Leakage current noise reduction for ionization chamber-based alarms

Abstract

As an example, an apparatus can include: an ionization chamber; the voltage source is used for driving the ionization chamber; the voltage sensor is used for measuring the output voltage of the ionization chamber; a calibration circuit for compensating the ionization chamber output voltage based on a correction factor; and a monitoring circuit for triggering an alarm when the compensated output voltage satisfies a predetermined condition. The calibration circuit can determine the correction factor to compensate for any leakage current that affects the ionization chamber output voltage.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of priority of Provisional Patent Application 63 / 451,127, filed on March 9, 2023, the content of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates to sensors and / or alarms. Various uses of the teachings herein can include environmental monitoring, such as smoke detectors and / or leakage current noise reduction for ionization chamber - based alarms. Background Art

[0004] Ionization chambers can be used to detect smoke particles in smoke detectors. These ionization chambers are typically driven by a relatively high voltage to generate a sufficient output signal to distinguish from noise sources. The output signal can be a voltage, which is usually buffered and then evaluated by a comparator. The source impedance of the ionization chamber can be in the tera - ohm range, which is significantly higher than the impedance of one of the most commonly used printed circuit board (PCB) materials.

[0005] The large impedance mismatch and the relatively high voltage used to drive the ionization chamber can lead to leakage current across the PCB insulation. This leakage current introduces an imbalance in the ionization voltage driver and may cause residues and dust from the PCB manufacturing process to accumulate over time, forming conductive dendrite growth that increases the board conductivity. As the resistivity of the PCB becomes lower over time, the leakage current may increase, which may promote further dendrite development. If the expected ionization chamber voltage output is pulled too far from the baseline (or leakage - current - free) value by the additional current conduction path, dendrite development may ultimately lead to device failure. This gradual device failure manifests itself during operation as a slow drift of the baseline signal over time closer to the alarm trip point level. As the baseline drift increases and the difference between the baseline and the alarm trip point decreases over time, the device sensitivity decreases, the chance of false alarms increases, and the safety decreases, thus putting lives and property at risk.

[0006] A first approach to solving this problem is to provide a guard ring to reduce leakage current. This includes using a buffer to track the input signal voltage and driving the outer traces of the guard ring with a voltage that tracks the input signal voltage. This surrounds and "protects" the internal input signal voltage. By driving the nearby guard traces with the same voltage as the input signal voltage, the effects of surrounding contamination are reduced, thus reducing the leakage current.

[0007] However, the buffer for the guard ring circuit is not an ideal operational amplifier. The amplifier will have a voltage offset (even if small) and will drift over time. This offset will introduce a voltage difference between the guard trace and the signal trace, causing leakage current and noise. This problem can be mitigated by using a precision amplifier or a zero-drift amplifier with a lower offset, but these products may be several times more expensive than standard operational amplifiers.

[0008] A second method of solving this problem is to use a conformal coating on the PCB, which reduces leakage current by first preventing factory contamination and / or airborne contamination from reaching the input traces. This is done by creating a physical barrier and thus providing a high impedance. Unfortunately, this method requires an additional manufacturing step, resulting in higher costs. Therefore, conformal coatings are less commonly used.

[0009] A third method of solving this problem is to bend the lead of the amplifier input so that the lead is in the air and in direct contact with the ionization chamber rather than the trace on the PCB. A fourth similar method of solving this problem is to drill a large hole corresponding to the position of the amplifier input lead to achieve a similar effect of blocking contact with the board and using air as an insulator. The third and fourth methods may require soldering wires in the air and rule out the use of only wave solder or solder reflow, thus adding additional manufacturing steps, additional costs, and introducing potential quality problems. Summary of the Invention

[0010] As an example of the teachings herein, a device may include: an ionization chamber; a voltage source for driving the ionization chamber; a voltage sensor for measuring the ionization chamber output voltage; a calibration circuit for compensating the ionization chamber output voltage based on a correction factor; and a monitoring circuit for triggering an alarm when the compensated output voltage meets a predetermined condition; wherein the calibration circuit is operable to determine the correction factor to compensate for any leakage current affecting the ionization chamber output voltage.

[0011] As another example, a smoke detector may include: an ionization chamber; an inlet for providing a sample to the ionization chamber; a voltage source for driving the ionization chamber; a voltage sensor for measuring the ionization chamber output voltage; a calibration circuit for compensating the ionization chamber output voltage based on a correction factor; and a monitoring circuit for triggering an alarm when the compensated output voltage meets a predetermined condition; wherein the calibration circuit is operable to determine the correction factor to compensate for any leakage current affecting the ionization chamber output voltage.

[0012] As another example, a method may include: driving an ionization chamber with a voltage source; measuring the output voltage of the ionization chamber with a voltage sensor; driving a lead to a second voltage different from the output voltage of the ionization chamber; measuring the response to the second voltage; analyzing the response and determining a correction factor based on the response to compensate for any leakage current affecting the output voltage of the ionization chamber; applying the correction factor to a signal using a calibration circuit; comparing the compensated signal to a predetermined standard, where the predetermined standard includes an alarm condition; and responding to the alarm condition if the compensated signal meets the predetermined standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The teachings of the present disclosure are further illustrated based on the drawings depicting examples of the present disclosure. In the drawings:

[0014] Figure 1 is a graph depicting the signal change in the output of a smoke detector caused by an increasing leakage current over time;

[0015] Figure 2A and Figure 2B is a diagram showing an example device incorporating the teachings of the present disclosure;

[0016] Figure 3A and Figure 3B is a diagram showing an example device for controlling sensing measurements incorporating the teachings of the present disclosure;

[0017] Figures 4A to 4C is a diagram showing an example device for protecting pin biasing incorporating the teachings of the present disclosure; and

[0018] Figures 5A to 5F is a flowchart depicting an example method incorporating the teachings of the present disclosure. DETAILED DESCRIPTION

[0019] Typically, during initial calibration of an ionization chamber smoke detector at the factory, a baseline "clean air / clean device" signal is recorded in the device memory. The recorded signal reflects the initial current output of the ionization chamber before deployment. During device operation, the ionization chamber smoke detector wakes up periodically to sample the output voltage of the ionization chamber. At the time of sampling, the ionization chamber smoke detector engages a calibration circuit to compensate for the baseline signal, as the baseline signal drifts slowly over time due to contamination and dust accumulation. The compensation includes measuring the difference between the initially factory-set "clean air / clean device" signal and the current baseline signal. This difference can be saved as a "compensation factor" and subtracted from the measurement or used to adjust the detection limit, thereby maintaining the device sensitivity for smoke detection.

[0020] Systems and / or methods for maintaining the sensitivity of a device despite the accumulation of dust and contamination can reduce the risk of false alarms and maintain its proper operation throughout the planned life of an ionization chamber smoke detector, thereby enhancing safety and protecting life and property. The firmware-based or state machine-based solutions described herein can be monitored and adjusted over time. The systems and / or methods described herein account for current leakage due to contamination and do not require any additional manufacturing steps. This allows for the selection and use of low-cost, standard performance operational amplifiers. This can also eliminate the need for conformal coatings or larger vias or special soldering designed to control board current leakage by increasing impedance and / or physically separating components. This can also enable the ionization chamber smoke detector to report these changes in baseline drift via interconnection, Wi-Fi, or other communication means to alert when cleaning or replacement of the device is required.

[0021] Figure 1 FIG. 100 is a graph depicting trace 120 of the output voltage of an ionization chamber smoke detector over time due to increased leakage current. FIG. 100 shows a trace corresponding to an example voltage signal output from an ionization chamber smoke detector after deployment. Trace 110 indicates the value of the ionization chamber output voltage of a clean air signal measured at the factory in a "clean" state prior to deployment of the ionization chamber smoke detector. As shown, trace 110 remains constant over time. Trace 120 shows the actual signal of clean air where the ionization chamber output voltage decreases over time due to an imbalance created in the chamber voltage divider by leakage current.

[0022] As shown, the leakage current can accumulate over time, driving trace 120 away from the clean state and closer to trace 130. Trace 130 represents the smoke detection threshold or alarm value. That is, if the measured voltage is equal to or below the limit shown on trace 130, the ionization chamber smoke detector senses smoke or fire. As trace 120 approaches trace 130, the chance of false positive signals increases. Additionally, since the leakage current distorts the chamber's response to the presence of smoke, the device loses its sensitivity range to real smoke or fire conditions.

[0023] The accumulation of residue and dust causes dendritic growth within the ionization chamber, which reduces the resistivity of the PCB. Dendritic growth increases the leakage current, which promotes further dendritic growth. When the ionization chamber output voltage is affected too much by leakage, this ultimately leads to device failure. Gradual device failure manifests itself as a slow drift of the baseline signal over time closer to the smoke detection threshold. As the baseline drift increases, the difference between the baseline and the smoke detection threshold decreases over time. The device sensitivity decreases, and the chance of false reporting increases, putting life and property at risk.

[0024] Figure 2A is a schematic diagram showing an example device incorporating the teachings of the present disclosure. As shown, the ionization chamber is driven by a voltage source. The voltage sensor measures the output voltage of the ionization chamber. This voltage can be provided to a monitoring circuit (shown in dashed lines) to determine if an alarm condition exists. However, as shown, the ionization chamber output voltage is first provided to a calibration circuit that is operable to apply a correction factor and compensate for any leakage current. Additionally, the calibration circuit is operable to determine the correction factor, as described herein.

[0025] Figure 2B is an illustration of an example device 200 incorporating the teachings of the present disclosure. Device 200 may include an ionization chamber 210, a calibration circuit 230, a voltage sensor 240, and an alarm circuit 250. Some of these components may be provided by a microcontroller (MCU), which can result in little or no additional end-product cost. A microcontroller is an intelligent semiconductor integrated circuit (IC) that includes a processor unit, a memory module, a communication interface, and in some cases, peripherals. Generally, the MCU operates by executing program instructions stored in the memory module using the processor unit. The instructions typically cause the MCU to drive the communication interface (e.g., sense inputs and drive outputs).

[0026] The ionization chamber 210 may include a chamber that is open to the ambient air in the room or space to be monitored. The natural flow of air through the chamber allows for the detection of smoke particles in the air. The ionization chamber 210 may include any circuitry suitable for measuring changes caused by a plurality of ion pairs in the sampled air. For example, some examples include a set of parallel plates that make up an anode and a cathode, or a cylinder (forming the cathode) that has a coaxial anode wire inside the cylinder. When a voltage potential is applied across the two electrodes, any gas atoms or molecules in the sample can be ionized and migrate towards the electrodes, thereby driving a signal displayed by the sensor. In some smoke detectors, for example, the ion chamber contains a small amount of an alpha particle (e.g., americium-241) emitter.

[0027] These alpha particles ionize the air and airborne particles, which are carried by the applied electric field that drives a steady baseline current in both the open air chamber and the closed chamber, thereby generating a voltage drop across each chamber and a voltage divided between the two chambers at the output. When smoke particles enter the open air chamber, they are also ionized, but are heavier than air particles and thus move more slowly in the electric field, resulting in less charge transfer and thus lower current flow. This effectively makes the open air chamber more resistive, increasing the voltage drop across the open air chamber and decreasing the voltage drop across the closed air chamber. The ionization chamber 210 provides a series current through the two chambers. The lower chamber resistance has not changed, but the current flow has decreased due to the lower current flow in the open air chamber. Therefore, due to the lower current on the same resistance, the lower chamber shows a voltage drop. Then, as smoke particles enter the open air chamber and are carried away by the electric field, the output voltage decreases.

[0028] The calibration circuit 230 may include any circuitry for compensating the output voltage signal from the ionization chamber 210 based on a factory baseline or other calibration.

[0029] The voltage sensor 240 may include any circuitry for transforming the ionization chamber 210 output voltage corresponding to the current generated in the ionization chamber 210.

[0030] The monitoring circuit 250 may include any circuitry for evaluating the voltage signal from the voltage sensor 240 (including evaluating smoke or fire conditions). The monitoring circuit 250 may trigger an alarm in response to an alarm condition, which may include but is not limited to an audible warning, a flashing light, a signal to a monitoring service, etc.

[0031] The device 200 incorporating the teachings of the present disclosure may allow for adjustment for the effects of contamination, issue a warning if the detector becomes too contaminated, issue a warning for detectors in production showing signs of on-site problems, may allow the use of an MCU instead of more complex and / or expensive components, and use surface mount technology instead of a through-hole solution.

[0032] Figure 3A and Figure 3B is a diagram showing an example device 300 for controlling sensing measurements incorporating the teachings of the present disclosure. As Figure 3AAs shown, the control sensing device 300 may include an MCU having a guard lead G, an ion sensing lead Si, and a control sensing lead Sc. The ion sensing lead Si is used to measure the ionization chamber output voltage. The control sensing lead Sc and associated traces surround the guard lead G and associated traces. The control sensing lead Sc and associated traces are typically biased from the guard lead G to ground or Vdd or another predetermined voltage difference. The bias current flowing between the guard lead G and the control sensing lead Sc is measured and recorded, and this bias current is used as a control measurement for leakage current increase to determine the appropriate offset of the ion sensing lead Si and the guard lead G. Alternatively, the control sensing lead Sc may be biased to a guard voltage level and periodically changed to another voltage to measure the leakage current, thereby determining the appropriate offset to compensate for the board leakage from the ion sensing lead Si to the guard lead G. Figure 3B A schematic version of the compensation scheme is shown.

[0033] In operation, the voltage at the control sensing lead Sc is periodically biased to a larger difference from the voltage at the guard lead G. The leakage current is measured. The measured leakage current is used to determine the condition of the board resistivity in the region between the guard lead G and the control sensing lead Sc. This resistivity is an indirect measurement of the board resistivity, which allows the measurement to be made without disturbing the output voltage of the ionization chamber 210. Using this regional resistivity, the calibration circuit 230 calculates any required offset of the ionization chamber output voltage caused by the leakage current. In one example, based on the difference between the guard lead G and the ion sensing lead Si, the control sensing lead Sc is biased from the guard lead G to a new voltage.

[0034] Figures 4A to 4C FIG. is a diagram showing an example device 400 for guard pin biasing incorporating the teachings of the present disclosure. The device 400 may include an MCU, a state machine, or discrete components having a guard lead G and an ion sensing lead Si. The guard pin biasing may be performed by internally disconnecting the guard ring from the buffer output and connecting the guard lead G to ground or Vdd or a voltage other than the ionization chamber output voltage connected to the ion sensing lead Si, and measuring the settling time, magnitude change, or rate of change of the voltage of the buffer disconnected from the guard lead G. A smaller offset (such as 100 millivolts) between the guard device and the buffered output may be used to improve the ionization chamber recovery time. A gradual change may be used to avoid a step function current flow disturbing the ionization chamber. The settling time of the ionization chamber, the change in magnitude, or the rate of change of the buffer output voltage may be considered an indication of the leakage current, since the settling time should be zero in the absence of leakage current and increases directly with an increase in the leakage between the guard lead G and the ion sensing lead Si. Figure 4B and Figure 4C A schematic diagram of the compensation scheme is shown.

[0035] In operation, the guard lead G is biased to the output voltage of the ionization chamber 210 to reduce any leakage current to the ion sensing lead Si. Periodically, the voltage applied to the protection device is switched to create a greater difference between the guard lead G and the ion sensing lead Si, thereby increasing the leakage current. This increased current creates an imbalance in the ionization divider, which in turn changes the output voltage. The change in the output voltage is used to determine the offset required to compensate for the leakage current during normal operation. In some examples, the leakage current from the system-generated voltage can be used to determine the required offset.

[0036] Examples of the present disclosure can reduce costs and allow the use of surface mount devices. Currently, through-hole components are mainly used, and the construction of a smoke detector can be performed by drilling through the PCB to connect the ionization chamber without contacting the PCB. Some examples can include digital calibration and tracking of the ion sensing lead Si to allow the use of surface mount components. Some examples can include digital tracking of the sense lead leakage to determine dendrite growth. Some examples can include producing a baseline to test cleanliness.

[0037] Figure 5A is a flowchart depicting an example method 500 incorporating the teachings of the present disclosure. Method 500 includes biasing a guard lead and sensing the voltage generated in response.

[0038] Step 510 may include driving the ionization chamber with a voltage source.

[0039] Step 520 may include measuring the output voltage from the ionization chamber using a voltage sensor.

[0040] Step 530 may include driving the guard lead to a voltage different from the ionization chamber output voltage.

[0041] Step 540 may include measuring a second output voltage from the ionization chamber.

[0042] Step 550 may include analyzing the change from the ionization chamber voltage output to the second output voltage.

[0043] Step 560 may include determining a correction factor to compensate for any leakage current.

[0044] Step 570 may include applying the correction factor to the ionization chamber output voltage.

[0045] Step 580 may include comparing the compensated signal to a predetermined standard.

[0046] Step 590 may include responding to an alarm condition if the compensated signal meets the predetermined standard.

[0047] Figure 5B is a flowchart depicting an example method 600 incorporating the teachings of the present disclosure. Method 600 includes biasing a guard lead and measuring the current generated in response.

[0048] Step 610 may include driving an ionization chamber with a voltage source.

[0049] Step 620 may include driving the guard lead to a voltage different from the ionization chamber output voltage.

[0050] Step 630 may include measuring the output current from the guard driver.

[0051] Step 640 may include analyzing the output current.

[0052] Step 650 may include determining a correction factor based on the output current.

[0053] Step 660 may include applying the correction factor to the ionization chamber output voltage.

[0054] Step 670 may include comparing the compensation signal to a predetermined standard.

[0055] Step 680 may include responding to an alarm condition if the compensation signal meets the predetermined standard.

[0056] Figure 5C is a flowchart depicting an example method 700 incorporating the teachings of the present disclosure. Method 700 includes biasing a guard lead and sensing the change in response voltage over time.

[0057] Step 710 may include driving an ionization chamber with a voltage source.

[0058] Step 720 may include measuring the ionization chamber output voltage.

[0059] Step 730 may include driving the guard lead to a voltage different from the ionization chamber output voltage and then driving it back to the ionization chamber output voltage.

[0060] Step 740 may include measuring the duration it takes for the ionization chamber output voltage to return to the unbiased guard level.

[0061] Step 750 may include determining a correction factor based on the measured duration.

[0062] Step 760 may include applying the correction factor to the ionization chamber output voltage.

[0063] Step 770 may include comparing the compensation signal to a predetermined standard.

[0064] Step 780 may include responding to an alarm condition if the compensation signal meets a predetermined criterion.

[0065] Figure 5D is a flowchart depicting an example method 800 incorporating the teachings of the present disclosure. Method 800 includes biasing a guard lead and sensing a response change in current.

[0066] Step 810 may include driving an ionization chamber with a voltage source.

[0067] Step 820 may include driving the guard lead to a voltage different from the ionization chamber output voltage and then driving it back to the ionization chamber output voltage.

[0068] Step 830 may include measuring the amount of time it takes for the output current from the guard driver to return to the unbiased guard level.

[0069] Step 840 may include determining a correction factor based on the change in the amount of time.

[0070] Step 850 may include applying the correction factor to the ionization chamber output voltage.

[0071] Step 860 may include comparing the compensation signal to a predetermined criterion.

[0072] Step 870 may include responding to an alarm condition if the compensation signal meets a predetermined criterion.

[0073] Figure 5E is a flowchart depicting an example method 900 incorporating the teachings of the present disclosure. Method 900 includes driving a control sense lead and measuring a response current.

[0074] Step 910 may include driving an ionization chamber with a voltage source.

[0075] Step 920 may include driving the current sense lead to a voltage different from the ionization chamber output voltage.

[0076] Step 930 may include measuring the output current from the control sense driver.

[0077] Step 940 may include determining a correction factor based on the output current.

[0078] Step 950 may include applying the correction factor to the ionization chamber output voltage.

[0079] Step 960 may include comparing the compensation signal to a predetermined criterion.

[0080] Step 970 may include responding to an alarm condition if the compensation signal meets a predetermined criterion.

[0081] Figure 5F It is a flowchart depicting an exemplary method 100 incorporating the teachings of the present disclosure. Method 1000 includes driving a control sense lead and measuring a response current.

[0082] Step 1010 may include driving an ionization chamber with a voltage source.

[0083] Step 1020 may include measuring the ionization chamber output voltage with a voltage sensor.

[0084] Step 1030 may include analyzing the signal generated by the voltage sensor.

[0085] Step 1040 may include determining a correction factor based on the signal.

[0086] Step 1050 may include applying the correction factor to the ionization chamber output voltage.

[0087] Step 1060 may include comparing the compensation signal with a predetermined standard.

[0088] Step 1070 may include responding to an alarm condition if the compensation signal meets the predetermined standard.

[0089] Although the exemplary embodiments have been described above, other variations and embodiments may be made by the present disclosure without departing from the essence and scope of these embodiments.

Claims

1. An apparatus, the apparatus comprising: An ionization chamber; A voltage source for driving the ionization chamber; A voltage sensor for measuring the output voltage of the ionization chamber; A calibration circuit for compensating the output voltage of the ionization chamber based on a correction factor; And A monitoring circuit for triggering an alarm when the compensated output voltage meets a predetermined condition; Wherein the calibration circuit is operable to determine the correction factor to compensate for any leakage current affecting the output voltage of the ionization chamber.

2. The apparatus according to claim 1, the apparatus comprising a memory storing a factory baseline signal corresponding to the original factory condition of the ionization chamber before deployment.

3. The apparatus according to any one of claims 1 to 2, wherein the calibration circuit is operable to: Drive a guard lead to a second voltage different from the output voltage of the ionization chamber; In response, measure a second output voltage from the ionization chamber; and Determine the correction factor at least in part based on the difference between the output voltage of the ionization chamber and the second output voltage.

4. The apparatus according to any one of claims 1 to 3, wherein the calibration circuit is operable to: Drive a guard lead to a second voltage different from the output voltage of the ionization chamber; Measure a first output current from a guard driver; and Determine the correction factor at least in part based on the first output current.

5. The apparatus according to any one of claims 1 to 4, wherein the calibration circuit is operable to: Drive a guard lead to a second voltage different from the output voltage of the ionization chamber and then return the guard lead to the output voltage of the ionization chamber; Measure a first duration required for the output voltage of the ionization chamber to return to an unbiased guard level; And Determine the correction factor at least in part based on a change in the first duration compared to a factory baseline.

6. The apparatus according to any one of claims 1 to 5, wherein the calibration circuit is operable to: Drive a guard lead to a second voltage different from the output voltage of the ionization chamber and then return the guard lead to the output voltage of the ionization chamber; Measure a second duration required for the current from a voltage driver to return to an unbiased guard level; And Determine the correction factor at least in part based on a change in the second duration compared to a factory baseline.

7. The apparatus according to any one of claims 1 to 6, wherein the calibration circuit is operable to: Drive a current sensing lead to a second voltage different from the output voltage of the ionization chamber; Measure a second output current from a control sensing driver; and Determine the correction factor at least in part based on the second output current.

8. The apparatus according to any one of claims 1 to 7, wherein the calibration circuit is operable to: Determine current leakage; and If the current leakage meets a predetermined threshold, activate a warning.

9. A smoke detector, the smoke detector comprising: An ionization chamber; An inlet for providing a sample to the ionization chamber; A voltage source for driving the ionization chamber; A voltage sensor for measuring the output voltage of the ionization chamber; A calibration circuit for compensating the output voltage of the ionization chamber based on a correction factor; And A monitoring circuit for triggering an alarm when the compensated output voltage meets a predetermined condition; Wherein the calibration circuit is operable to determine the correction factor to compensate for any leakage current affecting the output voltage of the ionization chamber.

10. The smoke detector according to claim 9, the smoke detector including a memory storing a factory baseline signal corresponding to the original factory condition of the ionization chamber before deployment.

11. The smoke detector according to any one of claims 9 to 10, wherein the calibration circuit is operable to: Drive the guard lead to a second voltage different from the output voltage of the ionization chamber; Measure a second output voltage from the ionization chamber; and Determine the correction factor at least in part based on the difference between the output voltage of the ionization chamber and the second output voltage.

12. The smoke detector according to any one of claims 9 to 11, wherein the calibration circuit is operable to: Drive the guard lead to a second voltage different from the output voltage of the ionization chamber; Measure a first output current from the guard driver; and Determine the correction factor at least in part based on the first output current.

13. The smoke detector according to any one of claims 9 to 12, wherein the calibration circuit is operable to: Drive the guard lead to a second voltage different from the output voltage of the ionization chamber and then return the guard lead to the output voltage of the ionization chamber; Measure a first duration required for the output voltage of the ionization chamber to return to an unbiased guard level; And Determine the correction factor at least in part based on the change in the first duration compared to the factory baseline.

14. The smoke detector according to any one of claims 9 to 13, wherein the calibration circuit is operable to: Drive the guard lead to a second voltage different from the output voltage of the ionization chamber and then return the guard lead to the output voltage of the ionization chamber; Measure a second duration required for the current from the voltage driver to return to an unbiased guard level; And Determine the correction factor at least in part based on the change in the second duration compared to the factory baseline.

15. The smoke detector according to any one of claims 9 to 14, wherein the calibration circuit is operable to: Drive the current sensing lead to a second voltage different from the output voltage of the ionization chamber; Measure a second output current from the control sensing driver; and Determine the correction factor at least in part based on the second output current.

16. The smoke detector according to any one of claims 9 to 15, wherein the calibration circuit is operable to: Determine current leakage; and If the current leakage meets a predetermined threshold, activate a warning.

17. The smoke detector according to any one of claims 9 to 16, wherein the smoke detector includes a memory that stores a factory baseline signal corresponding to the original factory condition of the ionization chamber before deployment; wherein the predetermined criterion is at least partially based on the factory baseline signal.

18. A method, the method comprising: driving an ionization chamber using a voltage source; measuring the output voltage of the ionization chamber using a voltage sensor; driving a lead to a second voltage different from the output voltage of the ionization chamber; measuring the response to the second voltage; analyzing the response and determining a correction factor based on the response to compensate for any leakage current affecting the output voltage of the ionization chamber; applying the correction factor to a signal using a calibration circuit; comparing the compensated signal with a predetermined criterion, wherein the predetermined criterion includes an alarm condition; and responding to the alarm condition if the compensated signal meets the predetermined criterion.

19. The method according to claim 18, wherein: the lead includes a guard lead; the response includes a second output voltage from the ionization chamber; and analyzing the response includes determining the difference between the output voltage and the second output voltage; and the compensation factor depends at least in part on the determined difference.

20. The method according to claim 18, wherein: the lead includes a guard lead; the response includes a first output current from a guard sensor; analyzing the response includes determining a value for the first output current; and the compensation factor depends at least in part on the value of the first output current.

21. The method according to claim 18, wherein: the lead includes a guard lead; the method further includes driving the guard lead back to the output voltage of the ionization chamber after driving the guard lead to a drive voltage; analyzing the response includes determining a first duration required for the output voltage of the ionization chamber to return to an unbiased guard level; and the compensation factor depends at least in part on the change in the determined first duration relative to a baseline duration.

22. The method according to claim 18, wherein: the lead includes a guard lead; the method further includes driving the guard lead back to the output voltage of the ionization chamber after driving the guard lead to the drive voltage; analyzing the response includes determining a second duration required for the output current from the voltage source to return to an unbiased guard level; and the compensation factor depends at least in part on the change in the determined second duration relative to a baseline duration.

23. The method according to claim 18, wherein: the lead includes a current sensing lead; analyzing the response includes determining a second output current from a control sensing driver; and the compensation factor depends at least in part on the second output current.

24. The method according to claim 18, wherein determining the compensation factor includes measuring a new baseline signal corresponding to an active leakage current.

25. The method according to claim 18, the method comprising: Measure a signal corresponding to an active leakage current; and if the signal meets a predetermined threshold, activate a warning.

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