CN103983616A - Transmission type visibility measurement device and system linear dynamic range expansion method - Google Patents

Abstract

The invention provides a transmission type visibility measurement device which is high in long-term reliability and capable of accurately measuring the visibility, and a system linear dynamic range expansion method. The device can be used for expanding the system dynamic range by combining an optical attenuation piece and a motor, so that the noise change influence caused by the change of feedback resistance can be eliminated, the problem of system output caused by detector saturation can be solved, and the system detection performance is improved; compared with a method of changing the size of an aperture, the system linear dynamic range expansion method does not change the distribution of light spots on a photoelectric detector. The device comprises a transmitting part and a detecting part, wherein the detecting part comprises a receiving unit, a photoelectric signal processing unit, a data acquisition unit and a computer unit; the receiving unit comprises a light receiver, a condensing lens and the photoelectric detector; the device is characterized in that the receiving unit also comprises an attenuation piece unit which is arranged between the light receiver and the condensing lens.

Description

Transmissive visibility measuring device and method for extending linear dynamic range of the system

Technical field:

The invention designs an optical radiation receiving and measuring device, in particular a transmission type atmospheric visibility measuring device. A device and method for automatically extending the linear dynamic range of a system for the measurement of extinction coefficient when optical radiation energy propagates in the atmosphere.

Background technique:

Visibility is one of the important meteorological elements. Its measurement can be applied to meteorology, aviation, navigation, road traffic and other departments, and it also has an important impact on laser communication and image transmission. Visibility measurement mainly includes scattering method, transmission method, visual method, etc., and transmission method is a strictly defined visibility measurement method. The core problem of visibility measurement is the measurement of atmospheric extinction coefficient, which is equal to the sum of absorption coefficient and scattering coefficient. For the transmissive visibility meter, when the emitted light intensity of the transmitter and the baseline are fixed, the extinction coefficient can be obtained from the received light intensity and emitted light intensity detected by the receiver, and the atmospheric visibility value can be retrieved according to the extinction coefficient. In the scattering method, the wavelength of light outside the atmospheric absorption region is selected, and the scattering coefficient in a certain direction is used to represent the total scattering coefficient during the beam transmission process, and the scattering coefficient is regarded as the atmospheric extinction coefficient.

The dynamic range of the system refers to the range of signal variation at the input terminal of the receiver when it can be detected normally. The lower limit of the dynamic range is limited by the sensitivity of the receiver, which is limited by the equivalent noise level at the input of the receiver without signal processing; the upper limit is limited by the specified value of amplifier overload saturation or nonlinear distortion of the waveform. Only the light intensity value measured within the dynamic range of the receiving system can calculate the accurate visibility. The dynamic range of the visibility meter is very important for its measurement, so expanding the dynamic range of the instrument has certain practical significance. At present, the existing practice is to use automatic gain control (AGC) technology to expand the dynamic range of the receiver, and the specific implementation method is to change the feedback resistance of the preamplifier. However, the electronic noise of the feedback resistor has a great influence on the measurement of the system, and the automatic gain control technology cannot improve the nonlinear response or saturation problem of the photodetector.

Invention content:

The purpose of the present invention is to provide a device with high long-term reliability and accurate visibility measurement. The device uses the combination of optical attenuation sheet and motor to expand the dynamic range of the system, eliminates the influence of noise changes caused by feedback resistance changes, and solves the problem of The system output problem caused by device saturation improves the detection performance of the system.

Another object of the present invention is to provide a method for extending the linear dynamic range of the system.

The purpose of the present invention is achieved through the following technical solutions:

A transmission type visibility measuring device, which includes a transmitting part and a detecting part, the detecting part includes a receiving unit, a photoelectric signal processing unit, a data acquisition unit and a computer unit, wherein the receiving unit includes a light receiver, a condenser lens and a photodetector, The receiving unit further includes an attenuation sheet unit located between the light receiver and the condenser lens.

A further design of the present invention is that the attenuation sheet unit includes a driving motor, an annular support, a glass sheet and n attenuation sheets with different attenuation rates, and the glass sheet and each attenuation sheet are evenly arranged on the circumference of the annular support in order of transmittance , the center of the annular bracket is provided with a rotating shaft, the rotating shaft is connected with the driving motor, and the motor is connected with the computer unit through the motor controller, wherein n≥2.

There are three groups of attenuating sheets, and the three groups of attenuating sheets and glass sheets are arranged at intervals of 90 degrees along the circumference of the ring support. The transmittances of the glass sheets and the three groups of attenuating sheets are T ₀ , T ₁ , T ₂ , and T _{3 ,} respectively. , where T ₀ >T ₁ >T ₂ >T ₃ , and are arranged in descending order of transmittance.

The transmittances T ₀ , T ₁ , T ₂ , and T ₃ of the glass sheet and the three groups of attenuating sheets are 96%, 75%, 50%, and 15%, respectively.

A method for extending the linear dynamic range of the system by utilizing the above-mentioned device, the method comprises the following steps:

1) The system starts, the transmitting part and the detecting part work, and the system measures the received optical signal I _Mj ;

2) When the received optical signal I _Mj ≥ I _TH , the system starts the drive motor, and switches the attenuator unit in a step-by-step decreasing manner according to the transmittance until the received optical signal I _Mj < I _TH ;

3) When the received optical signal I _Mj ≤ I _TL , the system starts the drive motor, and switches the attenuator unit in a step-by-step manner according to the transmittance until the received optical signal I _Mj >I _TL ; when the attenuator unit is switched to glass, If there is still a received optical signal I _Mj <I _TL , then keep the state of the attenuator;

Among them, I _TH is the saturation light intensity threshold of the system; I _TL is the light intensity threshold set for the low end of the system.

After the system has been adjusted above, the atmospheric visibility measurement can be carried out.

The method also includes the following steps: checking the initial position of the attenuation sheet unit when starting the system. The calibration of the initial position refers to placing the glass sheet of the attenuation unit at the initial position.

The method also includes the following step: when step 2) switches to the minimum transmittance attenuation sheet, the received light signal I _Mj is still greater than I _TH , and an alarm signal is sent.

Working principle of the present invention:

According to the provisions of the World Meteorological Organization, for meteorological visibility, the visual threshold ε = 0.02, according to Koschmieder's law, the visibility R is expressed as:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0.02</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0.02</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3.912</span>}}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

where σ is the atmospheric horizontal extinction coefficient.

For the meteorological optical range, ε=0.05, the visibility R is expressed as:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0.05</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0.05</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; 996</span>}}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

The optical schematic diagram of the transmissive visibility meter is shown in Figure 1.

According to the Bouguer-Lambert law, the atmospheric extinction coefficient σ:

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, L is the baseline length, that is, the distance between the transmitter and the receiver, I is the received light intensity attenuated by the transmission distance L, and I ₀ is the transmitted light intensity of the transmitter. According to Koschmieder's law, the calculation formula of meteorological visibility R can be obtained:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3.912</span>}\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

For transmissive visibility meters, when determining the lower limit of the visibility measurement range, in order to improve the detection of weak light signals by the receiving system, it is usually necessary to set a higher system sensitivity. However, in an environment with high atmospheric transparency and strong transmitted light, high sensitivity can easily saturate the system, which limits the dynamic range of the system and the upper limit of the visibility measurement range. Similarly, when determining the upper limit of the visibility measurement range, in order to prevent the strong light signal from saturating the system, a lower system sensitivity is usually set, but when the transparency of the atmosphere is low and the transmitted light is weak, the lower sensitivity will reduce the system’s sensitivity to weak light. The detection capability of the signal limits the lower limit of the visibility measurement range.

During the measurement, by setting the threshold of the received optical signal, when the received optical signal is lower than the threshold, the computer unit system sends a control signal, and the attenuation sheet is outside the optical path; when the received optical signal reaches the threshold, the computer unit system sends a control signal to drive the motor Rotate to switch the attenuator in the light path state. The attenuation film is used in the measurement, the transmittance of the attenuation film is set to α, the saturation threshold light intensity of the visibility measurement system is I _TH , and the maximum light intensity that the system can receive after adding the attenuation film is:

I _M =I _TH /α (5)

Known from (5), the light intensity measurement range of the system is extended by 1/α times. When the actual detection light intensity I is less than I _TH , the attenuation sheet is outside the optical path, and the light intensity I ₁ projected onto the photodetector is the actual detection light intensity I; when the actual detection light intensity I is greater than I _TH , it should be calculated by the following formula:

I=I ₁ /α (6)

Compared with the prior art, the present invention has the following advantages:

In the prior art, the automatic gain control technology is mainly used to expand the dynamic range of the system, and the multi-way switch is used to select feedback resistors with different resistance values, and the automatic adjustment of the system gain is realized through circuit feedback. When the received optical signal is weak, the system gain is increased. ; When the received optical signal is strong, reduce the system gain. However, the electronic noise of the automatic gain control technique has a great influence on the system measurement, and a strong optical signal can saturate the detector or even damage it. Compared with the method of changing the size of the aperture, the present invention does not change the distribution of light spots on the photodetector.

The invention utilizes the combination of the motor and the optical attenuation sheet to protect the photodetector to a certain extent by reducing the received light intensity, and also expands the linear range of system measurement.

Description of the drawings:

Figure 1 is the optical schematic diagram of the transmission visibility meter.

Figure 2 is a structural block diagram of the transmission visibility measuring instrument

Fig. 3 is the schematic structural diagram of the light emitting assembly of the embodiment

Fig. 4 is the structural schematic diagram of the light receiving assembly of the embodiment

Fig. 5 is a schematic structural diagram of the photoelectric detection, signal processing and acquisition electronic circuit assembly of the embodiment.

Fig. 6 is a schematic structural diagram of the attenuation unit.

Figure 7 is the output waveform diagram of the circuit without an attenuator.

Fig. 8 is a waveform diagram of the circuit output after adding an attenuation sheet (α=60%).

Fig. 9 is a circuit output waveform diagram of reducing the circuit gain by reducing the feedback resistance of the preamplifier without adding an attenuation sheet.

Figure 10 is the output waveform diagram of increasing the circuit gain only by increasing the feedback resistance of the preamplifier without adding an attenuation sheet.

Figure 11 is a diagram of the measurement results of the system without an attenuation sheet.

Fig. 12 is a diagram of measurement results of the system with attenuation sheet added (α = 60%).

Figure 13 is a diagram of the measurement results of the system without an attenuation sheet.

Fig. 14 is a diagram of measurement results of the system with attenuation sheet (α = 12%) added.

Fig. 15 is a flow chart of the main process of the system of the present invention.

Fig. 16 is a flow chart of judging the excess threshold (I _TH ).

Fig. 17 is a flow chart for judging that the value is lower than the threshold (I _TL ).

In the figure: a transmitter part, including light source and light collimator, b receiver part, including photodetector and signal processor, c baseline, d parallel detection beam; 1 installation base, 2 pillars, 3 light emitting assembly 4. Detection beam, 5. Light receiving assembly, 6. Pillar, 7. Controller box, 8. Mounting base; 9. Semiconductor light emitter drive power supply with optical power control and temperature control functions, 10. Semiconductor light emitter, 11. Detection beam alignment Straightener, 12, detection beam, 13 flat plate of optical receiver window, 14 glass window, 15 attenuation plate support, 16 servo motor, 17 condenser lens, 18 photodetector, 19 refrigerator, 20 placement substrate, 21 transmission line , 22 line interface, 23 preamplifier, 24 bandpass filter, 25 RMS converter, 26 intermediate amplifier, 27 A/D conversion, 28 computer unit, 29 data transmission interface, 30 motor controller, 31 TEC temperature control Device, 32-34 attenuation film, 35 rev pumping.

Detailed ways:

Embodiment one:

The atmospheric extinction coefficient measuring device of the present invention comprises a transmitting part a and a detecting part b, wherein the transmitting part a mainly includes a semiconductor light emitter, a driving power supply for the light emitter, and a beam collimation system; the detecting part b mainly includes a receiving unit and a photoelectric signal processing unit , a data acquisition unit and a computer unit, wherein the receiving unit includes a light receiver, a condensing lens and a photodetector, the receiving unit also includes an attenuation sheet unit, and the attenuation sheet unit is located between the light receiver and the condensing lens. The photoelectric signal processing unit includes a preamplifier circuit combination and a photoelectric signal conditioning circuit combination. The device is also provided with a transmitting system bracket, a receiving system bracket, an attenuation plate bracket and a motor, and the motor is connected with the computer unit through a motor controller.

Wherein, the attenuation sheet unit includes a drive motor, an annular support, a glass sheet and n attenuation sheets with different attenuation rates. The glass sheet and each attenuation sheet are evenly arranged on the circumference of the annular support in order of transmittance. The center of the annular support is set There is a rotating shaft, which is connected with a driving motor, and the motor is connected with a computer unit via a motor controller.

Wherein the semiconductor light emitter of the emission part a is connected to the driving power supply, and the beam collimation system is composed of an aberration-eliminating optical lens group, and the collimation system is placed at the output end of the light emitter, and after collimation, the light beam propagates a certain distance through the optical window and After the attenuation sheet reaches the light receiving probe, the receiving probe is composed of a metal cylinder, a convex lens, a photodetector and its mounting base, the convex lens is located at the front end of the receiving probe, and the light beam converges on the photodetector Above, the photodetector is located at the rear end of the receiving probe; the photodetector is combined with the preamplifier circuit, the preamplifier circuit is combined with the photoelectric signal conditioning circuit, and the photoelectric signal conditioning circuit is combined with the data acquisition unit connection, the data acquisition unit is connected with the computer unit, and the light receiving probe is installed on the light receiving assembly substrate.

The drive power supply of the illuminator can be equipped with a temperature control circuit, an optical power modulation circuit and an optical power stabilization circuit to ensure that the optical power emitted by the illuminator does not change with changes in the environment, and effectively suppress the impact of ambient light changes on the measurement. The photoelectric signal conditioning circuit combination includes a band-pass filter circuit, an amplifier and a precise effective value conversion circuit, and the data acquisition unit can use multiple synchronous sampling circuits and A/D converters.

The working process of the present invention: the semiconductor light emitter 10 emits a light pulse sequence with a frequency of 1.0 kHz under the drive of the driving power supply 9, and after passing through the beam collimator 11, it becomes a parallel beam, and after propagating a specified distance, it reaches the light receiving window 13, Through the glass window 14 or the attenuation sheet 15 on the bracket, the lens 17 converges and projects onto the photodetector 18, and the photodetector 18 converts the received optical signal into an electrical signal, and the output photoelectric signal passes through the preamplifier 23 Amplified, and then converted into a DC voltage signal through a band-pass filter 24 and an effective value converter 25, its size is proportional to the light power received by the photodetector, and then amplified by an intermediate amplifier 26, and converted by A/D 27 Entering the computer unit system 28, the average power of the optical signal received by the detector is obtained. The computer unit system 28 drives the motor 16 to rotate according to the set threshold, and sequentially switches the states of the glass windows 14 or the attenuation sheets 32-34 in the optical path; the computer unit system 28 according to the emitted optical power I ₀ , according to formula (3) and (1) or (2) or and (5) to calculate visibility.

During the measurement, the emitted light intensity of the LED light source is controlled by changing the amplitude of the modulation signal loaded to the LED light source. Set the saturation light intensity threshold of the system as I _TH , and use an attenuator with a transmittance of α=60%. According to theoretical calculations, the maximum light intensity that the system can receive is I _M =I _TH /α=1.67I _TH ; if the transmittance is used α=12% attenuation film, then I _M =8.33I _TH . The light intensity measurement range of the system is extended by 1/α times. When the light intensity projected onto the detector is higher than the set saturation light intensity threshold _ITH , the computer program controls the motor to rotate clockwise to switch the attenuation film with lower transmittance; when the light intensity projected onto the detector is lower than the low end Set the light intensity threshold I _TL , the computer program controls the motor to rotate counter clockwise, and switch the attenuation film with higher transmittance.

Embodiment two:

In this example, three groups of attenuating sheets are arranged, and the three groups of attenuating sheets and glass sheets are arranged at intervals of 90 degrees along the circumference of the annular support. The transmittance of the glass window sheet 14 is T ₀ , and for K9 glass, T ₀ is about 96%; The transmittance of the attenuating sheet 32 is T ₁ , the transmittance of the attenuating sheet 33 is T ₂ , and the transmittance of the attenuating sheet 34 is T ₃ , T ₀ , T ₁ , T ₂ , and T ₃ are arranged counterclockwise. Place one piece at every 90° position, the transmittance is T ₀ >T ₁ >T ₂ >T ₃ , and the transmittance T ₀ , T ₁ , T ₂ , T ₃ are about 96%, 75%, 50% respectively , 15%. During the measurement process, when the light intensity exceeds the range, the transmittance is gradually reduced by rotating the bracket turntable clockwise, and the received light intensity is gradually reduced. Assuming that the attenuation sheet 32-34 is not added or the glass window sheet 14 is placed in the optical path (regardless of the light energy loss caused by the reflection of the glass sheet), the range of received light intensity that the system can measure is [I _min , I _max ]; After adding the attenuation film, the range of received light intensity that the system can measure at this time [I _min /T ₁ , I _max /T ₃ ].

Embodiment two:

The main process flow of the system of the present invention is shown in Figure 15:

The main functions of the system program: (1) The system suddenly loses power during the rotation of the drive motor, and the program can correct the power-off position of the drive motor after the power is turned on again; (2) During the measurement process (the drive motor does not rotate or the rotation ends), When the system restarts after power-off, it can automatically judge the state of the attenuator in the optical path; (3) When the light intensity exceeds the threshold (I _TH ), the motor rotates clockwise to switch the attenuator in the optical path and gradually reduce the received light intensity , to expand the dynamic range of the system; (4) When the light intensity is lower than the threshold (I _TL ), the motor rotates counterclockwise to increase the filter transmittance step by step to complete the system's detection of weak light signals.

After the system is powered on, the microprocessor judges whether the driving motor is powered off during clockwise or counterclockwise rotation by reading the data from the external data memory, and corrects the power-off position. The glass sheet of the attenuation unit is at the initial position is in the optical path, and then switches the effective position of the attenuation sheet or the glass sheet of the attenuation unit in the optical path according to the received light intensity.

The block diagram of the ultra-threshold (I _TH ) judgment process is shown in Figure 16:

The attenuation unit of this method adopts the structure and arrangement of the second embodiment: in Fig. 16, K is the serial number of the attenuation sheet. K=1, corresponding to the glass window 14 ; K=2, corresponding to the attenuating sheet 32 ; K=3, corresponding to the attenuating sheet 33 ; K=4, corresponding to the attenuating sheet 34 .

Because of the transmittance T ₀ >T ₁ >T ₂ >T ₃ , when the read A/D data ≥ I _TH threshold I _TH , the drive motor rotates clockwise 90° to switch, gradually reducing the transmittance to Reduce the received light intensity until the received light signal I _Mj < I _TH , making it within the linear measurement area of the system; when the attenuator 34 is in the optical path and the A/D data still exceeds the threshold, the system sends an over-range warning signal. By switching attenuators with different transmittances, the linear dynamic range of the system is effectively expanded.

The flow chart for judging below the threshold (I _TL ) is shown in Figure 17:

When the intensity of the received optical signal is weaker than or equal to the threshold (I _TL ), the drive motor rotates counterclockwise to increase the transmittance of the received optical signal to increase the received optical signal until the received optical signal I _Mj >I _TL , making it in the system within the linear measurement range. When the received light signal is small, even if the glass sheet T ₀ is placed in the optical path, the received light signal is still lower than the threshold (I _TL ), through the design of the lower than threshold judgment program, T ₀ can always only carry out data in the optical path reading, so as not to affect the system's detection of weak signals.

Test instance:

Comparison of the effects of the two methods

Figure 7 is the output waveform of the circuit without an attenuator, the frequency is 1KHz, and the peak-to-peak value is 496mV pulse signal. Taking Fig. 7 as a reference, Fig. 8 is the circuit output waveform after adding the attenuation sheet (α=60%), and the circuit element parameters of the preamplifier are constant;

Figure 9 is the circuit output waveform without an attenuator, and the circuit gain is reduced only by reducing the feedback resistance of the preamplifier; Figure 10 is the output without an attenuator, and the circuit gain is increased only by increasing the feedback resistance of the preamplifier waveform. Generally, in order to reduce the offset noise voltage or current of the preamplifier, the circuit design of the preamplifier requires a resistance balance design for the non-inverting input and the inverting input. The preamplifier does not work optimally when only the feedback resistor is changed.

It can be seen from Figure 7 and Figure 8 that the waveform of the signal only decreases in amplitude before and after attenuation, and the waveform does not change; from Figure 7, Figure 9, and Figure 10, it can be seen that while the amplitude of the signal waveform changes, more glitch. It can be seen that adjusting the gain of the circuit through the attenuator will not introduce electronic noise, but adjusting the gain of the circuit by adjusting the feedback resistor will easily introduce more electronic noise.

Fig. 11 is without adding attenuation sheet, the measurement result diagram of the system, Fig. 12 is after adding the attenuation sheet with transmittance α=60%, the measurement result diagram of the system; Fig. 13 and Fig. 14 are when α=12%, without Diagram of measurement results with attenuation sheet and with attenuation sheet. It should be noted that Fig. 11 and Fig. 12 are the test results of the system under the same sensitivity, and Fig. 13 and Fig. 14 are the test results of the system under another same sensitivity.

It can be seen from the above test results that the present invention can effectively expand the linear dynamic range of the visibility test system, and can expand the high-end visibility test range. It is particularly noteworthy that the expansion of the dynamic range of the circuit by using the optical attenuation sheet will not introduce electronic noise, and to some extent overcome the influence of the nonlinear response or saturation of the photodetector on the measurement. Experimental results show that the method is simple and reliable. At the same time, attenuators with different attenuation rates can be selected to realize the flexible expansion of the linear dynamic range of the system.

Claims (7)

1. A transmissive visibility measuring device, which comprises a transmitting part and a detecting part, and the detecting part comprises a receiving unit, a photoelectric signal processing unit, a data acquisition unit and a computer unit, wherein the receiving unit comprises a light receiver, a condenser lens and a photoelectric detection unit The device is characterized in that: the receiving unit further includes an attenuating sheet unit, and the attenuating sheet unit is located between the light receiver and the condenser lens. 2. The transmissive visibility measurement device according to claim 1, characterized in that: the attenuation sheet unit comprises a driving motor, a ring support, a glass sheet and n attenuation sheets with different attenuation rates, and the glass sheet and each attenuation sheet are transparent The overrates are evenly arranged on the circumference of the annular support in order of magnitude, and the center of the annular support is provided with a rotating shaft, which is connected to a driving motor, and the motor is connected to a computer unit through a motor controller, wherein n≥2. 3. The transmissive visibility measuring device according to claim 2, characterized in that: the attenuation sheets are arranged in three groups, the three groups of attenuation sheets and the glass sheets are arranged at intervals of 90 degrees along the circumference of the annular support, and the glass sheets and the three groups The transmittances of the attenuators are T ₀ , T ₁ , T ₂ , and T ₃ respectively, where T ₀ >T ₁ >T ₂ >T ₃ , and are arranged in descending order of transmittance. 4. The transmissive visibility measurement device according to claim 3, characterized in that: the transmittances T ₀ , T ₁ , T ₂ , and T ₃ of the glass sheet and the three sets of attenuation sheets are 96% and 75% respectively , 50%, 15%. 5. A method utilizing the device expansion system linear dynamic range according to claim 2, the method comprising the following steps: 1) The system starts, the transmitting part and the detecting part work, and the system measures the received optical signal I _Mj ; 2) When the received optical signal I _Mj ≥ I _TH , the system starts the drive motor, and switches the attenuator unit in a step-by-step decreasing manner according to the transmittance until the received optical signal I _Mj < I _TH ; 3) When the received optical signal I _Mj ≤ I _TL , the system starts the drive motor, and switches the attenuator unit in a step-by-step manner according to the transmittance until the received optical signal I _Mj >I _TL ; when the attenuator unit is switched to glass, If there is still a received light signal I _Mj <I _TL , the state of the glass sheet is maintained; Among them, I _TH is the saturation light intensity threshold of the system; I _TL is the light intensity threshold set for the low end of the system. 6. The method according to claim 4, characterized in that: the method further comprises the following step: when starting the system, checking the initial position of the attenuation sheet unit. 7. The method according to claim 4, characterized in that: the method also includes the following steps: when step 2) the attenuation unit is switched to the minimum transmittance attenuation sheet, the received optical signal I _Mj is still greater than I _TH , then an alarm is issued Signal.