JP2001337058A - Thermal conductivity detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal conductivity detector in which a TCD cell has a good temperature stability and is stabilized in a short time. SOLUTION: In setting the TCD cell 13 via an insulating thin material 28 onto a temperature control block 26 and moreover heating the cell by a heater controller 24, a temperature of the TCD cell is made higher than a final reach temperature through the temperature control for a fixed time by a temperature higher than a set temperature, and then the temperature is controlled by the original set temperature. The TCD cell is thus brought closer to the set temperature from the side of higher temperatures than the final set temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermal conductivity detector used in a gas chromatograph analyzer.

[0002]

2. Description of the Related Art In a gas chromatograph, a gaseous sample to be analyzed is injected into a carrier gas (helium, hydrogen, etc.) flowing at a constant speed, and the sample is separated into its components by sending it to a separation column. This is a device that detects components in the gas by sending it to a detector. Here, a thermal conductivity detector is one of the detectors used in the gas chromatograph.

FIG. 5 shows a principle diagram of a thermal conductivity detector. Filaments 2a and 2b are enclosed by metal blocks 3a and 3b, and an analysis gas (a gas in which a sample gas is mixed in a carry gas) is contained in one of the metal blocks 3a.
Pure carrier gas is sent into the other metal block 3b. These two metal blocks constitute a TCD cell (thermal conductivity detector cell). TC
The filaments 2a and 2b constituting the D cell form a bridge circuit in combination with other resistors 2c and 2d used for adjustment, and the current 2 flows through the bridge circuit to heat the filaments 2a and 2b. You.
At this time, when the analysis gas containing the sample and the pure carrier gas not containing the sample flow near the filament in each metal block, the heated filament is cooled. Since the difference in thermal conductivity causes a difference in the ability to cool the filament, a temperature difference occurs between the two filaments, and a difference occurs in the electric resistance value of the filament according to the temperature difference.
A signal corresponding to the analysis gas can be detected by extracting a signal based on the resistance difference by the detection unit 4.

In the thermal conductivity detector, as described above, TC
Since the detection of the analysis gas is performed from the electric resistance value generated based on the temperature difference between the two heated filaments constituting the D cell, how stable the temperature of the TCD cell is maintained and the temperature of the TCD cell is not affected by the outside air temperature Is a problem. Therefore, a temperature control block having a large heat capacity with a temperature control function is used as a base table, and a TCD cell is mounted thereon to control the temperature to be maintained at a temperature higher than room temperature and to cover other surroundings. And the cover is filled with a heat insulating material to stabilize the temperature.

[0005]

In the conventional thermal conductivity detector, the temperature of the temperature control block on which the TCD cell is mounted is controlled in order to maintain the TCD cell at a constant temperature. At this time, the temperature stability of the TCD cell is also determined depending on the temperature stability of the temperature control block. The temperature control block actually used has an appropriate heat capacity. In other words, the greater the heat capacity, the better the temperature stability, but it takes a long time from the start of heating to stabilization at the set temperature. For this reason, the waiting time until the start of the analysis is long, and there is a practical problem. On the other hand, the smaller the heat capacity, the shorter the time to reach the set temperature, but the lower the stability at that temperature. Therefore, it has been difficult to achieve a TCD cell structure that simultaneously satisfies the conflicting issues of reaching the set temperature in a short time and having high constant temperature. An object of the present invention is to solve such a problem and to provide a thermal conductivity detector capable of maintaining a TCD cell at a set temperature in a short time.

[0006]

SUMMARY OF THE INVENTION A thermal conductivity detector according to the present invention, which has been made to solve the above-mentioned problems, comprises a TCD cell having a temperature-sensitive element inside, a TCD cell mounted thereon, and a TCD cell. A base provided with a temperature control means for controlling the temperature of the cell, wherein an analysis gas is caused to flow through the TCD cell maintained at a constant temperature by the temperature control means so as to come into contact with the internal temperature-sensitive element, A thermal conductivity detector for detecting a substance to be measured in an analysis gas based on a change in a resistance value, wherein the TCD cell is mounted on the base via a heat-insulating thin material, and the temperature adjusting means is provided for analysis. Before the start, a control is performed to hold the temperature at a temperature higher than the analysis-time set temperature for a certain period of time, and then reset the temperature to the analysis-time set temperature. In the thermal conductivity detector of the present invention, the temperature fluctuation of the temperature control block is made difficult to be directly transmitted to the TCD cell by the heat insulating thin material, while the TCD cell is heated at a temperature higher than the set temperature for a certain time at the start of heating. Temporarily raise the temperature to higher than the set temperature. And at least at the beginning of heating,
Make the temperature close to the set temperature from the high temperature state.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. FIG. 1 is a schematic configuration diagram of a thermal conductivity detector according to one embodiment of the present invention. The sample side block 11 is formed of a metal block, in which the filament 2a is sealed, and the gas sent from the analysis gas inlet 16 passes around the filament 2a and is discharged from the analysis gas outlet 18. Have been. Filament 2a
Is heated by supplying current from the filament wire 14. The filament wire 14 is connected to an external resistor (not shown) so as to form the bridge shown in FIG. Similarly, the reference side block 12 is configured such that the filament 2b is sealed therein, and the gas fed from the carrier gas inlet 20 passes around the filament 2b and is discharged from the carrier gas outlet 22. The filament 2b is also heated by supplying current from the filament wire 14, and is connected to a resistor (not shown) so as to form the bridge shown in FIG. These sample side blocks 11
And the reference-side block 12, the TCD cell 13
(Thermal conductivity detector cell). Temperature control block 2
Numeral 6 is made of a metal having good thermal conductivity (such as copper), on which a heat-insulating thin material 28 is laid. The heat insulating thin material 28 needs to have heat resistance enough to withstand the heating temperature, and for example, a polyimide film is preferable. A heater wire and a temperature sensor (not shown) are attached inside the block of the temperature control block 26, and the temperature is controlled by a heater controller 24 connected to these. Under the influence of the outside air temperature (room temperature where the thermal conductivity detector is installed), TC
The TCD cell cover 30 covers the periphery of the TCD cell 13 so that the temperature of the D cell does not fluctuate, and the inner space of the TCD cell cover 30 is filled with a heat insulating material 32 such as glass wool (not shown in the figure). Is).

Next, the operation of the temperature controller performed in the present invention will be described. First, as a comparative example for clarifying the features of the present invention, the heater controller 2 was used from the beginning of heating.
FIG. 4 shows how the TCD cell 13 is heated and the temperature of the TCD cell 13 changes when the TCD cell 13 is heated while the temperature setting of No. 4 is maintained at the original set temperature. As the temperature control by the heater controller 24, normal on / off control and PID control can be considered. When the heating is started by the on / off control, the heater is initially supplied with full power power. When the temperature control block 26 reaches the set temperature, the heating power (heater power) is turned off. Thereafter, the temperature gradually approaches the set temperature while repeating the ON state and the OFF state. PID
Even when performing temperature control by control, full power power is supplied at the beginning of heating, and when the temperature control block 26 approaches the set temperature, control is performed in a direction to suppress overshoot (or prevent overshoot), so that heating is performed. Power (heater output power) is limited. When the heating power is turned off or limited, the temperature of the TCD cell 13 has not yet reached the set temperature due to the presence of the heat insulating thin material 28. Therefore, thereafter, as shown by the broken line, the temperature approaches the attained temperature for a while from the low temperature side. that time,
The temperature of the temperature control block 13 is affected by the heat insulating thin material 28 provided for the purpose of making the temperature change.
Since it is necessary to wait for the temperature of the CD cell to stabilize, the temperature of the TCD cell gradually rises from the low temperature side, and it takes a long time to stabilize. In this case, the experiment required a waiting time of about 2 hours. That is, although the temperature change generated by the temperature control operation can be absorbed by the presence of the heat insulating thin material 28, the time from the start of heating to the stabilization of the TCD cell cannot be reduced. Therefore, the heat insulating thin material 28 is attached, and the control operation is changed as shown in FIG. That is, when the set temperature A is input to the heater controller 24 (st
1) The heater controller 24 reads the input set temperature A, and at the start of heating, temporarily changes the set temperature to A + α instead of the original set temperature A, and starts heating for a fixed time. (St2). Since the heating time varies depending on the heat capacity of the TCD cell and the heater power, it is preferable to determine the optimum time in advance by preliminary experiments or the like. At this time, it is necessary that the temperature of the TCD cell 13 be temporarily higher than the ultimate temperature at the end of the period of heating at A + α. Usually, the temperature α to be higher than the set temperature may be about 10 ° C., and the heating time at A + α may be about 10 minutes. After this time has elapsed, the temperature is reset to the original set temperature A (st3). FIG. 3 shows how the set temperature and the temperature change of the TCD cell 13 when such control is performed. As can be seen from the figure, the temperature of the TCD cell 13 temporarily becomes higher than the final temperature due to the influence of the high setting (A + α) at the beginning of heating. After that, when the set temperature is reset to A, the temperature reaches the ultimate temperature from the high temperature side for a while. By approaching the final temperature from the high temperature side, the time required to reach the final temperature can be significantly reduced, and the waiting time, which was required about 2 hours, can be reduced to 1 hour or less. That is, if the temperature is controlled from the beginning of the heating at the set temperature A, it takes time for the TCD cell to rise in temperature due to the presence of the heat-insulating thin material 28, but it is necessary to make excess time in advance. Therefore, the time can be reduced by approaching from the high temperature side.

[0009]

As described above, in the thermal conductivity detector of the present invention, a heat insulating thin material is used, and the temperature is temporarily held at a temperature higher than the set temperature in a preparation process before the start of analysis. The waiting time until the temperature of the thermal conductivity TCD cell becomes stable can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a thermal conductivity detector according to one embodiment of the present invention.

FIG. 2 is a flowchart of temperature control of a temperature control block executed in the present invention.

FIG. 3 is a diagram showing the relationship between the set temperature of a temperature control block and the temperature of a TCD cell when the present invention is implemented.

FIG. 4 shows a set temperature and TCD of a temperature control block in a conventional method.
The figure which shows the relationship with the temperature of a cell.

FIG. 5 is a configuration diagram of a bridge circuit that obtains a detection signal of a thermal conductivity detector.

[Explanation of symbols]

 2a, 2b: Filament 11: Sample side block 12: Reference side block 13: TCD cell 24: Heater controller 26: Temperature control block 28: Heat insulating thin material 30: TCD cell cover 32: Heat insulating material

Claims (1)

[Claims] 1. A temperature control device comprising: a TCD cell having a temperature-sensitive element therein; and a base on which the TCD cell is mounted and to which a temperature control means for controlling the temperature of the TCD cell is attached. T maintained at a constant temperature
A thermal conductivity detector for flowing an analysis gas through a CD cell to contact an internal temperature sensing element and detect a substance to be measured in the analysis gas based on a change in resistance of the temperature sensing element;
The CD cell is placed on the base via a heat insulating thin material, and the temperature control means holds the temperature at a temperature higher than the temperature set at the time of analysis for a certain period of time in the preparation step before the start of analysis, and then returns to the temperature set at the time of analysis. A thermal conductivity detector characterized by performing setting control.