JP2003254929A - Heat conductivity detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture, easily at low cost, a filament and a temperature compensation resistor made of the same material as the filament, concerning a heat conductivity detector fed by a constant-temperature circuit. <P>SOLUTION: A hollow part 16 opened on one face of a metal block 15 constituting a cell of this heat conductivity detector is provided, and a passage for flowing a test gas 5 through the hollow part 16 is bored. First and second thermal resistance elements 31, 32 are formed from a membrane of tungsten or the like on an insulating substrate 3 comprising silicon or glass material, and the insulating substrate 3 is bonded in piles so that the membrane face is brought into contact with the opened face of the hollow part 16 of the metal block 15. The thermal resistance element 31 equivalent to the filament is brought into contact with the test gas 5 passing inside the hollow part 16 to thereby sense its heat conductivity, and the thermal resistance element 32 equivalent to a thermal compensation resistance is brought into contact with the metal block 15 to thereby sense its temperature, namely, the detector temperature. By this constitution, the two thermal resistance elements 31, 32 are molded collectively by a membrane technology and manufactured easily at low cost. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal conductivity detector used in gas chromatography. FIG. 2 shows a basic configuration of a conventional thermal conductivity detector. In the figure, metal block 1
A cell 1 is formed by piercing the flow path of the test gas 5 in 5, expanding the middle of the flow path to form a hollow portion 16, and providing the filament 11 therein. The filament 11 is heated by supplying a current by a power supply circuit described later. Test gas 5
Is a mixed gas of a carrier gas flowing out of a column of a gas chromatograph (not shown) and a sample component. Usually, a helium gas having high thermal conductivity is used as the carrier gas. The cell 1 is housed in a constant temperature bath 4 and kept at a constant temperature so as to prevent the component substances in the test gas 5 from condensing and to eliminate the influence of the ambient temperature. 12
Is a temperature compensation resistor closely attached to the metal block 15. [0003] The thermal conductivity detector thus configured operates as follows. When the analysis is not performed, the test gas 5 is only the carrier gas, and its thermal conductivity is high as described above. Therefore, the heat generated in the filament 11 is transmitted to the metal block 15 through the carrier gas, The temperature of 11 is equilibrated at a relatively low temperature. When the sample component flows into the cell 1 on the carrier gas, the thermal conductivity of the sample component is lower than that of the carrier gas, so that the thermal conductivity of the test gas 5 is slightly reduced. As a result, the temperature of the filament 11 increases, and the resistance of the filament 11 also increases. If this resistance change is output as an electric signal by an appropriate electric circuit, the concentration of the component substances can be quantified. [0004] The temperature of the thermostat 4, that is, the temperature of the cell 1 (hereinafter referred to as the detector temperature) is set so that the sample components are kept in a gaseous state. It is known that the temperature of the filament 11 heated by passing an electric current becomes higher than the detector temperature, and the difference (hereinafter referred to as filament relative temperature) is substantially proportional to the detection sensitivity. However, the higher the filament temperature is, the lower the stability as a detector is, and the oxidation of the filament 11 proceeds and the deterioration is promoted. Therefore, the filament temperature should be used at a low temperature as long as the required detection sensitivity is secured. is there. In consideration of such requirements, the detector temperature and the filament temperature must be appropriately set each time according to the analysis purpose and the analysis target. As a power supply circuit for supplying a current for heating the filament 11, a constant voltage circuit or a constant current circuit has been used in the past, but a constant temperature circuit has recently been used. FIG. 3 shows a basic configuration of a constant temperature circuit as a conventional example. In the figure, reference numeral 11 denotes the filament, and 12 denotes a temperature compensation resistor having the same temperature coefficient as the filament 11, which is closely attached to the cell 1 as shown in FIG. Changes. Filament 11 and temperature compensation resistor 12
Constitutes a bridge circuit 10 together with the other two resistors 13 and 14 (the temperature coefficients of which are so small as to be negligible), and uses the connection point of the former two and the connection point of the latter two as a power supply terminal to supply power. Voltage V is supplied. The voltages V1 and V2 generated at the two connection points except for the power supply end are input to the differential amplifier 2, and the difference voltage V2-V1 (hereinafter, referred to as ΔV) is amplified and passed through the final transistor 21. The power supply voltage V to the bridge circuit 10 is controlled. Vo is a power supply voltage. The circuit of FIG. 3 works as follows. Now, it is assumed that an appropriate setting is made and the bridge circuit 10 is balanced (ΔV ≒ 0) in a state where only the carrier gas flows around the filament 11. If it flows, the filament temperature rises as described above, and the filament 1
1 also increases, and the voltage V1 increases. However, as a result, ΔV is biased negatively, and accordingly, the current flowing to the bridge circuit 10 through the final transistor 21 decreases, so that the filament temperature decreases. As a result, the voltage V1 also drops, and eventually balances again when ΔV ≒ 0. By such feedback control, the filament temperature is maintained substantially constant. After the re-equilibration, the value of the supply voltage V has changed from the value in the previous equilibrium state, and this change is caused by a change in the thermal conductivity of the gas flowing around the filament 11. Therefore, it can be said that the power supply voltage V includes information to be detected. Therefore, if an appropriate process such as bias removal is performed on the value of the power supply voltage V, an output signal of the detector can be obtained. [0007] The temperature compensating resistor 12 operates as follows, and exhibits its function when the detector temperature is changed. Now, assuming that the detector temperature is increased (the temperature set value of the thermostat 4 is increased), the temperature of the temperature compensation resistor 12 which is in close contact with the cell 1 increases, and the resistance value increases.
The voltage V2 rises and ΔV which is the input signal of the differential amplifier 2
Increases and the current flowing to the bridge circuit 10 increases. As a result, the current flowing through the filament 11 also increases, so that its temperature and resistance also increase, and the voltage V1 also rises and rebalances where V1 と こ ろ で V2. That is,
When the detector temperature is changed, the filament temperature automatically changes to keep the filament relative temperature substantially constant. Since the relative temperature of the filament is proportional to the detection sensitivity as described above, if a constant temperature circuit as shown in FIG. 3 is used, it is possible to freely change the detector temperature while keeping the detection sensitivity constant. . In the thermal conductivity detector, the same filament is provided in each of two parallel flow paths, one of which flows a test gas as a detection side and the other of which flows a reference gas (usually a carrier gas) as a reference side. In many cases, the dual flow cell is configured to cancel changes in temperature and flow rate. FIG. 4 shows a configuration in which the above-described constant temperature circuit is applied to a dual flow cell as a conventional example. In the figure, two sets of the same power supply circuits as those shown in FIG. 3 are used, and power is supplied to the filaments 11 and 11 'by the power supply circuits on the detection side (the left side in the figure) and the reference side (the same right side). The difference between the signals is extracted through the differential amplifier 25. In the figure, since the reference side has exactly the same configuration as the detection side, reference numerals of components other than the filament 11 'are omitted. In the above-described constant temperature circuit, it is necessary that the temperature compensation resistor 12 has the same temperature coefficient as that of the filament 11.
It is made of the same material as, for example, a tungsten alloy. Further, it is desirable that the temperature compensation resistor 12 generate a small amount of self-heating in order to accurately reflect the cell temperature. In order to suppress heat generation, it is necessary to reduce the current flowing therethrough. For this reason, the resistance value of the temperature compensation resistor 12 is selected to be a value that is at least two orders of magnitude larger than that of the filament 11. Therefore, the temperature compensating resistor 12 must be made of an extremely thin filament, and be manufactured in a form having good thermal response. However, it is difficult to manufacture such a resistor, and if it is intentionally manufactured, the cost will be high. Was a problem. The present invention has been made in view of such circumstances, and is a thermal conductivity detector fed by a constant temperature circuit, in which a temperature compensating resistor made of a filament and the same material is easily and inexpensively manufactured. It is an object of the present invention to provide a thermal conductivity detector configured to be manufactured by the method described above. SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a thermal conductivity detector fed by a constant temperature circuit, comprising a filament and a thermosensitive resistance element corresponding to a temperature compensation resistor. They were formed on the same insulating substrate with conductive thin films of the same material. Thus, since the two thermosensitive resistance elements are formed collectively by the thin film technology, the manufacturing is easy and the cost is low. FIG. 1 shows a structure of a thermal conductivity detector cell as one embodiment of the present invention. The figure shows a configuration in the case of a dual flow cell, which is symmetrical with respect to the center line c. Therefore, in the case of a single flow cell, only one of the right and left sides may be used. Further, in the following description, only one side (detection side) will be described, and description of the reference side having exactly the same structure will be omitted, and reference numerals in the drawings will be omitted. In FIG. 1, reference numeral 15 denotes a metal block similar to that shown in FIG. 2, and a hollow portion 16 is provided in the middle of a flow path formed in the metal block.
6 differs from the conventional structure in that a part of 6 is open on the surface of the metal block 15. It is assumed that one surface of the metal block 15 in which the cavity 16 is opened is finished smoothly, and is coated to ensure electrical insulation. 3 is
An insulating substrate made of silicon or glass material,
On this, the first and second thermosensitive resistance elements 31 and 32 corresponding to the filament and the temperature compensation resistance with a metal thin film are provided.
To form These resistance elements can be formed by a conventionally known film forming technique such as a sputter deposition method using a metal such as tungsten as a thin film material. Reference numeral 33 denotes a terminal portion also made of a thin film, and a lead wire is welded to the terminal portion to electrically connect with a power supply circuit. The insulating substrate 3
The metal block 15 is inverted as shown by the arcuate arrow in the drawing.
To be glued. That is, the thin film surface is in contact with the surface of the metal block 15 where the hollow portion 16 opens, and is adhered so as to maintain airtightness. Thereby, the opening of the cavity 16 is closed, and the first thermosensitive element 31 corresponding to the filament is exposed toward the space in the cavity 16, while the second thermosensitive element 31 corresponding to the temperature compensation resistance is exposed. The resistance element 32 is in close contact with the metal block 15 with an insulating coating film interposed therebetween. With such a configuration, the first thermosensitive resistance element 31 corresponding to the filament comes into contact with the test gas 5 passing through the cavity 16, so that the resistance value is changed according to the thermal conductivity. In addition, the second element corresponding to the temperature compensation resistor
The heat-sensitive resistance element 32 contacts the metal block 15 and senses its temperature, that is, the detector temperature, and changes its resistance value. In other words, it has a function equivalent to that of the conventional configuration shown in FIG. 2, and since the two heat-sensitive resistance elements are formed collectively by the thin film technology, the manufacturing is easy and the cost is low.
In addition, the condition that they have the same temperature coefficient is also satisfied. Note that the above shows one embodiment of the present invention, and the present invention is not limited to this. As described above in detail, according to the present invention, a heat-sensitive resistance element corresponding to a conventional filament and a heat-sensitive resistance element corresponding to a temperature compensation resistance are formed on the same insulating substrate by the same conductive material of the same material. Since the thermal conductivity detector is formed of a thin film, it is easy to manufacture and the cost is low.

[Brief description of the drawings] FIG. 1 is a diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing a conventional configuration. FIG. 3 is a diagram showing a conventional circuit configuration. FIG. 4 is a diagram showing another conventional circuit configuration. [Explanation of symbols] 1 ... cell 3. Insulating substrate 15 ... Metal block 16 ... Cavity 31. 1st thermosensitive resistance element (filament) 32... Second thermal resistance element (temperature compensation resistance) 33 ... Terminal section

Claims (1)

Claims: 1. A first thermosensitive element that is in thermal contact with a test gas flowing in a cell and a second thermosensitive element that has the same temperature coefficient and is in thermal contact with the cell. In the bridge circuit forming two sides adjacent to each other, the difference in voltage between both ends of each of the two thermosensitive resistance elements is fed back to control the amount of power supplied to the bridge circuit.
A thermal conductivity detector configured to control the temperature of the thermal resistance element, wherein both thermal resistance elements are formed of a conductive thin film of the same material on the same insulating substrate. Detector.