Patent Description:
Photoelectric detector devices, such as smoke detectors, typically use a light source transmitted at an angle relative to a photo detector that prevents a sufficiently high level of light from being detected by the photo detector under nominal conditions. When smoke is present, smoke particles scatter the light from the light source and some portion of the light is detected by the photo detector. The signal level detected by the photo detector can vary due to a number of effects, such as environmental conditions, component variations, component age, and the like. <CIT> discloses a fire monitoring system including a smoke detector, that can correct a measured value of smoke density derived from detected light, using reference values and correction coefficients.

According to a first aspect of the invention, a detector device includes a light source disposed within a chamber; a sensor disposed within the chamber physically offset from the light source, the sensor being for detecting light from the light source as it is scattered by particles in the chamber, wherein the sensor is a photo detector sensor; a compensator circuit electrically coupled with the sensor wherein the compensator circuit comprises an amplification circuit operable to amplify a sensor output of the sensor as an amplified sensor signal and a summing circuit operable to sum the amplified sensor signal with a compensation offset signal to produce a compensated sensor signal, wherein the summing circuit is an analog circuit; an analog-to-digital converter operable to sample and quantize the compensated sensor signal as a digital value; a digital-to-analog converter operable to convert the compensation offset signal from a digital signal to an analog signal prior to summing at the summing circuit; and a controller. The controller is operable to de-energize the light source; receive a sensor signal generated by the sensor, wherein the sensor signal received at the controller is the amplified sensor signal as sampled and quantized through the analog-to-digital converter when the compensation offset signal has a zero offset value; determine one or more error sources included in a clean air value of the sensor signal with the light source de-energized; determine a compensation factor to adjust the sensor signal, wherein the compensation factor is determined as the adjustment needed to reach a target baseline clean air value representing a starting value for comparison to an alarm limit based on the one or more error sources; generate the compensation offset signal based on the compensation factor, and output the compensation offset signal to the compensator circuit to produce a compensated sensor signal as an adjustment to the sensor signal. The controller is further operable to energize the light source and monitor the compensated sensor signal with respect to the alarm limit, and trigger an alarm event based on the compensated sensor signal exceeding the alarm limit.

According to a second aspect of the invention, a detector device includes a light source disposed within a chamber; a sensor disposed within the chamber physically offset from the light source, the sensor being for detecting light from the light source as it is scattered by particles in the chamber, wherein the sensor is a photo detector sensor; a compensator circuit electrically coupled with the sensor wherein the compensator circuit comprises an amplification circuit operable to amplify a sensor output of the sensor as an amplified sensor signal and a summing circuit operable to sum the amplified sensor signal with a compensation offset signal to produce a compensated sensor signal, wherein the summing circuit is an analog circuit; a digital-to-analog converter operable to convert the compensation offset signal from a digital signal to an analog signal prior to summing at the summing circuit; and a controller comprising an analog-to-digital converter operable to sample and quantize the compensated sensor signal as a digital value. The controller is operable to de-energize the light source; receive a sensor signal generated by the sensor, wherein the sensor signal received at the controller is the amplified sensor signal when the compensation offset signal has a zero offset value; determine one or more error sources included in a clean air value of the sensor signal with the light source de-energized; determine a compensation factor to adjust the sensor signal, wherein the compensation factor is determined as the adjustment needed to reach a target baseline clean air value representing a starting value for comparison to an alarm limit based on the one or more error sources; generate the compensation offset signal based on the compensation factor, and output the compensation offset signal to the compensator circuit to produce a compensated sensor signal as an adjustment to the sensor signal. The controller is further operable to energize the light source and monitor the compensated sensor signal with respect to the alarm limit, and trigger an alarm event based on the compensated sensor signal exceeding the alarm limit.

Optionally, the controller is further operable to determine whether the compensated sensor signal has increased above a baseline value and increase the compensation offset signal until the compensated sensor signal is at or below the baseline value.

Optionally, the controller is further operable to detect a hush request, increase the compensation offset signal until the compensated sensor signal is below the alarm limit responsive to the hush request, and reset the compensation offset signal after a predetermined period of time elapses from detection of the hush request.

Optionally, the controller is further operable to monitor a temperature sensor to determine a current temperature value and determine the compensation factor based on the current temperature value and a temperature to compensation offset mapping.

Optionally, the controller is further operable to track an average value of the compensated sensor signal over an extended time period and decrease the compensation offset signal based on the average value until the compensated sensor signal is at or below a long-term target value.

According to a third aspect of the invention, a method of operating a detector device includes de-energizing a light source; receiving, at a controller of the detector device, a sensor signal generated by a sensor in a chamber of the detector device, wherein the light source is disposed within the chamber along with the sensor that is physically offset from the light source, the sensor being for detecting light from the light source as it is scattered by particles in the chamber, and the sensor is a photo detector; determining one or more error sources included in a clean air value of the sensor signal with the light source de-energized; determining, by the controller of the detector device, a compensation factor to adjust the sensor signal, wherein the compensation factor is determined as the adjustment needed to reach a target baseline clean air value representing a starting value for comparison to an alarm limit based on the one or more error sources; generating a compensation offset signal based on the compensation factor; converting, by a digital-to-analog converter, the compensation offset signal from a digital signal to an analog signal prior to summing at a summing circuit; and outputting the compensation offset signal to a compensator circuit to produce a compensated sensor signal as an adjustment to the sensor signal, wherein the compensator circuit comprises an amplification circuit operable to amplify a sensor output of the sensor as an amplified sensor signal and the summing circuit operable to sum the amplified sensor signal with the compensation offset signal to produce the compensated sensor signal, wherein the summing circuit is an analog circuit. The method also includes sampling and quantizing, by an analog-to-digital converter, the compensated sensor signal as a digital value; energizing the light source and monitoring the compensated sensor signal with respect to the alarm limit; and triggering an alarm event based on the compensated sensor signal exceeding the alarm limit; wherein the sensor signal received at the controller is the amplified sensor signal as sampled and quantized through the analog-to-digital converter when the compensation offset signal has a zero offset value.

According to a third aspect of the invention, a method of operating a detector device includes de-energizing a light source; receiving, at a controller of the detector device, a sensor signal generated by a sensor in a chamber of the detector device, wherein the light source is disposed within the chamber along with the sensor that is physically offset from the light source, the sensor being for detecting light from the light source as it is scattered by particles in the chamber, and the sensor is a photo detector; determining one or more error sources included in a clean air value of the sensor signal with the light source de-energized; determining, by the controller of the detector device, a compensation factor to adjust the sensor signal, wherein the compensation factor is determined as the adjustment needed to reach a target baseline clean air value representing a starting value for comparison to an alarm limit based on the one or more error sources; generating a compensation offset signal based on the compensation factor; converting, by a digital-to-analog converter, the compensation offset signal from a digital signal to an analog signal prior to summing at a summing circuit; and outputting the compensation offset signal to a compensator circuit to produce a compensated sensor signal as an adjustment to the sensor signal, wherein the compensator circuit comprises an amplification circuit operable to amplify a sensor output of the sensor as an amplified sensor signal and the summing circuit operable to sum the amplified sensor signal with the compensation offset signal to produce the compensated sensor signal, wherein the summing circuit is an analog circuit. The method also includes energizing the light source and monitoring the compensated sensor signal with respect to the alarm limit; and triggering an alarm event based on the compensated sensor signal exceeding the alarm limit; wherein the controller comprises an analog-to-digital converter operable to sample and quantize the compensated sensor signal as a digital value; wherein the sensor signal received at the controller is the amplified sensor signal when the compensation offset signal has a zero offset value.

Technical effects of embodiments of the present disclosure include compensating a detector of a detector device to enhance detection capabilities.

A detailed description of one or more embodiments of the disclosed apparatus and method is presented herein by way of exemplification and not limitation with reference to the Figures.

Referring now to <FIG>, an example of a detector device <NUM> is illustrated. The detector device <NUM> includes a housing assembly <NUM> having a first, upper housing portion <NUM> and a second, lower housing portion <NUM> that is removably connected to the first housing portion <NUM>. The detector device <NUM> further includes a control system <NUM> including at least one detector circuit <NUM> and at least one alarm circuit <NUM> described in more detail below with reference to <FIG> and <FIG>. When the first and second housing portions <NUM>, <NUM> are connected, the first and second housing portions <NUM>, <NUM> enclose the control system <NUM> and other components necessary to operation of the detector device <NUM>. As used herein, the terms "upper", " lower", and the like are in reference to the detector device <NUM> in use as it is mounted on a surface, such as a ceiling in a building for example. Therefore, the upper housing portion <NUM> is typically closer to the ceiling than the lower housing portion <NUM>, and the lower housing portion <NUM> is typically the portion of the detector device <NUM> that will face downward toward the floor of the building. In some embodiments, the detector device <NUM> may be mounted on a wall such that upper housing portion <NUM> is closer to the wall than the lower housing portion <NUM>, and the lower housing portion <NUM> is typically the portion of the device <NUM> that will face outward toward the interior space of the room or space to be monitored.

In the non-limiting embodiment of <FIG>, the upper housing portion <NUM> includes a base plate <NUM> and a trim plate <NUM> disposed upwardly adjacent the base plate <NUM>. The trim plate <NUM> is typically positioned adjacent to or flush with a mounting surface, such as a ceiling or wall for example. As shown, both the trim plate <NUM> and the base plate <NUM> include a centrally located opening <NUM>, <NUM> respectively, having a similar size and shape. In embodiments where the detector device <NUM> is "hardwired", a power source <NUM> located within the mounting surface, such as an AC power supply, for example, may extend into the aligned openings <NUM>, <NUM>.

A printed circuit board <NUM> is disposed generally between the base plate <NUM> and an adjacent surface of the lower housing portion <NUM>. The printed circuit board <NUM> includes the circuitry and/or components associated with the at least one detector circuit <NUM> and at least one alarm circuit <NUM>. In embodiments where the detector device <NUM> is "hardwired", the printed circuit board <NUM> is directly connected to the power source <NUM>. In such embodiments, part of the printed circuit board <NUM> may extend into the central opening <NUM>, <NUM> of the upper housing portion <NUM> to connect to the power source <NUM>. The printed circuit board <NUM> may be adapted to receive one or more batteries sufficient to provide power thereto to operate the detector device <NUM> for an extended period of time. The power provided by the batteries may be the sole source of power used to operate the detector device <NUM>, or alternatively, may be supplemental to the power source <NUM>, for example in the event of a failure or loss of power at the power source.

The detector device <NUM> can include a light transmission device <NUM>, such as a light pipe for example, positioned within the housing <NUM> generally between the printed circuit board <NUM> and the lower housing portion <NUM>. The light transmission device <NUM> can be a passive device formed from a clear or generally transparent plastic material and configured to diffuse and evenly distribute the light generated as an external indicator, such as a light emitting diode or other display element.

A sound generation mechanism <NUM> may be disposed between the printed circuit board <NUM> and the lower housing portion <NUM>. The sound generation mechanism <NUM> receives power from the printed circuit board <NUM> to generate a noise in response to detection of a condition. Coupled to the lower housing portion <NUM> is an actuatable mechanism <NUM>, such as a button. The actuatable mechanism <NUM> may be a button configured to perform one or more functions of the detector device <NUM> when actuated. Examples of operations performed via the actuatable mechanism <NUM> include, but are not limited to, a press to test function, an alarm "hush", a low battery "hush", and end of life "hush", radio frequency enrollment of additional detector devices <NUM> such as in a detection system including a plurality of detector devices <NUM> configured to communicate with one another wirelessly, and to reset the detector device <NUM> once removed from its packaging, for example.

In the illustrated, non-limiting embodiment, the actuatable mechanism <NUM> is received within an opening formed in the lower housing portion <NUM>, and is operably coupled to a control system <NUM> of the printed circuit board <NUM>. Although the actuatable mechanism <NUM> is shown positioned at the center of the lower housing portion, embodiments where the actuatable mechanism <NUM> is located at another position are also within the scope of the disclosure. Further, it should be understood that in embodiments where the actuatable mechanism <NUM> performs multiple operations, there may be only a single actuatable mechanism <NUM> located on the detector device <NUM> and no other mechanism is required. Alternatively, the detector device <NUM> may include a plurality of actuatable mechanisms <NUM>, each being operable to perform a distinct function or the actuatable mechanism <NUM> may be divided to form a plurality of actuatable mechanisms. In embodiments where the detector device <NUM> includes a plurality of separate actuatable mechanisms <NUM>, the actuatable mechanisms <NUM> may be located at any location relative to the housing <NUM>.

With reference to <FIG>, a schematic diagram of an example of a control system <NUM> of the detector device <NUM> of <FIG> and <FIG> is shown in more detail. The control system <NUM> includes a controller <NUM> operable to receive an input from the at least one detector circuit <NUM>, for example, from a chamber <NUM>. It should be understood that the detector device <NUM> may be adapted for detection of a variety of hazardous conditions, including but not limited to smoke, carbon monoxide, explosive gas, and heat, for example. Further, while the discussion herein refers to controller <NUM>, one skilled in the art will recognize that the functionality and intelligence associated with this element may be embodied in a microcontroller, a microprocessor, a digital signal processor (DSP), a programmable logic device (PLD), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other intelligent, programmable device with associated input/output interfaces, memory, and supporting circuitry. Therefore, the use of the term "controller" herein shall be construed to cover any of these structures.

The detector circuit <NUM> includes a sensor <NUM> operable to detect light from a light source <NUM> and conditioned by a compensator circuit <NUM> electrically coupled to the sensor <NUM> and controlled by controller <NUM>. According to the invention the sensor <NUM> is a photo detector sensor. The controller <NUM> also receives an input from a user-actuated switch <NUM> input, for example, coupled to the actuatable mechanism <NUM>. The controller <NUM> can also receive inputs from a temperature sensor <NUM>, an ambient light sensor <NUM>, and/or other sensors (not depicted). The controller <NUM> utilizes the inputs from these components <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to generate an output alarm condition when the sensed environmental conditions so dictate. An alarm circuit <NUM> is utilized to broadcast via the sound generation mechanism <NUM> an appropriate audible sound, depending on which condition has been detected. The alarm circuit <NUM> may include both tone and synthesized voice message generation capabilities, or may be a simple piezo-electric type device. The detector device <NUM> can also include a visual warning system <NUM> with an external indicator circuit <NUM> and an external indicator <NUM>. The external indicator <NUM> can be a light emitting diode or other display element used to externally convey status and alerts. It should be understood that the detector device <NUM> illustrated and described herein is intended as an example only and that a detector device <NUM> having any configuration and capability is contemplated herein.

In embodiments, the controller <NUM> energizes the light source <NUM> during normal operation, and the sensor <NUM>, which is physically offset from the light source <NUM> in the chamber <NUM>, detects light from the light source <NUM> as scattered by particles in the chamber <NUM>. The compensator circuit <NUM> can amplify the output of the sensor <NUM> and apply a compensation offset signal as further described herein.

<FIG> depicts an example of the compensator circuit <NUM> in greater detail. The compensator circuit <NUM> includes an amplification circuit <NUM> operable to amplify a sensor output <NUM> of the sensor <NUM> as an amplified sensor signal <NUM>. In the example of <FIG>, the amplification circuit <NUM> includes a first stage amplifier <NUM> to provide an initial amplification to the sensor output <NUM> and a second stage amplifier <NUM> to further scale the sensor output <NUM> as the amplified sensor signal <NUM>, which may be optimized for a voltage range of an analog-to-digital (A/D) converter <NUM>, e.g., about <NUM> to <NUM> volt range. In some embodiments, the voltage range of the A/D converter <NUM> can be different, such as about <NUM> volts to <NUM> volts, about -<NUM> volts to +<NUM> volts, and other such ranges. The A/D converter <NUM> can be part of the controller <NUM> or external to the controller <NUM> of <FIG>. The compensator circuit <NUM> also includes a summing circuit <NUM> operable to sum the amplified sensor signal <NUM> with a compensation offset signal <NUM> to produce the compensated sensor signal <NUM>. In the example of <FIG>, the summing circuit <NUM> is an analog circuit with a summing amplifier <NUM> operable on analog versions of the amplified sensor signal <NUM> and the compensation offset signal <NUM>. The A/D converter <NUM> is operable to sample and quantize the compensated sensor signal <NUM> as a digital value. Notably, a single instance of the A/D converter <NUM> can detect an offset compensated or a non-offset compensated instance of a sensor signal from the sensor <NUM> based on the value of the compensation offset signal <NUM>.

A digital-to-analog (D/A) converter <NUM> is operable to convert the compensation offset signal <NUM> from a digital signal to an analog signal prior to summing at the summing circuit <NUM>. Similar to the A/D converter <NUM>, the D/A converter <NUM> can be part of the controller <NUM> or external to the controller <NUM> of <FIG>. The compensation offset signal <NUM> generated by the controller <NUM> can adjust the amplified sensor signal <NUM> as the compensated sensor signal <NUM> prior to sampling by the A/D converter <NUM>. Performing signal adjustments external to the controller <NUM> and in an analog format can preserve the available range of the A/D converter <NUM> and enhance corrections beyond the levels possible with only digital adjustments, as described herein. By performing compensation in the analog domain prior to conversion to the digital domain, the range of detectable signals can be shifted down from a value that would otherwise saturate the A/D converter <NUM> upon conversion to the digital domain. For instance, if the A/D converter <NUM> saturates with an input value of <NUM> volts, any voltage level above <NUM> volts cannot be discerned. However, if compensation shifts a <NUM> volt signal down by <NUM> volts to <NUM> volts, values between <NUM>-<NUM> volts that would not otherwise be distinguishable (i.e., both appear as <NUM> volts at the controller <NUM> due to saturation of the A/D converter <NUM>) become observable levels of <NUM>-<NUM> volts at the A/D converter <NUM>.

<FIG> illustrates an exemplary plot <NUM> of the compensation provided by the compensator circuit <NUM> of <FIG> and <FIG> according to an embodiment and is described in reference to <FIG>. The A/D converter <NUM> has a fixed A/D range <NUM> that can be expressed in volts or counts. A clean air value <NUM> can be tracked as a sampled value of a sensor signal from the sensor <NUM> as observed at the A/D converter <NUM> and may initially be equivalent to the amplified sensor signal <NUM> when the compensation offset signal <NUM> is inactive or has a zero offset value. A detection margin <NUM> represents a difference between an alarm limit <NUM> and the clean air value <NUM>. The alarm limit <NUM> represents a value that, when exceeded, triggers the alarm circuit <NUM> to broadcast an appropriate audible sound via the sound generation mechanism <NUM>. The maximum number of counts of the A/D converter <NUM> represents a saturation limit <NUM>, where voltages that exceed the saturation limit <NUM> cannot be accurately read beyond the A/D range <NUM>. A saturation margin <NUM> represents a difference between the saturation limit <NUM> and the clean air value <NUM> in the example of <FIG>.

Over time, the clean air value <NUM> can drift higher due to various effects, such as light ingress, temperature, humidity, dust, and other factors which affect the capacity of sensor <NUM> to detect light from a light source <NUM>. As the clean air value <NUM> increases, the detection margin <NUM> is decreased if the alarm limit <NUM> remains fixed. There may be limited capacity to increase the alarm limit <NUM> before reaching the saturation limit <NUM>. As the clean air value <NUM> increases, the saturation margin <NUM> also decreases. The reduction in detection margin <NUM> may increase the risk of nuisance triggering of the alarm circuit <NUM> as a lesser amount of particles, such as smoke particles, is needed to push the sensor signal read by the A/D converter <NUM> above the alarm limit <NUM>.

When compensation is active <NUM>, the controller <NUM> generates a compensation offset signal <NUM> and outputs the compensation offset signal <NUM> through the D/A converter <NUM> as an analog signal to the summing circuit <NUM> of the compensator circuit <NUM>. The compensation offset signal <NUM> can be a negative offset to reduce the amplified sensor signal <NUM> at the summing circuit <NUM> or a positive offset to increase the amplified sensor signal <NUM> at the summing circuit <NUM>, producing the compensated sensor signal <NUM> as an adjustment to the sensor signal as sampled by the A/D converter <NUM>. The plot <NUM> illustrates how an uncompensated clean air value <NUM> can continue to increase absent compensation, while a compensated clean air value <NUM> can provide additional detection margin <NUM> and saturation margin <NUM> as compared to the uncompensated clean air value <NUM> by decreasing the uncompensated clean air value <NUM> before reaching the A/D converter <NUM>. Performing the compensation as an analog offset can effectively expand the range of offset signals that can be applied to the full range of the D/A converter <NUM> and the full range of the A/D converter <NUM>, rather than being limited to only the A/D range <NUM> of the A/D converter <NUM> as would be the case for a digital-only compensation. For example, if the D/A converter <NUM> supports a range of <NUM>-<NUM> volts and the A/D converter <NUM> supports a range of <NUM>-<NUM> volts, a maximum offset of <NUM> volts by the D/A converter <NUM> can shift a <NUM> volt signal at the A/D converter <NUM> down to <NUM> volts, thus making the signal observable without saturating the A/D converter <NUM>. It will be understood that various relationships can exist based on gain values and operative ranges of the A/D converter <NUM> and the D/A converter <NUM>.

<FIG> shows a process flow of a method <NUM> of operating the detector device <NUM> of <FIG>, in accordance with an embodiment of the disclosure. The method <NUM> is described in reference to <FIG> and can include additional steps beyond those depicted in <FIG>.

At block <NUM>, controller <NUM> receives a sensor signal generated by the sensor <NUM>. At block <NUM>, the controller <NUM> determines a compensation factor to adjust the sensor signal. The compensation factor can be set based on a number of conditions or modes of operation. For example, the compensation factor can adjust for manufacturing variations, ambient light, variations in the chamber <NUM>, circuit leakage in the printed circuit board <NUM>, temperature variations, electrical component variations, humidity, dust, and other factors as further described herein. At block <NUM>, controller <NUM> generates a compensation offset signal <NUM> based on the compensation factor.

At block <NUM>, controller <NUM> outputs the compensation offset signal <NUM> to the compensator circuit <NUM> to produce a compensated sensor signal <NUM> as an adjustment to the sensor signal. An amplification circuit <NUM> of the compensator circuit <NUM> is operable to amplify a sensor output <NUM> of the sensor <NUM> as an amplified sensor signal <NUM>. A summing circuit <NUM> of the compensator circuit <NUM> is operable to sum the amplified sensor signal <NUM> with the compensation offset signal <NUM> to produce the compensated sensor signal <NUM>. The A/D converter <NUM> is operable to sample and quantize the compensated sensor signal <NUM> as a digital value. The D/A converter <NUM> is operable to convert the compensation offset signal <NUM> from a digital signal to an analog signal prior to summing at the summing circuit <NUM>. The sensor signal received at the controller <NUM> can be the amplified sensor signal <NUM> as sampled and quantized through the A/D converter <NUM> when the compensation offset signal <NUM> has a zero offset value (e.g., no positive or negative offset adjustment).

At block <NUM>, controller <NUM> monitors the compensated sensor signal <NUM> with respect to an alarm limit <NUM>. During normal operation, controller <NUM> can periodically energize the light source <NUM> to support monitoring for increases in the compensated sensor signal <NUM> indicative of particles, such as smoke particles. The controller <NUM> can trigger an alarm event based on the compensated sensor signal <NUM> exceeding the alarm limit <NUM>.

As previously noted, the compensation described herein can adjust for a number of conditions using the compensator circuit <NUM>. The controller <NUM> can use the compensator circuit <NUM> to establish a consistent setting for a clean air value <NUM> in dark conditions of the chamber <NUM>. For example, the controller <NUM> can de-energize the light source <NUM>, determine one or more error sources included in a clean air value <NUM> of the sensor signal with the light source <NUM> de-energized, and determine the compensation factor as an adjustment needed to reach a target baseline clean air value based on the one or more error sources quantified from a combination of factors, such as printed circuit board leakage, component variations, light ingress, and the like. The clean air value <NUM> while the light source <NUM> is de-energized represents a starting value for comparison to the alarm limit <NUM> with detection margin <NUM>. In some embodiments, the ambient light sensor <NUM> can also be used, for instance, to establish an ambient light level external to the chamber <NUM> to further fine tune the correction factor. The compensation offset signal <NUM> can be adjusted through the D/A converter <NUM> (e.g., <NUM> volts +/- <NUM> volts) until the compensated sensor signal <NUM> reaches a target baseline clean air value , e.g., <NUM> millivolts as the target baseline clean air value, for example. This can compensate for manufacturing differences in components of the chamber <NUM> and other components of the detector device <NUM> while at nominal temperature/humidity conditions.

The controller <NUM> can also adjust the compensation factor to null effects of light ingress. For example, the controller <NUM> can determine whether the compensated sensor signal <NUM> has increased above a baseline value, and increase the compensation offset signal <NUM> until the compensated sensor signal <NUM> is at or below the baseline value. As ambient light leaks into the chamber <NUM>, the clean air value <NUM> may increase as observed by the compensated sensor signal <NUM>. The baseline value of the clean air value <NUM> may have previously been tuned to a value, e.g. a value of <NUM> millivolts, using the compensator circuit <NUM>. Light ingress can be confirmed using the ambient light sensor <NUM> to observe light levels external to the chamber <NUM>. When the compensated sensor signal <NUM> drifts above <NUM> millivolts due to light ingress, the compensation offset signal <NUM> can be increased, which results in a decrease of the compensated sensor signal <NUM>. Incremental increases of the compensation offset signal <NUM> can continue until the compensated sensor signal <NUM> reaches a clean air value <NUM> of <NUM> millivolts in this example.

The controller <NUM> can also use the compensator circuit <NUM> to implement a hush feature to temporarily remove an alarm limit trip condition and silence the sound generation mechanism <NUM>. For example, the controller <NUM> can detect a hush request (e.g., through actuatable mechanism <NUM> and switch <NUM>), increase the compensation offset signal <NUM> until the compensated sensor signal <NUM> is below the alarm limit <NUM> responsive to the hush request, and reset the compensation offset signal <NUM> after a predetermined period of time elapses from detection of the hush request. When the alarm circuit <NUM> triggers sound from the sound generation mechanism <NUM>, a user may determine that the inducing event has ended or is not a true emergency (e.g., a result of cooking food). Rather than adjusting the alarm limit <NUM> further upward in the A/D range <NUM> at risk of hitting the saturation limit <NUM>, the controller <NUM> uses the compensator circuit <NUM> to temporarily drive the compensated sensor signal <NUM> down below the alarm limit <NUM> by adjusting the compensation offset signal <NUM>. Prior to adjusting the compensation offset signal <NUM> for a hush event, the controller <NUM> can store a copy of the compensation offset signal <NUM>. After a pre-determined period of hush time has elapsed, e.g., fifteen minutes, the controller <NUM> can restore the compensation offset signal <NUM> with the previously saved value such that future alarm events will be triggered and other intermediate adjustments to the compensation offset signal <NUM> are not lost.

As another example, the controller <NUM> can monitor the temperature sensor <NUM> to determine a current temperature value. The controller <NUM> can determine the compensation factor based on the current temperature value and a temperature-to-compensation offset mapping. The temperature-to-compensation offset mapping can change a step size in compensation adjustments in the compensation offset signal <NUM> for higher or lower temperatures using, for example, a predetermined lookup table. The temperature to compensation offset mapping may be set up as absolute temperature based adjustments or relative adjustments depending upon a rate of temperature change versus time.

As a further example, the controller <NUM> can use the compensator circuit <NUM> to null effects of dust ingress into the chamber <NUM>. The controller <NUM> can track an average value of the compensated sensor signal <NUM> over an extended time period and decrease the compensation offset signal <NUM> based on the average value until the compensated sensor signal <NUM> is at or below a long-term target value. The long-term target value may be <NUM> millivolts as a clean air value, for example. If the dust ingress results in an average drop in the compensated sensor signal <NUM>, a decrease in the compensation offset signal <NUM> can be incrementally performed until the compensated sensor signal <NUM> increases back to the long-term target value.

Claim 1:
A detector device (<NUM>) comprising:
a light source (<NUM>) disposed within a chamber (<NUM>);
a sensor (<NUM>) disposed within the chamber physically offset from the light source, the sensor being for detecting light from the light source as it is scattered by particles in the chamber, wherein the sensor is a photo detector sensor;
a compensator circuit (<NUM>) electrically coupled with the sensor, wherein the compensator circuit comprises an amplification circuit (<NUM>) operable to amplify a sensor output (<NUM>) of the sensor as an amplified sensor signal (<NUM>) and a summing circuit (<NUM>) operable to sum the amplified sensor signal with a compensation offset signal (<NUM>) to produce a compensated sensor signal (<NUM>), wherein the summing circuit is an analog circuit;
an analog-to-digital converter (<NUM>) operable to sample and quantize the compensated sensor signal as a digital value;
a digital-to-analog converter (<NUM>) operable to convert the compensation offset signal (<NUM>) from a digital signal to an analog signal prior to summing at the summing circuit (<NUM>); and
a controller (<NUM>) operable to:
de-energize the light source (<NUM>);
receive a sensor signal generated by the sensor, wherein the sensor signal received at the controller (<NUM>) is the amplified sensor signal (<NUM>) as sampled and quantized through the analog-to-digital converter (<NUM>) when the compensation offset signal (<NUM>) has a zero offset value;
determine one or more error sources included in a clean air value (<NUM>) of the sensor signal with the light source de-energized;
determine a compensation factor to adjust the sensor signal, wherein the compensation factor is determined as the adjustment needed to reach a target baseline clean air value representing a starting value for comparison to an alarm limit (<NUM>) based on the one or more error sources;
generate the compensation offset signal (<NUM>) based on the compensation factor;
output the compensation offset signal to the compensator circuit (<NUM>) to produce a compensated sensor signal as an adjustment to the sensor signal;
energize the light source (<NUM>) and monitor the compensated sensor signal with respect to the alarm limit (<NUM>); and
trigger an alarm event based on the compensated sensor signal (<NUM>) exceeding the alarm limit.