JPH0489558A - Self diagnosis for gas chromatography - Google Patents

Abstract

PURPOSE:To facilitate the specifying of a cause of abnormality when an output of a gain amplifier section becomes abnormal by cutting off a supply current to a thermal conductivity detector to judge whether the gain amplifier section operates normally or not. CONSTITUTION:When a CPU20 inputs an abnormal digital counted value during an analysis of densities of various gases, it controls a current switching section 14 to cut off a supply current to a TCD sensor 13 and after the separation of the side of a sensor 13 from the side of an electric circuit, it judges whether a gain amplifier section 6 operates normally or not. Thus, when the generation of a zero point of an output voltage from the gain amplifier section 6, a drift of a span and an abnormal voltage are detected, where a cause of abnormality exists -- on the side of the TCD sensor 13 or on the side of the gain amplifier section 6 can be specified with ease and quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas chromatograph device that uses a thermal conductivity detector to detect the concentration of a sample gas transported by a carrier gas. The present invention relates to a self-diagnosis method for a gas chromatograph that performs diagnosis.

[Prior Art] FIG. 2 shows the configuration of the main parts of a conventional gas chromatograph apparatus of this type.

In the figure, 1 is the sample gas to be measured, 2 is the carrier gas which is the mobile phase, 3 and 4 are the concentrations of the incoming gas,
That is, a thermal conductivity detector (hereinafter referred to as a TCD sensor) detects the temperature by a change in resistance value, 5 is a constant current source that supplies a constant current to these TCD sensors, 6 is a gain amplifier section, 7 is a gain section, R1, r is a resistance, a is a gain switching signal, and ■ is an output voltage signal of the gain amplifier section 6.

The conventional device uses a filament or a thermistor as the TCD sensor 3.4, and these TCD sensors 3,
4 and resistors R1 and r in a bridge configuration as shown in FIG. 2 to detect the concentration of the sample gas 1. That is, the TCD sensor 4 always detects the carrier gas 2, and the TCD sensor 3 also normally detects the carrier gas 2. In this case, this bridge circuit is in a balanced state, and therefore no potential difference occurs between the two input voltages of the gain amplifier section 6, so the output voltage of this gain amplifier section 6 is OV.

After that, when sample gas 1 is transferred following carrier gas 2, the temperature of sample gas 1 is detected by TCD sensor 3, and as a result, the resistance value of TCD sensor 3 changes, so the bridge circuit is disabled. In equilibrium, a potential difference is generated between the two input voltages of the gain amplifier section 6,
Therefore, as shown in the graph of FIG. 3, the output voltage ■ of the gain amplifier section 6 increases from 0■, and when this sample gas 1 passes through the TCD sensor 3, it decreases to OV again. The graph in Figure 3 shows that such a sample gas
The output voltage of the gain amplifier unit 6 is shown when the voltage is transferred to the TCD sensor 3 at different time intervals.

[Problems to be Solved by the Invention] The conventional gas chromatograph device described above is configured with a bridge circuit, and the input voltage value to the gain amplifier section 6 cannot be freely set online.
If a drift in the zero point or span of the output voltage from the gain amplifier section 6 or an abnormal voltage occurs, it is impossible to determine whether the gain amplifier section 6 is correct or not, and therefore it is difficult to determine whether the cause of the abnormality is on the TCD sensor 3.4 side. Alternatively, there is a problem in that it is not possible to quickly identify whether the gain amplifier section 6 is present or not.

[Means for Solving the Problems] In order to solve these problems, the gas chromatograph self-diagnosis method according to the present invention turns off the current supplied to the TCD sensor and switches the gain of the gain amplifier section. Select each gain of the gain selection section, set the baseline cancel voltage to each value for canceling the baseline voltage from the output voltage of the TCD sensor at this selected gain, and adjust the voltage according to the set value. This method performs self-diagnosis of the gain amplifier section by reading each digital signal and comparing the difference with a value obtained by multiplying the selected gain by the difference between the respective baseline cancellation voltages.

[Operation] Since the current supplied to the TCD sensor is turned off to determine whether the gain amplifier section is correct or not, if the output of the gain amplifier section becomes abnormal, it is possible to check whether the cause of the abnormality is on the TCD sensor side or not.
Or it can be easily identified whether it is on the gain amplifier section side.

[Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an apparatus to which the gas chromatograph self-diagnosis method of the present invention is applied. In this figure, the same parts as those in the conventional configuration diagram of FIG. 2 are given the same reference numerals, and the explanation thereof will be omitted.

In FIG. 1, 10 is a constant temperature bath, and this constant temperature bath 10
Inside, there is an analyzer valve 11, a column 12 for passing sample gas 1 and carrier gas 2, and sample gas 1.
It is composed of a TCD sensor 13 that detects the concentration of , that is, its temperature, by a change in the value of resistance. Also, 14 is T
A current switching unit that switches the constant current supplied to the CD sensor 13, 15 an addition circuit, 16 a baseline cancel voltage generation unit that cancels the baseline voltage, and 17 a gain selection that selects and switches the gain of the gain amplifier unit 6. A voltage/frequency conversion unit 20 converts the voltage signal into a frequency and sends it out as a digital count value.
is the CPU.

In order to detect the concentration of a predetermined sample gas 1, the CPU 20 first supplies current to the TCD sensor 13 by switching the current switching unit 14 so as to be suitable for detecting the sample gas 1. put, and
While the carrier gas 2 is arriving at the TCD sensor 13, the output voltage of the TCD sensor 13 becomes a constant value and is supplied to one input terminal of the adder circuit 15, and this voltage signal is applied by the adder circuit 15. The signals are added together, further amplified by a predetermined gain by the gain amplifier section 6, and sent to the voltage/frequency conversion section 18. On the other hand, the voltage/frequency conversion section 18
, a signal with a frequency corresponding to the input voltage signal is generated, the generated frequency signal is counted, and the digital count value is transmitted to the CPU 20.

The CPU 20 inputs the digital count value and calculates the voltage value (baseline voltage value) due to the arrival of the carrier gas 2.
is determined, and control is performed to drive the baseline cancellation voltage generation unit 16 to subtract from the addition circuit 15 by the voltage value determined above.In this way, the baseline voltage is canceled while the carrier gas 2 is arriving. Therefore, the input voltage to the CPU 20 is set to O■.

After that, when the sample gas 1 is transferred onto the TCD sensor 13, the resistance value of the TCD sensor 13 changes more than when the carrier gas 2 arrives, and as a result, the output voltage from the TCD sensor 13 also changes. The signal becomes large and is sent to one input terminal of the adder circuit 15.

On the other hand, since the baseline voltage has been canceled in the adder circuit 15, a voltage signal corresponding to the sample gas 1 is outputted, and this outputted voltage signal is sent to the gain amplifier section 6 as described above. ．． It is transmitted to the CPU 20 as a digital count value via the voltage/frequency converter 18.

Then, the CPU 20 performs concentration analysis of the sample gas 1 based on the transmitted count value.

Further, when the output voltage of the gain amplifier section 6 is low and it becomes impossible to detect the sample gas 1, a higher gain is selected by controlling the gain selection section 17 by the CPU 20, and as a result, the gain amplifier section 6 Since a higher voltage signal is output from the sample gas 1, the sample gas 1 can be reliably detected. Note that 01 in the gain selection section 17 is a switch that selects a gain of 8 times, G2 is a switch that selects a gain of 40 times, G3 is a switch that selects a gain of 200 times, and GO selects a gain of 0 times. This is a switch to

During concentration analysis of various gases performed in this way, abnormal voltage signals, that is, abnormal digital count values, are detected by CP.
When U20 is input, in order to identify whether the cause is on the TCD sensor 13 side or on the electric circuit side that transmits the voltage signal from the TCD sensor 13 to the CPU 20, the CPU 20 first changes the current switching. The electric circuit side and the TCD sensor 13 side are separated by controlling the section 14 to turn off the current supplied to the TCD sensor 13.

Next, the CPU 20 controls the gain selection section 17 to close the switch G1 that selects the 8x gain, and drives the baseline cancellation voltage generation section 16 to set the baseline cancellation voltage to V. , then inputs the count value from the voltage/frequency converter 18 and stores this count value VFC1. After that, set the baseline cancellation voltage to ■
2, re-input the count value from the voltage/frequency converter 18, and store this count value ■FC2. Next, the CPU
20 determines whether the difference between these count values (VFC2-VFCl) is equal to G (V2 Vl). In addition,
Here, G represents a gain and is "8" in this case. In this way, if these two values are equal, the electric circuit side is normal and it is determined that an abnormality has occurred on the TCD sensor 13 side, and if both values are not equal, it is determined that an abnormality has occurred on the electric circuit side. It is determined that there is.

When such a test is completed, the CPU 20 then closes the switch G2 for selecting the next gain, performs the same test as above, and then sequentially selects G3. The same test is performed with the GO closed.

[Effects of the Invention] As explained above, the gas chromatograph self-diagnosis method according to the present invention determines whether the gain amplifier section is correct or not by turning off the supply current to the thermal conductivity detector. When a drift in the zero point or span of the output voltage from the output voltage or the occurrence of an abnormal voltage is detected, it is easy and quick to determine whether the cause of the abnormality is on the thermal conductivity detector side or on the gain amplifier side. There is an effect that it can be done.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an apparatus to which the gas chromatograph self-diagnosis method according to the present invention is applied, Fig. 2 is a block diagram of a conventional gas chromatograph apparatus, and Fig. 3 is a state of concentration of gas detected by this apparatus. This is a graph showing. 1...Sample gas, 2-...Carrier gas, 6
...-gain amplifier section, 10... constant temperature bath, 11.
...Analyzer valve, 12...Column, 13.
...Thermal conductivity detector (TCD sensor), 14...
Current switching unit, 15...addition circuit, 16...baseline cancel voltage generation unit, 17...gain selection unit, 18-...voltage-frequency conversion unit, 20...-
cpu. Patent applicant Yamatake Honeywell Co., Ltd.

Claims (1)

[Scope of Claim] A gas chromatograph device that performs analysis by detecting the concentration of a sample gas transported by a carrier gas by a change in the resistance value of a thermal conductivity detector, comprising: a current supplied to the thermal conductivity detector; a current switching unit that turns on and off; a baseline cancellation voltage generation unit that cancels a baseline voltage from the output voltage of the thermal conductivity detector; and a baseline cancellation voltage generator that cancels the baseline voltage of the thermal conductivity detector. A gain amplifier section that amplifies the output voltage, a gain selection section that switches the gain of the gain amplifier section, a voltage/frequency conversion section that converts the output voltage of the gain amplifier section into a digital signal, and a voltage/frequency conversion section. a CPU that analyzes the concentration of the sample gas by inputting digital signals from the thermal conductivity detector, and turns off the current supplied to the thermal conductivity detector;
Select each gain of the gain selection section, set the baseline cancellation voltage at the selected gain to each value, read the digital signals corresponding to the set values, and calculate the difference and the selected value. A self-diagnosis method for a gas chromatograph, characterized in that the self-diagnosis of the gain amplifier section is performed by comparing the obtained gain multiplied by the difference between the respective baseline cancellation voltages.