CN117007484A

CN117007484A - Method for detecting thin or small particle smoke

Info

Publication number: CN117007484A
Application number: CN202310869936.7A
Authority: CN
Inventors: 罗倩倩; 付琛
Original assignee: Wuxi Institute of Commerce
Current assignee: Wuxi Institute of Commerce
Priority date: 2023-07-17
Filing date: 2023-07-17
Publication date: 2023-11-07

Abstract

The application provides a method for detecting thin or small particle smoke, which aims at the condition of thin or small particle smoke caused by fire, a luminous tube emits light by using low driving current, weak light current caused by light scattering of the thin or small particle smoke is accumulated on a junction capacitance of a receiving tube, the receiving tube is disconnected from a receiving circuit in the detection process, an operational amplifier is not connected, after the accumulation time is reached, the accumulated charge on the receiving tube is measured by a signal acquisition circuit, and the detection of weak current caused by the thin or small particle smoke is realized by adopting a charge accumulation mode.

Description

Method for detecting thin or small particle smoke

Technical Field

The application relates to the technical field of photoelectric particle or smoke detection, in particular to a method for detecting thin or small particle smoke.

Background

The smoke detector, especially the photoelectric smoke detector is a mainstream product of the smoke detector in the current market, is mainly used for detecting fire in public places such as buildings, offices and families, detects whether smoke exists or not through the principle of optical scattering, and sends out an alarm signal when a certain threshold value is exceeded. In general, a photoelectric smoke detector is internally provided with one or more photoelectric emitting and receiving devices, a housing and corresponding mechanism components form an optical darkroom called a maze, and the basic detection principle is to judge the concentration of smoke according to the light intensity scattered by smoke particles and compare the concentration with an alarm threshold value.

However, in some more specific scenarios, such as: the thermal runaway monitoring of the electrochemical cells of new energy sources, the early thermal runaway process of the cells releases rarefaction smoke, possibly accompanied by fine particulate matter, which conventional smoke detectors may not be capable of. And in addition, small particulate matters are released in early stage of fire disaster of the switch cabinet and the electric cabinet of the charging pile due to overheat of wires, the particle size of the particles is generally smaller than 100nm or even 10nm, and the particles are not easy to capture by a traditional smoke detector. The traditional smoke detector is based on the detection principle of Mie scattering, and aims at smoke particles with the particle size range of 100 nm-1 um, so that the sensitivity is required to be increased for detecting finer particles, but the problem of frequent false alarm occurs with the smoke detector, and the traditional smoke detector is difficult to achieve the problems of high sensitivity and low false alarm. The two fire processes are generally irreversible, early warning is needed as soon as possible, and larger loss is avoided.

There are also smoke sensors for detecting particles specifically, as in the prior art, the patent with application number CN202121804266.3 discloses a dual wavelength aerosol particle scattering light sensing structure, which uses two laser transmitters with different wavelengths, and a light receiver forms a labyrinth structure in the shape of a Chinese character 'pin'. When no smoke enters the detector maze, the light pollution signal caused by the self reflection among the maze mechanisms is called background, and the smaller the background signal is, the better the background signal is, especially the application scene sensitive to the background signal is disclosed by the invention. The light intensity of the laser is high and concentrated, but the scanning area is smaller, requiring a large volume and a more complex mechanical design in order to reduce or eliminate optical reflection. Even if the designer sacrifices some other functions, such as taking up a larger volume, to reduce the internal background signal light pollution, the internal background signal light pollution is eliminated. Conventional current sensing circuits such as transconductance amplifiers require relatively large transconductance resistors and low noise op amps, where noise, output bias, and thermal noise of the transconductance resistors are the dominant sources of noise and measurement errors, and it is difficult for conventional transconductance amplifiers to detect signals if the input signal is weak below the noise floor of the overall input circuit. Therefore, even if cost is not considered, there is a limit to using an operational amplifier with better performance in a lump to reduce the contribution of system noise. The smoke detection equipment designed based on the traditional method is difficult to be weighed simultaneously in terms of power consumption, cost and high sensitivity and low false alarm performance in the system design.

Disclosure of Invention

When detecting thin or small particle smoke caused by fire, the existing smoke sensor has the problem that the power consumption, the cost and the performance are difficult to be simultaneously considered. In order to solve the problems, the invention provides a method for detecting thin or small particle smoke, which can effectively identify continuous thin or small particle smoke caused by fire, and can also effectively consider the power consumption and the cost, thereby meeting the performance requirement of high sensitivity.

The technical scheme of the invention is as follows: a method for lean or small particle smoke detection 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: the cathode of the receiving tube is connected with a reference voltage VREF1, and a switch SW1 with low leakage current is arranged 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, 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;

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: simultaneously eliminating charges at two ends of the receiving tube;

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 In which the accumulated charge 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 a 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: testing the current of the luminous tube from large to small and simultaneously observingThe value of the received photocurrent is recorded as the maximum allowable current ILED when the current of the receiving tube 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 a signal current I received by the receiver _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.

It is further characterized by:

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 Junction capacitance for the receiving tube;

it also includes: the method for entering the wide-range signal detection mode comprises the following steps of:

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 updating the value of (c) to the value corresponding to tc, performing steps S4 to S12 in a circulating manner;

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;

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: still maintaining the wide range signal detection mode and simultaneously executing step b2;

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;

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

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.

The application provides a method for detecting thin or small particle smoke, which aims at the condition of thin or small particle smoke caused by fire, a luminous tube emits light by using low driving current, weak light current caused by light scattering of the thin or small particle smoke is accumulated on a junction capacitance of a receiving tube, the receiving tube is disconnected from a receiving circuit in the detection process, an operational amplifier is not connected, after the accumulation time is reached, the accumulated charge on the receiving tube is measured by a signal acquisition circuit, and the detection of weak current caused by the thin or small particle smoke is realized by adopting a charge accumulation mode. The method uses The low driving current will have little internal light pollution problem with the same optical design because the power of the used emitter tube is very small and the light power is almost totally reflected and absorbed by the interior, even with dust accumulation or component aging problems. Meanwhile, the switch SW1 is in an off state in the charge accumulation process, and the receiving tube is not connected with the back-end circuit, so that the precision requirement on the signal acquisition circuit is not high, and the power supply can be directly turned off even in the period. Therefore, the method has the advantages of low cost, low power consumption and high robustness. The application designates the detection time threshold T of the weak signal with small measuring range according to the condition of the environment to be detected _ON And an alarm threshold for signal current, once the measurement time reaches T _ON And when the signal current on the receiving tube is larger than the alarm threshold, small particle alarm is carried out, so that conventional fire smoke can be detected, thin or small particle smoke of early fire can be detected, and the detection accuracy and robustness are improved. Meanwhile, in order to accumulate all photocurrents on the junction capacitance of the receiving tube, the method is used for preventing leakage current, a switch SW1 with low leakage current is arranged between the signal acquisition circuit and the receiving tube, the leakage current of the receiving tube PD only depends on the analog switch SW1 of the receiving tube connected with the back-end circuit and is irrelevant to other devices, the design complexity of the whole back-end system can be reduced, the whole area of the smoke detection equipment is effectively controlled, and the design cost of the system is reduced.

Drawings

FIG. 1 is a timing diagram of a driving method for lean or small particle smoke detection of the present application;

FIG. 2 is a schematic circuit topology of the present method;

FIG. 3 is a test verification curve of accumulated charge time.

Detailed Description

The application provides a method for detecting thin or small particle smoke, which comprises a weak light detection method based on charge accumulation and a conventional detection method matched 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, is used for being matched with the weak light detection method and is compatible with the conventional detection method.

In the weak light detection method based on charge accumulation, a device connected with a 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. Considering the range problem of the weak light detection method based on charge accumulation, the application designs the switching and compatibility of the conventional detection method, namely the wide range signal detection mode, so that the original detection mode and alarm threshold setting are not required to be changed, the weak light detection method based on charge accumulation not only can provide more product function options, but also improves the detection capability of rarefaction or small particle smoke and reduces false alarm rate. The method specifically comprises the following steps.

S1: setting a detection device, wherein the detection device comprises: the device comprises a signal acquisition circuit, a luminous tube and a receiving tube.

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

The luminous tube and the receiving tube in the application are realized based on diodes in the prior art, such as: the light emitting tube in the method is realized based on the osram light emitting tube SFH 4069. In a specific application, the specification acquirer through the diode corresponds to the optical power or the optical intensity Ee of the driving current. Such as: the nominal current recorded in the specification is 70mA, and the corresponding test pulse time is 20mS; if the light intensity is to be reduced: one way is to reduce the drive current I _F The method comprises the steps of carrying out a first treatment on the surface of the Another approach is to reduce the drive pulse time t _p . The lower the current when the luminous tube is below the nominal current, the higher the optical power conversion efficiency, namely the higher the optical power generated by the unit driving current. Then, the driving current of SFH4069 may be as low as 1mA, and the electro-optical conversion efficiency at the current is high, of course, the higher the power supply efficiency.

S2: the cathode of the receiving tube is connected with a reference voltage VREF1, and a switch SW1 with low leakage current is arranged between the receiving tube and the signal acquisition circuit; the reference voltage of the signal acquisition circuit is VREF2. For specific applications, VREF1 and VREF2 may be the same value.

Fig. 2 shows an embodiment of a schematic circuit topology used in the method. It comprises the following steps: a luminous tube 1 and a receiving tube 2. The light emitted by the reflection tube 2 encounters the scattered light of the particles of the smoke 3 and irradiates the receiving tube 2 to generate photocurrent. The electronic components are covered by a mechanical element called a labyrinth 4, the labyrinth 4 providing a stable optical detection environment.

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

the cathode of the receiving tube 2 is connected with a reference power supply VREF1, the anode is connected with one end of a switch SW1, the other end of the switch SW1 is connected with the input homodromous end of an amplifier 5 and one end of a switch SW3, the reverse input end of the operational amplifier 5 is connected with one end of a switch SW2 and the output end of the operational amplifier 5, the other end of the switch SW2 is connected with one end of a resistor Rin, the other end of the resistor Rin is connected with the other end of the switch SW3, one end of a transconductance resistor Rf and the reverse input end of an operational amplifier 6, the forward input end of the operational amplifier 6 is connected with the reference power supply VREF2, and the output end of the operational amplifier 6 is connected with the other end of the transconductance resistor Rf and then is connected with the input of an analog-to-digital converter ADC. For convenience of description, the circuit uses a very simple circuit structure, for example, a signal processing circuit of a photoelectric tube uses a single-ended mode, and a differential mode is also applicable.

The switch SW1 with low leakage current is realized based on the low leakage current switch in the prior art, and if the power supply range is larger than 5V, ADG1221 (refer to specification ver.b) of ADI can be considered, and the switch SW1 with low leakage current of 2pA and the equivalent injected charge of 0.5pC are very suitable for precise design; if less than 5V supply can be considered ADG701L (reference specification Ver. A) for ADI, with a 10pA off leakage current and an equivalent injected charge of 5 pC. The same is true for integrated chip index.

The application uses low driving current to drive the luminous tube, and the problem of internal light pollution is almost avoided under the same optical design, and the light emission is absorbed by the internal optical mechanism and has no influence even if dust is accumulated or components are aged because the power of the emitting tube under the low driving current is very small and the labyrinth design of the photoelectric smoke detector has certain light absorption capacity. Thus, this design has the advantage of low cost, low power consumption and high robustness.

Fig. 2 is merely a very simple circuit implementation for describing the way the circuit is handled. The signal acquisition circuit to the right of switch SW1 in fig. 2 has two functions.

Firstly, when the switch SW1 is closed after the accumulated charges are finished and the voltage on the photoelectric tube 2 is detected, the requirement of small-range weak signal detection is met.

The specific circuit is configured such that when SW1 is closed, SW2 is closed, SW3 is opened, and at this time, the operational amplifier 5 operates in a voltage following mode, the operational amplifier 6 operates in an inverse amplification mode, the amplification factor is equal to-Rf/Rin, and the operational amplifier 5 is used in cascade with the operational amplifier 6. The circuit captures the voltage of the receiver tube 2, where the voltage of the receiver tube 2 is based on the voltage of the reference VREF 1.

And secondly, when the detection signal is relatively large and exceeds the upper limit of accumulated charges, the mode is switched to a wide-range conventional transconductance amplifier mode.

The particular circuit is configured such that switches SW1 are closed, SW3 are closed and switch SW2 is open, so that a portion of the entire operational amplifier 5 is bypassed. The output of the receiving tube 2 enters the inverting input of the operational amplifier 6 through the switches SW1 and SW3, and at this time the operational amplifier 6 operates in the transconductance amplification mode to convert the collected current signal into a voltage signal. When switching to the wide-range conventional mode, the light intensity of the emitting tube is also increased to the conventional driving current, and the driving current of the luminous tube can be typically 70mA by taking SFH4069 as an example, so that the whole smoke detector maze can tolerate even if a certain background signal exists. The output of the operational amplifier 6 is connected to the analog-to-digital converter ADC at the back end, and is not described herein again because it does not belong to the present invention.

When the switch SW1 is turned off, the receiving tube 2 receives the photo current I generated by light _PD At time T _ACC Junction capacitance C accumulated in the photocell 2 itself during a period of time _PD Charge generated on Q _PD 。

In general, the number of charges accumulated on the capacitor CQ 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 the charging current of the capacitor according to the formula q=it, I is the charging time, T is the case assuming the current is a constant current, if not current sharing the total charge number is the integral of current over timeT is time, I is current, and T is time.

If the charging time is short, the current can be simply considered to be equal, the formula can be simplified to q=cv=it, and when C is a known quantity, V is a detectable quantity, and T is a known active control quantity, the current I can be solved: i=cv/T.

Therefore, in the method, under the state of detecting the small-range surrounding signal, 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 V is _PD Equivalent capacitance C of receiving tube _PD Voltage at C _PD Junction capacitance for the receiver tube; i _PD Photocurrent generated by the receiving tube PD under the irradiation of the receiving light; t (T) _ACC Is photocurrent I _PD T is equal to the cumulative time of (1) _ACC Working in the linear region of the photoelectric receiving tube, when T _ACC Short enough, typically of uS class, Q _PD The calculation may be performed using a linear formula.

For simplicity, assume a current I in a very short time _PD Is constant, so that the receiver tube PD current I can be calculated _PD ＝(C _PD ×V _PD )/T _ACC . Wherein C is _PD Is a known quantity, which can be obtained from specifications of the photocell or by conventional measurement methods; v (V) _PD Is based on the voltage of VERF1, is a measurement. T (T) _ACC Is a known quantity controlled by a processor or circuitry during the measurement process.

There are various ways to collect the voltage of the receiving tube, such as the normal phase input, the reverse phase input and the integrator mode of the op-amp, provided that the high input impedance and the low bleed current of the collecting path are maintained during the collection process, so that the normal phase input and the integrator mode of the op-amp are suitable. The input impedance of the forward input mode of the operational amplifier is related to the index of the operational amplifier; the integrator mode is similar to a charge mover, and only the switch SW1 is closed for integration within a limited time, the invention focuses on no acquisition circuit, so that the operational amplifier 5 is used for realizing the simplest voltage follower for voltage acquisition, and the following operational amplifier 6 is used for realizing the signal amplification task. In addition, the method of setting the analog switch SW1 between the receiving tube 2 and the acquisition circuit is helpful to isolate the influence of the acquisition circuit, namely, only the time period when the switch SW1 is closed is used for data acquisition, so that the design requirement on the acquisition circuit is reduced, and the cost is reduced.

Quantity Q of accumulated charges on receiving tube PD _PD Junction capacitance C with receiver tube _PD Related to the accumulated time T _ACC In this connection, it is therefore critical to determine in advance the linear operating region of the receiving tube and the accumulation time available, since the junction capacitance is of limited size, in the pF-level only, which would lead to charge overflow. Taking the specification of the osram receiver SFH2200 (Version 1.2) as an example, the junction capacitance is 60pF without reverse bias voltage and without illumination. The X-axis in fig. 3 is the receiver tube integration time T and the vertical axis is the voltage V across the receiver tube junction capacitance. Off Q _PD Relationship with accumulation time, and charge accumulation time T of receiving tube _ACC The measurement method of (2) is as follows:

because C _PD Can be obtained from the device specification of the receiving tube, thus Q _PD And the accumulation time, assuming a coefficient k. the cumulative time of t1 and t2 as shown in FIG. 3, t2>t1, thus when C _PD When constant, accumulate electric quantity Q _PD And voltage V _PD Is a linear relationship.

Because another calculation formula of accumulated charge is Q _PD ＝I _PD ×T _ACC ，V _PD ＝I _PD ×T _ACC /C _PD ，C _PD Is constant when the accumulated time T _ACC Short time, I _PD Is constant and therefore V _PD And T is _ACC In a linear relationship. By adjusting the accumulation time t1 and t2 and collecting the voltages V1 and V2 corresponding to different accumulation times, the default t2 >t1 and t2=kxt1, k being a coefficient greater than 1.

t1 takes a time length close to 0, and it is measured whether the voltages V2 and V1 generated by the accumulated charges under the same conditions satisfy the coefficient relation k, and if not, the value of t2 is reduced until a usable accumulation time is obtained. Taking into account junction capacitance C of receiver tube PD _PD The magnitude of (2) is affected by the temperature and thus the maximum value of the usable accumulation time takes a value of 80% of the maximum value measured at t 2. For example, assume that initially t1=10us, t2=200us, k=20, t2=kχt1. Then the corresponding acquired voltages v1 and v2 should also satisfy the relationship v2=kxv1. If not, the values of t2 and k are reduced until a usable accumulation time is obtained.

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

Receiving tube current I _PD The readings of the smoke detector are directly related to the particle scattering intensity of the smoke, namely the dimming rate, and the alarm threshold setting of the smoke detector is also related to the dimming rate, so that the alarm point thresholds of different types of smoke are only required to be calibrated according to the legal test and the placement thresholds of products are summarized. The light-reducing rate of the detection method for measuring rarefaction or small particles by adopting the charge accumulation method is far lower than the light-reducing rate threshold value of the conventional smoke alarm, and the detection method is used for detecting rarefaction smoke or electrolyte volatilization in early thermal runaway of a new energy battery-packaged lithium battery and can also be used for early fire disasters of a switch cabinet and a charging pile. The method is a high-sensitivity detection means and is compatible with the existing wide-range signal Conventional detection of numbers does not conflict, so both test modes can be used in combination. In the method, a small-range weak signal detection time threshold T is pre-designated _ON Ensure at T _ON Signal current I generated by micro-current during time period _PD A greater than preset alarm threshold is determined to be the presence of a rarefied or small particle smoke, although this threshold may be below the standard smoke threshold of regulations, ensuring that an early fire can be detected in a timely manner. Meanwhile, the embarrassing problem of traditional wide-range detection is effectively solved, namely the problem of missing report caused by the fact that sensitivity is improved and false report is reduced, and the problem of frequent false report and no reaction to lean gas is caused by the fact that the sensitivity is reduced.

Explaining the main idea and process of the present application with reference to the driving timing chart shown in fig. 1, the timing chart shown in fig. 1 includes five rows up and down, and the legend is sequentially SW1 switch (high switch closed), emitter driving (high switch open, light emitting tube light emitting), receiver charge (Q) _PD ) Data acquisition (high-order analog-to-digital conversion) and time axis information. The upper and lower short dashed lines are used for events for their respective moments. The whole process is divided into two large periods T1 and T2, the sampling period T1 is the accumulation and sampling period of dark current, and the sampling period T2 is the accumulation and sampling period of signal current.

S4: closing a switch SW1, resetting the signal acquisition circuit and the receiving tube, and opening the switch SW1 after the reset is finished;

the reset operation comprises the reset of the signal acquisition circuit and the receiving tube: resetting the signal acquisition circuit is normal reset of the circuit, and the circuit is restored to an initial state; resetting the receiver refers to eliminating the charge across the receiver, simply by passing the receiver output through switch SW1 and then to VREF1. Specifically by another switch (not shown) to VREF1 or by configuring VREF2 to be equal to VREF1.

In the resetting process, the SW1 and the back-end circuit are kept closed; the time T0 is the starting time of the whole period and the starting time of the sampling period T1, the time T1 is the resetting time of the whole system, at this time, the circuit of the whole system is reset, the acquisition circuit is reset, and the receiving tube clears charges. After these operations are completed, the signal acquisition circuit connecting switch SW1 to the back end is disconnected in preparation for subsequent charge accumulation.

In this embodiment, the charge on the receiving tube is removed by closing switch SW1 and connecting to the same voltage as the reference voltage VREF1 on the receiving tube, and the voltage across the receiving tube is consistent to cause the charge on the junction capacitance to discharge. Instead of connecting a switch in parallel to the receiving tube, this again increases leakage current. In the application, only one receiving tube is connected with the switch SW1, so that the possibility of leakage current is reduced on the basis of meeting the circuit requirement.

S5: the method for testing the cumulative dark current of the receiving tube comprises the following specific steps:

in the SW1 off state, the dark current detection time T is set at the receiving tube _OFF In, test the cumulative time T corresponding to the dark current of the receiving tube _OFF In which the accumulated charge Q _OFF 。

the time t2 is the initial time of the first accumulated charge, and the circuit releases the reset state to accumulate dark current in the junction capacitor C of the receiving tube _PD Charge is formed on the charge, and the accumulated time between the time T2 and the time T3 is T _OFF The charge amount accumulated in the period is Q _OFF The third row in the figure is represented by a small slope. At this time, the light emitting tube LED is in the off state, and the second row in the drawing is indicated by a dotted line, and the charge of the receiving tube continuously rises under the dark current, and at the same time, the voltage of the receiving tube also rises gradually. The times T1 and T2 may be closely related, depending only on the reset time, the accumulation time T between T2 and T3 _OFF Is a programmable, controllable timing for the processor. For example, if the time control precision of the processor is 1uS, then the processor set to 10 represents a time of 10uS. Such circuit timing is also well suited for state machine operation of integrated circuits, with programmable time intervals.

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

Immediately after t3 is completed, the switch SW1 is turned on at time t4, and the charge Q accumulated on the receiving tube PD at this time _PD The formed voltage can be obtained by a signal acquisition circuit at the back endThe voltage of the receiving tube is collected at the time t5 and is recorded as V _OFF 。

S7: the switch SW1 is closed, the signal acquisition circuit and the receiving tube are reset, and after the reset is finished, the switch SW1 is opened.

Similar to step S4, SW1 and the back-end circuit remain closed during reset; the time T6 is the starting time of the sampling period T2, the time T7 is the reset time of the whole system, the circuit of the whole system is reset at the moment, the acquisition circuit is reset, and the receiving tube clears the charge. After these operations are completed, the signal acquisition circuit connecting switch SW1 to the back end is disconnected in preparation for subsequent charge accumulation.

S8: turning on the luminous tube, entering a small-range weak signal detection mode, and monitoring the state of thin or small particle smoke in the region to be tested in real time;

assuming that the driving current of the luminous tube is ILED, the signal current generated by the scattering of particles under the irradiation of the luminous tube continuously accumulates to the junction capacitance C of the receiving tube _PD Applying;

ILED _MIN For driving the luminous tube to minimum current _MIN The value is as follows: the design of each circuit allows the lowest driving current and the LED device of the luminous tube allows the larger value of the minimum driving current;

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 。

The background, namely a smokeless background signal, refers to an optical pollution signal caused by self reflection of a labyrinth mechanism when no smoke enters the detector labyrinth when a luminous tube is turned on or lighted, and the smaller the signal, the better the signal, and particularly the application scene sensitive to the background signal is disclosed by the application. Generally, the background is measured by the method of determiningWhen no smoke exists in the maze, the luminous tube is opened, the data of the receiving tube is collected, the ideal measurement result is zero, but the ideal measurement result is probably not, and the background can be increased along with the increase of the power of the luminous tube. In the application, in order to meet the requirement of a charge accumulation method in a small-range weak signal detection mode, the influence of the background reflection light of the maze is minimized, so that a low-current driving part of a light emitting diode is used to test the background effect in a stable smoke detector maze, the current of a light emitting tube is tested from large to small, the value of a received photocurrent is observed at the same time, and when the light emitting tube is lightened, the current of the receiving tube synchronously measured is smaller than the range of a 1% signal acquisition circuit and recorded as the maximum allowable current ILED _MAX On this basis by reducing the drive current until the background signal is eliminated. Wherein the minimum current allowed by the specification and the luminotron driving circuit is recorded as ILED _MIN ，ILED _MAX ≥ILED _MIN . In the opposite ILED _MAX In order to perform the test, if the ILED falls to ILED _MIN The background current less than 1% of the acquisition circuit range is still not satisfied, and the optical design of the maze needs to be improved. The application reduces local signal by reducing drive current until background signal is eliminated, but everything has two sides, scattered light is weaker as light emitting current is smaller, and light current is weaker, so that detection circuit needs higher sensitivity and lower noise, and weak current detection with extremely low noise is facilitated by adopting charge accumulation method. Therefore, in the technical scheme of the application, the method for detecting weak photoelectric current by eliminating background and charge accumulation is complementary.

S9: the time point at which the light emitting tube is turned on and SW1 is turned off is recorded as: measuring the starting time;

starting with the measurement start time, when the measurement duration reaches T _ON And when the SW1 is opened, the accumulated charges on the receiving tube are connected into the signal acquisition circuit. For ease of calculation, T is generally made _ON ＝T _OFF 。

In the measuring process, the driving current of the luminous tube is ILED, and the generated signalThe current is continuously accumulated on the junction capacitance of the receiving tube, and the accumulated time is T _ON The accumulated charge is Q _ON 。

At time t8, which is the start time of the second accumulated charge, the circuit releases the reset state and accumulates the signal current to the junction capacitance C of the receiving tube _PD Charge is formed on the charge, and the accumulated time between the time T8 and the time T9 is T _ON The charge amount accumulated in the period is Q _ON The third row in the figure is indicated by a large bump. At this time, the light emitting tube LED is in a lighting state, and the second row in the figure is indicated by a solid line, and the charge of the receiving tube continuously rises under the perfusion of the signal current, and at the same time, the voltage of the receiving tube also rises gradually. The times T7 and T8 may be closely related, depending only on the reset time, the accumulation time T between T8 and T9 _ON Is programmable. For example, if the time control precision of the processor is 1uS, then the processor set to 10 represents a time of 10uS. In general, T _ON And T _OFF Having the same time control accuracy and programming duration ensures that the accumulated charge and extremely voltage for both time periods can be directly subtracted. Because of the equivalent capacitance C of the receiving pipe PD _PD Small, so the time control accuracy needs to be as high as possible, typically on the order of 1uS, sub uS or nS. Such circuit timing is also well suited for state machine operation of integrated circuits, with programmable time intervals.

S10: voltage V of receiving tube is measured based on signal acquisition circuit _ON 。

Immediately after t9 is finished, the switch SW1 is turned on at the time t10, and the voltage of the receiving tube is acquired at the time t11 by the signal acquisition circuit at the rear end and is recorded as V _ON 。

S11: calculating charge Q accumulated on measurement receiving tube _PD And a signal current I received by the receiver _PD ；

Q _PD ＝Q _ON -Q _OFF ；

I _PD ＝Q _PD /T _ON 。

the data acquisition process at times t5 and t11 is generally fast, represented by narrow pulses in the figure. Labyrinth structure inside smoke detectorCan provide a darkroom effect, i.e. no external ambient light is incident on the receiving tube under the condition of no lighting of the luminous tube, and the accumulation time T _OFF The generated charge Q _OFF All contribute to dark current, and the accumulated time T is when the luminous tube is lighted _ON The generated charge Q _ON Is the sum of the signal and dark current. Therefore, the method also comprises a receiving tube dark current calibration method:

in practical application, the receiving tube dark current calibration method 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 Which is the junction capacitance of the receiver tube.

The dark current of the receiver tube PD is always present, in particular as a function of temperature, the higher the temperature the greater the dark current, and possibly the greater the photocurrent to be detected, so that calibration of the dark current is a necessary step, in particular for scenes detected for weak light signals. The dark current of the receiver tube PD is thus also part of the background signal and can be calibrated out at one time during the calibration process.

The steps just describe logical relationships, and actual operations may be different steps in a free combination.

Besides a small-range weak signal detection mode of rarefaction or small-particle smoke detection, the application also provides a large-range signal detection mode, namely a conventional detection mode, and a function of switching the small-range weak signal detection mode and the large-range signal detection mode, so that the requirements of small-range weak signal detection and large-range large-signal detection are met.

The entering mode of the wide range signal detection mode comprises the following steps.

a1: a detection circuit for a conventional smoke test is provided.

This application disclosesThe detection circuit of the conventional smoke test in the application is as follows: referring to fig. 2, the switch SW1 is turned on, and the receiving tube is directly connected to the back-end signal acquisition circuit through the switch SW 1. The method uses a general acquisition circuit for signal detection. Taking a transconductance amplifier as an example, it can directly convert the input signal current into voltage V _ON ＝-I _PD ×R _TIA RTIA is a transconductance resistor, which inputs current signal I _PD Converted into a voltage signal V _ON The transconductance amplifier operates in an inverse amplification mode and is therefore preceded by a negative sign.

The voltage when the receiving tube is saturated is recorded as VSA, and when the receiving tube is saturated, more illumination cannot cause voltage change, so that corresponding charges cannot be increased;

the saturated charge corresponding to the saturated voltage VSA is denoted as QSA, so the QSA may be an experimental value or estimated from the open circuit voltage and junction capacitance of the receiver tube specification;

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

Because the circuit based on FIG. 2 cannot directly measure the charge Q on the receiving tube _ON By measuring the corresponding voltage V _ON ＝Q _ON /C _PD Obtain T _ON Is the threshold value of experimental calibration, and V can be obtained in saturation in the experimental process _ON Is a maximum value of (a).

then tc is decreased to 0<tc<T _ON 。

For example: in this embodiment, tc is adjusted to 0.6XT _ON <tc<0.9×T _ON The accumulated charge is again tested for values within the range, if V is obtained _ON If the value is still the maximum value VSA, the accumulated charge of the receiving tube is saturated and exceeds the detection range of the weak signal with a small range; switching the circuit to a detection circuit for conventional smoke testing, and performing a wide-range detection mode; if V is _ON Is also a proportional decrease in the number of the elements,the accumulated time T is updated _ON ＝T _OFF ＝tc。

the circuit for detecting the conventional signal in the application comprises the following steps: 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.

In the method, the method for switching from the wide-range signal detection mode to the small-range weak signal detection mode comprises the following steps: when the detection is performed by adopting a wide-range detection mode, and no data change is found in the past period, the detection mode is switched to a small-range weak signal detection mode, but if the saturation problem still occurs after the detection is switched to a small-range weak signal monitoring state, the threshold value TH is larger, the TH value is reduced by a certain proportion, and then the wide-range signal detection mode is continuously used, so that the system is prevented from repeatedly switching the detection mode to be deadlocked.

The method specifically comprises the following steps.

wherein the number of samples n is correlated with the monitored time t, depending on the detected data output rate ODR. For example, if odr=2 Hz, the acquisition time t=5s for the acquired samples, then the number of samples n=10 obtained during the acquisition time t. In specific implementation, the number of samples n under the conditions that t is more than or equal to 5s and n is more than or equal to 5 is satisfied, and the ODR is a natural number depending on the ODR.

The range switching threshold TH is the charge number or the voltage number of the monitored object, and is generally a voltage signal to be measured due to the linear relationship between the charge number and the voltage number, TH refers to the minimum distinguishable voltage, and is generally 1% or less of the full range input by the detection circuit, and is less than the value, so that the detection is difficult to use a traditional detection method or the resolution is very low.

Confirming measured values of monitoring objects corresponding to the continuous n samples;

otherwise, step b4 is performed.

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

after step b3 is performed, an anti-lock measure is also required.

The anti-lock measure comprises the following steps:

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

According to the application, the problem of deadlock of the state machine caused by the fact that the TH initial value is set too high and the detection range of the weak signal with a small range is exceeded and the detection mode with a large range is returned is avoided through anti-deadlock measures.

In this embodiment, a transconductance amplifier is used to provide a wide range signal measurement, i.e., conventional signal detection. If the signal obtained by the conventional signal detection is unchanged, the method can be switched to a small-range weak signal detection mode to detect small particles and thin smoke.

The application adopts low driving current to drive the luminous tube, the light power conversion efficiency of the low driving current is higher, which is beneficial to reducing or eliminating the internal light pollution and simultaneously avoids the saturation of the receiving circuit. The method of 'exposure' is adopted for weak light detection. Similar to the principle of shooting starry sky weak light by prolonging exposure time of a single-lens reflex camera, a receiving tube is disconnected from a receiving circuit in the process of 'exposure', and the receiving tube is not connected with the receiving circuit Operational amplifier, thereby enabling the photoelectrons to have junction capacitance C at the receiving tube PD itself _PD Accumulated on the upper surface. Accumulate sufficient charge Q _PD Then, the voltage V of the receiving tube _PD ＝Q _PD /C _PD When receiving the tube voltage V _PD When the signal is raised to a detectable range, the signal acquisition circuit at the rear end can be connected for data acquisition. To accumulate all photocurrent at C _PD In this way, the leakage current of the receiving tube PD is prevented from depending only on the analog switch SW1 connected to the back-end circuit, which reduces the complexity of the design of the back-end system and the cost of the device, since the signal is only collected at the moment when the switch SW1 is turned on, and is not always connected to the detection. The method of detecting weak light signals using the method of accumulating charge "exposure" of the receiver tube PD is greatly affected by the dark current of the receiver tube PD itself, which is in turn dependent on the environment, particularly the temperature, and thus calibration of the dark current is also a problem to be considered. Since the labyrinth and optical design of the smoke detector itself easily ensures that there is no disturbance of the external ambient light, the interior of the labyrinth resembles the effect of a dark room when the light emitting tube is turned off. The influence of the dark current is just calibrated by subtracting the data of T1 from the data of T2 through at least two periods, namely a period T1 of closing the luminous tube to detect the dark current and a period T2 of opening the luminous tube to detect the signal, and the method is a universal ambient light elimination technology, but is quite suitable in combination with a charge accumulation method of 'exposure' of the natural environment of the maze design. According to the technical scheme, the method combining the small-range weak signal detection and the large-range large-signal conventional signal detection is adopted, so that the problem of insufficient range of the quasi-compensation accumulated charge method is solved, a conventional detection mode can be compatible, and the method can be regarded as expansion of the conventional mode. Meanwhile, the conventional mode is not necessary to be entangled in a zero background design due to enough measuring range, and the detection of weak signals with small measuring range is very sensitive, so that the driving current of the luminous tube is required to be reduced and the charge accumulation method is matched. Thus, the present application allows for a compromise between performance and cost and a balance in terms of practical use scenarios and methods of applying pain points to improve existing solutions.

Claims

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:

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;

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 ；

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;

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 ；

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 ；

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:

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;

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

then tc is decreased to 0<tc<T _ON ；

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:

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:

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

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.