CN209513532U - A kind of laser dust monitor that dark current automatically removes - Google Patents

Abstract

A laser dust meter for automatic removal of dark current, including a laser tube, a constant light power drive circuit, an oscillation circuit, a PIN diode, an I-V conversion circuit, a voltage amplification circuit, an analog switch, a low-pass filter, and a signal acquisition and processing display circuit. The oscillating circuit generates a square wave signal with a duty cycle of 50%, which controls the constant light power drive circuit to drive the laser tube to emit laser light periodically; at the same time, the analog switch is controlled to switch the polarity of the received signal, thereby realizing the automatic elimination of dark current. The utility model eliminates the measurement error caused by the change of dark current caused by the change of working conditions such as working temperature and working voltage through the dark current automatic removal circuit, and ensures the measurement accuracy of the laser dust meter; it also eliminates the need for long-time work The measurement error caused by the change of the dark current caused by the change of the performance of the photodiode prolongs the service life of the laser dust meter; the accuracy of the laser dust meter is higher, the stability is better, and the service life is longer.

Description

A laser dust meter for automatic removal of dark current

technical field

The utility model relates to the field of dust monitoring, in particular to a laser dust meter for automatic removal of dark current.

Background technique

Dust is a kind of solid particles that can exist in the air in the form of floating for a long time. Dust can cause lung disease, skin infection, cancer and other diseases, seriously affecting people's health. The dust discharged outside the factory building will also pollute the environment outside the factory area, affect the health of residents around the factory area, and affect the production of agriculture, forestry, and animal husbandry. In recent years, air pollution has become more serious, and dust pollution is also a very important factor. As people's requirements for production and living environment are getting higher and higher, people are paying more and more attention to environmental protection. The monitoring and control of dust is also paid more and more attention.

The dust detector is a special instrument used to detect the concentration of dust in the air. In practical applications, there are usually three commonly used dust detection methods: weighing method, laser method and induction method.

The laser method measures the dust concentration by measuring the attenuation or scattering of the laser light passing through the measured air containing dust. The higher the dust concentration, the stronger the attenuation and scattering.

Most of the existing laser dust meters adopt the continuous driving mode, and there is an inevitable problem that the dark current changes with the fluctuation of the working temperature and working voltage. As the working time increases, the performance of the receiving photodiode changes and the dark current increases, which leads to an increase in the error of the measurement result.

How to reduce the influence of dark current, so as to reduce the measurement error and prolong the service life of the dust meter, is one of the problems that the laser dust meter needs to solve at present.

Contents of the invention

The purpose of the utility model is to provide a laser dust meter with automatic dark current removal for the defects of the existing laser dust meter, so as to reduce measurement errors and prolong the service life of the dust meter.

For realizing the above object, the utility model adopts the following technical solutions:

A laser dust meter for automatic removal of dark current, comprising a laser tube and a receiving device for receiving laser light emitted by the laser tube; it is characterized in that:

The output of the receiving device is connected to an I-V conversion circuit to convert the output current signal into a voltage signal;

The output of the I-V conversion circuit is connected to a voltage amplifier circuit to amplify the output voltage signal;

The output of the voltage amplifying circuit is simultaneously connected to a positive input terminal and a negative input terminal of an analog switch;

The analog switch is connected to an oscillating circuit, and the positive input terminal and the negative input terminal of the analog switch are controlled to be connected through the output of the oscillating circuit; the output of the analog switch is connected to a low-pass filter;

The output of the low-pass filter is connected to the signal acquisition and processing display circuit;

The signal collection processing display circuit is used to collect the output signal of the low-pass filter, and the output shows the dust concentration;

The oscillating circuit is connected to the constant light power drive circuit at the same time, and the output of the constant light power drive circuit is controlled by an oscillation signal;

The output of the constant light power drive circuit is connected to the laser tube, so that the laser tube periodically emits laser light.

It is further characterized in that: the oscillating circuit outputs a square wave.

Preferably: the square wave is a square wave with a duty cycle of 50%.

The laser tube is a laser diode with a wavelength of 650nm and a maximum power of 10mW; the oscillating circuit is built with an NE555 integrated chip; the receiving device is a S1226-44BK PIN diode; the analog switch is a CD4053 chip; the low-pass filter is RC filter.

The utility model outputs the oscillation signal through the oscillation circuit and simultaneously controls the laser tube to periodically emit laser light and switch the analog switch, so that the dark current and normal current signals are superimposed on the low-pass filter, thereby offsetting the influence of the dark current. Reduce the measurement error caused by dark current changes due to fluctuations in operating temperature and operating voltage; at the same time reduce the measurement error caused by the performance change of the receiving device due to long-term work, thereby prolonging the service life of the dust meter.

Description of drawings

Figure 1 is a schematic diagram of the principle of the utility model.

Detailed ways

As shown in FIG. 1 , a laser dust meter for automatic removal of dark current includes a laser tube 1 and a PIN diode 23 for receiving laser light emitted by the laser tube 1 .

The output of the PIN diode 23 is connected to the I-V conversion circuit 24 to convert the output current signal into a voltage signal.

The output of the I-V conversion circuit 24 is connected to the voltage amplifying circuit 25 to amplify the output voltage signal.

The output of the voltage amplifying circuit 25 is simultaneously connected to the positive input terminal and the negative input terminal of an analog switch 26 .

The analog switch 26 is connected to an oscillating circuit 22 , and the positive and negative input terminals of the analog switch 26 are controlled to be connected by the square wave signal output by the oscillating circuit 22 ; the output of the analog switch 26 is connected to a low-pass filter 27 .

The output of the low-pass filter 27 is connected to a signal acquisition, processing and display circuit 28 .

The signal collection, processing and display circuit 28 is used to collect the output signal of the low-pass filter 27, and the output shows the dust concentration.

The oscillating circuit 22 is connected to the constant light power drive circuit 21 at the same time, and controls the output of the constant light power drive circuit 21 through a square wave signal.

The output of the constant optical power drive circuit 21 is connected to the laser tube 1, so that the laser tube 1 periodically emits laser light.

Preferably: the laser tube 1 adopts a laser diode with a wavelength of 650nm and a maximum power of 10mW. The oscillating circuit 22 can be constructed using an NE555 integrated chip. PIN diode 23 adopts S1226-44BK. The analog switch 26 can be implemented using a CD4053 chip. The low-pass filter 27 can be implemented using resistance-capacitance filtering. The square wave signal is a square wave with a duty cycle of 50%.

When the utility model is working, the oscillating circuit 22 generates a square wave signal with a duty ratio of 50%, and the constant light power drive circuit 21 is turned off at low level, the laser tube 1 does not emit laser light, and the analog switch 26 is connected to the negative output terminal at the same time. At this time, the PIN diode 23 does not receive light, and the dark current signal of the PIN diode 23 is output after passing through the I-V conversion circuit 24 and the voltage amplifying circuit 25 , and the dark current signal is reversely connected to the low-pass filter 27 . When the level is high, the constant optical power drive circuit 21 is turned on, the laser tube 1 emits laser light, and the analog switch 26 is connected to the positive output terminal at the same time. At this time, the PIN diode 23 receives the scattered light, and the normal current signal of the PIN diode 23 is output after passing through the I-V conversion circuit 24 and the voltage amplifying circuit 25 , and the normal current signal is forwardly connected to the low-pass filter 27 . The dark current and normal current signals are superimposed on the low-pass filter 27 by switching back and forth, thereby canceling the influence of the dark current.

Claims (4)

1. A laser dust meter for automatic removal of dark current, comprising a laser tube and a receiving device for receiving said laser tube emitting laser light; it is characterized in that: The output of the receiving device is connected to an I-V conversion circuit to convert the output current signal into a voltage signal; The output of the I-V conversion circuit is connected to a voltage amplifier circuit to amplify the output voltage signal; The output of the voltage amplifying circuit is simultaneously connected to a positive input terminal and a negative input terminal of an analog switch; The analog switch is connected to an oscillating circuit, and the positive input terminal and the negative input terminal of the analog switch are controlled to be connected through the output of the oscillating circuit; the output of the analog switch is connected to a low-pass filter; The output of the low-pass filter is connected to the signal acquisition and processing display circuit; The signal collection processing display circuit is used to collect the output signal of the low-pass filter, and the output shows the dust concentration; The oscillating circuit is connected to the constant light power drive circuit at the same time, and the output of the constant light power drive circuit is controlled by an oscillation signal; The output of the constant light power drive circuit is connected to the laser tube, so that the laser tube periodically emits laser light. 2. The laser dust meter for automatic removal of dark current according to claim 1, characterized in that: the oscillation circuit outputs a square wave. 3. The laser dust meter for automatic removal of dark current according to claim 2, wherein the square wave is a square wave with a duty cycle of 50%. 4. The laser dust meter for automatic removal of dark current according to any one of claims 1-3, characterized in that: the laser tube is a laser diode with a wavelength of 650nm and a maximum power of 10mW; the oscillation circuit is built with an NE555 integrated chip ; The receiving device is a S1226-44BK PIN diode; the analog switch is a CD4053 chip; the low-pass filter is a resistance-capacitance filter.