JP2000180360A - Gas analyser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply perform extinction necessary for the span calibration of a analyser. SOLUTION: The rotary speed of a motor 7 is controlled through a motor control part 13 by the indicating signal from a CPU control circuit 11 and the rotary speed of the rotary sector 8 having an optical chopper function driven by the motor 7 is made variable to provide extinction function with respect to the dose of infrared rays emitted from a light source 1. A detection signal at the time of the introduction of zero gas is stored in a memory part 12 in this extinction state. The intermittent time of an optical chopper is changed for a predetermined time and the detection signal at thigh time is set to a value at the time of extinction and a span calibration value is calculated from the ratio of the value of the detection signal at the time of span calibration using the stored span gas and the value of the detection signal at the time of extinction and accurate span calibration is performed without using the span gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the target component in the sample gas _{(NOx, SO 2, CO,} CO 2 , etc.) to a gas analyzer for measuring the concentration of.

[0002]

2. Description of the Related Art Generally, molecules composed of different atoms have a property of absorbing infrared rays having a specific wavelength, for example. A non-dispersive infrared absorption method is a method for selectively measuring the concentration of gas (gas) using this characteristic. Such a gas analyzer is used as a continuous concentration analyzer for processes or a portable concentration analyzer. Many are used.

In order to perform accurate measurement using such a gas analyzer, a zero point calibration using a zero point adjusting gas (hereinafter, referred to as a zero gas) and a span adjusting gas (hereinafter, referred to as a span gas) are usually performed. Span calibration must be performed periodically or before measurement. In particular, in the case of a portable analyzer that requires such calibration before measurement, if there are a plurality of measurement components and measurement ranges, the number of span gases is required, and it is troublesome to carry a large number of gas cylinders.
For this reason, before bringing the measuring instrument to the measurement site, the zero point and span are calibrated, their detection signals are stored, zero gas is introduced, and the mechanism for reducing the transmitted light of the sample cell is activated. The detector signal when the amount of light introduced into the detector is changed by a predetermined amount is stored. Then, at the measurement site, without using span gas, the dimming mechanism was activated,
Span calibration is performed by ratio calculation from the detection signal at that time and the stored detection signal.

FIG. 3 is a schematic diagram showing the optical system of this conventional analyzer. Infrared rays emitted from a light source 21 are supplied to a sample cell 22 by a rotating sector 28 driven by a motor 27.
Are alternately introduced into the comparison cell 23 in a pulsed manner. The infrared light transmitted through the cells 22 and 23 alternately reaches the detector 25 via the light collector 24. The comparison cell 23 is filled with nitrogen or air and does not absorb infrared light. However, when the sample gas contains the component to be measured, the sample cell 22 absorbs infrared light according to the concentration. The detector 25 is separated into two chambers, a front chamber and a rear chamber. A pressure difference proportional to the gas concentration between the two chambers is detected by the condenser membrane 26.

The infrared light transmitted through the comparison cell 23 does not absorb the infrared light in the cell and is a constant output signal, whereas the infrared light transmitted through the sample cell 22 is the infrared light generated by the component to be measured in the sample gas. , An output signal corresponding to the concentration can be detected. A zero point and a span width are set in advance from a signal at the time of introduction of the zero gas and a detection signal at the time of introduction of the span gas, and the concentration of the sample gas is calculated within the range of the span and used as an output signal of the analyzer. Also, if the brightness of the light source changes due to the temperature, etc.,
Since this effect occurs in both the comparison signal and the measurement signal, the change in the measurement signal is corrected from the change in the comparison signal so that the sensitivity does not change.

A conventional dimming mechanism for correcting the sensitivity without introducing a span gas is a mechanism for moving a light-shielding film into and out of a measurement optical path. Concentrator 24 and detector 25
In between, a light-shielding film 32 is provided which can diminish a certain amount of light from the cell and which can enter and exit freely. The light is reduced by inserting the plate-shaped light-shielding film 32 into the measurement optical path by the solenoid 31. Sensitivity correction is performed by operating the dimming mechanism and detecting a signal stored in advance when the span gas is introduced and a state where the zero gas is introduced and dimmed, and a detection signal when the zero gas is introduced and dimmed before the measurement. The span is calibrated by calculating the correction value based on the ratio.

[0007]

As described above, in the span adjustment at the measurement site, a detection signal when the span gas is introduced and a dimming state stored in advance and a detection signal when the light is dimmed at the measurement site are stored. Calibration is performed according to the ratio with the value of, but it is necessary to have a dimming mechanism that moves the light-shielding film in and out for span adjustment, and in order to ensure the reproducibility of the conventional dimming mechanism, its assembly, Since high precision is required for mounting and adjustment to the device, a great deal of labor is required. An object of the present invention is to provide a gas analyzer that solves such a problem.

[0008]

In order to achieve the above object, the present invention introduces a control mechanism capable of arbitrarily varying the intermittent time of an optical chopper, a detection signal at the time of span calibration using span gas, and introduction of zero gas after span calibration. And a storage unit for storing a detection signal when the intermittent time of light by the optical chopper is changed for a predetermined time.In the subsequent span calibration, zero gas is introduced and the intermittent time of the optical chopper is changed for a predetermined time. The span calibration value is calculated from the ratio of the value of the detection signal to the stored value, so that accurate span calibration can be performed without using span gas.

[0009]

FIG. 1 schematically shows an optical system of an infrared gas analyzer. That is, infrared rays emitted from the light source 1 are alternately introduced into the sample cell 2 and the comparison cell 3 in a pulsed manner by the rotating sector 8 driven by the motor 7 and having an optical chopper function. The infrared rays transmitted through the cells 2 and 3 alternately reach the detector 5 via the condenser 4. The comparison cell 3 is filled with nitrogen or air and does not absorb infrared light, but the sample cell 2 absorbs infrared light according to the concentration of the component to be measured when the sample gas contains the component to be measured. The detector 5 is separated into two chambers, a front chamber and a rear chamber, by a capacitor film 6, and the pressure difference between the two chambers is detected by the capacitor film 6 as an electric signal to detect a concentration value. After being converted into an electric signal proportional to the gas concentration by an amplifier 9 including an oscillator and converted into a digital signal by an analog / digital converter 10,
It is input to the CPU control circuit 11.

A CPU control circuit 11 stores data obtained by introducing zero gas and span gas in a storage unit 12, controls the rotation speed of the motor 7 via a motor control unit 13, and is driven by the motor 7. By varying the rotation speed of the rotating sector 8 having the optical chopper function, a function of reducing infrared rays emitted from the light source 1 was provided, zero gas was introduced after span calibration, and the intermittent time of light by the optical chopper was changed for a predetermined time. The data of the detection signal at the time is stored in the storage unit 12, and further, at the time of measurement, the data of the concentration of the gas to be measured is fetched, and a correction calculation is performed using the data stored in the storage unit 12 in advance. It has a function to output.

FIG. 2 graphically illustrates span calibration with a dimming system. That is, a signal at the time of span calibration performed by introducing a span gas is denoted by A0, and immediately after that, a signal obtained by introducing a zero gas and dimming is denoted by B0. These values are stored in the storage unit 12. Next, when the span calibration is performed without using the span gas, the zero gas is introduced again to reduce the light intensity. At this time, if there is no drift due to a change in the brightness of the light source 1 or contamination of the cell, the same signal B0 as the signal obtained in the previously dimmed state is obtained. The output signal at that time is B1. Even when span gas flows,
Similarly, assuming that the signal changes, AX is obtained by the following equation, and span calibration is performed using the AX signal value. AX = (A0 / B0) * B1 In the dimming method for obtaining B0 and B1, as shown in FIG. 1, a signal from the CPU control circuit 11 is transmitted to the motor control unit 13 to control the rotation speed of the motor 7. By having a mechanism, the rotational speed of the motor 7 is increased to shorten the incident time of the infrared light to the measurement cell, thereby dimming the light, thereby obtaining B0 and B1.

Although the present invention has been described above, the present invention is not limited to the above and illustrated examples, but includes various modifications. For example, if the amount of infrared light reaching the detector decreases due to contamination of the cell, etc., the intermittent time of the optical chopper is changed so as to increase the light incident time on the cell and increase the amount of light. Can reduce the sensitivity reduction that was required. Furthermore, in the above description, the infrared gas analyzer was described, but other than the infrared gas analyzer,
The present invention is also applicable to an analyzer using a principle of light absorption having a mechanism of intermittently transmitting light to a sample, for example, an ultraviolet gas analyzer.

[0013]

Since the present invention is configured as described above, even when performing span calibration simply by dimming, high-accuracy span calibration can be realized with good reproducibility, and the number of parts can be reduced. Thus, the number of steps for assembling, mounting and adjusting can be greatly reduced, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of an optical system of an analyzer according to the present invention.

FIG. 2 graphically illustrates span calibration with a dimming system.

FIG. 3 shows a schematic diagram of an optical system of a conventional analyzer.

[Explanation of symbols]

1 --- light source 21 --- light source 2 --- sample cell 22 --- sample cell 3 --- comparison cell 23 --- comparison cell 4 --- concentrator 24 --- concentrator 5- --Detector 25 --- Detector 6 --- Capacitor film 26 --- Capacitor film 7 --- Motor 27 --- Motor 8 --- Rotating sector 28 --- Rotating sector 9 --- Amplifier 29 --- Amplifier 10 --- Analog / Digital converter 30 --- Measurement control circuit 11 --- CPU control circuit 31 --- Solenoid 12 --- Storage unit 32 --- Shading film 13 --- Motor control Department

Claims (1)

[Claims] 1. A measurement cell divided into a sample cell and a comparison cell, a light source for irradiating the measurement cell with the measurement light, and a detector for alternately introducing the transmission light of the sample cell and the transmission light of the comparison cell to the detector. In a gas analyzer equipped with an optical chopper and a detector that receives the measurement light transmitted through the measurement cell, a mechanism that can arbitrarily change the light intermittent time by the optical chopper, and the detection signal and span calibration during span calibration using span gas After that, a zero gas is introduced, and a storage unit for storing a detection signal when the intermittent time of light by the optical chopper is changed for a predetermined time is provided. A predetermined time is changed, and the span calibration is performed based on the detection signal at that time, the detection signal at the time of span calibration stored in the storage unit, and the detection signal at the time of a change in the light intermittent time. Gas analyzer, characterized in that the so that.