JPS6243488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved automatic calibration device for a light scattering particulate meter.

The factors that determine the sensitivity of a light scattering particle meter (the ratio between the particle size and the peak value of the detected pulse signal) are the refractive index of the particles themselves, the sensor optical system conditions (the wavelength of the light used for measurement), and the refractive index of the particles themselves. In addition to factors that are determined at the sensor design stage and do not change afterward (e.g., mechanisms that capture light scattered by particles, etc.), brightness of the light source, optical system losses (e.g., There are some things that change while using a particle meter, such as the degree of cloudiness (cloudiness), the sensitivity of the photoelectric converter, and the amplification factor of the electronic circuit, so it is necessary to check the sensitivity of the particle meter before starting measurements. be.

Normally, before a light scattering particle meter is manufactured and shipped, standard particles whose particle size and refractive index are known are separated one by one and added to the counter to calibrate the sensitivity. requires special equipment and techniques, and is not suitable as a means for users to easily calibrate.

For this reason, conventional light scattering particle counters introduce irradiated light into an optical fiber, convert the light into pulses using a rotating disk with holes (optical chopping), and then apply the light to a photoelectric converter through a condensing system. It has a built-in self-diagnosis device. According to this method, the peak value of the calibration pulse taken out from the preamplifier connected to the photoelectric converter is measured with a meter,
If you adjust it so that the instructions are the same as those at the time of manufacturing shipment,
Sensitivity calibration can be easily performed at the measurement site without having to go through the trouble of calibrating using standard particles. The internal reference light method using optical chopping is called a secondary calibration in contrast to the primary calibration using the standard particle described above.

Although the conventional secondary proofreader described above is convenient, since the proofreading is performed manually, there are problems such as meter reading errors, operational errors, or forgetting the proofreading.

This invention solves the above problem, and has the effect of automatically performing self-diagnosis and adjusting sensitivity every time immediately before starting measurement, and obtaining highly reliable measured values. be.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. In FIG. 1, light from a light source 1 such as a halogen lamp is focused and irradiated onto an irradiation area P by an irradiation lens system 2. A sample air flow 4 ejected from the nozzle 3 passes through this irradiation area P. 5 is an inhalation pipe. Scattered light caused by particulates in the sample air stream is focused by a focusing lens system 6 onto a photoelectric converter such as a photomultiplier tube 7. The measurement optical system of the conventional sensor has been described so far.

This invention uses a solenoid 8 as a calibration optical system.
A shutter 9 driven by the shutter 9 is arranged on an extension of the optical axis 2A of the irradiation lens system 2, the input end 10A of the optical fiber 10 is brought close to the shutter 9, and the output end 10
B is made to coincide with the optical axis 6A of the condensing lens system 6 and directed to the photomultiplier tube 7. Since the irradiation optical axis 2A and the condensing optical axis 6A form an appropriate angle θ (for example, 70°), the input end 10 of the optical fiber 10
The angle formed between A and the output end 10B is also made to match this θ.

In the operation of the above calibration optical system, the shutter 9 is opened by the solenoid 8 only during calibration, and the irradiation light used for measurement is applied to the photomultiplier tube 7 through the optical fiber 10. It is easy to configure so that the solenoid 8 always operates to open the shutter 9 before starting measurement.

Next, FIG. 2 shows an electronic processing section for automatic calibration, in which a reference power source 13 is connected to a pulse height discrimination circuit 12 connected to a photomultiplier tube 7 via a preamplifier 11. The output side of the pulse height discrimination circuit 12 is connected to a control terminal of an up-down counter 15 to which an oscillator 14 is connected. The digital output of the up-down counter 15 is output from the D-A converter 16.
The voltage is converted into a voltage and applied to the photomultiplier tube 7 .The voltage is applied to a voltage control section provided in the high voltage power source 17 to change the output voltage of the high voltage power source 17 .

Regarding the operation of the above configuration, when the shutter 9 is opened, a current flows through the photomultiplier tube 7 due to light passing through the optical fiber 10. This current is converted into voltage by the preamplifier 11, and the pulse height discrimination circuit 12
The voltage is compared with the voltage of the reference power supply 13. If the voltage is higher than the reference voltage value by, for example, 1% or more, a countdown command signal is issued to the up-down counter 15, and conversely, if it is lower than the reference voltage value by 1% or more, a count-up command signal is issued. The up-down counter 15 is
The pulse height discrimination circuit 12 uses the output from the oscillator 14.
According to addition and subtraction commands from
9998, etc. It has the function to change. Since the D-A converter 16 has the function of converting, for example, a digital signal of 10,000 counts into an analog quantity of 1 volt, the wave height discrimination circuit 12
When a subtraction command is issued to the up-down counter 15 from
It gradually decreases to 0.9998V... Next, this analog signal is transmitted to the voltage control section of the high-voltage power supply 17 that determines the sensitivity of the photomultiplier tube 7, and the voltage gradually decreases, and the output current of the photomultiplier tube 7 also decreases (because the sensitivity has decreased). ), and the voltage applied to the pulse height discrimination circuit 12 decreases. When this voltage falls within ±1% of the reference voltage value, the command signal from the wave height discrimination circuit 12 to the up-down counter 15 is stopped, and the up-down counter 15
continues to have the value at that point.

In this way, the calibration is completed, but all operations are performed approximately 1/100 times after the shutter 9 opens.
It finishes in about seconds. When the calibration is finished, the shutter 9
automatically closes and begins particle measurement.

The particle meter equipped with the automatic calibration device described above does not require manual sensitivity adjustment, so there is no need to provide a meter or knob for calibration on the panel surface. For example, it is sufficient to install a blue indicator light that displays "CAL" and, if this indicator light is lit, confirm that the particle meter is operating normally.

As described above, the present invention has the remarkable effect of quickly and accurately calibrating the sensitivity of a light scattering particle meter, and brings about great industrial benefits.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of the main parts of an optical system according to an embodiment of the present invention, and FIG. 2 is a block diagram of the electronic processing section. DESCRIPTION OF SYMBOLS 1...Light source, 2...Irradiation lens system, 3...Nozzle, 4...Sample air flow, 5...Suction tube, 6...Condensing lens system, 7...Photomultiplier tube, 8...Solenoid , 9...Shutter, 10...Optical fiber,
P...irradiation area.

Claims (1)

[Scope of Claims] 1. A light scattering particle meter that focuses scattered light generated by irradiating an irradiation area P of a sample air flow 4 onto a photoelectric converter 7 and counts the pulse output from the photoelectric converter 7. In the shutter 9 placed on the extension of the irradiation optical axis 2A,
an optical fiber 10 with its input end 10A brought close to it and its output end 10B directed toward the photoelectric converter 7; a pulse height discrimination circuit 12 to which a reference power source 13 is connected and to which the output of the photoelectric converter 7 is applied; and the wave height discrimination circuit. The output of the up-down counter 15 controlled by the output of 12 and driven by the oscillator 14 is
An automatic calibration device for a light scattering particulate meter, comprising a high voltage power source 17 for the photoelectric converter 7, which is controlled by a voltage control unit applied via a converter 16. 2. An automatic calibration device for a light scattering particle meter according to claim 1, wherein the shutter 9 is driven by the solenoid 8.