Improved response for thermal detectors with surface mounted thermistors

Abstract

The invention relates to an improved response of a thermal detector with a surface mount thermistor. Apparatuses, systems, and methods are described herein for providing a surface mount thermistor based point heat detector. A point heat detector of a fire sensing system includes: a circuit board body having a plurality of corners; at least two surface mounted thermistors, each thermistor mounted on a different one of the corners; two of the surface-mounted thermistors are arranged in the middle of the surface-mounted thermistors; and a processor executing instructions stored in the memory to determine a temperature of at least one of the two surface mount thermistors and the intermediate position.

Description

Technical Field

[0001] The present disclosure relates to apparatus, systems, and methods for providing an improved response of a thermal detector having a surface mounted thermistor. Background Art

[0002] Facilities (e.g., buildings) such as commercial facilities, office buildings, hospitals, etc. may have a fire detection system that can be triggered during an emergency (e.g., a fire) to warn occupants to evacuate. For example, the fire detection system may include a fire alarm control panel within the building and a plurality of point heat detectors located throughout the facility (e.g., on different floors of the facility and / or in different rooms of the facility) that can sense thermal conditions indicative of a fire occurring in the facility and provide notification of the thermal condition to occupants of the facility and / or building monitoring personnel via an alarm or other mechanism.

[0003] Point heat detectors used in fire detection systems typically sense when the temperature rises above a threshold value. When this occurs, the point heat detector may send a signal to a control unit (e.g., within the point heat detector housing or at a fire protection system control panel), which may analyze the signal to determine whether to raise an alarm (e.g., to indicate that a fire may be occurring in the space monitored by the detector device) or send an alert to other devices.

[0004] Spot heat detectors use one or more thermistors that sense the temperature at the location of the spot heat detector. Because the thermistors are positioned within the spot heat detector housing, the thermistors have little ability to detect the direction from which a fire or smoke may be originating. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a bottom view of a spot heat detector system according to one or more embodiments of the present disclosure with the outer cover and detector lid removed, the bottom view showing a corner of a circuit board having a surface mount thermistor disposed therein.

[0006] Figure 2 is a schematic diagram illustrating an actual process and an estimation process for determining a thermistor temperature within a space monitored by a point thermal detector according to one or more embodiments of the present disclosure.

[0007] Figure 3 is a schematic diagram illustrating a dynamic system process for determining thermistor temperature within a space monitored by a point thermal detector according to one or more embodiments of the present disclosure.

[0008] Figure 4 is a circuit diagram of a reduced model of a thermistor according to one or more embodiments of the present disclosure.

[0009] Figure 5is a schematic diagram of a differential analysis engine according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0010] The present invention discloses an apparatus, system and method for providing an improved response of a thermal detector having a surface mounted thermistor. A thermal detector of a fire sensing system embodiment of the present disclosure includes: a circuit board body having a plurality of corners; at least two surface mounted thermistors, each thermistor being mounted on a different one of the corners; an intermediate position between two of the surface mounted thermistors; and a processor that executes instructions stored in a memory to determine a temperature of at least one of the two surface mounted thermistors and the intermediate position.

[0011] A surface mount thermistor based solution as disclosed herein provides good sensing performance, can determine the estimated direction of a heat source, and will overcome other problems of existing designs, as discussed herein. This can be advantageous in part because surface mount thermistors are less expensive than leaded temperature sensors. Since surface mount thermistors can be installed during the circuit board manufacturing process, the manufacturing process can also be simplified, thereby eliminating a separate manufacturing step used in existing designs.

[0012] Additionally, positioning the thermistors at the edge of the housing or protruding from the housing allows each thermistor to sample ambient air adjacent to the thermistor location. Additionally, novel directional process and temperature estimation technique implementations are taught herein.

[0013] One example of a thermal detector embodiment of the present disclosure includes a thermal detector device having a point-type thermal detector using a surface-mounted thermistor, such as four surface-mounted NTC (negative temperature coefficient) thermistors placed at the corners of a polygonal circuit board or on a circular circuit board (e.g., 90° apart). In various embodiments, the thermistor sensors can be angularly spaced at certain intervals (e.g., such as at regular intervals such as every 90 degrees, every 45 degrees, etc.) around the center point of the circuit board. As used herein, these locations are sometimes referred to as corners because they represent the corners of a polygon. When used on a circular circuit board, the periphery of the circle can circumscribe the corners of the polygon formed within the circle by the locations of the spaced-apart thermistor sensors.

[0014] A phenomenon known as directionality produces inaccurate sensing data due to where the thermistor is located relative to the detector device itself. This type of multi-sensor design reduces directionality issues in thermal detectors, among other benefits.

[0015] This is because having thermistors spaced apart and / or angled from each other allows airflow to be sensed from different locations and / or directions around the spot heat detector device, and therefore, the direction of the heat source can be inferred and can be considered when determining whether to trigger an alarm. This data can also be used to determine the likely direction of the heat source relative to the location of the heat detector device. For example, if a first thermistor senses a change in airflow (e.g., a heat source caused the change in airflow), and then a second thermistor at another location senses the change in airflow, the direction of the source of the change in airflow can be inferred (e.g., the source may be located between the two thermistors that sensed the change in airflow).

[0016] Furthermore, if the thermistors sense airflow entering the outer housing of the detector device from different directions, the sensing of heated airflow or the sensing of heated airflow by one thermistor but not another may also indicate in which direction the heat source is located.

[0017] The effects of directionality can be further reduced by using a proportional integral observer (PIO) process for each thermistor. For example, as described herein, the effects of thermal inertia can be offset by an observer process (e.g., a PIO process). Specifically, the PIO process can be used to estimate the airflow temperature using the temperature measured by the thermistor and a model of the airflow-thermal detector system.

[0018] PIO itself does not reduce directivity, but compensates for thermal inertia. For example, in a quad-thermistor implementation, applying four different PIO models, each to a different one of the four thermistors, reduces directivity because it takes into account different mechanical configurations.

[0019] Due to the lower profile of the embodiments of the present disclosure, a circuit board with a surface mounted system can be placed in a low profile housing whose mechanical configuration is designed to effectively direct airflow to the surface mounted thermistor. Utilizing the surface mounted thermistor based embodiments as disclosed herein, fire protection system devices (generally referred to herein as thermal detector devices) with point heat detectors designed herein can be manufactured with integrated thermal detection, including, for example, thermal detectors, photothermal detectors, multi-standard (e.g., COPTIR) detectors, which have a lower profile (and therefore better aesthetics) and lower cost. The COPTIR device combines four separate sensing elements into one unit:

[0020] 1. Electrochemical cell technology monitors carbon monoxide (CO) produced by smoldering fires;

[0021] 2. Photoelectric (P) chamber senses airborne particles for smoke detection;

[0022] 3. Thermal (T) detection monitors temperature; and

[0023] 4. Infrared (IR) sensing measures ambient light levels and flame characteristics.

[0024] This cost reduction includes component costs, as one leaded thermistor costs more than four surface mount thermistors. The manufacturing process costs are also less, as the complete surface mount installation process can be accomplished through a unique production cell, where multiple detector types for photodetectors, heat detectors, and photothermal fire detectors can be produced. In addition, multiple circuit boards can be manufactured simultaneously, further reducing the time required and manufacturing costs of the device.

[0025] The disclosed devices may also lead to smaller device sizes and increasingly smaller packaging components. For example, the disclosed devices may affect the reduction of plastic parts because new low-profile detector covers for light detectors, heat detectors, and photothermal detectors may be used, and current plastic components used to compensate for directionality in some photothermal detectors may be eliminated.

[0026] In some proposed embodiments, the proposed mechanical solution integrates four surface mounted thermistors in a rectangular circuit board body with specific mechanical features in the detector cover (e.g., to direct airflow, protect thermistors, and drain water therefrom), and in some embodiments, dedicated software compensates for system thermal inertia that cannot be overcome by physical design. The software may be stored in a memory on the detector device and can be executed by a controller such as a microprocessor. For example, the processor and memory may be on the circuit board body. The above features are features that are not possible in the prior art.

[0027] In one embodiment, the proposed surface mount solution for thermal detection in a fire sensor comprises: four surface mount thermistors (e.g., 0603 NTC thermistors) mounted in the corners of a square or rectangular circuit board near the edge of the circuit board. In some embodiments, the square / rectangular shape of the circuit board provides a compact and therefore low-cost circuit board panel layout with a suitable aperture pattern between the four surface mount thermistors and the rest of the circuit board to minimize the impact of the circuit board on the surface mount thermistors in terms of thermal inertia. Using at least two spaced apart thermistors can be beneficial, for example, because it can avoid the directionality problem of the thermal detector.

[0028] Additionally, in some embodiments, the mechanical configuration of the plastic parts (cover and base) of the fire detector can be provided with a surface mounting configuration on a circuit board so as to effectively direct the airflow toward the surface mounted thermistor and ensure a certain degree of protection for the circuit board and thermistor.

[0029] As discussed above, embodiments may also include dedicated software to correct the measured thermistor temperature based on an airflow temperature model. This functionality may be used, for example, to compensate for the thermal inertia of a surface mount configuration.

[0030] The airflow temperature model can be implemented, for example, by measuring the actual airflow temperature (input) of the real system and the thermistor output. Dedicated software calculates the airflow temperature to feed the system model so as to minimize the difference between the effective measured temperature and the estimated value of the thermistor temperature (e.g., using a proportional integral observer (PIO) process). The parameters of the model can be stored in a memory on the device.

[0031] In various embodiments, each thermistor has a measured temperature and each intermediate location has an estimated temperature. In such embodiments, each thermistor and each intermediate location may have a thermal inertia, and instructions stored in the memory may apply a temperature compensation adjustment factor (e.g., determined using a POI process) to each estimated thermal inertia.

[0032] The data type obtained by the dedicated software can be a volatile integer data representing the ambient temperature. In addition, this data can be stored in a random access memory (RAM) and used for fire alarm generation, or stored in a non-volatile RAM (NVRAM) or read-only memory (ROM) at the application level for diagnostic purposes to evaluate the ambient temperature using different types of algorithms (e.g., average, modulus, etc.). The PIO process can be used to estimate the temperature between physical thermistor locations. This data can also be provided to a fire system control panel, for example.

[0033] In this detailed description, reference is made to the accompanying drawings which form a part hereof. The drawings show, by way of illustration, the manner in which one or more embodiments of the disclosure may be practiced.

[0034] These embodiments are described in sufficient detail to enable one of ordinary skill in the art to practice one or more embodiments of the present disclosure. It is to be understood that other embodiments may be utilized and process, electrical and / or structural changes may be made without departing from the scope of the present disclosure.

[0035] It should be understood that the elements shown in the various embodiments herein may be added, exchanged, combined and / or eliminated to provide multiple additional embodiments of the present disclosure. The proportions and relative sizes of the elements provided in the drawings are intended to illustrate embodiments of the present disclosure and should not be limiting.

[0036] The drawings herein follow the following numbering convention: one or more first digits correspond to the drawing number, and the remaining digits identify the element or component in the drawing. Similar elements or components between different drawings may be identified by using similar numerals. For example, 102 in FIG. Figure 1can refer to component "02" in , while similar components are Figure 2 It can be represented by 202.

[0037] As used herein, "a" or "several" things may refer to one or more such things, and "plurality" things may refer to more than one such things. For example, "several components" may refer to one or more components, and "plurality components" may refer to more than one component.

[0038] Figure 1 is a bottom view of a spot heat detector system according to one or more embodiments of the present disclosure with the outer cover and detector lid removed, the bottom view showing a corner of a circuit board having a surface mount thermistor disposed therein.

[0039] Thermal detectors are important components in some types of fire detection systems. Likewise, controllers that provide detection analysis, alarm functions, and communication functions with other fire protection system devices based on data from thermistors of thermal detector devices are important. Circuit boards 103 designed according to embodiments of the present disclosure can provide these functions in one integrated circuit board.

[0040] exist Figure 1 In the illustrated implementation, the surface mount thermistors 102-1, 102-2, 102-3, 102-4 are disposed at the corners of the circuit board 103 of the thermal detector device 100. In this manner, costs, manufacturing time, and complexity may be reduced, among other benefits.

[0041] As shown in this embodiment, the sensors can be angularly spaced at certain intervals around the center point of the circuit board (e.g., at regular intervals such as every 90 degrees, every 45 degrees, etc.). As used herein, these locations are referred to as corners. When used on a circular circuit board, the circumference of the circle can be defined by the locations of the spaced sensors to define the corners of the polygon formed within the circle.

[0042] like Figure 1 As shown, the housing 106 of the thermal detector device 100 also includes a plurality of cutout portions in the side surfaces of the housing 106 to allow one or more corners of the circuit board to protrude out of the housing. In this way, the one or more thermistors 102 can be exposed to airflow in the area to be monitored (the air surrounding the thermal detector device 100, rather than the air within the housing 106).

[0043] Figure 1 is a bottom view of a point heat detector according to one or more embodiments of the present disclosure, with the outer housing removed, showing a corner of a circuit board with a surface mounted thermistor disposed therein. Such embodiments can be used to provide directionality to a heat source detected by the thermistor.

[0044] For example, Figure 1 The system shown in has four surface mount thermistors mounted near the edge of a circuit board, with a cover 106 mounted on the circuit board. Since the surface mount thermistors are mounted on the corners of a rectangular (e.g., square) circuit board 103, the angle difference between adjacent thermistors is 90°, with the thermistors reporting their data to a microcontroller (e.g., on the circuit board 103) to measure the air temperature in four equidistant directions.

[0045] To further optimize directional detection, some embodiments may include a digital compass (e.g., Honeywell 1-axis low-cost magnetoresistive sensor HMC1051) integrated into the thermal detector device 100 to provide a unique reference system (e.g., the direction of the earth's magnetic field) for all installed detectors (regardless of their installation orientation). The novel dedicated software described herein can then be used to determine the direction of the airflow based on the measurements of the four thermistors and the indication of the direction of the earth's magnetic field from the digital compass. This concept of directionality will be discussed in more detail below.

[0046] Thermal inertia can be reduced, for example, due to exposed corner designs of circuit boards and plastic parts of detectors, but the temperature measured by the thermistor may still be affected by the residual thermal inertia. To increase the accuracy of temperature measurements, processes based on control system theory (e.g., unknown inputs and state observers) have been created to estimate the temperature of the monitored space.

[0047] The thermal detector device 100 may be programmed to have an alarm threshold that is met when the estimated temperature value at any time is greater than or equal to the temperature threshold (S-point thermal detector) or when the function of the rate of temperature rise is greater than or equal to a certain value (R-point thermal detector). Thus, in this embodiment, there are several ways to quantify whether an alarm should be activated.

[0048] The airflow temperature measurement takes into account several phenomena, such as nonlinear convection resistance (attributable to factors such as air velocity and temperature differential), thermal conduction resistance, thermal capacitance due to the thermistor and other elements of the system. It is desirable to estimate the airflow temperature by removing other elements that affect the result due to system conditions. This can be accomplished using mathematical models and system control theory. This can be an iterative process where each estimate is compared to the measured thermistor temperature and the estimate is corrected to be closer to the measured thermistor temperature until the difference between the measured thermistor temperature and the estimated thermistor temperature is very small.

[0049] The point heat detectors analyze this information to determine the direction of the possible location of the heat source (fire), which can be used to guide emergency personnel and / or determine evacuation strategies, among other uses.

[0050] The heat flow direction process using mathematical algorithms can be very helpful in determining the location of the heat source.

[0051] One such process reads the temperature sensed at each Thermistor 1, Thermistor 2, Thermistor 3, and Thermistor 4. The heat flow direction process then calculates the heat flow direction based on the balance between the two thermistors and the thermal readings, for example down to 45 degrees initially. To further refine the position, the controller can determine a correction factor based on the temperature slope difference between adjacent thermistors. The detector then combines these values ​​to calculate a more precise direction.

[0052] In some embodiments, digital compass data may also be used. Here, digital compass data is determined, and the non-compass direction data is then rotated to correlate with digital compass reference direction information (e.g., correlated with a true north digital compass reading). For example, in some implementations, the spot heat detector includes a digital compass, and the controller combines the data received from the thermistor and the digital compass to determine the direction of the heat source.

[0053] for Figure 1 , the direction of the heat source can be accurate to 45 degrees (the middle of two thermistors at 90 degrees to each other). For example, if thermistor 3 and thermistor 4 record elevated temperature readings, the controller can determine whether the heat source is located in direction C, D, or DC, depending on whether one or both of the sensed temperatures meet a threshold indicating that the heat source is close to the thermistor. Alternatively, the evaluation can be based on whether one or both of the slopes of the temperature data meet a threshold indicating that the heat source is close to the thermistor. In some embodiments, the analysis can include determining that the change in temperature is above a threshold when the elevated temperature is compared to the temperature of a thermistor that is not elevated or is also elevated but not compared to the level of a thermistor with a higher temperature.

[0054] As briefly described above, in this embodiment, the detector may calculate, via the controller, a correction factor that may further refine the direction determined by the analysis of the detector.

[0055] For example, evaluating the differences between the temperature slopes (ROR: rate of rise of the outputs of the four thermistors) by the function DifROR(T1, T2, T3, T4) allows calculation of a correction factor β which is added to α (the direction determined based on the sensed temperature data which determine which thermistors have rising readings) in order to obtain a more accurate assessment of the direction of heat flow (α' = α + β).

[0056] The digital compass provides a unique reference system (the direction of the Earth's magnetic field) for the mounted detector (regardless of its mounting orientation): This produces the angle between the direction of the Earth's magnetic field and the reference orientation of the board. The corresponding digital value (e.g., the axis between thermistor th1 and thermistor th4). Finally, the rotation of the reference system is applied In order to calculate the base point CP (the most accurate determination of the direction of heat flow). Therefore, the possible values ​​of CP are: unknown direction, N, S, E, W, NE, NW, SE, SW.

[0057] As discussed, by using embodiments of the present disclosure, point heat detectors can be more compact, easier and more cost-effective to produce, have more consistency and less opportunity for human error between produced devices, and can be more accurate in detecting airflow temperature and determining the direction of heat sources. Such features can be very beneficial in detecting fires early in the event of a fire and alerting emergency personnel and building occupants, among other benefits.

[0058] exist Figure 1 In an embodiment of the invention, the device is a hot spot detector with four SMD thermistors. This configuration gives the related advantages: low cost of thermistor components, a fully automated SMD mounting process for thermistors (with higher reliability and lower cost of a manual mounting process for leaded thermistors). In particular, the four thermistors can be placed in the corners of a square circuit board or in the outside of a circular circuit board.

[0059] In this manner, the angular coordinates of the thermistor positions are relative to the center of the detector, with an angular distance of 90° between two adjacent thermistors. With this configuration, if the response of the thermal detector is considered to be the maximum of the four thermistor readings, the response is faster in the orientations corresponding to the four thermistors (0°, 90°, 180°, 270°, if 0° is considered to be the orientation corresponding to the thermistor) because the sensing element is hit head-on by the airflow, and slower in the intermediate position orientations (45°, 135°, 225°, 315°).

[0060] Furthermore, the responses corresponding to the four thermistor orientations (0°, 90°, 180°, 270°) may also be different for the presence of different mechanical features. For example, the presence of a rotary switch with a corresponding plastic holder, or simply a different geometry of the rear of the detector housing under the thermistor may result in different thermal inertias in the four orientations. Thus, the presence of such asymmetry may also result in different responses in the intermediate orientations (45°, 135°, 225°, 315°).

[0061] The response time of spot heat detectors should not be overly dependent on the direction of the airflow around them. To overcome or minimize this problem, some mechanical features can be implemented that help direct a portion of the airflow toward the thermistors when the airflow is from an intermediate direction relative to the locations of two adjacent thermistors.

[0062] This and similar mechanical solutions reduce the directional dependence of the thermal detector response, but have some limitations and have some impact on the design of the detector cover. In addition, if the response at the four thermistor orientations (0°, 90°, 180°, 270°) is not the same, the same mechanical features cannot eliminate these asymmetries in the detector response.

[0063] In a previous design of the system (proposed in filed patent application serial number 17 / 481,577, the disclosure of which is incorporated herein in its entirety), it may have been assumed that a symmetrical configuration in which all four thermistors had the same thermal inertia would have the same response. Under this assumption, the response was the same every 90°, with the more sensitive orientation being 0° (because the sensing element is hit head-on by the airflow) and the less sensitive orientation being 45° (an intermediate orientation between the two thermistors, such that the thermistors are not hit head-on by the airflow).

[0064] In previous disclosures, a concept called a proportional-integral observer was used for one thermistor and the same response was assumed for all four thermistors. Under this assumption, only three parameters were sufficient to identify the system model and thus implement a proportional-integral observer model.

[0065] But in actual implementations, the actual parameters of each thermistor may be different, and the directional problem may occur for different reasons. For example, the intermediate directions (45°, 135°, 225°, 315° between thermistor positions) are inherently less sensitive than the orientations corresponding to thermistors (0°, 90°, 180°, 270°) where the sensing element (thermistor) is hit head-on by the airflow, and may also be less sensitive in different proportions to each other based on their positions relative to the airflow.

[0066] Each thermistor may also have a different thermal inertia because there may be different geometric housing or other thermal detector device structures near them. For example, the presence of a rotary switch under two thermistors and / or a different mechanical configuration at the chamber base or housing rear near four thermistors may change the thermal inertia of nearby thermistors. Some mechanical features (e.g., mechanical features of the detector housing or detector cover, not shown) may mitigate the directional phenomenon, but such efforts may be expensive in terms of development activities, and the custom mechanical solutions required for each new detector design may often be incompatible with aesthetic and / or other functional requirements.

[0067] Embodiments of the present disclosure provide modeling of a thermal detector with four thermistors implemented via firmware and can be used to reduce thermal directionality errors regardless of the mechanical configuration employed. Embodiments herein can be used, for example, as a firmware or software application and can therefore be a low-cost and flexible solution that allows the use of four SMD thermistors (a configuration that is cheaper than one through-hole thermistor) without directionality issues. It can also be used for configurations with two through-hole thermistors where a solution with one through-hole thermistor is not possible due to directionality issues due to the presence of specific mechanical features of the self-test unit.

[0068] Figure 2 is a schematic diagram illustrating an actual process and an estimation process for determining a thermistor temperature within a space monitored by a point thermal detector according to one or more embodiments of the present disclosure.

[0069] In this process, the physical state of the system cannot be determined by direct observation (indirect angular orientation, such as 45 degrees). Instead, indirect effects on the indirect orientation system are observed through the system output. If the system is observable, a state observer can be used to reconstruct the system state from its output measurements. In control theory, a state observer is a system that provides an estimate of the internal state of a given actual system based on measurements of the inputs and outputs of that actual system. From this, the airflow temperature can be calculated to feed a mathematical model of the system in order to minimize the difference between the measured and estimated thermistor temperatures.

[0070] exist Figure 2 In the example of , the actual system measurement is shown at 210, where the actual airflow temperature is represented at 214. It interacts with an actual system 216 including at least one thermistor. This process can be done using thermistors that are adjacent to two thermistors (e.g., at an intermediate angle (e.g., 45 degrees) between 0 degrees and 90 degrees). This analysis can be performed for each adjacent thermistor. As shown, the one or more thermistors measure the temperature at their location 218.

[0071] Also shown at 220 is a modeling system that estimates the thermistor temperature. Here, at 224, data is fed into a model that represents estimated airflow. The system mathematical model 226 is designed to simulate what happens in the real world when airflow and thermistors interact, and the model produces an estimated thermistor temperature at 228.

[0072] In some embodiments, machine learning can be used to adjust the system mathematical model to improve its accuracy. This can be achieved, for example, by recursively comparing the estimated thermistor temperature to the measured thermistor temperature, adjusting the parameters in the model, and comparing again until the estimated thermistor temperature and the measured thermistor temperature results are within an accuracy threshold.

[0073] For example, in some embodiments, the controller compares the measured thermistor temperature with the estimated thermistor temperature to determine the model thermistor temperature. The controller determines a difference by comparing the measured thermistor temperature with the estimated thermistor temperature. The controller then uses the difference to update the sensor model, and the controller uses the difference to update the airflow temperature estimation model.

[0074] Figure 3 is a schematic diagram illustrating a dynamic system process for determining thermistor temperature within a space monitored by a point thermal detector according to one or more embodiments of the present disclosure. Figure 3 Representing that when the modeling has been sufficiently optimized for accuracy, the resulting analysis 330 is the same for both real world measurements and estimated measurements.Here, the airflow temperature 334 (whether real or estimated) is given to the system 336, and the exact thermistor temperature 338 can be determined.

[0075] Figure 4 is a circuit diagram of a reduced model of a thermistor according to one or more embodiments of the present disclosure. The model for estimating the temperature of the thermistor simulates a Figure 4 Circuit 440 is shown with input air flow temperature 442, linear conduction resistance 444 resulting in thermistor temperature 446, which is held from ground state 449 by capacitor 448. This model is beneficial because it is a single pole approach, has unity gain, and utilizes time component values, where the primary time constant can be T of the thermistor model. dom = R*C (characteristic response time of thermistor), and other benefits.

[0076] Figure 5 is a schematic diagram of a differential analysis module according to one or more embodiments of the present disclosure. The analysis module shows temperature calculation via a proportional-integral observer model for a thermistor.

[0077] In an example that illustrates why this approach may be beneficial, in real-world testing, the responses of two thermistors located near the rotary switch on the detector device (T3→270° and T4→180°) were observed to be slower because there was more plastic / non-thermistor device material, which resulted in higher thermal inertia of the corresponding adjacent thermistors: In general, asymmetries in the shape and / or placement of non-thermistor device components can produce different responses of adjacent thermistors.

[0078] As discussed herein, for each thermistor, this phenomenon can be mitigated by reducing the model to account for its specific thermal inertia. In addition, additional temperature compensation terms can be utilized that, for orientations that are inconsistent with the location of the thermistors (angles where there are no thermistors), utilize information from, for example, the two nearest thermistors to compensate for the higher thermal inertia of the configuration.

[0079] For example, an algorithm such as:

[0080]

[0081] Can be used to estimate the airflow temperature based on the temperature measured by one thermistor. In some embodiments, this calculation can be performed for each thermistor, and in other embodiments, the same response can be used for multiple or all thermistors. The components of the above formula include:

[0082] in:

[0083] A: state transition matrix (e.g., pure number); calculated as dom / (Τ dom+1 )

[0084] E: unknown input matrix (e.g., pure number); calculated as 1 / (Τ dom+1 )

[0085] C: Output matrix coefficients (e.g., C = 1)

[0086] A and E depend on T dom

[0087] · Τ dom : Main time constant of thermistor model (characteristic response time of thermistor)

[0088] ·K 1 :Reaction gain in thermistor temperature evaluation (state under observation)

[0089] ·K 2 : Counteraction gain in airflow temperature evaluation (enhancement state in the model)

[0090] ·y n: Current thermistor measurement

[0091] ·x n : Estimated current thermistor temperature

[0092] ·x n+1 : New estimated thermistor temperature

[0093] ·d n : Estimated current airflow temperature

[0094] ·d n+1 : New estimated airflow temperature

[0095] Therefore, a thermistor model can be represented by three constants T dom , K 1 and K 2 to be sure.

[0096] The process of obtaining a model of the thermistor temperature estimation system can be applied to each thermistor based on the response to the air flow. Thus, the estimation system includes four models describing the response of the detector device from four main orientations (0°, 90°, 180°, 270°).

[0097] With this determined generalization and the storage of data in a memory, possible asymmetries in the design of the detector device, for example due to the presence of different amounts of material near the thermistors (e.g. due to the presence of specific components such as a self-test unit, a rotary switch, etc.), can be taken into account. The estimation and measurement system is characterized by 12 (4 thermistors x 3 parameters (T dom , K 1 and K 2 ))parameter.

[0098] As discussed above, an additional temperature compensation term (ΔT1) may be utilized that compensates for the higher thermal inertia of such configurations for orientations that are inconsistent with the location of the thermistor (angles at which there is no thermistor).

[0099] T1 n =T1 est +ΔT1, where:

[0100] ΔT1=max((T2 est *RoR 2 / K adj2 ),(T3 est *RoR 3 / K adj3 ))

[0101] Tmax =max(T1 n ,T2 n ,T3 n ,T4 n )

[0102] And, where:

[0103] Ti est : The airflow temperature estimated by thermistor i using its PI observer model

[0104] RoR i: The rate of rise of thermistor i (ratio of temperature rise)

[0105] Kadj i: compensation coefficient related to thermistor i

[0106] Ti n : Thermistor i Airflow temperature estimated using the PIO model and directionality compensation

[0107] Tmax: airflow temperature estimated by the thermal detector

[0108] In an exemplary embodiment with four thermistors, the four compensation coefficients Kadj may be stored, for example, in a memory of the detector device, for example in an EEPROM.

[0109] Different types of thermal detectors may be constructed so that the thermal inertia of thermistors may be different from one thermal detector type to another. For example, a wired and wireless thermal detector may each have a set of thermistors, and one of the sets of thermistors may have a different thermal inertia relative to the other set. Thermal detectors used in different countries may have different thermal inertias based on different laws that may affect the types of component materials that may be used around the thermistors and / or the placement of components near the thermistors, in addition to other factors that may affect thermal inertia.

[0110] These issues can make it difficult to configure or manufacture thermal detectors because the software / firmware may be different to build each type of detector device. To mitigate or eliminate this and other issues discussed herein, a proportional-integral observer model can be derived for each thermistor that takes into account its specific thermal inertia and its specific interaction with the airflow contacting the thermistor.

[0111] As discussed herein, in some embodiments, the proportional-integral observer model may be calculated independently for each thermistor. However, in other embodiments, for multiple groups of thermistors installed in the same type of heater, the proportional-integral observer model may be calculated once and applied to all thermistors of that type of detector device.

[0112] In this calculation of the proportional-integral observer model, the airflow temperature is estimated based on measurements at a specific thermistor. These measurements can be made under laboratory conditions, during installation or commissioning, or during initial use after commissioning.

[0113] Also, as discussed, intermediate locations between adjacent thermistors will have weaker thermal inertia than locations having thermistors that interact directly with the airflow contacting a particular thermistor. Therefore, a temperature compensation adjustment factor may be added to the proportional-integral observer model to compensate for this weakness (e.g., the presence of a detector device component between a thermistor adjacent to a particular intermediate location and that intermediate location).

[0114] Although specific implementations have been illustrated and described herein, those of ordinary skill in the art will appreciate that any arrangement calculated to achieve the same technique may be substituted for the specific implementations shown. This disclosure is intended to cover any and all modifications or variations of various implementations of the present disclosure.

[0115] It should be understood that the above description is given in an illustrative rather than limiting manner.By reading the above description, combinations of the above embodiments, as well as other embodiments not specifically described herein, will be apparent to those skilled in the art.

[0116] The scope of the various embodiments of the present disclosure includes any other applications using the above-described structures and methods.The scope of the various embodiments of the present disclosure should therefore be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0117] In the above detailed description, various features are grouped together in the exemplary embodiments shown in the drawings for the purpose of simplifying the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the present disclosure require more features than are expressly recited in each claim.

[0118] Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment.Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims

1. A point heat detector for a fire sensing system, comprising: A circuit board body, wherein the circuit board body has a plurality of corners; at least two surface mount thermistors, each thermistor mounted at a different one of the corners; an intermediate position between two of the surface mounted thermistors; and A processor executes instructions stored in the memory to determine a temperature of at least one of the two surface mount thermistors and the intermediate location.

2. The spot heat detector according to claim 1, wherein the processor and the memory are on the circuit board body. 3 . The point heat detector according to claim 1 , wherein the temperature at the thermistor is a measured temperature, and the temperature at the intermediate position is an estimated temperature.

4. The point heat detector of claim 1, wherein each thermistor has a measured temperature and each intermediate location has an estimated temperature.

5. The point heat detector of claim 1, wherein each thermistor and each intermediate location has a thermal inertia, and wherein the instructions stored in the memory apply a temperature compensation adjustment factor to each estimated thermal inertia.

6. The point heat detector of claim 1, wherein the calculation of temperature is calculated via a proportional-integral observer model for a thermistor.

7. A point heat detector according to claim 1, wherein the temperature at the thermistor is a measured temperature and the temperature at the intermediate position is an estimated temperature, and wherein each thermistor has a thermal inertia determined according to the measured temperature and each intermediate position has an estimated thermal inertia calculated according to the estimated temperature.

8. The point heat detector according to claim 1, wherein the circuit board has a thermistor mounted at each corner of the circuit board body.

9. The point heat detector of claim 8, wherein the detector has an intermediate position defined between each of the thermistors.

10. The point heat detector of claim 1, wherein the controller analyzes a time value of received data to determine a direction of a heat source.

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