US2852702A

US2852702A - Condition responsive apparatus

Info

Publication number: US2852702A
Application number: US633997A
Authority: US
Inventors: Balthasar H Pinckaers
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1957-01-14
Filing date: 1957-01-14
Publication date: 1958-09-16
Anticipated expiration: 1975-09-16

Description

Sept. 16, 1958 B. H. PINCKAERS 2,852,702

CONDITION RESPONSIVE APPARATUS Filed Jan. 14, 1957 MJJOFFZOU mm 0% 5050 0k mm li|\, Q

' INVENTOR. BALTHASAR H. -PINCKAERS ATTORMYY CONDITION RESPONSIVE APPARATUS Balthasar I-I. Piuckaers, Hopkins, Minn., assignor to Minueapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January 14, 1957, Serial No. 633,997

5 Claims. (Cl. 307-132) This invention is concerned with an improved condition responsive apparatus and more particularly with a condition responsive apparatus having a self-checking arrangement.

Condition responsive apparatus is usually utilized to check a condition which causes the apparatus to change from a first condition of operation to a second condition of operation. For example, a photocell may be utilized to check for the presence of fire or flame and to control an output relay in accordance therewith. These devices are capable of an unsafe failure wherein the unit-fails to properly respond to either the presence or absence of the condition. The present invention is directed to an improved condition responsive apparatus having aselfchecking feature and also utilizing a novel signal transmission arrangement.

The present invention utilizes semi-conductor devices which are essentially current operated devices. By use of a relaxation oscillator arrangement, the minute electrical currents derived from a condition sensing means are periodically supplied to a semi-conductor type of monostable network to cause the network to cycle between a stable and an unstable condition, with output means provided to respond only to the continuous cycling of the monostable network between the two conditions. In such a manner, in the event that the components of the apparatus fail to cause the monostable network to continuously operate in one or the other of its two conditions or states, the output means is not actuated.

It is an object of the present invention to provide a condition responsive apparatus having condition sensing means arranged to charge a capacitor of a relaxation oscillator upon being subjected to a condition, and periodically discharging the capacitor of the relaxation oscillator to trigger a monostable electronic network to thereby control a cycling relay. I

It is a further object of the present invention to provide a condition responsive apparatus having condition detecting means arranged to provide pulsating signals of relatively short time duration which are applied to a pulse stretching circuit to thereby derive pulsating signals of relatively long time duration, and having cycling means connected to the output of the pulse stretching means.

These and other objects of the present invention will be apparent to those skilled in the art upon reference to the following specification, claims, and drawing, of which The single figure is a schematic representation of the preferred embodiment of the present invention.

In the single figure, the reference numeral designates a fuel burner unit which may be a burner in a furnace. The manner in which fuel is admitted to burner 10 and is ignited has not been shown as it forms no part of the present invention.

The reference numeral 11 designates a photo emissive cell so positioned and arranged as to respond to the presence of flame at the burner unit 10. Photo emissive cell 11 is provided with a cathode 12 and an anode 13. Upon the electromagnetic wave energy, supplied by a United States Patent 0 Patented Sept. 16, 1958 flame, impinging upon the cathode 12 in the photocell, electrons are emitted from the cathode and when the anode 13 has a positive voltage thereon, the electrons pass to the anode. Therefore, photo emissive cell 12 acts as a rectifying diode upon being subjected to electromagnetic wave energy present in the flame. It should be noted at this time that it is within the teaching of the present invention to provide other types of condition sensing means other than the specific one represented by the photo emissive cell 11. For example, photo emissive cell 11 could be replaced by a flame rod.

Photocell 11 derives its operating voltage from a transformer 14 having a primary winding 15 and having

secondary windings

16, 17 and 18. The primary winding 15 of this transformer is connected to a source of alternating voltage, not shown. The secondary winding 18 has its upper terminal connected by means of conductor 19 to the cathode 12 of the photocell 11. The lower terminal of this secondary winding is connected by means of conductor 20, resistor 21 and capacitor 22 to the anode 13 of photocell 11.

Upon photocell 11 being subjected to the condition to be detected, in the preferred embodiment this is a flame at the burner unit 10, the photocell 11 rectifies the alternating voltage present in'the secondary winding 18 and the capacitor 22 is charged, the polarity of this charge being indicated in the single figure.

Capacitor 22 forms a part of a relaxation oscillator designated generally by the reference numeral 23 and including a resistor 24 and a gas tube 25. As is well known, gas tube 25 is normally nonconducting and upon sufficiently high voltage being applied to the electrodes thereof, the gas breaks down, and the tube substantially becomes a short circuit.

Also included in circuit of the relaxation oscillator is a .base electrode 26 and an emitter electrode 27 of a transistor 28, a transistor 28 also having a collector electrode 29. Transistor 28 forms a portion of a pulse stretching and pulse amplifying circuit designated generally by the reference numeral 30. This pulse stretching circuit includes a second transistor 31 having a base electrode 32, an emitter electrode 33, and a collector electrode 34. The

base electrodes

26 and 32 are also known as common electrodes while the emitter electrodes 27 and p 33 and the collector electrodes 29 and 34 are also known as input and output electrodes respectively. While P-N-P type transistors are shown, the invention is not limited thereto.

The operating voltage for the pulse stretching circuit 30 is provided by means of secondary winding 17 which in cooperation with a rectifying diode 35 and a capacitor 36 forms a direct current source of voltage having a negative terminal at 37 and a positive terminal at 33. The pulse stretching circuit 30 is a monostable type network having the two transistors or electronic valves 28 and 31 and having a first stable condition of operation 41 comprise a voltage dividing means which is connected across the

terminals

37 and 38 and which has an intermediate terminal 42 which is directly connected to the emitter electrode 33 of transistor 31. The base electrode 32 of transistor 31 is directly connected to the collector electrode 29 of transistor 28. The collector electrode 34 of transistor 31 is connected by means of a load 3 t in the form of a relay winding 43 to the negative terminal 37 of the direct current voltage source.

The collector electrode 34 of transistor 31 is likewise connected through an ROnetwork designated generally by the reference numeral 44 and having a capacitor 45 and

resistors

46 and 47 to the base electrode 26 of transistor 28. From the above traced connections, it can be seen that the voltage present across resistor 41 in the voltage dividing means is of the polarity indicated in the single figure. This voltage is of the proper polarity to make it possible and practical for transistor 28 to bias transistor 31 toward and into the nonconducting region. Furthermore, the emitter to base current of transistor 28 flows through the capacitor 45 of the RC network to charge the capacitor as indicated. The charge on'this capacitor continuously tends to leak off through the

resistors

46 and 47 and therefore the emitter to base current continuously flows in transistor 28. This current fiow circuit can be traced from positive terminal 38 through

conductors

48 and 49, emitter 27 and base 26 of transistor 28, conductor 50, RC network 44,

conductors

51 and 52, winding 43, and conductor 53 to the negative terminal 37. In this above traced circuit, by far the greater portion of the voltage present between the

terminals

37 and 38 is dropped across the RC network 44 and therefore very little voltage is developed across the relay winding 43, thereby causing the relay winding 43 to remain effectively de-energized.

As is well known, when an emitter to base current flows in transistor 28, also an emitter to collector current flows in this transistor. If now resistor 39 is of such value of resistance that the emitter to collector voltage of transistor 28 is less than the voltage present across resistor 41 then the base electrode 32 of transistor 31, being directly connected to the lower terminal of resistor 39 is positive with respect to emitter electrode 33 of transistor 31, thereby causing this transistor to be cut ofif. This then is the stable condition of the monostable electronic network 30 wherein transistor 28 is in the conducting condition and transistor 31 is in the nonconducting condition.

Referring now to the relay 43,'this relay is provided with a switch means having a movable switch blade 54 and having

stationary contacts

55 and 56. This switch means of relay 43 controls a charge and discharge network for a capacitor 57. With the switch blade 54 in the position shown, that is with-relay 43 de-energized, the rectifying diode 58 charges capacitor 57 through a resistor 59 by means of a circuit which can be traced from the lower terminal of transformer secondary winding 16 v through diode 58, contact 56 and switch blade 54 of relay 43, resistor 59, and capacitor 57 to the upper terminal of transformer secondary winding 16. Upon relay 43 subsequently being energized, the movable switch blade 54 disengages contact 56 and moves into engagement with contact 55. The charged capacitor 57 is now discharged through a circuit including the winding 60 of a relay 61 having a movable switch blade 62 and a stationary contact 63. This circuit can be traced from the right hand plate of capacitor 57 through conductor 64, relay winding 60 and parallel connected capacitor 65, conductor 66, contact 55 and switch blade 54, and resistor 59 to the left hand plate of capacitor 57. The charge on capacitor 57 is therefore transferred to the winding of relay 61 and likewise charges capacitor 65. This causes the winding 60 to be energized and so long as the switch means of relay 43 continues to cycle between

contacts

55 and 56 at a predetermined rate the relay 61 remains continuously energized and the movable switch blade '62 of relay 61 engages contact 63. The exact manner in which the switch means of relay 60 is utilized forms no part of this invention and in the single figure it has been indicated that the switch means of relay 61 controls a circuit to be controlled, in accordance with the presence of flame at the burner unit 10.

The components of the improved condition responsive apparatus and a portion of the operation thereof has been above descirbed. However, for a detailed explana" tion of the operation of the apparatus it will first be assumed that no flame is present at the burner unit 10. This is the standby condition of the condition responsive apparatus wherein it is conditioned to detect a flame at the burner unit 10 should a flame subsequently be estab lished. In this condition, the photo emissive cell 11 is nonconductive and the capacitor 22 is in an uncharged state. The monostable electronic network 30 is continuously in its first stable condition wherein transistor 28 is conductive and transistor 31 is nonconductive. The relay 43 is continuously de-energized and therefore the capacitor 57 is continuously connected through diode 58 to be charged from the transformer secondary winding 16.

Assume now that a flame is established at the burner unit 10. The electromagnetic wave energy emitted from this flame impinges upon the cathode 12 of photocell 11 and every half cycle of the alternating source consisting of transformer secondary winding 18 in which the anode 13 is positive with respect to the cathode 12, a pulse of current flows to the capacitor 22. After a given time period the voltage present on capacitor 22 builds up to a sufiiciently high magnitude and the gas tube 25 fires. The capacitor 22 is then quickly discharged through a circuit which can be traced from the upper plate of capacitor 22 through resistor 24, gas tube 25, base electrode 26 and emitter electrode 27 of transistor 28, and conductors 70 and 71 to the lower plate of capacitor 22. The direction of this current flow is such that the transistor 28 is cut off. In other words, no current flows from the emitter 28 to the base 26 of this transistor and therefore no current flows from the emitter 27 to the collector 29.

In this condition, the emitter to collector current of this transistor becomes relatively low and there is substantially no voltage drop across the load resistor 39, thereby effectively connecting the base electrode 32 of transistor 31 directly to the negative terminal 37 of the power supply. This causes the transistor 31 to become conductive and a current flows from the positive terminal 38 of the power supply through conductor 48, resistor 41, emitter electrode 33 and base electrode 32, resistor 39, and

conductors

72, 73 and 53 to negative terminal 37. An emitter to collector current also flows from the positive terminal 38 through conductor 48, resistor 41, emitter 33 and collector 34,

conductors

74 and 52, relay 43, and conductor 53 to the negative terminal 37. This last traced current flow energizes the winding of relay 43 and causes movable switch blade 54 to move into engagement with contact 55.

As above described, the charge on capacitor 57 is then transferred to the capacitor 65 shunting the winding of relay 60 and the movable switch blade 62 of relay 61 moves into engagement with contact 63.

As has been mentioned, the pulse of current derived I from the relaxation oscillator 23 is of relatively short time duration and the RC network 44 is provided in the monostable electronic network 30 to provide for a time delay giving a predetermined time period of operation of the network 30 in the second or unstable condition. This time delay is obtained in the following manner: Before the initiating pulse, derived from the relaxation oscillator 23, occurs the voltage drop across relay coil 43 is small, so that the voltage drop across resistor 47 is slightly less than the D. C. voltage present between

terminals

37 and 38. This difference in voltage includes the residual forward biasing voltage on transistor 28. The capacitor 45 is charged to nearly the same value of voltage as exists across resistor 47. Incidentally at that point the charging current of capacitor 45 is very small so that the D. C. current which flows from emitter to base of transistor 28 and through resistor 47 must be suificiently large to cause a large enough collector current in transistor 28 to hold transistor 31 biased off. As a matter of fact this current must be large enough to cause transistor 31 to become non-conductive and transistor 28 to become conductive even when. starting out with transistor 31 in the conductive or on-state in order to achieve reset from the unstable to the stable condition. The initiating current pulse from the relaxation oscillator 23 must be higher in amplitude than this D. C. emitter to base bias current which normally exists in transistor 28 in order to cause a change of state in the transistors from the stable to the unstable condition. Immediate reset to the stable condition, after the very short initiating current pulse disappears, is prevented by the action of capacitor 45.

This has the effect of holding transistor 31 in the conductive state for a short time after the initiating pulse has disappeared.

This comes about in the following manner: When transistor 31 is made conductive by the initiating pulse, the

voltage drop across the relay suddenly increases to a value a little less than the D. C. supply voltage between

terminals

37 and 38. Therefore the voltage drop across resistor 47 suddenly decreases from a relatively high voltage to a very low voltage. Capacitor 45, being charged to the high value of voltage which existed across resistor 47, must therefore discharge. One can also say that when the voltage drop across resistor 47 is suddenly decreased to a much lower value that capacitor 45 discharges through resistor 47. This in effect places a voltage source equal to discharge current of capacitor 45 times the resistance of resistor 47 in opposition to the residual forward biasing voltage, above mentioned. The charge on capacitor 45 gradually leaks off through resistor 47 and after a time interval a net forward biasing voltage is once again present on transistor 28 which causes the monostable electronic network 30 to assume its stable condition. The transistor 28 then becomes conductive and upon becoming conductive the emitter to collector voltage of transistor 28 becomes less than the voltage present across resistor 41, and as explained before, transistor 31 is biased to cutoff, thereby de-energizing relay 43 and causing movable switch blade 54 to again engage contact 56 and disengage contact 55. The above description has traced one cycle of operation of the condition responsive apparatus.

As a flame is still present at the burner unit 10, the capacitor 22 is again charged and after a time period the relaxation oscillator 23 is again effective to cut off transistor 28. Furthermore, the capacitor 57 which was discharged into capacitor 65 is now again charged from transformer secondary winding 16 by means of rectifying diode 58. Therefore, after a short time period, capacitor 22 again has a charge build up thereon sufliciently high to cause gas tube 25 to again ionize and the monostable electronic network'30 is again tripped to its unstable condition wherein transistor 28 is cut off and transistor 31 becomes conductive to thereby again energize relay 43. Energization of relay 43 causes movable switch blade 54 to move into engagement with contact 55 and to disengage contact 56. Once again, the charge on capacitor 57 is distributed to capacitor 65 and to the winding 60 of relay 61.

It can be seen that so long as the frequency of cycling of relay 43, which is caused by the cycling of the monostable electronic network 30 between its stable and unstable conditions, is of a given frequency, the charge on capacitor 65 does not have time to completely leak off through the winding 60 of relay 61 before it is recharged by capacitor 57. So long as the flame is continuously detected at the burner unit by means of the photocell 11, the relaxation oscillator 23 cyclically causes the monostable electronic network30 to cycle between its stable and its unstable condition, thereby causing relay 43 to be cyclically energized and de-energized. This in turn causes capacitor 57 to be first charged from transformer secondary winding 16 and then to be discharged into capacitor 65 and the winding 60 of relay 61 to thereby maintain relay 61 continuously energized.

It can be seen from the above description that for proper operation and proper detection of the flame at the burner unit 10, the apparatus must cycle between a first and a second condition. Any failure within the condition responsive apparatus which tends to cause the apparatus to continuously operate in one of its two conditions causes relay 43 to either remain in its energized or its def" ergized condition. This in turn causes the winding 6056f relay 61 to be de-energized and the switch blade 63 of relay 61 to disengage contact 63. It can therefore be seen that I have provided an improved condition responsive apparatus which is of the self-checking type and which utilizes a novel electronic type pulse stretching circuit in the form of a monostable electronic network to control a relay in a cyclic manner in response to the presence of a condition to be detected.

Other modifications of the present invention will be apparent to those skilled in the art and it is intended that the scope of the present invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. Flame responsive apparatus comprising; flame sensing means arranged to be subjected to a flame and to conduct a low magnitude electrical current when so subjected, a source of voltage, a capacitor; circuit means including said flame sensing means, said source of voltage and said capacitor arranged to charge said capacitor to a given voltage with said low magnitude current upon said flame sensing means being subjected to the flame, a relaxation oscillator including said capacitor arranged to discharge said capacitor upon said capacitor having said given voltage thereon and to produce a series of high magnitude electrical current pulses of short time duration in response to said flame sensing means being subjected to the flame, amplifying and pulse stretching means having an input and an output, circuit means connecting the input of said pulse stretching means to said relaxation oscillator to thereby apply said pulses of relatively short time duration to the input, the output of said pulse stretching means being a series of amplified electrical pulses of relatively long time duration, and cycling means controlled by the output of said pulse stretchin means and responsive only to said series of electrical pulses of relatively long time duration.

2. Condition responsive apparatus comprising; condition detecting means including condition sensing means arranged to be subjected to a given condition, said condition detecting means being constructed and arranged to provide reoccurring pulses of electrical energy of a relatively short time duration upon said condition sensing means being subjected to the given condition, pulse stretching means having an input and an output, circuit means connecting said condition detectin means to the input of said pulse stretching means to thereby cause a reoccurring pulse of electrical energy of a relatively long time duration to appear at the output of said pulse stretching means, and cycling relay means including a winding connected to the output of said pulse stretching means and responsive only to said reoccurring pulses of relatively long time duration.

3. Condition sensing apparatus comprising; condition sensing means arranged to be subjected to a given condition and to conduct a law magnitude electrical current when so subjected, afirst capacitor, a source of voltage, circuit means including said condition sensing means, said source of voltage and said first capacitor arranged to charge said first capacitor upon said condition sensing means being subjected to the given condition, a first and a second transistor each having a base, an emitter, and

-a collector electrode, a source of direct current voltage having a positive and a negative terminal, circuit means connecting said emitter electrodes of said first and second transistors to said positive terminal, circuit means connecting the collector electrode of said first transistor to said negative terminal, a relay having a winding and switch means controlled thereby, circuit means including said relay winding connecting the collector electrode of said second transistor to said negative terminal, a second capacitor and a resistor co nected in parallel, circuit means connecting said para el connected second capacitor and resistor between the base electrode of said first transistor and the collector electrode of said second transistor, circuit means connecting the base electrode of said second transistor to the collector electrode of said first transistor, a normally non-conductive gas tube capable of being rendered conductive upon a predetermined voltage being applied thereto, circuit means including said gas tube connecting the base and emitter electrodes of said first transistor to said first capacitor to form a relaxation oscillator circuit such that upon a predetermined charge being accumulated on said first capacitor said gas tube discharges a pulse of current of relatively short time duration through the emitter to base circuit of said first transistor in a manner to substantially cut oil? said first transistor, the charge on said second capacitor maintaining said first transistor cutoff for a relatively long time duration to thereby render said second transistor conductive to maintain said relay winding energized for said relatively long time duration, and means responsive to continue cycling of said relay switch means.

4. Condition responsive apparatus comprising; condition detecting means having condition sensing means arranged to be subjected to a condition to be detected, said condition detecting means being constructed and arranged to provide rc-occurring pulses of electrical energy of relatively short time duration upon said condition sensing means being subjected to the condition to be detected; a monostable electronic network having a first stable condition and a second unstable condition to which said electronic network is triggered upon a pulse of electrical energy being applied to the input thereof, said monostable electronic network having a time delay means arranged to maintain said monostable electronic network in said second unstable condition for a given time period of a relatively long time duration; circuit means connecting said condition detecting means to the input of said monostable electronic network to thereby cause said monostable electronic network to be triggered from said stable to said unstable condition in a pulsating manner upon said condition sensing means being subjected to the condition, and cycling relay means having a winding connected to the output of said monostable electronic network and responsive to continuous cycling of said monostable electronic network between said stable and said unstable condition in response to the presence of the condition to be detected.

5. Condition responsive apparatus comprising; a first source of voltage, condition sensing means, a capacitor, circuit means connecting said first source of voltage, said condition sensing means and said capacitor in circuit in a manner to charge said capacitor upon said condition scnsing means being subjected to a given condition; a monostable electronic network having a first and a second electronic valve, each of said electronic valves having a common electrode, an input electrode, and an output electrode,-a source of direct current voltage having a first and a second terminal, circuit means connecting the input electrode of said first electronic valve to said first terminal, circuit means connecting the output electrode of said first electronic valve through a load impedance to said second terminal, voltage dividing means connected across said first and second terminals, circuit means connecting the input electrode of said second electronic valve to an intermediate point on said voltage dividing means, a relay having a winding and switch means controlled thereby, circuit means connecting the output electrode of said second electronic valve through said relay winding to said second terminal, circuit means connecting the common electrode of said second electronic valve to the output electrode of said first electronic valve, an electrical energy storage network connected from the output electrode of said second electronic valve to the common electrode of said first electronic valve, said monostable electronic network having a first stable condition wherein said first electronic valve is conductive to cause a current to flow between the input and output electrodes and said second electronic valve is cut off such that no current flows between the input and output electrodes; a gas discharge tube, circuit means connecting said gas discharge tube and the common electrode and input electrode of said first electronic valve in series across said first capacitor such that upon the voltage on said capacitor reaching a given value said gas tube is ionized and a pulse of electrical current of relatively short time duration flows between the common and input electrodes of said first electronic valve to thereby trigger said mbnostable electronic network from said stable condition to said unstable condition, said monostable electronic network being maintained in said unstable condition for a relatively long time duration as determined by said electrical energy storage network, said-monostable electronic network thereby cycling between said stable and said unstable condition upon said condition sensing'means being subjected to the given condition to thereby cyclically energize and de-energize said relay winding; and further means controlled by said relay switch means and responsive only to continuous cycling of said relay switch means.

References Cited in the file of this patent UNITED STATES PATENTS 2,747,112 Deiziel et al. May 22 1956