JPH07101209B2 - Gas chromatograph self-diagnosis method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas chromatograph device for detecting the concentration of a sample gas transferred by a carrier gas by a thermal conductivity detector, and particularly to a gas chromatograph device when operating this device. The present invention relates to a self-diagnosis method of a gas chromatograph adapted to self-diagnose a conductivity detector.

[Prior Art] FIG. 4 shows a configuration of a main part of a conventional gas chromatograph apparatus of this type.

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

The conventional device uses filaments or thermistors as TCD sensors 3 and 4, and these TCD sensors 3 and 4 and resistors R1 and r1
And the 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, the 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 that the output voltage of the gain amplifier section 6 is 0V.

After that, when the sample gas 1 is transferred following the carrier gas 2, the sample gas 1 is transferred to the TCD sensor 3
Temperature is detected, and as a result, the resistance value of the TCD sensor 3 changes, the bridge circuit becomes unbalanced, and a potential difference occurs between the two input voltages of the gain amplifier section 6, and therefore the As shown in the graph, the output voltage v of the gain amplifier section 6 rises from 0V, and this sample gas 1
When it passes through the TCD sensor 3, it drops and becomes 0V again. Fifth
The graph in the figure shows the output voltage of the gain amplifier section 6 when three kinds of such sample gases are transferred to the TCD sensor 3 at a certain time interval.

[Problems to be Solved by the Invention] The above-described conventional gas chromatograph apparatus is configured by a bridge circuit, and two output terminals of this bridge circuit are directly connected to two input terminals of the gain amplifier section 6, respectively. However, if the resistance values of the TCD sensors 3 and 4 cannot be measured in the mounted state, and a zero point or span drift of the output voltage from the gain amplifier unit 6 and an abnormal voltage occur, it is determined whether the gain amplifier unit 6 is right or wrong. There is a problem that it is not possible to make a determination, and therefore it is not possible to quickly identify whether the cause of the abnormality is on the TCD sensor 3, 4 side or the gain amplifier section 6 side.

[Means for Solving the Problem] In order to solve such a problem, a gas chromatograph self-diagnosis method according to the present invention stores an initial resistance value of a TCD sensor and, when a carrier gas arrives, the TCD sensor Supply a constant current to the sensor and control it so that the output voltage value from the gain amplifier section becomes "0".
This is a method in which the resistance value of the sensor is measured, and the deterioration of the TCD sensor is detected by measuring the change with time of the resistance value of the TCD sensor based on the measured resistance value and the stored resistance value.

[Operation] Since the resistance value of the TCD sensor is measured from the constant supply current and the voltage value which controls so that the output voltage value of the gain amplifier unit becomes “0”, the resistance value can be measured in the mounted state. Therefore, even when the output voltage of the gain amplifier unit becomes abnormal, it is possible to easily specify whether the cause is the TCD sensor side or the gain amplifier unit side.

EXAMPLES Next, the present invention will be described 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 the figure, the same parts as those in the conventional configuration diagram of FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, reference numeral 10 is a thermostatic bath. Inside the thermostatic bath 10, an analyzer valve 11, a column 12 for passing a sample gas 1 and a carrier gas 2, a concentration of the sample gas 1,
That is, TCD that detects the temperature by the change of resistance value
It is composed of a sensor 13. Further, 14 is a current switching unit that switches the constant current supplied to the TCD sensor 13, 15 is an adder circuit, 16 is a baseline cancel voltage generation unit that cancels the baseline voltage, and 17 is a gain amplifier 6 gain. A gain selecting unit for switching the voltage signal by a switch, a voltage / frequency converting unit for converting a voltage signal into a frequency and transmitting it as a digital count value, a CPU for 20 and an alarm transmitting unit for 21.

Then, in order to detect the concentration of the predetermined sample gas 1, the CPU 20 first supplies the supply current to the TCD sensor 13 by switching the current switching unit 14 so as to match the detection of the sample gas 1. deep. While the carrier gas 2 is arriving at the TCD sensor 13, the TCD sensor 1
The output voltage of 3 has a constant value and is supplied to one input terminal of the adder circuit 15. This voltage signal is amplified by the gain amplifier section 6 with a predetermined gain through the adder circuit 15, and the voltage It is sent to the frequency conversion unit 18. On the other hand, in the voltage / frequency conversion unit 18, a signal having a frequency corresponding to the input voltage signal is generated, the generated frequency signal is counted, and the digital count value is calculated by the CPU 20.
Communicate to.

The CPU 20 inputs the digital count value, determines the voltage value (baseline voltage value) due to the arrival of the carrier gas 2, drives the baseline cancellation voltage generator 16, and adds only the voltage value determined above. Control to subtract from 15. Thus, since the baseline voltage is canceled during the arrival of the carrier gas 2, CP
The input voltage to U20 is set to 0V.

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

On the other hand, in the adder circuit 15, since the baseline voltage has been canceled, a voltage signal corresponding to the sample gas 1 is output, and this output voltage signal is the gain amplifier unit 6 in the same manner as described above. , Voltage / frequency converter 18
Is transmitted to the CPU 20 as a digital count value via. Then, the CPU 20 analyzes the concentration of the sample gas 1 based on the transmitted count value. When the output voltage of the gain amplifier unit 6 is low and the sample gas 1 cannot be detected, the CPU 20 controls the gain selection unit 17 to select a higher gain, and as a result, the gain amplifier unit 6 is detected. A higher voltage signal is output from the device, and the sample gas 1 can be reliably detected. In the gain selection unit 17, G1 is a switch for selecting a gain of 8 times, G2 is a switch for selecting a gain of 40 times, and G3 is 20.
A switch for selecting 0 times gain, and G0 is a switch for selecting 0 times gain.

Next, a method of measuring the resistance value R _H of the TCD sensor 13 when the gas chromatograph device is operating as described above will be described. Fig. 2 shows the resistance value R of the TCD sensor 13.
It is an explanatory view for explaining a method of measuring _H. In the figure, reference numeral 22 denotes a constant current source, which supplies a constant current I to the TCD sensor 13 by switching of the current switching unit 14, and this current value I is stored in the CPU 20 and this C
Data of the initial value of the TCD sensor 13 resistance is also stored in the PU 20. Hereinafter, a method for measuring the resistance value R _H of the TCD sensor 13 will be described.

The CPU 20 reads the output voltage V ₂ of the addition circuit 15 when the carrier gas 2 is transferred to the TCD sensor 13 as a digital count value via the gain amplifier unit 6 and the voltage / frequency conversion unit 18, and this value is “0”. A variable voltage V ₁ such that " ₁ " is generated by driving the baseline cancellation voltage generator 16. When the variable voltage V ₁ thus generated is applied to one input terminal of the adder circuit 15, the output voltage value of the adder circuit 15 becomes 0 V, and the CPU 20 outputs this output voltage value to the gain amplifier unit 6, the voltage
While reading through the frequency converter 18 for confirmation,
The voltage value corresponding to this variable voltage V ₁ is stored.

Then, at this time, the voltage value of the other input terminal of the adding circuit 15 is −V ₁ , so that in this case, the TCD sensor 1
The resistance value R _{H of} 3 can be obtained by the following formula. That is, R _H = V ₁ / I Here, the CPU 20 determines that the voltage value V ₁ and the current value I
Therefore, the resistance value R _H can be easily measured by the above calculation, and as a result, the CPU 20 causes the TCD sensor 13
When an abnormal voltage signal is input from, it is possible to identify whether the cause is the TCD sensor 13 side or the electric circuit side that inputs the voltage signal from the TCD sensor 13 and transmits it to the CPU 20.

When the resistance value of the TCD sensor 13 is measured in this way, C
The PU20 divides the measured resistance value minus the pre-stored initial resistance value by the initial resistance value, and when the divided value exceeds the pre-stored threshold value, an alarm is sent. While driving the part 21 to display an alarm, hold this alarm information inside,
During communication with the portable communicator or a host device, the held alarm information is sent to these devices.

Further, the CPU 20 divides the value obtained by subtracting the initial resistance value stored in advance from the measured resistance value by the initial resistance value,
The TCD sensor 1 calculates the rate of change of this divided value over time.
Predict the time until 3 becomes abnormal due to deterioration. That is, for example, a database of the relationship between the resistance change rate and the usage time as shown in the graph of FIG.
Calculate the time to reach the threshold value from this database, predict the time until this TCD sensor becomes abnormal (time when the resistance change rate is 5% in the example of FIG. 3), and notify the remaining time. You can also do it.

[Effects of the Invention] As described above, in the gas chromatograph self-diagnosis method according to the present invention, the resistance value of the thermal conductivity detector is set to a constant supply current and the output voltage value of the gain amplifier section is "0". It is possible to measure the resistance value of the thermal conductivity detector in the mounted state, and as a result, even if the output voltage of the gain amplifier part becomes abnormal, the cause is There is an effect that it is possible to easily specify whether is on the thermal conductivity detector side or the gain amplifier section side. Further, deterioration of the thermal conductivity detector is detected by measuring the change with time of the resistance value of the thermal conductivity detector from the initial resistance value of the thermal conductivity detector stored in advance and the measured resistance value. By doing so, there is an effect that it is possible to predict the replacement time of the thermal conductivity detector.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus to which a gas chromatograph self-diagnosis method according to the present invention is applied, FIG. 2 is a diagram for explaining this self-diagnosis method, and FIG. 3 is a use of a sensor used in this apparatus. FIG. 4 is a graph showing the relationship between time and the rate of resistance change, FIG. 4 is a block diagram of a conventional gas chromatograph apparatus, and FIG. 5 is a graph showing the gas concentration state detected by this apparatus. 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), 1
4 …… Current switching section, 15 …… Adding circuit, 16 …… Baseline cancel voltage generating section, 17 …… Gain selecting section, 18 ……
Voltage / frequency converter, 20 …… CPU, 21 …… Alarm transmitter, 22 …… Constant current source.

Claims (1)

[Claims] 1. A gas chromatograph apparatus for performing analysis by detecting the concentration of a sample gas transferred by a carrier gas based on a change in resistance value of a thermal conductivity detector, wherein a current supplied to the thermal conductivity detector is turned on. A current switching unit that is turned off, a baseline cancellation voltage generation unit that cancels a baseline voltage from the output voltage of the thermal conductivity detector, and an output of the thermal conductivity detector in which the baseline voltage is canceled A gain amplifier unit for amplifying a voltage, a gain selection unit for switching the gain of the gain amplifier unit, a voltage / frequency conversion unit for converting the output voltage of the gain amplifier unit into a digital signal, and a voltage / frequency conversion unit. And a CPU for analyzing the concentration of the sample gas by inputting the digital signal of, and storing the initial resistance value of the thermal conductivity detector. At the same time, when the carrier gas arrives, a constant current is supplied to the thermal conductivity detector so that the output voltage value from the gain amplifier unit becomes “0”. The output voltage is controlled to measure the resistance value of the thermal conductivity detector, and the change with time of the resistance value of the thermal conductivity detector is measured based on the measured resistance value and the stored resistance value. A method for self-diagnosis of a gas chromatograph, characterized in that deterioration of the thermal conductivity detector is detected.