JPH0489560A - Correction of gas chromatography - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas chromatograph device that detects the concentration of a sample gas transported by a carrier gas using a thermal conductivity detector. The present invention relates to a gas chromatograph correction method for correcting variations in detector characteristic values.

[Prior Art] The configuration of the main parts of a conventional gas chromatograph apparatus of this type is shown in FIG.

In the figure, 1 is the sample gas to be measured, 2 is the carrier gas which is the mobile phase, 3.4 is the concentration of the arriving 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 filaments and thermistors as the TCD sensors 3 and 4, and these TCD sensors 3 and
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 an equilibrium state, and therefore Since no potential difference occurs between the two input voltages of the gain amplifier section 6, the output voltage of the gain amplifier section 6 is 0.

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. 5, the output voltage (2) of the gain amplifier section 6 rises from OV, and when this sample gas 1 passes through the TCD sensor 3, it drops and becomes OV again. The graph in Figure 5 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.

Each of the TCD sensors 3.4 has different characteristic values and there are variations between them.
In order to correct for variations in these characteristic values, each TCD sensor is calibrated by adding a standard gas different from the above-mentioned gas to each of the devices.

[Problem to be solved by the invention] The conventional gas chromatograph correction method described above is based on the TC
Since the resistance value of the D sensor and this temperature cannot be measured,
Since a standard gas is introduced into each device to calibrate variations in the characteristic values of individual TCD sensors, there is a problem in that a large amount of man-hours and expense are required.

[Means for Solving the Problems] In order to solve such problems, the gas chromatograph correction method according to the present invention calculates the rate of change in resistance with respect to temperature of the TCD sensor as a sensitivity value, and The sensitivity values obtained are retained as standard calibration data.
This method corrects variations in the characteristic values of the TCD sensor based on this calibration data.

1 Effect] Variations in the characteristic values of the TCD sensor are corrected based on the held sensitivity values.

“Example 1 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 correction method of the present invention is applied. In this figure, the same parts as those in the conventional configuration diagram of FIG. 4 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.

First, in order to detect the concentration of a predetermined sample gas 1,
The CPU 20 supplies current to the TCD sensor 13 by switching the current switching section 14 so as to be suitable for detecting the sample gas 1. Then, while the carrier gas 2 is arriving at the TCD sensor 13, the TCD
The output voltage of the sensor 13 becomes a constant value, and the output voltage of the sensor 13 becomes a constant value.
This voltage signal passes through the adder circuit 15, is further amplified by a predetermined gain by the gain amplifier section 6, and is sent to the voltage/frequency conversion section 18. On the other hand, the voltage/frequency converter 18 generates a signal with a frequency corresponding to the input voltage signal, counts the generated frequency signal, and transmits the digital count value 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 cancel pressure generating section 16 to subtract from the adding 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 Ov.

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 detection of the sample gas 1 becomes impossible, 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

Next, a method of correcting the resistance value of the TCD sensor 13 of the gas chromatograph apparatus that operates as described above will be described.

The relationship between the resistance value of the resistor used as the TCD sensor 13 and the temperature is generally approximated by the following quadratic equation, as shown in the graph of FIG.

Ra = Ro (1+aT, +b'rH2), +
111 Here, R is the resistance value [Ω] at the reference temperature,
a is the first-order temperature coefficient [1/”C], b is the second-order temperature coefficient [1
/'C2], and the temperature TWI of the TCD sensor at this time is T) I - T To ["C]. Also, assuming that the characteristic values of the TCD sensor 13 vary individually, Resistance value Ro.

Input the temperature coefficients a and b as data, and
20 to be memorized.

Next, as shown in the graph of FIG. 3, the temperature TH1 of the TCD sensor 13 corresponding to the baseline voltage, that is, the temperature T due to the arrival of the carrier gas 2, is measured. The resistance value RR at the baseline voltage must be determined using the block circuit shown in the figure.

FIG. 2 is an explanatory diagram for explaining a method of measuring the resistance value R) of the TCD sensor 13. In the same figure, 22 is a constant current source, which is controlled by switching the current switching section 14.
A constant current is supplied to the CD sensor 13, and this current value ■ is stored in the CPU 20. Addition circuit 15 when carrier gas 2 is transferred to TCD sensor 13
The output voltage ■2 of the gain amplifier section 6. It is read as a digital count value via the voltage/frequency converter 18, and the baseline canceling voltage generator 16 is driven to generate a variable voltage ■l that makes this value "0". When the variable voltage V1 generated in this way is applied to one input terminal of the adder circuit 15, the output voltage value of the adder circuit 15 is Ov
The CPU 20 outputs this output voltage value to the gain amplifier section 6. It is read and confirmed via the voltage/frequency converter 18, and the voltage value corresponding to this variable voltage V□ is stored.

At this time, since the voltage value of the other input terminal of the adder circuit 15 is -V1, the TCD in this case
The resistance value R8 of the sensor 13 can be determined by the following equation. That is, R14=vl/I...a Note that here, since the CPU 20 stores this voltage value Vl and current value ■, the resistance value R is determined by the above calculation.
H can be measured and stored.

In this way, by storing the resistance values R, , R and temperature coefficients a and b as data, it is possible to calculate the temperature TH at the baseline voltage by calculating the following equation (5). That is, it is corrected based on the formula.

or b Once the temperature TH is calculated in this way, the sensitivity of the TCD sensor 13 near the baseline voltage can be determined by differentiating equation (1). In other words, TH Once the sensitivity of the TCD sensor 13 near the baseline voltage is calculated in this way, this sensitivity value is stored as standard calibration data, and from then on, when sample gas 1 arrives, the graph shown in FIG. Measure the peak height PH or peak area PA of sample gas 1 as shown in , and calculate the peak height PH from this measurement value and the stored sensitivity value.
Or, each correction value of the peak area PA is as follows.As a result, the concentration of the sample gas 1 [ v01%] can be calculated.

In this way, even if the temperature of the TCD sensor 13 changes due to the arrival of various gases, the sensitivity value of the TCD sensor 13 can be stored as standard calibration data and the TCD sensor 13 can be corrected using this. , it is no longer necessary to add standard gas and perform correction every time various gases are measured.

[Effects of the Invention] As explained above, the gas chromatograph correction method according to the present invention calculates the rate of change in resistance of the thermal conductivity detector with respect to temperature as a sensitivity value, and uses this calculated sensitivity value as a standard. Thermal conductivity detectors are stored as calibration data, and variations in the thermal conductivity detector's characteristic values are corrected based on this calibration data.Thermal conductivity detectors can be calibrated without using a standard gas, making the calibration easier. This has the effect of significantly reducing the number of man-hours required.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a device to which the gas chromatograph correction method according to the present invention is applied, Fig. 2 is a diagram for explaining this correction method, and Fig. 3 shows the resistance value of the sensor used in this device. FIG. 4 is a graph showing the relationship with temperature, FIG. 4 is a block diagram of a conventional gas chromatograph device, and FIG. 5 is a graph showing the state of gas concentration detected by this device. 1...Sample gas, 2...Carrier cassette, 6
... Gain amplifier section, 10 ... Constant temperature bath, 11.
...Analyzer valve, 12...Column, 13...
...Thermal conductivity detector (TCD sensor), 14--Current switching section, 15--Addition circuit, 16--Baseline cancel voltage generation section, 17--Gain selection section, 18...Voltage/frequency conversion section, 20...C
PU, 22... Constant current source. Patent applicant Yamatake Honeywell Co., Ltd.

Claims (1)

[Scope of Claims] A gas chromatograph apparatus that analyzes the concentration of the sample gas by detecting the temperature of the sample gas transferred by a carrier gas by a change in the resistance value of a thermal conductivity detector, comprising: the thermal conductivity detector; The rate of change in resistance with respect to temperature is calculated as the sensitivity value, and this calculated sensitivity value is retained as standard calibration data, and variations in the characteristic values of the thermal conductivity detector are corrected based on this calibration data. A method for correcting a gas chromatograph, characterized in that: