CN117007484A - Method for detecting thin or small particle smoke - Google Patents

Abstract

This application provides a method for detecting thin or small particle smoke. In view of the situation of thin or small particle smoke caused by fire, the luminous tube uses low driving current to emit light, and the thin or small particle smoke causes the larger scattering of light. The weak photocurrent accumulates on the junction capacitance of the receiving tube itself. During the detection process, the receiving tube is disconnected from the receiving circuit and the operational amplifier is not connected. After the accumulation time is reached, the accumulated charge on the receiving tube is measured through the signal acquisition circuit. The detection of weak current caused by thin or small particle smoke based on the charge accumulation method is realized.

Description

A method for thin or small particle smoke detection

Technical field

The present invention relates to the technical field of photoelectric particle or smoke detection, specifically a method for thin or small particle smoke detection.

Background technique

Smoke detectors, especially photoelectric smoke detectors, are commonplace. Photoelectric smoke detectors are the mainstream smoke detector products currently on the market. They are mainly used for fire detection in buildings, offices and other public places as well as homes. They use optical scattering to The principle detects the presence of smoke and sends an alarm signal when it exceeds a certain threshold. Usually, a photoelectric smoke detector has one or more photoelectric transmitting and receiving devices inside. The outer casing and corresponding mechanical components form an optical darkroom called a labyrinth. The basic detection principle is to judge the concentration of smoke based on the light intensity scattered by smoke particles. And compare it with the alarm threshold.

However, in some special scenarios, such as: thermal runaway monitoring of new energy electrochemical batteries, the smoke released by the early battery thermal runaway process is relatively thin and may be accompanied by fine particulate matter. Traditional smoke detectors There may not be much that can be done. For example, in the early stages of fires in switch cabinets and electrical cabinets of charging piles, some small particles will be released due to overheating of wires and other reasons. The size of these particles is generally less than 100nm or even 10nm, and these are not easily captured by traditional smoke detectors. Traditional smoke detectors are based on the detection principle of Mie scattering and are aimed at smoke particles in the particle size range of 100nm to 1um. Therefore, in order to detect finer particles, the sensitivity needs to be increased, but with this comes the Frequent false alarms are a problem, and it is difficult for traditional smoke detectors to balance high sensitivity and low false alarms. The above two fire processes are generally irreversible, and early warning is required to avoid greater losses.

There are also smoke sensors that specifically detect particles. For example, in the existing technology, the patent application number CN202121804266.3 discloses a dual-wavelength aerosol particle scattered light sensing structure, which uses two laser emitters of different wavelengths. A light receiver forms a labyrinth structure in the shape of "a". When there is no smoke entering the detector maze, the light pollution signal caused by the reflection between the maze mechanisms is called the background. The smaller the background signal, the better, especially in the application scenario of the present invention that is sensitive to the background signal. The light intensity of the laser is high and concentrated, but the scanning area is smaller. In order to reduce or eliminate optical reflection, a large volume and a more complex mechanical design are required. Even if the designer sacrifices some other functions in order to reduce the internal background signal light pollution, for example, it may occupy a larger volume to eliminate the internal background signal light pollution. Traditional current detection circuits such as transconductance amplifiers require larger transconductance resistors and low-noise operational amplifiers to detect small currents. The noise of the operational amplifier itself, output bias, and thermal noise of the transconductance resistor are the main noise and measurement sources. The source of error is that if the input signal is so weak that it falls below the noise floor of the entire input circuit, it will be difficult for a traditional transimpedance amplifier to detect the signal. Therefore, even if cost is not considered, the contribution of blindly using better-performing op amps to reducing system noise is limited. For smoke detection equipment designed based on traditional methods, it is difficult to balance power consumption, cost, and high sensitivity and low false alarm performance at the same time in system design.

Contents of the invention

When existing smoke sensors detect thin or small smoke particles caused by fires, it is difficult to take into account power consumption, cost and performance issues at the same time. In order to solve these problems, the present invention provides a method for thin or small particle smoke detection, which can effectively identify the continuous thin or small particle smoke caused by fire, while effectively taking into account power consumption, cost, and satisfying High sensitivity performance requirements.

The technical solution of the present invention is as follows: a method for thin or small particle smoke detection, which includes the following steps:

S1: Set up detection equipment, which includes: signal acquisition circuit, light emitting tube and receiving tube;

The light-emitting tube emits light, and the receiving tube receives the light; the signal collection circuit is connected to the receiving tube;

It is characterized in that it also includes the following steps:

S2: The cathode of the receiving tube is connected to the reference voltage VREF1, and a low leakage current switch SW1 is set between the receiving tube and the signal acquisition circuit; the reference voltage of the signal acquisition circuit is VREF2;

S3: According to the environment to be detected, specify the small-range weak signal detection time threshold T _ON and alarm threshold used when the receiving tube detects small particles and thin smoke, and specify the dark current detection time T _OFF of the receiving tube;

S4: Close the switch SW1 and perform the reset operation. After the reset operation is completed, the switch SW1 is opened;

The reset operation includes: signal acquisition circuit reset operation and receiving tube reset operation;

The reset operation of the signal acquisition circuit is to restore the circuit to the initial state; the reset operation of the receiving tube is to simultaneously eliminate the charges at both ends of the receiving tube;

S5: Test the accumulated dark current of the receiving tube. The specific method is:

In the OFF state of SW1, within the dark current detection time T _OFF of the receiving tube, test the accumulated charge Q _OFF within the accumulated time T _OFF corresponding to the dark current of the receiving tube;

S6: Close SW1, connect the receiving tube to the signal acquisition circuit, measure the dark current of the receiving tube, and obtain the voltage V _OFF corresponding to the accumulated charge Q _OFF ;;

S7: Close the switch SW1, perform the reset operation on the signal acquisition circuit and the receiving tube, and open the switch SW1 after the reset operation is completed;

S8: Turn on the luminous tube, enter the small-range weak signal detection mode, and monitor the thin or small particle smoke state in the area to be tested in real time;

Assuming that the driving current of the light-emitting tube is ILED, the signal current generated by particle scattering under the illumination of the light-emitting tube continues to accumulate on the junction capacitance of the receiving tube;

The driving current ILED uses a small current, and the value of ILED satisfies: ILED _MIN ≤ ILED ≤ ILED _MAX ;

ILED _MIN is the minimum driving current of the light-emitting tube, and the value of ILED _MIN is the larger value of the minimum driving current allowed by the design of each circuit and the minimum driving current allowed by the LED device of the light-emitting tube;

ILED _MAX is the maximum allowable current of the light-emitting tube drive. The method for determining the value of ILED _MAX is: test the light-emitting tube current from large to small, and observe the value of the receiving photocurrent. When the light-emitting tube is lit, the synchronously measured receiving tube current is less than 1 % of the range of the signal acquisition circuit is recorded as the maximum allowable current ILED _MAX ;

S9: Record the time point when the light-emitting tube lights up and the SW1 turns off at the same time as: measurement start time;

Taking the measurement start time as the starting point, when the measurement duration reaches T _ON , open SW1 and connect the accumulated charge on the receiving tube to the signal acquisition circuit;

S10: Measure the voltage V _ON of the receiving tube based on the signal acquisition circuit;

S11: Calculate the accumulated charge Q _PD on the receiving tube and the signal current I _PD received by the receiving tube;

_QPD = _QON - _QOFF ;

I _PD =Q _PD /T _ON ;

S12: When the signal current I _PD is greater than the preset alarm threshold, a smoke alarm is issued; otherwise, steps S4 to S12 are executed in a loop to continue detecting the environment to be detected.

It is further characterized by:

It also includes the receiving tube dark current calibration method, which specifically includes the following steps:

When T _OFF = T _ON , the charge accumulated by the signal current Q _PD = Q _ON - Q _OFF = (V _ON - V _OFF ) × C _PD is used to calibrate out the influence of dark current;

Where, C _PD is the junction capacitance of the receiving tube;

It also includes: a large-range signal detection mode, and the entry method of the large-range signal detection mode includes the following steps:

a1: Set the detection circuit for conventional signal detection;

a2: Assume that the measurement duration is tc, and the initial value of tc is set to T _ON ;

The charge amount when the receiving tube is saturated is recorded as: saturation charge QSA;

The saturation charge corresponding to the saturation voltage VSA is recorded as QSA;

VSA=QSA/C _PD , C _PD is the junction capacitance of the receiving tube;

a3: During the implementation of steps S7 to S10, if within tc time, the accumulated charge of the receiving tube reaches saturation;

Then adjust tc to a smaller value, 0<tc<T _ON ;

a4: Again within tc time, test the accumulated charge on the receiving tube and the voltage of the receiving tube;

If the voltage of the receiving tube still reaches VSA, switch to the detection circuit of the conventional smoke test and perform a large-range signal test;

Otherwise, if the voltage of the receiving tube is less than VSA, update the value of the small-scale weak signal detection time threshold T _ON to the value corresponding to tc, and then execute steps S4 to S12 in a loop;

The detection circuit of the conventional signal detection is: the switch SW1 is closed, the receiving tube is directly connected to the back-end signal acquisition circuit through the switch SW1, and SW1 remains closed during the acquisition process;

It also includes: switching the large-range signal detection mode to the small-range weak signal detection mode, including the following steps:

b1: The time period t monitored by the preset range switching, the number of samples n and the range switching threshold TH;

The range switching threshold TH includes: the number of charges or voltages of the monitored object; n≥10;

b2: Confirm the measurement values of the monitoring objects corresponding to the continuous n samples;

If the average value of the corresponding measured values of n sample data is less than TH, it is determined to be lower than the monitoring range of the large-range signal detection mode, and step b3 is executed;

Otherwise, execute step b4;

b3: Switch to the small-range weak signal detection mode;

b4: Still maintain the large-range signal detection mode, and perform step b2 at the same time;

After step b3 is executed, anti-locking measures need to be implemented;

The anti-locking measures include the following steps:

c1: Assume that the measurement duration is tl, and the initial value of tl is set to T _ON ;

c2: During the implementation of steps S7 to S12, within the tl time, the accumulated charge of the receiving tube reaches saturation, then the range switching threshold TH is adjusted to: TH=TH*0.8;

Switch to the large-range signal detection mode and perform step b2 at the same time;

In the small-range weak signal detection mode, the expression of the charge Q _PD accumulated on the receiving tube includes:

Q _PD =C _PD ×V _PD =C _PD ×(V _ON -V _OFF )

Or Q _PD =I _PD ×T _ACC

or

Among them, C _PD is the junction capacitance of the receiving tube; T _ACC is the accumulated charge time period of the photocurrent I _PD generated by the receiving tube PD receiving light. T _ACC ensures that the photoelectric receiving tube operates within the linear range.

This application provides a method for detecting thin or small particle smoke. In view of the situation of thin or small particle smoke caused by fire, the luminous tube uses low driving current to emit light, and the thin or small particle smoke causes the larger scattering of light. The weak photocurrent accumulates on the junction capacitance of the receiving tube itself. During the detection process, the receiving tube is disconnected from the receiving circuit and the operational amplifier is not connected. After the accumulation time is reached, the accumulated charge on the receiving tube is measured through the signal acquisition circuit. The detection of weak current caused by thin or small particle smoke based on the charge accumulation method is realized. This method uses low driving current, and under the same optical design, there will be almost no internal light pollution problems, because the power of the emitting tube used is very small, and almost all the optical power is internally reflected and absorbed, even if there are dust accumulation or component aging problems It has no effect either. At the same time, since the switch SW1 is in the off state during the charge accumulation process, the receiving tube is not connected to the back-end circuit, so the precision of the signal acquisition circuit is not high, and the power supply can even be turned off directly during this period. Therefore, this method has the advantages of low cost, low power consumption and high robustness. This application specifies the small-range weak signal detection time threshold T _ON and the alarm threshold of the signal current according to the conditions of the environment to be detected. Once the measurement time reaches T _ON , the charge accumulated on the receiving tube is measured. When the signal current on the receiving tube When it is greater than the alarm threshold, a small particle alarm is performed, which can not only detect conventional fire smoke but also detect thin or small particle smoke in early fires, improving the detection accuracy and robustness. At the same time, in this method, in order to accumulate all the photocurrent on the junction capacitance of the receiving tube itself and prevent leakage current, a low leakage current switch SW1 is set between the signal acquisition circuit and the receiving tube. The leakage current of the receiving tube PD It only depends on the analog switch SW1 of the receiving tube connected to the back-end circuit, and has nothing to do with other devices. This design can reduce the design complexity of the entire back-end system, effectively control the overall area of the smoke detection equipment, and reduce the system cost. design costs.

Description of the drawings

Figure 1 is a timing diagram of the driving method for thin or small particle smoke detection of the present application;

Figure 2 is a schematic diagram of the circuit topology of this method;

Figure 3 is the test verification curve of accumulated charge time.

Detailed ways

This application provides a method for detecting thin or small particle smoke, which includes a weak light detection method based on charge accumulation and a conventional detection method combined with weak light detection. The weak light detection method based on charge accumulation is a small-range weak signal detection mode, and the conventional signal detection method is a large-range signal detection mode, which is used to cooperate with the low-light detection method and is compatible with traditional detection methods.

In the weak light detection method based on charge accumulation, the device connected to the receiving tube has only one switch SW1, and the data acquisition work is completed through timing operations and back-end circuits. Considering the range problem of the weak light detection method based on charge accumulation, the present invention designs switching and compatibility with the conventional detection method, that is, the large-range signal detection mode. Therefore, there is no need to change the original detection mode and alarm threshold settings. Based on charge accumulation, The low-light detection method not only provides more product function options, but also improves the detection ability of thin or small particle smoke and reduces the false alarm rate. It specifically includes the following steps.

S1: Set up detection equipment. The detection equipment includes: signal acquisition circuit, light-emitting tube and receiving tube.

The luminous tube emits light, and the receiving tube receives ambient light; the signal acquisition circuit is connected to the receiving tube.

The light-emitting tube and receiving tube in this application are implemented based on diodes in the prior art. For example, the light-emitting tube in this method is implemented based on OSRAM light-emitting tube SFH4069. In specific applications, the optical power or light intensity Ee corresponding to the driving current is obtained from the diode specification sheet. For example: the nominal current recorded in the specification book is 70mA, and the corresponding test pulse time is 20mS; if you want to reduce the light intensity: one way is to reduce the driving current I _F ; the other way is to reduce the driving pulse time t _p . When the light-emitting tube is lower than the nominal current, the lower the current, the higher the optical power conversion efficiency, that is, the higher the optical power generated per unit drive current. Then, the driving current of SFH4069 can be as low as 1mA, and the electro-optical conversion efficiency under current is higher. Of course, the higher the power efficiency.

S2: The cathode of the receiving tube is connected to the reference voltage VREF1, and a low leakage current switch SW1 is set between the receiving tube and the signal acquisition circuit; the reference voltage of the signal acquisition circuit is VREF2. In specific applications, VREF1 and VREF2 can have the same value.

As shown in Figure 2, it is an embodiment of a schematic diagram of the circuit topology used in this method. It includes: luminous tube 1 and receiving tube 2. The light emitted by the reflective tube 2 encounters the scattered light of the particles of the smoke 3 and irradiates the receiving tube 2 to generate a photocurrent. The above electronic components are covered by a mechanical component called Maze 4, which provides a stable optical detection environment.

The embodiment of the signal acquisition circuit includes: operational amplifier 5, operational amplifier 6, switches SW2, SW3, resistors Rin and Rf;

The cathode of the receiving tube 2 is connected to the reference power supply VREF1, the anode is connected to one end of the switch SW1, the other end of the switch SW1 is connected to the non-inverting end of the input of the amplifier 5 and one end of the switch SW3, and the inverting input end of the operational amplifier 5 is connected to one end of the switch SW2 and the operational The output terminal of the amplifier 5, the other terminal of the switch SW2 is connected to one terminal of the resistor Rin, the other terminal of the resistor Rin is connected to the other terminal of the switch SW3, one terminal of the transconductance resistor Rf and the inverting input terminal of the operational amplifier 6, and the positive terminal of the operational amplifier 6. The reference power VREF2 is connected to the input terminal, and the output terminal of the operational amplifier 6 is connected to the other terminal of the transconductance resistor Rf and then connected to the input of the analog-to-digital converter ADC. For the convenience of description, the above circuit uses a minimalist circuit structure. For example, the signal processing circuit of the photoelectric tube uses a single-ended method, and the differential method is also applicable.

Among them, the low leakage current switch SW1 is based on the low leakage current switch in the existing technology. If the power supply range is greater than 5V, you can consider ADI's ADG1221 (refer to the specification book Ver.B), which has a turn-off leakage current of 2pA and a 0.5pC The equivalent injected charge is very suitable for precision design; if the power supply is less than 5V, you can consider ADI's ADG701L (refer to the specification Ver.A), which has a turn-off leakage current of 10pA and an equivalent injected charge of 5pC. Integrated chip indicators are also considered in this way.

In this application, low driving current is used to drive the luminous tube. Under the same optical design, there will be almost no internal light pollution problem. Since the power of the emitting tube under low driving current is very small, and the labyrinth design of the photoelectric smoke detector itself has certain light absorption. ability, so most of the light emission will be absorbed by the internal optical mechanism, even if there is dust accumulation or component aging problems, it will not be affected. Therefore, this design has the advantages of low cost, low power consumption and high robustness.

Figure 2 is just a minimalist circuit implementation used to describe the processing method of the circuit. The signal acquisition circuit on the right side of switch SW1 in Figure 2 has two functions.

One is to detect the voltage on the photoelectric tube 2 when the switch SW1 is closed after the accumulated charge is completed to collect, to meet the needs of weak signal detection in a small range.

The specific circuit configuration is when SW1 is closed, SW2 is closed, and SW3 is open. At this time, the operational amplifier 5 works in the voltage following mode, and the operational amplifier 6 works in the reverse amplification mode. The amplification factor is equal to -Rf/Rin. The operational amplifier 5 and the operational amplifier Amplifiers 6 are used in cascade. This circuit collects the voltage of the receiving tube 2. At this time, the voltage of the receiving tube 2 is based on the voltage of the reference VREF1.

The second is to switch to a large-range conventional transconductance amplifier mode when the detection signal is relatively large and exceeds the upper limit of accumulated charge.

The specific circuit configuration is that switch SW1 is closed, SW3 is closed, and switch SW2 is open, so that the entire operational amplifier 5 is bypassed. The output of the receiving tube 2 enters the reverse input of the operational amplifier 6 through the switches SW1 and SW3. At this time, the operational amplifier 6 works in the transconductance amplification mode to convert the collected current signal into a voltage signal. When switching to the large-range conventional mode, the light intensity of the emission tube is also increased to the conventional driving current. Taking SFH4069 as an example, the luminous tube driving current can be a typical 70mA. At this time, even if there is a certain Background signals are also tolerated. The output of the operational amplifier 6 is connected to the back-end analog-to-digital converter ADC. Since it does not belong to the content of the present invention, it will not be described again here.

When the switch SW1 is turned off, the photocurrent I _PD generated by the receiving tube 2 receiving light accumulates on the junction capacitance C _PD of the photoelectric tube 2 itself during the time period T _ACC to generate a charge Q _PD .

Usually, the number of charges Q accumulated on the capacitor C can be calculated by two methods. One is according to the formula Q = CV, C is the capacitance of the capacitor, V is the voltage of the capacitor; the other is according to the formula Q = IT, I is the charging current of the capacitor, and T is the charging time. This is assuming that the current is a constant current. If it is not a current equalizer, the total charge is the integral of the current over time. t is time, I is current, and T is time.

If the charging time is very short, the current can be simply considered as current sharing, and the formula can be simplified as Q=CV=IT. When C is a known quantity, V is a detectable quantity, and T is a known active control quantity, the current I can be Solve it out: I=CV/T.

Therefore, in this method, under the small-range surrounding signal detection state, the expression of the charge Q _PD accumulated on the receiving tube includes:

Q _PD =C _PD ×V _PD =C _PD ×(V _ON -V _OFF );

Or Q _PD =I _PD ×T _ACC ;

or

Among them, V _PD is the voltage on the equivalent capacitance C _PD of the receiving tube, C _PD is the junction capacitance of the receiving tube; I _PD is the photocurrent generated by the receiving tube PD under the irradiation of receiving light; T _ACC is the accumulation of photocurrent I _PD Time, T _ACC works in the linear range of the photoelectric receiving tube. When T _ACC is short enough, usually at the uS level, Q _PD can be calculated using a linear formula.

For the sake of simplicity, it is assumed that the current I _PD in a very short period of time is constant, so the receiving tube PD current I _PD = (C _PD ×V _PD )/T _ACC can be calculated. Among them, C _PD is a known quantity, which can be obtained from the photoelectric tube specification sheet or through conventional measurement methods; V _PD is the voltage based on VERF1, which is the measured value. T _ACC is a known quantity controlled by the processor or circuit during the measurement process.

There are many ways to collect the voltage of the receiving tube. For example, the positive input of the op amp, the inverting input, and the integrator mode can all collect the voltage. The premise is that the high input impedance and low leakage current of the collection path are maintained during the collection process. Therefore, The forward input and integrator modes of the op amp and other similar modes are more suitable. The input impedance of the forward input mode of the op amp is related to the index of the op amp; the integrator mode is similar to the charge mover, and only closes the switch SW1 within a limited time to integrate. The focus of the present invention is not on the acquisition circuit, so it only The operational amplifier 5 is used to implement the simplest voltage follower to collect voltage, and the subsequent operational amplifier 6 implements the signal amplification task. In addition, the method of setting the analog switch SW1 between the receiving tube 2 and the acquisition circuit helps to isolate the influence of the acquisition circuit, that is, data acquisition is only performed during the period when the switch SW1 is closed, which reduces the design requirements for the acquisition circuit and helps reduce the cost of the acquisition circuit. cost.

The amount of accumulated charge Q _PD on the receiving tube PD is related to the junction capacitance C _PD of the receiving tube and also to the accumulation time T _ACC . Therefore, it is very critical to determine the linear working area of the receiving tube and the available accumulation time in advance, because the junction capacitance The size is limited, only at the pF level, and excessive accumulation time will cause charge overflow. Taking the specification sheet (Version 1.2) of the Osram receiver tube SFH2200 as an example, its junction capacitance is 60pF when there is no reverse bias voltage and no light. The X-axis in Figure 3 is the accumulation time T of the receiving tube, and the vertical axis is the voltage V on the junction capacitance of the receiving tube. The relationship between Q _PD and accumulation time, as well as the measurement method of the charge accumulation time T _ACC of the receiving tube is as follows:

Because the typical value of C _PD can be obtained from the device specification of the receiving tube, there is a direct proportional relationship between Q _PD and accumulation time, assuming the coefficient is k. t1 and t2 are the accumulation times shown in Figure 3, t2>t1, so when C _PD is constant, the accumulated power Q _PD and the voltage V _PD have a linear relationship.

Because another calculation formula for accumulated charge is Q _PD =I _PD ×T _ACC , V _PD =I _PD ×T _ACC /C _PD , C _PD is a constant, and when the accumulation time T _ACC is very short, I _PD is a constant, Therefore, V _PD has a linear relationship with T _ACC . By adjusting the accumulation time t1 and t2 and collecting the voltages V1 and V2 corresponding to different accumulation times, the default is t2>t1 and t2=k×t1, k is a coefficient greater than 1.

t1 takes a time length close to 0, and measures whether the voltages V2 and V1 generated by accumulated charges under the same conditions satisfy the coefficient relationship k. If not, reduce the value of t2 until a usable accumulation time is obtained. Considering that the junction capacitance C _PD of the receiving tube PD is affected by temperature, the maximum value of the available accumulation time is 80% of the maximum value measured by t2. For example, assume that the initial t1=10uS, t2=200uS, k=20, t2=k×t1. Then the corresponding collected voltages v1 and v2 should also satisfy the relationship of v2=k×v1. If not, reduce the values of t2 and k until the available cumulative time is obtained.

S3: According to the environment to be detected, specify the small-range weak signal detection time threshold T _ON and alarm threshold used when the receiving tube detects small particles and thin smoke, and specify the dark current detection time T _OFF of the receiving tube.

The reading of the receiving tube current I _PD is directly related to the particle scattering intensity of the smoke, that is, the dimming rate. The alarm threshold setting of the smoke detector is also related to the dimming rate. It is only necessary to test and calibrate the alarm point thresholds of different types of smoke in accordance with regulations and summarize the product. Just put the threshold value. The charge accumulation method used in the present invention detects thin or small particles and uses a dimming rate that is far lower than the dimming rate threshold used by conventional smoke alarms, and is used to detect early thermal runaway of lithium batteries in new energy battery packs. Thin smoke or electrolyte volatilization can also be used to cause early fires in switch cabinets and charging piles. This is a highly sensitive detection method that does not conflict with the existing conventional detection of large-range signals, so the two test modes can be used in combination. In this method, by pre-specifying the small-scale weak signal detection time threshold T _ON , it is ensured that the signal current I _PD generated by the microcurrent during the T _ON time period is greater than the preset alarm threshold, and it is judged that there is thin or small particle smoke. Although this threshold May be below regulatory standard smoke thresholds, ensuring timely detection of early stage fires. At the same time, it effectively solves the embarrassing problems of traditional large-range detection, that is, increasing the sensitivity and reducing false alarms will lead to false alarms, while lowering the sensitivity will cause frequent false alarms, and there is no response to thin gases.

The main ideas and processes of this application are explained in conjunction with the driving timing diagram shown in Figure 1. The timing diagram shown in Figure 1 includes five lines above and below. The legend is in sequence SW1 switch (high means the switch is closed), emitter drive (high means open, emitting light). tube light emission), receiving tube charge (Q _PD ), data acquisition (high-bit analog-to-digital conversion) and time axis information. The short dashed lines above and below are used for events at various times. The whole process is divided into two large periods T1 and T2. The sampling period T1 is the accumulation and sampling period of the dark current, and the sampling period T2 is the accumulation and sampling period of the signal current.

S4: Close the switch SW1, reset the signal acquisition circuit and the receiving tube, and open the switch SW1 after the reset is completed;

The reset operation includes the reset of the signal acquisition circuit and the receiving tube: the reset of the signal acquisition circuit is the normal reset of the circuit, returning to the initial state; the reset of the receiving tube refers to the elimination of the charge at both ends of the receiving tube. The simple method is to remove the receiving tube. The output is connected to VREF1 through switch SW1. Specifically, it is connected to VREF1 through another switch (not shown in the figure) or VREF2 is configured to be equal to VREF1.

During the reset process, SW1 and the back-end circuit remain closed; time t0 is the starting time of the entire cycle and the starting time of the sampling period T1. Time t1 is the reset time of the entire system. At this time, the entire system circuit is reset, the acquisition circuit is reset, and the reception The tube clears the charge. After completing these operations, the connection switch SW1 is disconnected from the back-end signal acquisition circuit to prepare for the subsequent accumulation of charges.

In this embodiment, the charge on the receiver tube is cleared by closing the switch SW1 and connecting it to the same voltage as the reference voltage VREF1 of the receiver tube. The voltage at both ends of the receiver tube is consistent to cause the charge on its junction capacitance to be discharged. Instead of connecting another switch in parallel to the receiving tube, this will still increase the leakage current. In this application, the receiving tube has only one connection switch SW1, which reduces the possibility of leakage current while meeting the circuit requirements.

S5: Test the accumulated dark current of the receiving tube. The specific method is:

In the OFF state of SW1, within the dark current detection time T _OFF of the receiving tube, test the accumulated charge Q _OFF within the accumulated time T _OFF corresponding to the dark current of the receiving tube.

Time t2 is the starting time for the first accumulation of charge. At this time, the circuit releases the reset state and accumulates dark current to the junction capacitance C _PD of the receiving tube to form charge. The accumulation time between time t2 and time t3 is T _OFF . During The accumulated charge is Q _OFF , represented by a small slope in the third line of the figure. At this time, the light-emitting tube LED is in the off state. The second line in the figure is represented by a dotted line. The charge of the receiving tube continues to increase under the perfusion of dark current. At the same time, the voltage of the receiving tube also gradually increases. The times t1 and t2 can be very close, depending only on the reset time. The accumulated time T _OFF between t2 and t3 is a programmable and controllable timing sequence of the processor. For example, if the processor's time control accuracy is 1uS, then the processor setting is 10, which means the time is 10uS. Such circuit timing is also very suitable for state machine operation of integrated circuits, with programmable time intervals.

S6: Close SW1, connect the receiving tube to the signal acquisition circuit, measure the dark current of the receiving tube, and obtain the voltage V _OFF corresponding to the accumulated charge Q _OFF .

At the moment t4 immediately after the end of t3, the switch SW1 is closed. At this time, the voltage formed by the charge Q _PD accumulated on the receiving tube PD can be collected by the back-end signal acquisition circuit. The voltage of the receiving tube is collected at time t5. Marked as V _OFF .

S7: Close the switch SW1, reset the signal acquisition circuit and the receiving tube, and open the switch SW1 after the reset is completed.

Similar to step S4, SW1 and the back-end circuit remain closed during the reset process; time t6 is the starting time of the sampling period T2, and time t7 is the reset time of the entire system. At this time, the entire system circuit is reset, the acquisition circuit is reset, and the receiving tube is cleared charge. After completing these operations, the connection switch SW1 is disconnected from the back-end signal acquisition circuit to prepare for the subsequent accumulation of charges.

S8: Turn on the luminous tube, enter the small-range weak signal detection mode, and monitor the thin or small particle smoke status in the area to be tested in real time;

Assuming that the driving current of the light-emitting tube is ILED, the signal current generated by the particle scattering of the light-emitting tube under the illumination of the light-emitting tube continues to accumulate to the junction capacitance C _PD of the receiving tube;

The driving current ILED uses a small current, and the value of ILED satisfies: ILED _MIN ≤ ILED ≤ ILED _MAX ;

ILED _MIN is the minimum drive current of the light-emitting tube. The value of ILED _MIN is the larger of the minimum drive current allowed by the design of each circuit and the minimum drive current allowed by the LED device of the light-emitting tube;

ILED _MAX is the maximum allowable current of the light-emitting tube drive. The method for determining the value of ILED _MAX is: test the light-emitting tube current from large to small, and observe the value of the receiving photocurrent. When the light-emitting tube is lit, the synchronously measured receiving tube current is less than 1 % of the range of the signal acquisition circuit is recorded as the maximum allowable current ILED _MAX .

The so-called background, that is, the smoke-free background signal, refers to the light pollution signal caused by the reflection of the maze mechanism itself when no smoke enters the detector maze when the luminous tube is turned on or lit. The smaller the signal, the smaller the signal. Well, especially in application scenarios like this invention that are sensitive to background signals. Usually, the method of measuring the background is to turn on the light-emitting tube and collect the data of the receiving tube when ensuring that there is no smoke in the maze. The ideal measurement result is zero, but it may not be, and the background will change as the power of the light-emitting tube increases. big. In this application, in the small-range weak signal detection mode, in order to meet the needs of the charge accumulation method, the influence of the maze background reflected light must be minimized. Therefore, the low-current driving part of the light-emitting diode is used in a stable smoke detector. Test the background effect in the maze, test the luminous tube current from large to small, and observe the value of the received photocurrent. When the luminous tube lights up, the synchronously measured receiving tube current is less than 1% of the range of the signal acquisition circuit and is recorded as the maximum. The allowable current ILED _MAX is based on which the drive current is reduced until the background signal is eliminated. Among them, the minimum current allowed by the specification and the light-emitting tube drive circuit is recorded as ILED _MIN , and ILED _MAX ≥ ILED _MIN . During the test of ILED _MAX , if the ILED still cannot meet the requirement that the background current is less than 1% of the acquisition circuit range after the ILED drops to ILED _MIN , the optical design of the labyrinth needs to be improved. It is easy to reduce the drive current of the light emitting tube. This application reduces the local signal by reducing the drive current until the background signal is eliminated. However, everything has two sides. The smaller the light emitting current, the weaker the scattered light will be, and the resulting photocurrent will also be Weaker, so the detection circuit requires higher sensitivity and lower noise, so the use of charge accumulation method helps to achieve extremely low-noise weak current detection. Therefore, in the technical solution of the present application, the methods of background elimination and charge accumulation method for detecting weak photoelectric current are complementary to each other.

S9: Record the time point when the luminous tube lights up and SW1 turns off at the same time as: measurement start time;

Taking the measurement start time as the starting point, when the measurement duration reaches T _ON , open SW1 and connect the accumulated charge on the receiving tube to the signal acquisition circuit. For the convenience of calculation, T _ON =T _OFF is generally made.

During the measurement process, the driving current of the light-emitting tube is ILED, and the generated signal current continues to accumulate on the junction capacitance of the receiving tube. The accumulated time is T _ON and the accumulated charge is Q _ON .

Time t8 is the starting time for the second accumulation of charge. At this time, the circuit releases the reset state and accumulates the signal current to the junction capacitance C _PD of the receiving tube to form charge. The accumulation time between time t8 and time t9 is T _ON . During The accumulated charge is Q _ON , represented by the large bump in the third line of the figure. At this time, the LED of the light-emitting tube is on. The second line in the figure is represented by a solid line. The charge of the receiving tube continues to increase under the injection of signal current, and at the same time, the voltage of the receiving tube also gradually increases. The times t7 and t8 can be very close, depending only on the reset time, and the accumulated time T _ON between t8 and t9 is programmable. For example, if the processor's time control accuracy is 1uS, then the processor setting is 10, which means the time is 10uS. Generally speaking, T _ON and T _OFF have the same time control accuracy and programming duration, so it is ensured that the accumulated charges and voltages in the two time periods can be directly subtracted. Because the equivalent capacitance C _PD of the receiving tube PD is very small, the time control accuracy needs to be as high as possible, generally at the 1uS level, sub-uS or nS level. Such circuit timing is also very suitable for state machine operation of integrated circuits, with programmable time intervals.

S10: Measure the voltage V _ON of the receiving tube based on the signal acquisition circuit.

Open the switch SW1 at t10 immediately after the end of t9. At this time, the back-end signal acquisition circuit collects the voltage of the receiving tube at t11, which is recorded as V _ON .

S11: Calculate and measure the accumulated charge Q _PD on the receiving tube and the signal current I _PD received by the receiving tube;

_QPD = _QON - _QOFF ;

I _PD =Q _PD /T _ON .

The data collection process at t5 and t11 is generally very fast and is represented by narrow pulses in the figure. The labyrinth structure inside the smoke detector can provide the effect of a dark room, that is, when the luminous tube is not lit, no external ambient light is incident on the receiving tube, and the charge Q _OFF generated by the accumulation time T _OFF is a dark current contribution. , when the luminous tube is lit, the charge Q _ON generated by the accumulated time T _ON is the sum of the signal and dark current. Therefore, this method also includes the receiver tube dark current calibration method:

In practical applications, the calibration method for the dark current of the receiver tube is: when T _OFF = T _ON , the charge accumulated in the signal current Q _PD = Q _ON - Q _OFF = (V _ON - V _OFF ) × C _PD , and the dark current is calibrated The influence of; where, C _PD is the junction capacitance of the receiving tube.

The dark current of the receiving tube PD always exists, especially as the temperature changes. The higher the temperature, the greater the dark current. The dark current may be greater than the photocurrent to be detected, so calibrating the dark current must be done. steps, especially for low-light signal detection scenarios. Therefore, the dark current of the receiving tube PD is also part of the background signal and can be calibrated out at one time during the calibration process.

The above steps only describe the logical sequence, and actual operations can be freely combined into different steps.

S12: When the signal current I _PD is greater than the preset alarm threshold, a smoke alarm is issued; otherwise, steps S4 to S12 are executed in a loop to continue detecting the environment to be detected.

In addition to the small-range weak signal detection mode for thin or small particle smoke detection, this application also provides a large-range signal detection mode, that is, the conventional detection mode, as well as the function of switching between the small-range weak signal detection mode and the large-range signal detection mode to meet the requirements Requirements for small range weak signal detection and large range large signal detection.

Entering the large-range signal detection mode includes the following steps.

a1: Set the detection circuit for conventional smoke test.

The detection circuit of the conventional smoke test in this application is: referring to Figure 2, the switch SW1 is turned on, and the receiving tube is directly connected to the back-end signal acquisition circuit through the switch SW1. This method uses a general acquisition circuit for signal detection. Taking the transconductance amplifier as an example, it can directly convert the input signal current into the voltage V _ON =-I _PD × R _TIA , where RTIA is the transconductance resistance, and convert the input current signal I _PD into the voltage signal V _ON , and the transconductance The amplifier works in reverse amplification mode, so there is a negative sign in front of it.

a2: Assume that the measurement duration is tc, and the initial value of tc is set to T _ON ;

The voltage when the receiving tube is saturated is recorded as VSA. When the receiving tube is saturated, more light will not cause a change in voltage, so the corresponding charge will not increase;

The saturation charge corresponding to the saturation voltage VSA is recorded as QSA, so QSA can be an experimental value or estimated based on the open circuit voltage and junction capacitance of the receiving tube specification sheet;

VSA=QSA/C _PD , C _PD is the junction capacitance of the receiving tube.

Because the circuit based on Figure 2 cannot directly measure the charge Q _ON on the receiving tube, it can be obtained by measuring the corresponding voltage V _ON =Q _ON /C _PD . T _ON is the experimentally calibrated threshold, and the saturated V _ON can be obtained during the experiment. the maximum value.

a3: During the implementation of steps S7 to S10, if within tc time, the accumulated charge of the receiving tube reaches saturation;

Then adjust tc to a smaller value, 0<tc<T _ON .

For example: In this embodiment, adjust tc to a value in the range of 0.6×T _ON <tc<0.9×T _ON , and test the accumulated charge again. If the obtained V _ON is still the maximum value VSA, it means that the accumulated charge of the receiving tube is saturated. , exceeding the detection range of small-range weak signals; switch the circuit to the detection circuit of the conventional smoke test and perform large-range detection mode; if V _ON also decreases proportionally, update the accumulation time T _ON =T _OFF =tc .

a4: Again within tc time, test the accumulated charge on the receiving tube and the voltage of the receiving tube;

If the voltage of the receiving tube still reaches VSA, switch to the detection circuit of the conventional smoke test and perform a large-range signal test;

Otherwise, if the voltage of the receiving tube is less than VSA, update the value of the small-scale weak signal detection time threshold T _ON to the value corresponding to tc, and then execute steps S4 to S12 in a loop;

The conventional signal detection circuit in this application is: the switch SW1 is closed, the receiving tube is directly connected to the back-end signal acquisition circuit through the switch SW1, and SW1 remains closed during the acquisition process.

In this method, the method of switching from the large-range signal detection mode to the small-range weak signal detection mode is: when the large-range detection mode is used for detection and no data changes are found in the past period of time, then switch to the small-range weak signal detection mode. However, if the saturation problem still occurs after switching to the small-range weak signal monitoring state, it means that the threshold TH is too large. Reduce the TH value by a certain proportion and continue to use the large-range signal detection mode to prevent the system from deadlocking due to repeated switching of detection modes.

Specifically, it includes the following steps.

b1: The time period t monitored by the preset range switching, the number of samples n and the range switching threshold TH;

Among them, the number of samples n is related to the monitored time t, and depends on the detected data output rate ODR. For example, if ODR=2Hz and the collection time of collecting samples is t=5s, then the number of samples obtained during the collection time t is n=10. During specific implementation, the number of samples n that satisfies the conditions of t≥5s and n≥5 depends on ODR, which is a natural number.

The range switching threshold TH is the charge number or voltage number of the monitored object. Since the two are linearly related, the voltage signal is generally measured. TH refers to the smallest distinguishable voltage. The general value is 1% or 1% of the full range of the detection circuit input. Lower, less than this value is difficult to detect using traditional detection methods or the resolution is very low.

Confirm the measurement values of the monitoring objects corresponding to the continuous n samples;

If the average value of the corresponding measured values of the n sample data is less than TH, it is determined to be below the monitoring range of the large-range signal detection mode, and step b3 is executed;

Otherwise, proceed to step b4.

b3: Switch to small range weak signal detection mode;

b4: Still maintain the large-range signal detection mode, and perform step b2 at the same time;

After step b3 is executed, anti-locking measures need to be implemented.

Anti-locking measures include the following steps:

c1: Assume that the measurement duration is tl, and the initial value of tl is set to T _ON ;

c2: During the implementation of steps S7 to S12, within the tl time, the accumulated charge of the receiving tube reaches saturation, then the range switching threshold TH is adjusted to: TH=TH*0.8;

Switch to the large-range signal detection mode and perform step b2 at the same time.

In this application, anti-locking measures are used to prevent the initial value of TH from being set too high, exceeding the range of small-range weak signal detection and returning to the large-range detection mode, causing state machine deadlock problems.

In this embodiment, a large range of signal measurement, that is, conventional signal detection, is provided based on a transconductance amplifier. If there is no change in the signal obtained by conventional signal detection, you can switch to the small-range weak signal detection mode to detect small particles and thin smoke.

This application uses low driving current to drive the light emitting tube. The optical power conversion efficiency of low driving current is higher, which helps to reduce or eliminate internal light pollution and avoid saturation of the receiving circuit. Use the "exposure" method for low-light detection. Similar to the principle of extending the exposure time of a SLR camera to shoot weak light in the starry sky, during the "exposure" process, the receiving tube is disconnected from the receiving circuit and the operational amplifier is not connected, allowing photoelectrons to accumulate on the junction capacitance C _PD of the receiving tube PD itself. . After sufficient charge Q _PD is accumulated, the voltage of the receiving tube V _PD =Q _PD /C _PD . When the voltage of the receiving tube V _PD rises to a detectable range, the back-end signal acquisition circuit can be connected for data acquisition. In order to accumulate all the photocurrent on C _PD and prevent leakage current, the leakage current of the receiver tube PD only depends on the analog switch SW1 connected to the back-end circuit. This design can reduce the design complexity of the entire back-end system. And reduce the cost of the device, because the signal is only collected at the moment when the switch SW1 is turned on, and is not always connected for detection. The method of detecting weak light signals by using the accumulated charge "exposure" of the receiving tube PD is greatly affected by the dark current of the receiving tube PD itself, and the dark current is related to the environment, especially the temperature, so the calibration of the dark current must also be considered. . Since the labyrinth and optical design of the smoke detector itself can easily ensure that there is no interference from external ambient light, the interior of the labyrinth has an effect similar to that of a dark room when the luminous tube is turned off. Through at least two cycles, a period T1 in which the light-emitting tube is turned off to detect dark current and a period T2 in which the light-emitting tube is turned on to detect the signal, the data of T2 minus the data of T1 just corrects the influence of the dark current. Although this is a universal ambient light Elimination technology, but it is very suitable to combine the natural environment of the maze design with the "exposure" charge accumulation method. The technical solution of this application adopts a method that combines small-range weak signal detection and large-range large signal conventional signal detection, which helps to compensate for the problem of insufficient range of the accumulated charge method. It is also compatible with conventional detection modes and can be regarded as an improvement on conventional detection. Extension of the pattern. At the same time, the normal mode does not have to worry about the zero-background design because the range is sufficient, but the detection of weak signals in the small range is very sensitive, so it is necessary to reduce the driving current of the light-emitting tube and use a charge accumulation method. Therefore, this application takes into account actual usage scenarios and application pain points to improve existing solutions, achieving a compromise and balance between performance and cost.

Claims (9)

1. A method for lean or small particle smoke detection, comprising: a small-range weak signal detection mode and a large-range signal detection mode;

the small-range weak signal detection mode is a weak light detection method based on charge accumulation and a conventional detection method matched with weak light detection;

the wide-range signal detection mode is a conventional signal detection method, is used for being matched with a weak light detection method and is compatible with a conventional detection method;

in the small-range weak signal detection mode, the device connected with the receiving tube is provided with only one switch SW1, and the data acquisition work is completed through time sequence operation and a back-end circuit.

2. A method for lean or small particle smoke detection according to claim 1, comprising the steps of:

s1: setting a detection device, the detection device comprising: the device comprises a signal acquisition circuit, a luminous tube and a receiving tube;

the luminous tube emits light, and the receiving tube receives the light; the signal acquisition circuit is connected with the receiving tube;

the method is characterized by further comprising the following steps:

s2: a switch SW1 with low leakage current is arranged between the receiving tube and the signal acquisition circuit;

S3: according to the environment to be detected, designating a small-range weak signal detection time threshold T used when the receiving tube detects small particles and thin smoke _ON And an alarm threshold, designating the receiving tube dark current detection time T _OFF ；

S4: closing a switch SW1, and implementing a reset operation, wherein the switch SW1 is opened after the reset operation is finished;

s5: the cumulative dark current of the receiving tube is tested by the following specific method:

in the SW1 off state, the dark current detection time T of the receiving tube _OFF In, testing the accumulated time T corresponding to the dark current of the receiving tube _OFF Accumulation inCharge Q _OFF ；

S6: closing SW1, connecting the receiving tube to the signal acquisition circuit, and measuring dark current of the receiving tube to obtain the accumulated charge Q _OFF Corresponding voltage V _OFF ；；

S7: closing a switch SW1, and implementing the reset operation on the signal acquisition circuit and the receiving tube, wherein the switch SW1 is opened after the reset operation is finished;

s8: turning on the luminous tube, entering the small-range weak signal detection mode, and monitoring the state of thin or small particle smoke in the area to be tested in real time;

assuming that the driving current of the luminous tube is ILED, and continuously accumulating signal current generated by particle scattering under the irradiation of the luminous tube onto the junction capacitance of the receiving tube;

The driving current ILED uses a small current, and the ILED value satisfies: ILED (ed) _MIN ≤ILED≤ILED _MAX ；

ILED _MIN For the minimum driving current of the luminous tube, ILED _MIN The value is as follows: a larger value of the minimum driving current allowed by the design of each circuit and the minimum driving current allowed by the LED device of the luminous tube;

ILED _MAX for driving maximum allowable current of luminous tube _MAX The value method comprises the following steps: the current of the luminous tube is tested from large to small, the value of the received photocurrent is observed at the same time, and the maximum allowable current ILED is recorded when the current of the receiving tube, which is synchronously measured when the luminous tube is lighted, is smaller than the measuring range of the 1% signal acquisition circuit _MAX ；

S9: the time point at which the lighting of the light emitting tube and the turning off of the SW1 are simultaneously satisfied is recorded as: measuring the starting time;

starting from the measurement start time, when the measurement duration reaches T _ON When the signal acquisition circuit is started, the SW1 is opened, and the accumulated charges on the receiving tube are connected into the signal acquisition circuit;

s10: measuring the voltage V of the receiving tube based on the signal acquisition circuit _ON ；

S11: calculating the charge Q accumulated on the receiving tube _PD And said receivingThe received signal current I _PD ；

Q _PD ＝Q _ON -Q _OFF ；

I _PD ＝Q _PD /T _ON ；

S12: when the signal current I _PD When the alarm value is larger than a preset alarm threshold value, giving out a smoke alarm; otherwise, the steps S4 to S12 are circularly executed, and the environment to be detected is continuously detected.

3. A method for lean or small particle smoke detection according to claim 2, characterized in that: the method for calibrating the dark current of the receiving tube comprises the following steps:

let T _OFF ＝T _ON At the time, the charge Q accumulated by the signal current _PD ＝Q _ON -Q _OFF ＝(V _ON -V _OFF )×C _PD Calibrating out the effect of dark current;

wherein C is _PD Is the junction capacitance of the receiving tube.

4. A method for lean or small particle smoke detection according to claim 1, characterized in that: the entering mode of the wide-range signal detection mode comprises the following steps:

a1: setting a detection circuit for detecting a conventional signal;

a2: assuming that the measurement duration is tc, the initial value of tc is set to T _ON ；

The charge amount at the saturation of the receiving tube is noted as: a saturated charge QSA;

the saturated charge corresponding to the saturated voltage VSA is recorded as QSA;

VSA＝QSA/C _PD ，C _PD junction capacitance for the receiving tube;

a3: in the implementation of steps S7-S10, if the accumulated charge of the receiving tube reaches saturation in the tc time;

then tc is decreased to 0<tc<T _ON ；

a4: again, in the time tc, testing the accumulated charge on the receiving tube and the voltage of the receiving tube;

if the voltage of the receiving tube still reaches the VSA, switching to a detection circuit of a conventional smoke test to perform a wide-range signal test;

Otherwise, if the voltage of the receiving tube is smaller than VSA, the small-range weak signal is detected by a time threshold T _ON After the value of tc is updated to the value corresponding to tc, steps S4 to S12 are cyclically executed.

5. A method for lean or small particle smoke detection according to claim 4, wherein: the detection circuit for detecting the conventional signal comprises: the switch SW1 is closed, the receiving tube is directly connected to the rear-end signal acquisition circuit through the switch SW1, and the switch SW1 is kept closed in the acquisition process.

6. A method for lean or small particle smoke detection according to claim 4, wherein: it also includes: the wide-range signal detection mode is switched to the small-range weak signal detection mode, and the method comprises the following steps of:

b1: presetting a time period t monitored by range switching, the number n of samples and a range switching threshold value TH;

the span switching threshold TH includes: monitoring the charge number or the voltage number of the object; n is more than or equal to 10;

b2: confirming measured values of monitoring objects corresponding to the continuous n samples;

if the average value of the corresponding measured values of the n sample data is smaller than TH, judging that the average value is lower than the monitoring range of the wide-range signal detection mode, and executing the step b3;

Otherwise, executing the step b4;

b3: switching to the small-range weak signal detection mode;

b4: the wide range signal detection mode is still maintained and step b2 is performed simultaneously.

7. A method for lean or small particle smoke detection according to claim 6, wherein: step b3, after execution, an anti-lock measure is needed to be executed;

the anti-lock measure comprises the following steps:

c1: assuming that the measurement duration is tl, the initial value of tl is set to T _ON ；

c2: in the implementation process of steps S7 to S12, the receiving tube accumulated charge reaches saturation in tl time, and the span switching threshold TH is adjusted to be: th=th×0.8;

and switching to the wide range signal detection mode, and simultaneously executing the step b2.

8. A method for lean or small particle smoke detection according to claim 2, characterized in that: in the small-range weak signal detection mode, the charge Q accumulated on the receiving tube _PD The expression mode of (2) comprises:

Q _PD ＝C _PD ×V _PD ＝C _PD ×(V _ON -V _OFF )

or Q _PD ＝I _PD ×T _ACC

Or alternatively

Wherein C is _PD Junction capacitance for the receiving tube; t (T) _ACC Photocurrent I generated for receiving light by receiving tube PD _PD T is equal to the accumulated charge period of (1) _ACC The photoelectric receiving tube is ensured to work in a linear interval.

9. A method for lean or small particle smoke detection according to claim 2, characterized in that: the reset operation includes: a signal acquisition circuit reset operation and a receiving tube reset operation;

The signal acquisition circuit is reset to restore the circuit to an initial state; the receiving tube resetting operation is as follows: and simultaneously eliminating charges at two ends of the receiving tube.