said cut-oil? potential; and said first and second charg ing circuits being the only circuits in which said condenser is connected. n

5. In flame detecting apparatus; an electrically operated device whose energization is to be controlled in accordance with the presence or absence of a burner flame; an electronic amplifier comprising a cathode, an anode, and a control electrode; a source of alternating power; circuit connections for controlling said electrically operated device; including a connection from said anode to one point 01 said source oi! power and a connection between said cathode and a second point of said source of power, said circuit connections being effective to cause energization of said electrically operated device when the potential of said control electrode is positive with respect to a predetermined cut-ofl' value which is substantially negative with respect to said anode: a condenser; a connection between said control electrode and a third point or said source of power whose voltage phase with respect to said second point is opposite to that of said first named point to which said anode is connected, said connection including said condenser; a first charging circuit for said condenser consisting solely of said last named connection, said control electrode, said cathode, and said connection between said cathode and said second point of said source of power, said first charging circuit tending to cause said condenser to become charged in such a manner that the potential of the grid is negative with respect to said cut-oi! potential and a second charging circuit for said condenser comprising a connection from said condenser to a fourth point of said source of power whose voltage phase with respect to said second point is also opposite to that of said first point, said last named connection comprising a gap adapted to be located in the path of a flame; said condenser being effective whensaid gap is bridged by a flame in the right direction to assume a charge such as to cause the potential of the grid to assume a value positive with respect to said cut-oil. potential; and said first and second charging circuits being the only circuits in'which said condenser is connected.

6. In flame detecting apparatus; an electrically operated device whose energization is to be controlled in accordance with the presence or absence of a burner flame; an electronic amplifier comprising a cathode, an anode, and a control electrode; a source of alternating power; circuit connections for controlling said electrically operated device including a connection from said anode to a first point of said source of power and a connection between said cathode and a second point of said source of power, said circuit connections being efiective to cause energization of said electrically operated device when the potential of said control electrode is positive with respect to a predetermined cut-oft value which is substantially negative with respect to said anode; a condenser; a connection between said control electrode and a third point of said source of power whose voltage phase with respect to said second point is opposite to that of said first named point to which said anode is connected, said connection including said condenser; a first charging circuit for said condenser consisting solely of said last named connection, said control electrode, said cathode, and said connection between said cathode and said second point of said source of power, said first charging circuit tending to cause said condenser to become charged in such a manner that the potential oi the grid is negative with respect to said cut-ofi potential; and a second charging circuit for said condenser comprising a connection from said condenser to a fourth point of said source of power whose voltage phase with respect to said second point is also opposite to that 01 said first point, said last named connection comprising an impedance of not less than 12 positive with respect to said cut-oil potential;

and said first and second charging circuits being the only circuits in which said condenser is connected.

FREDERICK E. LANGE.

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