GAS ANALYZER CIRCUITRY

• US 3,801,972 A
• Filed: 10/26/1972
• Issued: 04/02/1974
• Est. Priority Date: 06/23/1971
• Status: Expired due to Term

• Current Assignee: Bacharach Inc. (MSA Safety, Inc.)
• Original Assignee: Neil M. King, Young Ho Kim
• Inventors: Ho Kim, Young, King, Neil M.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Myer, Daniel
• Application Number:
  US05/301,207
• Time in Patent Office: 523 Days
• Field of Search: 340/237,409,214
• US Class Current: 340/510
• CPC Class Codes: G08B 17/117 by using a detection device for specific gases, e.g. combustion products, produced by the fire G08B17/103, G08B17/11 take precedence

Abstract

Apparatus for detecting and indicating the presence of substances such as smoke and combustible gasses. One or more detectors generate output signals which are applied to a comparator amplifier. The magnitude of the detector output signals varies unidirectionally as a function of the concentration detected. The comparator amplifier output varies unidirectionally as a function of the difference in magnitude of the detector signals. Failure detection circuitry is included which detects failure to actuate the detectors or failure of the detectors to apply their output signals to the comparator. Apparatus test circuitry is provided which is independent of the detector elements and may be preselected during testing to not actuate any safety circuits or latching relays which the apparatus may control. In a preferred embodiment, circuitry is utilized to automatically compensate for detector sensor drift or for long term concentration changes, so that only large rapid changes in concentration are detected.

Claims

1. In a gaseous detection apparatus, the combination of:

comparator means having a first signal input and a second signal input and operable to generate an output whose magnitude is a function of a difference in magnitude between signals applied to the first and second signal inputs;

first input signal generating means operable to detect the presence of a preselected substance and to generate a first signal for application to the first signal input of a magnitude which varies unidirectionally from a nominal value as a function of the concentration of the substance being detected and including means for inhibiting the variation in magnitude of the first signal from its nominal value unless the rate of change of concentration detected exceeds a pre-selected rate and variable resistance means whose resistance varies as a function of gas concentration detected and in which the inhibiting means includes variable current generator means having an input to which an electrical potential is applied, the magnitude of which controls the current generated by the generator means, voltage divider means including means connecting said variable resistance means and said variable current generator means in series across a source of electrical potential to produce an output signal whose magnitude is a function of the voltage drop across the variable resistance means relative to the voltage drop across the generator means, means for generating a control signal which is a function of deviation in magnitude of the output signal from a preselected value, and means for applying the control signal to the generator means input for changing current flow in the generator means so as to return the output signal to the preselected value and including a time delay circuit to which the control signal is applied as an input and whose output is applied as the generator means input, said time delay circuit having a charge time constant which is preselected in magnitude so as to predetermine the rate of of change of current flow in the generator means;

second input signal generating means operable to generate a second signal of said nominal magnitude for application to the second signal input;

output signal generating means operable to generate an output signal in response to variations in thE magnitude of the output from the comparator means;

means for applying the comparator output to the output means; and

means for applying the first and second signals to the first and second signal inputs, including circuit failure detection means connected to the first input signal generating means and the second input signal generating means and operable to indicate circuit failure upon the failure of either of said input signal generating means to apply its signal to said comparator means.

2. The combination of claim 1, and in which the means for generating a control signal comprises:

a source of reference voltage of said preselected value, voltage comparator circuit means whose output constitutes the control signal and having a pair of inputs, means for applying said reference voltage to one of said comparator inputs, and means for applying the voltage divider output signal to the other of said comparator inputs.

3. The combination of claim 2, and in which the time delay circuit comprises:

a diode and a capacitor serially connected together at a junction, means for applying the control signal to the diode as a reverse bias, and means electrically connecting the junction to the generator means input to provide the electrical potential whose magnitude controls the current flow in the generator means.

4. The combination of claim 3, and in which the time delay circuit comprises:

a diode and a capacitor serially connected together at a junction, means for applying the control signal to the diode as a reverse bias, and means electrically connecting the junction to the generator means input to provide the electrical potential whose magnitude controls the current flow in the generator means.

5. The combination of claim 4 and in which the first input signal generating means includes a plurality of detectors remote one from another and connected in parallel and in which said first input signal generating means is operable to generate said first signal such that its magnitude is a function of the greatest concentration of said substance being detected by any of said detectors.

6. The combination of claim 4 and in which the first signal input generating means includes means for inhibiting the variation in magnitude of the first signal from its nominal value unless the rate of change of concentration detected exceeds a preselected rate.

7. The combination of claim 4 and in which the second input signal generating means includes a plurality of detectors remote one from another and connected in parallel and in which said second input signal generating means is operable to generate said second signal such that its magnitude is a function of the greatest concentration of said substance being detected by any of said detectors.

8. Apparatus for detecting the presence of smoke or combustible gas comprising:

at least one first detector of the type whose output signal varies unidirectionally in magnitude in a given direction from a nominal value as a function of smoke or combustible gas concentration;

at least one second detector of the type whose output signal varies unidirectionally in magnitude in the opposite direction in said nominal value as a function of smoke or combustible gas concentration;

a comparator of the differential amplifier type having a first input to which the first detector output signal is applied, a second input to which the second detector output signal is applied, and an output which varies in magnitude unidirectionally in a first direction from a nominal value as a function of a differential in magnitude between signals applied to the first and second inputs;

a source of an actuating potential;

interconnection and failure detection means operable to apply the actuating potential to the first and second detectors to actuate the same, to apply the first and second detector output signals to the respective comparator inputs, and operable upon a failurE in application of the actuating potential to either of the detectors or a failure of either of the detectors to generate said output signals or a failure to either of said output signals to be applied to the comparator to indicate failure of the apparatus and including an actuation failure circuit controlled by current flow through the detectors in response to their actuation by the application thereto of the actuating potential, whereby an operational failure of any detector is detected by a decrease in said current flow, said actuation failure circuit being operable in response to said decreased current flow to indicate a failure in the apparatus operation; and

output signal generating means connected to the comparator and actuated by said comparator output.

9. Apparatus according to claim 8 and in which the interconnection and failure detection means includes a signal application failure circuit operable in response to a change in the magnitude of the comparator output from its nominal value in a direction opposite the first direction to indicate a failure in apparatus operation;

means connected to the comparator to cause the comparator output to change in magnitude from its nominal value in a direction opposite said first direction in response to failure to apply a signal from any detector to the comparator; and

means for applying the comparator output to said signal application failure circuit.

10. Apparatus according to claim 8, and in which the second detector includes:

variable resistance means whose resistance varies as a function of gas concentration;

variable current generator means having an input to which an electrical potential is applied, the magnitude of which controls the current flow in the generator means, voltage divider means including means connecting said variable resistance and said variable current generator means in series across a source of electrical potential to produce an output signal whose magnitude is a function of the voltage drop across the variable resistance relative to the voltage drop across the generator means, means for generating a control signal which is a function of deviation in magnitude of the output signal from a preselected value, and means for applying the control signal to the generator means input for changing current flow in the generator means so as to return the output signal to the preselected value and including a time delay circuit to which the control signal is applied as an input and whose output is applied as the generator means input, said time delay circuit having a charge time constant which is preselected in magnitude so as to predetermine the rate of change of current flow in the generator means.

11. Apparatus for detecting the presence of smoke or combustible gas comprising:

at least one first detector of the type whose output signal varies unidirectionally in magnitude in a given direction from a nominal value as a function of smoke or combustible gas concentration;

at lease one second detector of the type whose output signal varies unidirectionally in magnitude in the opposite direction in said nominal value as a function of smoke or combustible gas concentration;

a comparator of the differential amplifier type having a first input to which the first detector output signal is applied, a second input to which the second detector output signal is applied, and an output which varies in magnitude unidirectionally in a first direction from a nominal value as a function of a differential in magnitude between signals applied to the first and second inputs;

a source of an actuating potential;

interconnection and failure detection means operable to apply the actuating potential to the first and second detectors to actuate the same, to apply the first and second detector output signals to the respective comparator inputs, and operable upon a failure in application of the actuating potential to either of the detectors or a failure of either of tHe detectors to generate said output signals or a failure to either of ssid output signals to be applied to the comparator to indicate failure of the apparatus and including a signal application failure circuit operable in response to a change in the magnitude of the comparator output from its nominal value in a direction opposite the first direction to indicate a failure in apparatus operation;

means connected to the comparator to cause the comparator output to change in magnitude from its nominal value in a direction opposite said first direction in response to failure to apply a signal from any detector to the comparator;

means for applying the comparator output to said signal application failure circuit; and

output signal generating means connected to the comparator and actuated by said comparator output.

12. Apparatus for detecting the presence of smoke or combustible gas comprising:

at least one first detector of the type whose output signal varies unidirectionally in magnitude in a given direction from a nominal value as a function of smoke or combustible gas concentration;

at least one second detector of the type whose output signal varies unidirectionally in magnitude in the opposite direction in said nominal value as a function of smoke or combustible gas concentration;

a comparator of the differential amplifier type having a first input to which the first detector output signal is applied, a second input to which the second detector output signal is applied, and an output which varies in magnitude unidirectionally in a first direction from a nominal value as a function of a differential in magnitude between signals applied to the first and second inputs;

a source of an actuating potential;

interconnection and failure detection means operable to apply the actuating potential to the first and second detectors to actuate the same, to apply the first and second detector output signals to the respective comparator inputs, and operable upon a failure in application of the actuating potential to either of the detectors or a failure of either of the detectors to generate said output signals or a failure to either of said output signals to be applied to the comparator to indicate failure of the apparatus and including variable resistance means whose resistance varies as a function of gas concentration;

variable current generator means having an input to which an electrical potential is applied, the magnitude of which controls the current flow in the generator means;

voltage divider means including means connecting said variable resistance and said variable current generator means in series across a source of electrical potential to produce an output signal whose magnitude is a function of the voltage drop across the variable resistance relative to the voltage drop across the generator means;

means for generating a control signal which is a function of deviation in magnitude of the output signal from a preselected value;

means for applying the control signal to the generator means input for changing current flow in the generator means so as to return the output signal to the preselected value and including a time delay circuit to which the control signal is applied as an input and whose output is applied as the generator means input, said time delay circuit having a charge time constant which is preselected in magnitude so as to predetermine the rate of change of current flow in the generator means; and

output signal generating means connected to the comparator and actuated by said comparator output.

13. In a detection apparatus of the Wheatstone bridge type, the combination of a comparator of the differential amplifier type having a first input to which a first signal is applied, a second input to which a second signal is applied, at least one of said signals being an output signal derived from the Wheatstone bridge, and an output which varies in magnitude unidirectionally in a first direcTion from a nominal value as a function of a differential in magnitude between signals applied to the first and second inputs;

a source of an actuating potential;

malfunction detection means operable to connect the actuating potential to the Wheatstone bridge to actuate the same and to apply the first and second signals to the respective comparator inputs, and operable, in response to a failure in application of the actuating potential to the Wheatstone bridge or a failure to generate said first and second signals or a failure of either of said signals to be applied to the comparator or a failure of the comparator normally to generate said nominal value output signal, to detect the malfunction of the apparatus;

test input signal generating means, independent of said Wheatstone bridge, for selectively generating a test input signal for application to the comparator, the application of which to the comparator produces a comparator output which corresponds to a malfunction of the apparatus;

output means for indicating malfunction of the apparatus, said output means being connected to the comparator and being actuated by the comparator output, said output means including a first output circuit of the visible indicator type and a second output circuit; and

output circuit actuation means operable, upon the detection by the malfunction detection means of an actual malfunction to actuate both said output means first and second output circuits, and operable in response to the application of the test input signal to the comparator to actuate only the output means first output circuit.

14. The combination of claim 13 and in which the output means second output circuit is of the latching relay type including means for resetting said latching relay type output circuit subsequent to the termination of the application to the comparator of the signal producing the malfunction detection.

15. In a detection apparatus of the Wheatstone bridge type, the combination of a comparator of the differential amplifier type having a first input to which a first signal is applied, a second input to which a second signal is applied, at least one of said signals being an output signal derived from the Wheatstone bridge, and an output which varies in magnitude unidirectionally in a first direction from a nominal value as a function of a differential in magnitude between signals applied to the first and second inputs;

a source of an actuating potential;

malfunction detection means operable to connect the actuating potential to the Wheatstone bridge to actuate the same and to apply the first and second signals to the respective comparator inputs, and operable, in response to a failure in application of the actuating potential to the Wheatstone bridge or a failure to generate said first and second signals or a failure of either of said signals to be applied to the comparator or a failure of the comparator normally to generate said nominal value output signal, to detect a malfunction of the apparatus;

test input signal generating means, independent of said Wheatstone bridge, for selectively generating a test input signal for application to the comparator, the application of which to the comparator produces a comparator output which corresponds to a malfunction of the apparatus;

output means for indicating malfunction of the apparatus, said output means being connected to the comparator and being actuated by the comparator output, said output means including a first output circuit of the visible indicator type and a second output circuit; and

output circuit actuation means operable, upon the detection by the malfunction detection means of an actual malfunction to actuate both said output means first and second output circuits, said output circuit actuation means being preselectively operable in response to the application of the test input signal to the comparator to actuate either both said output means first and second output circuits or onlY one of said output means output circuits.

16. The combination of claim 15 and in which the output means second output circuit is of the latching relay type including means for resetting said latching relay type output circuit subsequent to the termination of the application to the comparator of the signal producing the malfunction detection.

17. Apparatus for automatically compensating for changes in resistance of a variable resistance comprising:

variable current generator means having an input to which an electrical potential is applied, the magnitude of which controls the current flow in the generator means, voltage divider means including means connecting said variable resistance and said variable current generator means in series across a source of electrical potential to produce an output signal whose magnitude is a function of the voltage drop across the variable resistance relative to the voltage drop across the generator means, means for generating a control signal which is a function of deviation in magnitude of the output signal from a preselected value, and means for applying the control signal to the generator means input for changing current flow in the generator means so as to return the output signal to the preselected value and including a time delay circuit to which the control signal is applied as an input and whose output is applied as the generator means input, said time delay circuit having a charge time constant which is preselected in magnitude so as to predetermine the rate of change of current flow in the generator means.

18. The combination of claim 17, and in which the means for generating a control signal comprises:

a source of reference voltage of said preselected value, voltage comparator circuit means whose output constitutes the control signal and having a pair of inputs, means for applying said reference voltage to one of said comparator inputs, and means for applying the voltage divider output signal to the other of said comparator inputs.

19. The combination of claim 18 and in which the time delay circuit comprises:

a diode and a capacitor serially connected together at a junction, means for applying the control signal to the diode as a reverse bias, and means electrically connecting the junction to the generator means input to provide the electrical potential whose magnitude controls the current flow in the generator means.

20. The combination of claim 17 and in which the time delay circuit comprises:

a diode and a capacitor serially connected together at a junction, means for applying the control signal to the diode as a reverse bias, and means electrically connecting the junction to the generator means input to provide the electrical potential whose magnitude controls the current flow in the generator means.