阅读说明：本技术 一氧化碳警报监督 (Carbon monoxide alarm supervision ) 是由 W·金 J·库洛贝特 E·约翰逊 于 2018-07-31 设计创作，主要内容包括：使用专用集成电路(ASIC)和微控制器监控和测试一氧化碳(CO)警报器。其中电化学CO传感器与其检测电路隔离并且其上改变了电压电荷,则CO传感器重新连接到检测电路,其中CO传感器上的电压电荷随着时间的推移而恢复到平衡状态。从电压对时间的结果中确定CO传感器和CO检测电路是否正常工作。所有测试和控制电路均可由ASIC设置。(Carbon monoxide (CO) alarms are monitored and tested using an Application Specific Integrated Circuit (ASIC) and a microcontroller. Wherein the electrochemical CO sensor is isolated from its detection circuit and has a voltage charge altered thereon, the CO sensor is reconnected to the detection circuit wherein the voltage charge on the CO sensor returns to an equilibrium state over time. From the voltage versus time results, it is determined whether the CO sensor and CO detection circuit are operating properly. All test and control circuits can be provided by the ASIC.)

1. A method for carbon monoxide alarm supervision, the method comprising the steps of:

decoupling the electrochemical carbon monoxide sensor from the carbon monoxide operational amplifier;

using a current source or a receiver to change a voltage charge on the electrochemical carbon monoxide sensor;

recoupling the carbon monoxide operational amplifier to the electrochemical carbon monoxide sensor;

measuring the voltage at the output of the carbon monoxide operational amplifier until it is substantially unchanged;

evaluating the elapsed time until the voltage does not substantially change; and

determining from the elapsed time whether the carbon monoxide sensor and the operational amplifier circuit are operating.

2. The method of claim 1, further comprising the steps of: determining whether a voltage charge across the electrochemical carbon monoxide sensor is within an expected range.

3. The method according to any one of claims 1 to 2, further comprising the steps of:

storing the measured voltage and time in a memory; and

the time voltage profile for carbon monoxide alarm supervision thereof was evaluated.

4. The method of claim 2, wherein the step of determining whether the voltage charge on the electrochemical carbon monoxide sensor is within the expected range comprises the steps of:

measuring a voltage charge between inputs of the carbon monoxide operational amplifier coupled to the electrochemical carbon monoxide sensor; and

comparing the measured voltage charge to the expected range.

5. A method for carbon monoxide alarm supervision, the method comprising the steps of:

measuring and storing an initial voltage from an output of the carbon monoxide operational amplifier in a memory;

decoupling an electrochemical carbon monoxide sensor from the carbon monoxide operational amplifier;

using a current source or a receiver to change a voltage charge on the electrochemical carbon monoxide sensor;

recoupling the carbon monoxide operational amplifier to the electrochemical carbon monoxide sensor;

comparing a voltage on the output of the carbon monoxide operational amplifier to the stored initial voltage;

determining a time until a first one of the voltages on the output of the carbon monoxide operation is approximately equal to the initial voltage; and

determining from the time whether the carbon monoxide sensor and the operational amplifier circuit are operating.

6. The method of claim 5, further comprising the steps of: determining whether a voltage charge across the electrochemical carbon monoxide sensor is within an expected range.

7. The method according to any one of claims 5 to 6, further comprising the steps of:

storing the voltage on the output of the carbon monoxide operational amplifier and its time in a memory; and

the time voltage profile for carbon monoxide alarm supervision thereof was evaluated.

8. The method of claim 6, wherein the step of determining whether the voltage charge on the electrochemical carbon monoxide sensor is within the expected range comprises the steps of:

measuring a voltage charge between inputs of the carbon monoxide operational amplifier coupled to the electrochemical carbon monoxide sensor; and

comparing the measured voltage charge to the expected range.

9. A carbon monoxide alarm with surveillance, comprising:

an electrochemical carbon monoxide sensor having a first terminal and a second terminal;

an operational amplifier having first and second inputs coupled to the first and second terminals, respectively, of the electrochemical carbon monoxide sensor, wherein the operational amplifier has an output that can be enabled and disabled, whereby the output is at a high impedance when disabled;

a voltage reference source having an output coupled to the first terminal of the electrochemical carbon monoxide sensor and the first input of the operational amplifier;

a feedback resistor coupled between the output and the second input of the operational amplifier;

a first current source or receiver coupled to the first terminal of the electrochemical carbon monoxide sensor and the first input of the operational amplifier for charging or discharging the electrochemical carbon monoxide sensor, wherein the first current source or receiver output is capable of being disabled and enabled;

a multiplexer having inputs coupled to the first and second inputs and the output of the operational amplifier, and an output adapted to be coupled to a first analog input of a microcontroller;

the output of the operational amplifier is coupled to a second analog input of the microcontroller;

a supervisor alarm controller having control outputs coupled to the multiplexer, operational amplifier, and current source, and an input coupled to the microcontroller; wherein

During testing of the carbon monoxide alarm, disabling the operational amplifier and enabling the first current source or receiver, whereby the output of the operational amplifier provides a voltage to the microcontroller, the voltage representing a voltage charge between the first and second terminals of the electrochemical carbon monoxide sensor while the voltage charge is in equilibrium; and is

During normal carbon monoxide monitoring, the operational amplifier is enabled and the first current source or receiver is disabled, whereby the output of the operational amplifier provides a voltage to the microcontroller, the voltage being representative of a voltage charge between the first and second terminals of the electrochemical carbon monoxide sensor.

10. The carbon monoxide alarm as set forth in claim 9, further comprising:

a second current sink or source coupled to the second terminal of the electrochemical carbon monoxide sensor and the second input of the operational amplifier for discharging or charging the electrochemical carbon monoxide sensor, wherein the second current sink or source output may be disabled and enabled.

11. A carbon monoxide alarm as claimed in any one of claims 9 to 10 further comprising a microcontroller for controlling the first current source or receiver, the multiplexer and the supervisor alarm controller.

12. A carbon monoxide alarm as in claim 11 further comprising a memory having said microcontroller for storing voltage and time values.

13. A carbon monoxide alarm as claimed in any one of claims 9 to 12 wherein an Application Specific Integrated Circuit (ASIC) comprises the operational amplifier, the voltage reference source, the first current source or receiver and the multiplexer.

14. A carbon monoxide alarm as in claim 11, wherein the microcontroller comprises the operational amplifier, the voltage reference source, the current source or receiver, and the multiplexer.

15. A carbon monoxide alarm as claimed in any one of claims 9 to 12 wherein the operational amplifier includes a tri-state circuit for enabling and disabling its output.

16. A carbon monoxide alarm as claimed in any one of claims 9 to 12 wherein the operational amplifier includes an open collector circuit for enabling and disabling its output.

17. A carbon monoxide alarm as claimed in any one of claims 9 to 12, further comprising a switch coupled between the operational amplifier and the feedback resistor and the multiplexer for enabling and disabling its output.

18. A carbon monoxide alarm as claimed in claim 17 wherein the switch is controlled by the supervisor alarm controller.

Technical Field

The present disclosure relates to carbon monoxide detection, and in particular to carbon monoxide (CO) alarm supervision.

Background

The U.S. safety testing institute (UL) has standards for single and multi-station carbon monoxide alarms, UL-2034. In the UL standard, it is required to supervise the operating conditions of carbon monoxide (CO) alarms, as outlined in paragraph 38.1.1 of UL-2034. To meet this standard, some prior art CO alarms require the use of external components to isolate the CO alarm sense amplifier. In addition, other CO alarm supervision solutions are limited to creating current receivers. In addition, other solutions may take a considerable amount of time to operate while waiting for the output of the CO detection circuit to return to equilibrium. For a complete diagnosis of the CO alarm circuit this may be many seconds, or even as much as 10-15 seconds.

Disclosure of Invention

Therefore, there is a need for better, faster and lower cost carbon monoxide alarm supervision solutions.

According to one embodiment, a method for carbon monoxide alarm supervision may comprise the steps of: decoupling the electrochemical carbon monoxide sensor from the carbon monoxide operational amplifier; changing the voltage charge on the electrochemical carbon monoxide sensor using a current source or receiver; recoupling the carbon monoxide operational amplifier to the electrochemical carbon monoxide sensor; measuring the voltage at the output of the carbon monoxide operational amplifier until it is substantially unchanged; evaluating the elapsed time until the voltage does not substantially change; and determining from the elapsed time whether the carbon monoxide sensor and the operational amplifier circuit are likely to be operating.

According to another embodiment of the method, a step of determining whether a voltage charge across the electrochemical carbon monoxide sensor can be within an expected range may be included. According to another embodiment of the method, the following steps may be included: storing the measured voltage and its time in a memory; and evaluating its time-voltage profile for carbon monoxide alarm supervision.

According to another embodiment of the method, the step of determining whether the voltage charge on the electrochemical carbon monoxide sensor is likely to be within an expected range may comprise the steps of: measuring a voltage charge between inputs of a carbon monoxide operational amplifier coupled to the electrochemical carbon monoxide sensor; and comparing the measured voltage charge to an expected range.

According to another embodiment, a method for carbon monoxide alarm supervision may comprise the steps of: measuring and storing an initial voltage from an output of the carbon monoxide operational amplifier in a memory; decoupling the electrochemical carbon monoxide sensor from the carbon monoxide operational amplifier; changing the voltage charge on the electrochemical carbon monoxide sensor using a current source or receiver; recoupling the carbon monoxide operational amplifier to the electrochemical carbon monoxide sensor; comparing the voltage at the output of the carbon monoxide operational amplifier with the stored initial voltage; determining a time until a first one of the voltages on the output of the carbon monoxide operation may be approximately equal to the initial voltage; and determining from the time whether the carbon monoxide sensor and the operational amplifier circuit are likely to be operating.

According to another embodiment of the method, a step of determining whether a voltage charge across the electrochemical carbon monoxide sensor can be within an expected range may be included. According to another embodiment of the method, the following steps may be included: storing the voltage at the output of the carbon monoxide operational amplifier and its time in a memory; and evaluating its time-voltage profile for carbon monoxide alarm supervision.

According to another embodiment of the method, the step of determining whether the voltage charge on the electrochemical carbon monoxide sensor may be within a desired range may comprise the steps of: measuring a voltage charge between inputs of a carbon monoxide operational amplifier coupled to the electrochemical carbon monoxide sensor; and comparing the measured voltage charge to an expected range.

According to another embodiment, a carbon monoxide alarm with supervision may comprise: an electrochemical carbon monoxide sensor having a first terminal and a second terminal; an operational amplifier having first and second inputs coupled to the first and second terminals, respectively, of the electrochemical carbon monoxide sensor, wherein the operational amplifier has an output that can be enabled and disabled, whereby the output may be at a high impedance when it may be disabled; a voltage reference source having an output coupled to a first terminal of the electrochemical carbon monoxide sensor and a first input of the operational amplifier; a feedback resistor coupled between the output terminal and the second input terminal of the operational amplifier; a first current source or receiver coupled to a first terminal of the electrochemical carbon monoxide sensor and a first input of the operational amplifier for charging or discharging the electrochemical carbon monoxide sensor, wherein the first current source or receiver output may be disabled and enabled; a multiplexer having inputs coupled to the first and second inputs and to an output of the operational amplifier, and an output adapted to be coupled to a first analog input of the microcontroller; the output of the operational amplifier may be coupled to a second analog input of the microcontroller; a manager alarm controller having control outputs coupled to the multiplexer, the operational amplifier, and the current source, and an input coupled to the microcontroller; wherein during testing of the carbon monoxide alarm, the operational amplifier may be disabled and the first current source or receiver may be enabled, whereby the output of the operational amplifier may provide a voltage to the microcontroller, the voltage being representative of the voltage charge between the first terminal and the second terminal of the electrochemical carbon monoxide sensor while the voltage charge is in equilibrium; and during normal carbon monoxide monitoring, the operational amplifier may be enabled and the first current source or receiver may be disabled, whereby the output of the operational amplifier provides a voltage to the microcontroller that may be representative of the voltage charge between the first and second terminals of the electrochemical carbon monoxide sensor.

According to another embodiment, a second current source or receiver may be coupled to the second terminal of the electrochemical carbon monoxide sensor and the second input of the operational amplifier for discharging or charging the electrochemical carbon monoxide sensor, wherein the second current source or receiver output may be disabled and enabled. According to another embodiment, the microcontroller may control the first current source or receiver, the multiplexer, and the supervisor alarm controller. According to another embodiment, a memory having a microcontroller may store voltage and time values.

According to another embodiment, an Application Specific Integrated Circuit (ASIC) may include an operational amplifier, a voltage reference source, a first current source or receiver, and a multiplexer. According to another embodiment, the microcontroller may include an operational amplifier, a voltage reference source, a first current source or receiver, and a multiplexer. According to another embodiment, the operational amplifier may comprise a tri-state circuit for enabling and disabling its output. According to another embodiment, the operational amplifier may comprise open collector circuits for enabling and disabling its output. According to another embodiment, a switch coupled between the operational amplifier and the feedback resistor and a multiplexer for enabling and disabling its output may be included. According to another embodiment, the switch may be controlled by a supervisor alarm controller.

Drawings

A more complete understanding of the present disclosure may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic block diagram of a carbon monoxide detector with microcontroller alarm supervision according to one particular example embodiment of the present disclosure;

FIG. 2 shows a schematic voltage versus time diagram of an operational test of a carbon monoxide detector according to the teachings of the present disclosure, illustrating its normal operation; and is

Fig. 3 and 4 show schematic program flow diagrams of carbon monoxide alarm supervision according to specific example embodiments of the present disclosure.

While the disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific exemplary embodiments is not intended to limit the disclosure to the forms disclosed herein.

Detailed Description

Embodiments of the present disclosure include systems and methods for diagnosing several common failure modes in carbon monoxide (CO) sensors, detectors, alarms, and monitors. The failure mode may be due to damage to wires, components or foreign objects. Failures may also be caused by short circuits in the components and/or printed circuit board conductors. Embodiments of the present disclosure may also include systems and methods for characterizing the overall condition and operating conditions of CO sensors, detectors, alarms, and monitors. Embodiments of the present disclosure may be used to meet the requirements of section 38.1.1 in UL-2034.

Embodiments of the present disclosure may diagnose an operating condition or state of a CO sensor by selectively delivering or receiving current to the CO sensor. Furthermore, embodiments of the present disclosure may be configured to tri-state the output of an operational amplifier associated with a CO sensor. Further, embodiments of the present disclosure may be configured to monitor an input of an operational amplifier associated with the CO sensor during a diagnostic check. This may provide a faster method to quantify the operating conditions and performance of the CO sensor.

Embodiments of the present disclosure may be implemented with on-integrated circuit on-chip test features. This feature may allow for separation of the CO operational amplifier from the external CO sensor. Thereby, the self-diagnosis test can be performed. On-chip features may be embedded in mixed-signal (analog and digital) integrated circuits, such as microcontrollers, Application Specific Integrated Circuits (ASICs), and the like, hereinafter "microcontrollers". The test sequence for testing the CO sensor and alarm may be implemented using a microcontroller. The test sequence may be customizable. Further, this and other features may be accessed using any suitable bus, such as, for example, but not limited to, a Serial Peripheral Interface (SPI) bus. The test voltage used in the testing of the CO alarm may be buffered.

Embodiments of the present disclosure may include varying a voltage charge on an electrochemical CO sensor. Varying the voltage charge may be performed with an on-chip current source or receiver. Subsequently, a reestablishment of the equilibrium operation of the CO sensor can be characterized. This feature may show the operating condition or state of the CO sensor. Embodiments of the present disclosure may internally isolate the feedback path of the CO operational amplifier when a charge or discharge current is applied to the CO sensor. The feedback path may then be re-established to allow the voltage charge balance of the CO sensor to be restored. The voltage at the input of the CO operational amplifier may be measured (the CO operational amplifier output is disabled) during the application of the charging current or the discharging current. The voltages at the input and output of the CO operational amplifier (enabled output) may then be measured during the voltage-charge balance recovery of the electrochemical CO sensor.

By isolating the output of the CO op amp (e.g., tri-state), and then changing the charge balance of the CO sensor and the internal current source or receiver, the system can check the condition of the CO sensor and its associated circuitry. While changing this charge balance, the voltage change between the CO sensor terminals with respect to the charge/discharge time of the capacitance of the CO sensor can be monitored to achieve a voltage balance that can be measured at the input of the CO operational amplifier. The return time to reach capacitance-voltage equilibrium is a function of both the operating conditions of the sensor and the internal interconnectivity of the circuit, and provides a characteristic signal of the CO detection circuit performance. It is contemplated and within the scope of the present disclosure that a switch (not shown in fig. 1), such as a FET switch, may be used to isolate the output of the CO operational amplifier.

After the charge balance on the CO sensor is changed, then by re-enabling the CO operational amplifier, the CO detection circuit will re-establish the time varying charge balance. Over time, this re-establishment of charge balance will be observable in the output performance of the CO operational amplifier. Thus, the output performance of the CO operational amplifier can be evaluated over time to characterize the operating conditions of the CO sensor and detection circuit. In addition, the input of the CO operational amplifier (voltage charge on the CO sensor) can also be evaluated during this time.

Referring now to the drawings, the details of exemplary embodiments are schematically illustrated. Like elements in the drawings will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix.

Referring now to fig. 1, a schematic block diagram of a carbon monoxide detector with microcontroller alarm supervision is shown, according to a specific example embodiment of the present disclosure. A carbon monoxide detector with microcontroller alarm supervision, generally represented by the numeral 100, may include a microcontroller 104 with memory, a carbon monoxide (CO) sensor 106, an anti-polarization transistor 108, a supervisor alarm controller 110, a multiplexer and buffer 112, a carbon monoxide operational amplifier 114, a current source/receiver 116, a current source/receiver 118, a buffer amplifier 120, a voltage reference 122, and a feedback resistor 124. An Application Specific Integrated Circuit (ASIC)102 (or the like) may be configured to set a supervisor alarm controller 110, a multiplexer and buffer 112, a carbon monoxide operational amplifier 114, a current source/receiver 116, a current source/receiver 118, a buffer amplifier 120, and a voltage reference source 122. It is contemplated and within the scope of the present disclosure that the functionality of ASIC 102 may be included as part of microcontroller 104 and configured in one integrated circuit assembly.

The supervisor alarm controller 110 receives commands from the microcontroller 104 through a control bus (CTRL), such as, but not limited to, a Serial Peripheral Interface (SPI). With these instructions, it may control multiplexer and buffer 112, carbon monoxide op amp 114, current source/receiver 116, and current source/receiver 118. The output of the CO operational amplifier 114 may be enabled or brought into a high impedance state (e.g., tri-state), open collector disabled, etc. with a switch, effectively disconnecting the output from the circuit. Current sources/ receivers 116 and 118 may be enabled or disabled and, when enabled, their current values may be programmed. The outputs of current source/ receivers 116 and 118 may be controlled in a similar manner as the outputs of CO operational amplifier 114. The current sources/receivers 116 and/or 118 may be used to increase or decrease the voltage charge on the CO sensor 106.

The multiplexer and buffer 112 selectively couples and buffers the voltages at the output and input of the operational amplifier 114 to the analog input (BUF _ OUT) of the microcontroller 104. The output of the operational amplifier 114 is also coupled to another analog input (CO OUT) of the microcontroller 104.

The voltage reference source 122 provides a voltage reference source for the CO sensor 106 and is buffered by a buffer amplifier 120 having an output coupled to the counter (C) terminal of the CO sensor 106. The CO sensor 106 may be a capacitive electrochemical CO sensor and holds a voltage charge that can be varied when CO gas is detected. The change in voltage charge on the CO sensor 106 is coupled to and amplified by the CO operational amplifier 114. The electrochemical CO sensor may be, for example, but not limited to Figaro's model TGS5042, TGS5141, or the like.

During normal operation of the carbon monoxide detector 100, the voltage charge on the CO sensor 106 is in equilibrium, as indicated by a certain voltage on the output of the CO operational amplifier 114. This balanced output voltage is coupled to an analog input (CO OUT) of the microcontroller 104, where a sufficient change in its voltage may indicate a CO gas detection event. The CO operational amplifier 114 is configured as a standard differential input operational amplifier with a gain setting feedback resistor 124. The anti-polarization transistor 108 may also be connected in parallel with the differential input of the CO operational amplifier 114 and the operational (C and W) terminals of the CO sensor 106. During its normal operation, current source/ receivers 116 and 118 are effectively decoupled from the CO detection circuit.

During test mode operation of the carbon monoxide detector 100, the output of the CO operational amplifier 114 may be disabled and enter a high impedance state, effectively decoupling the operational amplifier 114 from the CO detection circuitry. The input of the operational amplifier 114 is high impedance and therefore does not substantially load the circuit voltage. During testing, when the current source/receiver 116 is enabled as a current source, a charging current may be injected into the C terminal of the CO sensor 106, effectively increasing the voltage at the C terminal relative to the voltage at its W terminal. When the current source/receiver 118 is enabled as a current receiver, the discharge current may be removed from the W terminal of the CO sensor 106, effectively reducing the voltage at the W terminal relative to the voltage at the C terminal. The source and receiver configurations of current sources/ receivers 116 and 118 may be reversed to effectively reduce the voltage at the C terminal and/or increase the voltage at the W terminal. The configuration and operation of current sources/ receivers 116 and 118 may be controlled by supervisor alarm controller 110 by receiving a control signal (CTRL) from microcontroller 104, for example, via a serial SPI bus.

The voltages on the C and W terminals of the CO sensor 106 may be monitored over time by the microcontroller 104. When the CO operational amplifier 114 output is disabled and then re-enabled, the C terminal voltage and the W terminal voltage may be monitored. When the current source/ receiver 116 or 118 is disabled (decoupled) and the output of the CO operational amplifier 114 is re-enabled, the voltage charge on the CO sensor 106 will rebalance over time. The voltage versus time schedule may be implemented in a memory (not shown) of the microcontroller 104 and used to verify proper operation of the CO sensor 106 and overall operation of the carbon monoxide detector 100.

Referring now to fig. 2, there is shown a schematic voltage versus time diagram of an operational test of a carbon monoxide detector according to the teachings of the present disclosure, illustrating its normal operation. The sink current pulse is applied to the terminal of the CO sensor 106 for about five (5) seconds, and then the voltage between the C and W terminals of the CO sensor 106 is measured when it returns to equilibrium for more than about seven (7) seconds. The equilibrium voltage is about 0.3 volts and then jumps to over 3 volts after a pulse of about-2.1 microamps of current draw.

Referring now to fig. 3 and 4, schematic program flow diagrams of carbon monoxide alarm supervision are shown, according to specific exemplary embodiments of the present disclosure. After the output of the CO operational amplifier 114 is disabled, the current source or receiver pulse unbalances the voltage balance of the CO sensor 106. Then, the CO operational amplifier 114 output is re-enabled, and the change in voltage charge between the C and W terminals of the CO sensor 106 is observed over time. A properly operating CO detector will have a characteristic voltage/time response when the voltage charge is rebalanced back to equilibrium after a current pulse is applied to its CO sensor 106.

Fig. 3 shows a schematic program flow diagram for changing the voltage charge of the CO sensor 106 and the current source/receiver 116 and/or the current source/receiver 118, then measuring the output voltage of the CO operational amplifier 114 over time while characterizing the reestablishment of the voltage charge balance on the electrochemical CO sensor 106. Step 302 initiates a test procedure. Step 304 sets the sample count n to zero (0). Step 308 disables the output of the CO operational amplifier 114. Step 310 enables the current source or receiver 116 or 118 for a period of time S. In step 312, the voltage charge on the CO sensor 106 is charged or discharged by the current source or receiver 116 or 118, causing the voltage charge thereon to become unbalanced. In step 314, the current source or receiver 116 or 118 is disabled, resulting in charging or discharging of the CO sensor 106.

In step 316, the output of the CO operational amplifier 114 is re-enabled, including the closed loop feedback circuit of the CO operational amplifier 114, the CO voltage reference 122, and the feedback resistor 124; the voltage charge on the CO sensor 106 is forced back to equilibrium, e.g., a static voltage value over time. In step 318, the voltage sample at the output of the CO operational amplifier 114 is taken at time t (n), and in optional step 320, the voltage sample at time t (n) may be stored in a memory, for example, a microcontroller memory as shown in fig. 1. In step 322, n is increased by 1. Step 324 checks whether the previous time voltage sample has about the same value as the current voltage sample. If not, the next voltage sample is taken in step 318 and stored in step 320. If so, the voltage charge on the CO sensor 106 has reached equilibrium, and step 326 evaluates the elapsed time T (n) to determine if the quiescent voltage state of charge has been reached within the expected time period. An optional further step 328 may be used to determine whether the voltage charge on the CO detector 106 is an expected value, for example, measuring the voltage between the C and W terminals of the CO detector 106. If the results of steps 326 and 328 are yes, then in step 330 the CO detector 100 has been determined to be operational. If not, the CO detector 100 circuit is defective.

Fig. 4 shows a schematic program flow diagram for changing the voltage charge of the CO sensor 106 and the current source/receiver 116 and/or the current source/receiver 118, then measuring the output voltage of the CO operational amplifier 114 over time while characterizing the reestablishment of the voltage charge balance on the electrochemical CO sensor 106. Step 402 initiates a test procedure. Step 406 measures the voltage on the output of the CO op amp 114 (and is stored in, for example, a memory of the microcontroller 104). Step 408 disables the output of the CO operational amplifier 114. Step 410 enables the current source or receiver 116 or 118 for a period of time S. In step 412, the voltage charge on the CO sensor 106 is charged or discharged by the current source or receiver 116 or 118, causing the voltage charge thereon to become unbalanced. In step 414, the current source or receiver 116 or 118 is disabled, resulting in charging or discharging of the CO sensor 106. Step 404 sets the sample count n to zero (0).

In step 416, the output of the CO operational amplifier 114 is re-enabled, including a closed loop feedback circuit of the CO operational amplifier 114, the CO voltage reference 122, and the feedback resistor 124; the voltage charge on the CO sensor 106 is forced back to equilibrium, e.g., a static voltage value over time. In step 418, a voltage sample at the output of the CO operational amplifier 114 is taken at time t (n), and in step 420, the voltage sample at time t (n) is stored in a memory, for example, a microcontroller memory as shown in fig. 1. In step 422, n is increased by 1. Step 424 checks whether the current voltage sample at t (n) is substantially the same as the stored voltage value obtained in step 406. If not, the next voltage sample is taken in step 418 and stored in step 420. If so, the voltage charge on the CO sensor 106 has reached equilibrium, and step 426 evaluates the elapsed time T (n) to determine if the quiescent voltage state of charge has been reached within the expected time period. An optional further step 428 may be used to determine whether the voltage charge on the CO detector 106 is an expected value, for example, measuring the voltage between the C and W terminals of the CO detector 106. If the result of steps 426 and 428 is yes, then in step 430 the CO detector 100 has been determined to be operational. If not, the CO detector 100 circuit is defective.

The present invention has been described in terms of one or more preferred embodiments, and it is to be understood that many equivalents, alternatives, variations, and modifications, in addition to those explicitly recited (e.g., methods of manufacture, products-by-process, etc.), are possible and are within the scope of the invention.