JP2005221474A - Gas chromatograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas chromatograph having a filament protecting mechanism in a heat conductivity detector while minimizing a rise in cost. <P>SOLUTION: The gas chromatograph is constituted so as to control the flow rate of the gas flowing to a heat conductivity detector 5 by an electronic control type flow rate control part 2 and provided with a protective mechanism 6 constituted so that a pressure sensor 24 provided in order to control a flow rate is used in order to protect a filament 51 to feed power to the filament 51 only when the output signal of the pressure sensor 24 exceeds a predetermined value. By this constitution, the filament protecting mechanism of the heat conductivity detector 5 can be added to the gas chromatograph without adding a new sensor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gas chromatograph, and more particularly to a gas chromatograph provided with a protection mechanism against overheating of a filament of a thermal conductivity detector.

  A thermal conductivity detector, one of the detectors for gas chromatographs, heats the filament provided in the flow of gas flowing out from the column of the gas chromatograph by energizing and heating it when the gas composition changes. Since the temperature of the filament changes in response to the change in conductivity, the change in the electrical resistance of the filament due to this is changed into a change in voltage through a bridge circuit or the like and is taken out.

FIG. 2 shows a conventional configuration example of a gas chromatograph in which a thermal conductivity detector is incorporated.
In the figure, 1 is a cylinder which is a carrier gas supply source, 2 is a flow rate control unit for adjusting the carrier gas flow, 3 is a sample introduction unit for introducing a sample to be analyzed into the carrier gas flow, 4 is A column 5 for separating the introduced sample into each component, and 5 is a thermal conductivity detector for detecting each separated component.

  As the flow rate control unit 2, a pressure regulating valve, a mass flow rate control valve, or the like has been used in the past. The flow rate control by this method is performed by a control valve 21 that can be electrically adjusted in opening degree, a flow path resistance 22 connected in series thereto, a pressure sensor 23 that detects a differential pressure between both ends, and a carrier in the vicinity thereof. A flow rate value is calculated by a predetermined calculation formula based on output signals from the two pressure sensors 23 and 24 by a control unit 25 including a computer, which is configured by a pressure sensor 24 for detecting gas pressure, and the flow rate value. Is performed by adjusting the opening of the control valve 21 so as to approach the set value (see, for example, Patent Document 1). This electronic control method enables control modes such as constant pressure control for keeping the pressure of the carrier gas constant, constant flow control for keeping the flow rate constant, or program flow rate control for gradually changing the flow rate according to the program.

  In the thermal conductivity detector 5, the filament 51 inside is heated by the current supplied from the power supply circuit 52, and the carrier gas flowing out from the column 4 flows in contact therewith. The temperature of the filament 51 is maintained at a certain temperature at which the amount of heat generated by the current and the amount of heat released by the carrier gas are balanced. When the sample component is transported from the column 4 to the carrier gas, the amount of heat released from the filament 51 changes due to the difference in thermal conductivity, the equilibrium is lost, and the temperature of the filament 51 changes. Therefore, this resistance change is converted into a voltage signal through a bridge circuit (not shown) or the like, and is taken out as an output signal of this gas chromatograph.

  As described above, since the temperature of the filament 51 is determined by the balance between the amount of heat generated by the current and the amount of heat released by the carrier gas, if the filament 51 is energized when the carrier gas is not flowing, The temperature may rise excessively, causing disconnection or other damage. When the carrier gas is not flowing, air enters by diffusion from the outlet side of the thermal conductivity detector 5 (open to the atmosphere), and oxidation of the high temperature filament 51 proceeds by oxygen in the air. There is also an increased possibility of promoting deterioration and shortening the service life. In order to prevent such a situation, a sensor (not shown) is provided separately to confirm that the carrier gas is flowing in the thermal conductivity detector 5 and power supply to the filament 51 is performed unless this confirmation is performed. A gas chromatograph configured so as to be impossible has also been proposed (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 9-15222 JP-A-6-324028

The above-described protection mechanism that prohibits energization of the filament 51 when the carrier gas is not flowing is highly effective in preventing the filament 51 from being disconnected or deteriorated in the thermal conductivity detector 5 and prolonging the life. However, since it is necessary to separately provide a sensor for confirming that the carrier gas is flowing, there is a problem that the cost increases.
This invention is made | formed in view of such a situation, and it aims at providing the gas chromatograph provided with the filament protection mechanism in a thermal conductivity detector, suppressing an increase in cost to the minimum.

In order to solve the above-described problems, the present invention provides a filament protection mechanism that combines the pressure sensor used in the above-described electronically controlled flow control unit with a sensor for confirming that gas is flowing. Configured. That is, the device of the present invention is configured such that the opening degree of the control valve that controls the flow rate of the gas flowing through the thermal conductivity detector is adjusted based on the output signal of the pressure sensor that detects the pressure in the gas supply path. In this gas chromatograph, the gas chromatograph is provided with a protection mechanism that enables power supply to the filament only when the output signal of the pressure sensor exceeds a predetermined value.
With such a configuration, it is possible to add a filament protection mechanism in the thermal conductivity detector to the gas chromatograph without adding a new sensor.

  Since the present invention is configured as described above, it is possible to provide a gas chromatograph to which a filament protection mechanism has been added with a minimum cost increase, so that no gas flows through the thermal conductivity detector. Since it is possible to prevent disconnection and deterioration due to energization of the filament, it can be expected to extend the life of the thermal conductivity detector.

FIG. 1 shows an embodiment of the present invention. In the figure, the same components as those in FIG.
When this embodiment is compared with the conventional configuration shown in FIG. 2, it is different from the conventional configuration in that a protection mechanism 6 that receives a signal from the pressure sensor 24 and outputs a signal to the power feeding circuit 52 is provided.

Since the column 4 has a resistance determined by its length, inner diameter, and in the case of a packed column, the particle size of the packing material packed therein, the pressure (column inlet pressure) is applied to the inlet side of the column 4 when the carrier gas is flowing. ) Occurs. Since there is almost no pressure difference in the flow path from the inlet side of the column 4 to the point b where the pressure sensor 24 is provided, the pressure sensor 24 may be considered to observe the column inlet pressure. Since the column inlet pressure is generated when the carrier gas flows through the column 4, it can be determined that the carrier gas is flowing when a column inlet pressure of a certain value or higher is observed. This is the same whether the control mode of the flow control unit 2 is constant pressure control or constant flow control.
The protection mechanism 6 compares the column inlet pressure value input from the pressure sensor 24 with a preset threshold value, and energizes the filament 51 of the thermal conductivity detector 5 only when the column inlet pressure value exceeds the threshold value. Thus, the signal is output to the power feeding circuit 52.

The present embodiment configured as described above operates as follows.
In the state where the carrier gas is flowing normally, the value of the column inlet pressure obtained by the pressure sensor 24 is larger than the threshold value set in the protection mechanism 6 (the threshold value is set as such). The protection mechanism 6 outputs a signal that enables the filament 51 to be energized from the power supply circuit 52, and the thermal conductivity detector 5 is in an operable state.
For example, when the gas in the cylinder 1 is exhausted and the carrier gas does not flow, the column inlet pressure decreases, and when the pressure falls below the threshold value, a signal indicating that energization is not possible is output from the protection mechanism 6, and thereby, the filament 51 Since the energization of the filament 51 is stopped, overheating of the filament 51 is prevented.
In addition, when the operation of the gas chromatograph is mistakenly started without the column 4 being connected, the carrier gas does not flow to the thermal conductivity detector 5, so that in the conventional case, the filament that is energized In this embodiment, since the column inlet pressure is not generated in this case, the output signal of the pressure sensor 24 becomes lower than the threshold value, and the protection mechanism 6 is activated to supply the filament 51. Power is not supplied. Thereby, the filament 51 is protected from overheating.

  Although the protection mechanism 6 is functionally shown as an independent block as shown in the figure, the actual device configuration can be configured by software on a computer program common to the control unit 25, so that an output interface such as a relay is provided. There is almost no hardware to add. That is, the cost for adding the protection mechanism 6 characterizing the present invention is negligible.

  The configuration of the electronically controlled flow control unit 2 has conventionally been modified in some ways, and the pressure sensor 24 measures the point a downstream of the control valve 21 in FIG. 1 or the internal pressure of the sample introduction unit 3. In such a case, the present invention has the same effects as described above.

Conventionally, the thermal conductivity detector 5 includes two filaments 51 that work differentially, one of which is supplied with a carrier gas flowing out from the column 4 in the same manner as described above, and the other is the same type of carrier gas as a reference gas. However, the present invention can be applied to the carrier gas in that case, and the flow rate of the reference gas is also controlled by an electronic control method. If applicable, it is applicable.
When a capillary column is used as the column 4, a makeup gas is introduced into the thermal conductivity detector 5 in addition to the carrier gas. The present invention can be similarly applied to this makeup gas. .

It is a figure which shows one Embodiment of this invention. It is a figure which shows the conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Flow control part 3 Sample introduction part 4 Column 5 Thermal conductivity detector 6 Protection mechanism 21 Control valve 22 Flow path resistance 23 Pressure sensor 24 Pressure sensor 25 Control part 51 Filament 52 Feeding circuit

Claims (1)

A thermal conductivity detector configured to detect a change in the thermal conductivity of the gas flowing in contact with the filament heated by the power supply as a change in the electrical resistance of the filament and flowing to the thermal conductivity detector; In a gas chromatograph configured such that an opening degree of a control valve for controlling a gas flow rate is adjusted based on an output signal of a pressure sensor for detecting a pressure in the gas supply path, an output signal of the pressure sensor is A gas chromatograph comprising a protection mechanism that enables power supply to the filament only when a predetermined value is exceeded.

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