JPH0536363U - Gas chromatograph temperature controller - Google Patents

Abstract

(57) [Summary] [Purpose] When the hot plate method is used as the heating method in the constant temperature oven, the setting accuracy is improved even if the heat source and the temperature control target are separated. [Structure] A temperature sensor 13 is provided in the vicinity of a TCD (thermal conductivity detector) in a hot plate type thermostatic chamber 1 separately from a heater temperature control temperature sensor. Then, the detected value PV of the temperature sensor 13 and the preset target value SP are compared by the comparison unit 21, the control output corresponding to the deviation is obtained by the PID calculation unit 22, and the heater output based on the control output. The ON / OFF control unit 25 is controlled. Thus, TC
By feeding back the output of the temperature sensor 13 for D temperature control to perform temperature control, the temperature of the TCD can be accurately controlled even if the heater of the heat source and the position of the TCD are distant from each other.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a gas chromatograph in which a sample gas transferred by a carrier gas is introduced into a column to be separated into respective gas components, which are detected by a thermal conductivity detector (hereinafter abbreviated as TCD) for gas analysis. In particular, the present invention relates to a temperature control device for a thermostatic chamber that houses the column.

[0002]

[Prior Art]

 Gas chromatographs have been generally used as a monitoring device for performing component analysis on process gas in petrochemical processes, steel processes, etc., and monitoring each process step and performing various controls based on the analysis results. Has been.

FIG. 4 is a diagram showing a basic configuration of this type of gas chromatograph, which is a thermostatic chamber 1, which constitutes an analyzer main body kept at a predetermined temperature, a sample valve 2 and a column 3 arranged in the thermostatic chamber 1. Further, the detector 4, the measuring pipe 5, the pressure reducing valve 6 for reducing the carrier gas CG made of an inert gas such as helium to a predetermined pressure are provided, and the flow path is changed from the solid line state to the broken line state in the sample valve 2 during measurement. By switching, the sample gas SG to be measured, which is sampled by the measuring pipe 5, is fed into the column 3 by the carrier gas CG.

The column 3 is packed with powder having a uniform particle size, such as activated carbon, activated alumina, and molecular sieve, as a stationary phase, which varies depending on the sample gas SG. The respective gas components are separated from each other by utilizing the difference in the moving speed based on the difference in the adsorptivity with respect to each gas component or the distribution coefficient, and this is detected by the detector 4 such as TCD and converted into an electric signal. This electric signal is proportional to the gas component concentration, and the controller 7 waveform-processes it or records it on recording paper. On the other hand, at the time of non-measurement, the flow path of the sample valve 2 is switched to the state shown by the solid line to guide the carrier gas CG to the column 3 and the detector 4.

By the way, in such a gas chromatograph, there are two heating methods of the constant temperature bath 1 for heating the column 3 and the like to a predetermined temperature. One is a hot air method in which hot air is circulated and air is used as a medium to transfer heat to each part. The other is the hot plate type. This hot plate method is a method in which a column is brought into close contact with a metal block heated by a heater and heat is supplied by utilizing heat conduction of metal. In this temperature control, the heater is placed in the controlled object of the thermostatic chamber, and a temperature sensor such as a thermistor is installed near the heater so that the detected value of the controlled object, that is, the PV value is higher than the target value. The ON / OFF control method in which the heater is turned off and the heater is turned on when the target value is higher than the PV value is mainly used.

[0006]

[Problems to be solved by the device]

 However, in the case of this hot plate type constant temperature bath, if the temperature distribution of the metal block itself is not constant and there is a control target such as a column or TCD at a position away from the heater of the heat source, accurate temperature control is not possible. It will be difficult. Especially when TCD is used as a detector, it is necessary to keep the temperature of the column and the detector constant with high accuracy.

The present invention has been made in view of the above points, and when a hot plate type is used as a heating method in a constant temperature bath, it is possible to improve the setting accuracy even if the heat source and the temperature control target are separated from each other. An object is to provide a temperature control device for a tograph.

[0008]

[Means for Solving the Problems]

 In order to achieve the above object, a temperature control device for a gas chromatograph according to the present invention is provided with a heater for heating a column at a constant temperature and a heater for heating the column to a constant temperature in a hot plate type constant temperature bath containing the column. Further, a first temperature sensor for controlling the heater temperature is provided, and a second temperature sensor is provided in the vicinity of the TCD in the constant temperature bath separately from the first temperature sensor. The TCD temperature is kept constant by comparing preset target values with each other to obtain a control output according to the deviation and controlling the heater based on the control output.

[0009]

[Action]

 In the present invention, the temperature of the TCD can be accurately controlled even if the heat source and the temperature control target are separated.

[0010]

【Example】

 FIG. 1 is a block diagram showing an embodiment of a temperature control device for a gas chromatograph according to the present invention, and FIG. 2 is a schematic diagram showing the positional relationship between columns in a constant temperature bath and temperature sensors. In these figures, the same or corresponding parts as in FIG. 4 are designated by the same reference numerals.

Here, in the constant temperature bath 1, as shown in FIG. 2, a column 3 is brought into close contact with a metal block 10 heated by a heater 11, and heat is transferred by utilizing heat conduction of the metal. A similar hot plate type is provided with a temperature sensor 13 such as a thermistor for controlling the TCD temperature in the vicinity of the TCD 4 as a detector arranged at an upper position facing the heater 11.

The detection value of the temperature sensor 13 is input to the comparison unit 21 as a control value PV as shown in FIG. A preset target value SP is input to the comparison unit 21, the target value SP is compared with the detection value PV of the temperature sensor 13 for TCD temperature control, and the deviation is input to the PID calculation unit 22. . The PID calculator 22 obtains a control output based on the deviation and inputs the control output V _REF to the temperature sensor circuit 23.

As shown in FIG. 3, the temperature sensor circuit 23 is composed of an operational amplifier 31 and an operational amplifier 32 including the temperature sensor 12 for controlling the heater temperature, and also has a control output V _REF obtained from the PID calculator 22. A signal corresponding to the resistance value of the temperature sensor 12 is detected, and the signal is input to the duty ratio control unit 24.

As shown in FIG. 3, the duty ratio controller 24 includes an A / D converter 33, a CPU 34, and a timer 35. The duty ratio controller 24 obtains a duty ratio corresponding to the output obtained from the temperature sensor circuit 23, and the duty ratio is calculated. The heater ON / OFF control unit 25 is driven by the output to control ON / OFF of the heater 11 in the constant temperature bath 1. That is, the control value PV of the TCD temperature control temperature sensor 13 is much lower than the target value SP in order to change the duty ratio for ON-driving the heater 11 according to the temperature detected by the TCD temperature control temperature sensor 13. Sometimes the duty ratio is high and the duty ratio is made smaller as the control value PV approaches the target value SP, so that the heater 11 is turned on / off by a signal according to the duty ratio to control the temperature of the TCD 4 constant. It is supposed to do.

The heater ON / OFF control section 25 is generally composed of a known switching element 36, an inverter circuit 37, and an AC switch section 38 with a zero-cross circuit. In FIG. 3, 39 is an AC power source, and V _D is a DC drive voltage.

As described above, according to the temperature control device of the present embodiment, the temperature sensor 13 is provided in the hot plate type constant temperature bath 1 in the vicinity of the TCD 4 facing the heater 11 separately from the temperature sensor 12 for controlling the heater temperature. By feeding back the detection output of the temperature sensor 13 to control the temperature, the temperature of the TCD 4 can be controlled to be constant. This control method is particularly effective when the heat capacity of the controlled object is large. Further, by placing the measuring pipe 5 near the heater 11, the temperature of the measuring pipe 5 can be represented by the temperature of the heater 11. Therefore, the temperature dependence of the amount of the sample gas taken into the measuring pipe 5 can be canceled by the correction, and the temperature characteristics of the concentration output by the TCD 4 can be improved.

Further, according to the present embodiment, when the heater 11 is ON / OFF-controlled, its duty ratio is changed according to the detection output of the temperature sensor 13 for TCD temperature control, so that highly accurate temperature control can be achieved. Is possible. That is, in the conventional ON / OFF control system, the heater itself has a large heat capacity, and if the heat capacity of the controlled object is large, it becomes difficult to perform highly accurate control. Especially when trying to adopt a complicated control method, the target setting value must be made variable, and the setting becomes complicated.

On the other hand, according to the present embodiment, the duty ratio of ON / OFF of the heater 11 is made variable, and when the detected value of the TCD temperature control temperature sensor 13 is much lower than the target value SP, the duty ratio is decreased. Is set high and the duty ratio is reduced as the detected value of the temperature sensor 13 approaches the target value SP, whereby more accurate control can be performed. Further, since it is possible to support a complicated control method by changing the duty ratio and control can be performed in a longer cycle than the phase control method, the AC that constitutes the heater ON / OFF control unit 25 can be controlled. If a zero-cross circuit is used for the switch unit 38, noise associated with the on / off state of the switch does not occur. Further, since the time during which the heater 11 is ON-driven becomes short, there is an advantage that power saving can be achieved.

[0019]

[Effect of the device]

 As described above, according to the temperature control device of the gas chromatograph according to the present invention, the temperature sensor for the temperature control is provided in the vicinity of the TCD installed in the hot plate type thermostatic chamber separately from the heater of the heat source. By performing temperature control by feeding back the detection output of the temperature sensor, the temperature of the TCD can be accurately controlled even if the heater of the heat source and the TCD are far from each other.

Further, according to the present invention, it is possible to perform highly accurate temperature control by changing the ON / OFF duty ratio of the heater, and to cope with a complicated control method by changing the duty ratio. The effect is that you can.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a temperature control device for a gas chromatograph according to the present invention.

FIG. 2 is a diagram showing an arrangement relationship between columns and temperature sensors in the constant temperature bath of this embodiment.

FIG. 3 is a circuit configuration diagram showing a specific example of a main part of the present embodiment.

FIG. 4 is a diagram showing a basic configuration of a general gas chromatograph.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot plate type constant temperature bath 3 Column 4 TCD (thermal conductivity detector) 10 Metal block 11 Heater 12 Temperature sensor for heater temperature control 13 Temperature sensor for TCD temperature control 21 Comparison part 22 PID calculation part 23 Temperature sensor circuit part 24 Duty ratio control unit 25 Heater ON / OFF control unit

Claims (2)

[Scope of utility model registration request] 1. A gas chromatograph having a hot plate type thermostat for accommodating a column, wherein a sample gas component separated by the column is detected and analyzed by a thermal conductivity detector. And a first temperature sensor for controlling the temperature of the heater, which is arranged in the vicinity of the heater, and a first temperature sensor in the vicinity of the thermal conductivity detector in the constant temperature bath. A second temperature sensor is provided separately from the above, and a detected value of the second temperature sensor is compared with a preset target value to obtain a control output corresponding to the deviation, and based on the control output, A temperature control device for a gas chromatograph, characterized in that a heater is controlled to keep the temperature of a thermal conductivity detector constant. 2. The temperature control device for a gas chromatograph according to claim 1, wherein an ON / OFF control means is used as the heater control means, and the ON / OFF duty ratio is changed.