How does the time counter work? Please, great gods.

The light source is the key component of the dust particle counter, which has a great influence on the performance of the instrument. The light source requires high stability, long life and no interference. There are two kinds of light sources: ordinary light sources and laser light sources. The common light source is iodine tungsten lamp, which has large volume, high calorific value and short life, and needs preheating after starting. The laser light source is a laser with small volume, high stability and long service life. It is usually integrated with a detection cavity and a photodetector to form a sensor. Common laser light sources are HeNe laser and laser diode. The dust particle counter of ordinary light source has a very low response to the particle signal below 0.3μm, and its signal amplitude is almost the same as the noise amplitude of the counter itself, so it is difficult to detect the signal from the noise. Although this kind of instrument is marked with a channel of 0.3μm, it is only suitable for measuring particles larger than 0.3μm, especially larger than 0.5 μ m. Because of the good monochromaticity of laser, the light energy concentration is stable, and the sensor signal-to-noise ratio of the dust particle counter of laser light source is high, some of these instruments can detect particles of 0.1μ m. 3.2 The measuring cavity is a space for particle observation, and the collected air must pass through the measuring cavity. The optical system of the instrument makes the light source shine into the measuring cavity through the lens and slit, forming a photosensitive area with a volume of about several cubic millimeters. When the dust in the air passes through the photosensitive area, some light energy will be scattered, which will be collected by the condenser lens at a certain angle (90 degrees or 70 degrees) with the incident light, and then projected onto the photodetector. 3.3 Photodetector Photodetector is a photoelectric conversion device that converts scattered light energy into electrical signals. The most commonly used photodetectors in dust particle counters are photomultiplier tubes and photodiodes. The photomultiplier tube amplifies photoelectrons by tens of thousands of times and converts them into electrical signals of several millivolts to several tens of millivolts. Its advantages are good spectral linearity, fast response time, small dark current and large volume. When the photomultiplier tube works, it needs to add a negative high voltage of several hundred volts, and there is a corresponding high voltage generating circuit in the instrument. Pay attention to safety when debugging or calibrating the instrument. Photodiode is a kind of semiconductor element, which can generate electrons after being irradiated. It has the characteristics of small volume and simple peripheral circuit, and is often integrated with the detection cavity. 3.4 Flow Monitoring The sampling flow of dust particle counters is generally 2.83L/min or 28.3L/min, and imported instruments are often marked as 0. 1cfm (cubic feet per minute) or 1cfm, mainly for the convenience of calculating the cleanliness in line with Fed-Std-209E. Large flow sampling (28.3L/min) can reflect the air cleanliness more accurately, but it reduces the maximum sampling concentration. 3.5 Air pump and filter air pump are located inside the instrument, so that the instrument can generate sampling flow. Air pump requires low noise, small vibration and stable airflow. The filter should be able to filter out particles above 0.3μm, so as not to affect the clean area by the air discharged from the instrument. 3.6 Circuit System After the particles with different particle sizes are converted by the photoelectric system of the dust particle counter, electric pulse signals with different amplitudes (voltages) will be generated. The larger the particle size, the higher the pulse voltage. The relationship between signal voltage and particle size is also called conversion sensitivity. For a given dust particle counter, the particle size corresponds to the pulse voltage one by one. For example, the conversion sensitivity of a dust particle counter is 0.3μm at 69mv, 0.5μm at 53 1mv,1mv at 7010 μ m, and so on. If the dust particle counter detects a pulse of 100 millivolts, the particle size must be greater than 0.00. Dust particle counter is an instrument for measuring the number of particles greater than or equal to a certain particle size, and its internal circuit is a circuit for counting the number of pulses greater than or equal to a certain voltage value. For the example in the previous paragraph, measuring the number of particles greater than or equal to 0.3μm in the air means counting the number of pulses greater than or equal to 69mv in the circuit, and measuring the number of particles greater than or equal to 0.5μm in the circuit means counting the number of pulses greater than or equal to 53 1mv, and so on. Therefore, the measurement of dust particles by the instrument mainly depends on the parameter of conversion sensitivity. In addition, it should be noted that the conversion sensitivity of each dust particle counter is different. Before and after leaving the factory, the standard particles should be calibrated regularly to obtain the best conversion sensitivity value. The circuit system is a circuit that completes the amplification, discrimination and counting of pulse signals. In addition, it also includes power supply, control, display, calculation, printing and other circuits, and there are other kinds of/view/3cce8f8941ea76e58fa0410.html.

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