JP2517459B2 - Gas chromatograph - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas chromatograph for performing gas analysis by utilizing a difference in adsorptivity between a packing material packed in a column and a gas, and particularly to a gas chromatograph of the column. That is, the present invention relates to a gas chromatograph having a self-diagnosis function for monitoring.

[Conventional technology]

A gas chromatograph has been generally used as a detector for analyzing components of a process gas in a petrochemical process or a steel process and monitoring each process step or performing various controls based on the analysis result. .

By the way, in such a gas chromatograph, although the column varies depending on the sample gas, activated carbon,
Powders with a uniform particle size such as activated alumina and molecular sieves are packed as the stationary phase, and the difference in the moving speed based on the difference in the adsorption and partition coefficient between the stationary phase and each gas component in the sample gas is used. The gas components are separated from each other and detected by a detector such as a thermal conductivity element (TCD sensor).

[Problems to be Solved by the Invention]

However, this type of conventional gas chromatograph has a problem in that there are many problems that the column is clogged and the performance is deteriorated due to dust, mist, etc. contained in the so-called process gas.

In view of the above points, the present invention has been made to solve the above-mentioned conventional problems, and provides a gas chromatograph capable of performing a self-diagnosis of a column by monitoring clogging by dust and mist of the column. The purpose is to

[Means for solving the problem]

In order to achieve the above object, the gas chromatograph of the present invention detects the change in resistance value caused by the thermal conductivity of the components of each gas separated in the column by utilizing the heat generated by itself on the same substrate. A flow rate detector that is arranged at a position close to the thermal conductivity element on the flow path of the thermal conductivity element and the gas, and detects the flow rate of the gas by utilizing the temperature difference of the gas heated by the thermal conductivity element. A microdiaphragm sensor formed with an element is used as a detector, a pressure sensor provided in a secondary pressure side flow path of a pressure reducing valve that sets the pressure of carrier gas, and a carrier according to a signal detected by the flow rate detection element. A carrier gas flow rate control unit for automatically controlling the set pressure of the pressure reducing valve so that the flow rate of the gas is set and the flow rate is kept constant by a signal obtained from the pressure sensor. When, those having a diagnostic means for diagnosing the column based on the comparison result by comparing the was predetermined and a signal obtained from the pressure sensor threshold.

[Action]

In the present invention, the pressure sensor provided in the secondary pressure side flow path of the pressure reducing valve and the flow rate detecting element of the micro diaphragm sensor are used to set the pressure of the pressure reducing valve (secondary pressure so as to keep the flow rate of the carrier gas constant. ) Is automatically changed. As a result, when the fluid resistance increases due to the blockage of the column arranged on the secondary pressure flow path side of the pressure reducing valve, the secondary pressure of the pressure reducing valve increases. Therefore, by monitoring this pressure, the blockage of the column can be detected and the column life can be known.

[Examples] Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

FIG. 1 is a basic configuration diagram showing an embodiment of a gas chromatograph according to the present invention. An analyzer main body 1, which forms a thermostatic chamber and is maintained at a predetermined temperature, a sample valve 2 arranged inside the analyzer main body 1, a column. 3 and detector 4, measuring tube
5, equipped with a pressure reducing valve 6 for reducing the carrier gas CG consisting of an inert gas such as helium to a predetermined pressure P _O , and switching the flow path of the sample valve 2 from the solid line state to the broken line state during measurement The sample gas SG to be measured separated by the tube 5 is fed into the column 3 by the carrier gas CG. The column 3 is packed with powder of activated carbon, activated alumina, etc. as a stationary phase, and the difference in the moving speed based on the difference in the adsorption property and distribution coefficient between this stationary phase and each gas component in the sample gas SG is used. Then, each gas component is separated from each other, and this is detected by the detector 4 and converted into an electric signal. This electric signal is proportional to the gas component concentration, and this signal is subjected to waveform processing by a signal processing system or recorded 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 of the solid line, so that the carrier gas CG is supplied to the column 3
And to the detector 4.

The pressure reducing valve 6 includes a chamber 11 and two chambers 11 above and below the chamber 11.
A diaphragm 12 for partitioning into A and 11B, a carrier gas supply passage 13 and a carrier gas discharge passage 14 communicating with the room 11
, A poppet valve 15, a compression coil spring 16, etc., and the lower chamber 11A forms a pressure chamber and the upper chamber 11B forms a back pressure chamber. Further, the back pressure chamber 11B of the pressure reducing valve 6 for reducing the pressure of the carrier gas CG sent from the carrier gas supply passage 13 to a predetermined pressure P _O has one inlet / outlet port 17, and this inlet / outlet port 17 is the carrier gas. A back pressure channel 18 that branches from the supply channel 13 and communicates with the carrier gas discharge channel 14 is communicated via a branch channel 19. A fixed throttle 20 made of sintered metal or the like is arranged in the branch path 10. On the other hand, two electromagnetic valves 21 and 22 located on the upstream side and the downstream side of the back pressure flow path 18 with the branch path 19 interposed therebetween are arranged, and two pressure reducing valves 6 are provided on the downstream side of the downstream side electromagnetic valve 22. A pressure sensor 7 for detecting the side pressure P _O is provided.

Therefore, the carrier gas CG is the carrier gas supply channel.
Together and sent as the primary pressure P _S to 13 via the pressure chambers 11A side of the pressure reducing valve 6, opening the upstream-side electromagnetic valve 21, the back pressure passage 18
-Branch path 19-Back pressure _PN through fixed throttle 20 and back pressure chamber 11B
This back pressure P _N is made to correspond to the sum of the primary side pressure P _S and the spring pressure of the compression coil spring 16. And back pressure P _N
Decreases when the downstream solenoid valve 22 is opened.

25 is a solenoid valve drive circuit, which is a detection signal from the pressure sensor 7.
When PV and the carrier flow rate setting signal SP from the CPU (microcomputer) 23 are input via the D / A converter 24, these two signals are compared and two solenoid valves 21, 22 are based on the comparison result. Is controlled so that the secondary pressure P _O is always equal to the set pressure. In this case, carrier gas CG
The relationship between the primary pressure P _S , back pressure P _N, and secondary pressure P _O is
_S ≧ P _N > P _O.

That is, when the detection signal PV is less than or equal to the lower limit value of the carrier flow rate setting signal SP, the secondary pressure P _O is lower than the set pressure. At this time, while the upstream solenoid valve 21 is opened by the signal from the solenoid valve drive circuit 25, the downstream solenoid valve 22 is held in a fully closed state,
The flow rate of the carrier gas CG supplied to the back pressure chamber 11B is increased. Then, the back pressure P _N increases, the diaphragm 12 is displaced downward against the compression coil spring 16, and the poppet valve 15 is opened. Therefore, the flow rate of the carrier gas CG supplied to the pressure chamber 11A increases, and the secondary pressure P _O increases. When the secondary pressure P _O increases and matches the set pressure, the detection signal PV
Is within the range of the carrier flow rate setting signal SP, the upstream side solenoid valve 21 is closed. When the secondary pressure P _O becomes larger than the set pressure due to disturbance or the like and the value of the detection signal PV exceeds the upper limit value of the carrier flow rate setting signal SP, this time the downstream solenoid valve 22 is opened to lower the back pressure P _N. . Then, the diaphragm 12 is displaced upward by that amount, the poppet valve 15 is closed, and the secondary side pressure P _O is reduced. When the secondary pressure P _O matches the set pressure, the downstream solenoid valve 22 is closed.

FIG. 2 is a schematic plan view of a pattern structure showing an example of the micro diaphragm sensor used as the detector 4.
This microdiaphragm sensor 30 is a thin film heater made of permalloy or the like in the central portion on a single crystal silicon substrate 31 as shown in FIG. 2 using a normal semiconductor manufacturing process.
32 as a thermal conductivity element, and the thin film heater
The upstream side temperature sensor 33 and the downstream side temperature sensor 34, which are independent from each other, are formed on both sides of 32 as flow rate detecting elements. A large number of thin slits 35 for etching are provided on the surface of the silicon substrate 31, and a large number of thin slits are provided on the surface of the silicon substrate, below and around the thin film heater 32 and the temperature sensors 33, 34. By using an anisotropic etching method such as an etching solution such as potassium hydroxide through 35, a void is formed to form a void 36 having a pattern of a substantially inverted trapezoidal cross section. As a result, the upper portion of the void 36 is spatially separated from the silicon substrate 31 in a diaphragm shape, and the thin film heater 32, the upstream temperature sensor 33, and the downstream temperature sensor 34 are separated from the substrate.
A diaphragm 37, which is thermally insulated and supported, is formed. The thin film heater 32, each temperature sensor 33, 34
Is covered with a protective film such as silicon nitride. In FIG. 2, 38 is a sensor for measuring temperature,
39 shows the flow of gas.

The micro diaphragm sensor 30 manufactured in this way is
As shown in FIG. 3, the thin film heater 32 is provided with a current detection circuit 40 including an operational amplifier for detecting a change in the constant current i _{a of} about 100 mA and heating the thin film heater 32 to a predetermined temperature. Moreover, the concentration of the gas can be detected as the voltage output V _TCD by utilizing the fact that the resistance value of the thin film heater 32 changes depending on the thermal conductivity of the gas component. Further, the upstream side temperature sensor 33 and the downstream side temperature sensor 34 are connected to each side of the bridge circuit 41 including the fixed resistors 42 and 43 and the zero-adjustment variable resistor 44, and a difference consisting of operational amplifiers 46 to 48 for detecting the output thereof. The dynamic amplifier circuit 45 is configured. When the thin-film heater 32 is heated and the measurement gas flows, the upstream temperature sensor 33
Is cooled and the resistance value decreases, while the downstream temperature sensor
Since 34 is heated and its resistance value increases, the flow rate of the carrier gas can be detected as a voltage output V _FLOW from the difference. Further, the temperature measuring sensor 38 can pass a constant current i _{b of} about several mA, take a change in the current with a current detection circuit 49 including an operational amplifier, and detect the temperature as a voltage output V _TEMP . The third figure 50 and 51 is a current limiting resistor, V ₁ ~V ₃ is a driving power source of each.

By the way, since the gas chromatograph analyzes, it is necessary to keep the flow rate at the microdiaphragm sensor 30 as the detector 4 constant. However, in the present embodiment, the flow rate output V _FLOW of the microdiaphragm sensor 30 is input to the CPU 23 via the A / D converter 26, and when it changes from the predetermined carrier flow rate, the CPU 23 sets the value of the carrier flow rate setting signal SP. By changing the set pressure of the pressure reducing valve 6 via the solenoid valve drive circuit 25 to change the carrier pressure, a constant carrier flow rate is maintained. And solenoid valve drive circuit
Detection signal of the pressure sensor 7 which is a feedback signal of 25
By sending PV to the CPU 23 via the A / D converter 27, the CPU 23 can read the change in the carrier pressure. That is, assuming that the column 3 becomes clogged with the passage of time, the detection output PV of the pressure sensor 7 as shown in FIG.
Changes. Therefore, the CPU 23 can obtain the carrier pressure at the limit of use of the column 3 as a threshold value in advance, and notify the column exchange at the time t ₁ when the threshold PV _TH is exceeded. It should be noted that reference numeral t _{0 in} FIG. 4 indicates the start time point, and PV ₀ indicates the output value of the pressure sensor 7 at the start time.

〔The invention's effect〕

As described above, according to the gas chromatograph of the present invention, the carrier gas is utilized by utilizing the pressure sensor provided in the secondary pressure side flow path of the pressure reducing valve that sets the carrier pressure and the flow rate detection element provided in the microdiaphragm sensor. By automatically controlling the set pressure of the pressure reducing valve to keep the flow rate of the column constant, and by monitoring the detection output of the pressure sensor, it is possible to detect clogging caused by column dust and mist and perform column self-diagnosis. become. As a result, the maintenance and maintenance of the device can be improved.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing an embodiment of a gas chromatograph according to the present invention, FIG. 2 is a schematic plan view of a pattern structure showing an example of the microdiaphragm sensor of FIG. 1, and FIG. 3 is the above microdiaphragm sensor. FIG. 4 is a circuit configuration diagram showing an example of the detection circuit of FIG. 4, and FIG. 4 is an explanatory diagram for explaining the operation of the above embodiment. 1 ... Analyzer body, 2 ... Sample bus, 3 ...
Column, 4 ... Detector, 5 ... Measuring pipe, 6 ... Pressure reducing valve,
7 ... Pressure sensor, 23 ... CPU, 24 ... D / A converter, 25 ...
… Solenoid valve drive circuit, 26,27 …… A / D converter, 30 …… Micro diaphragm sensor, 31 …… Silicon substrate, 32 …… Thin film heater (thermal conductivity element), 33,34 …… Temperature sensor ( Flow rate detection element), 41 …… Bridge circuit, 45 …… Differential amplifier circuit.

Claims (1)

(57) [Claims] 1. A gas chromatograph in which a carrier gas is introduced into a column through a pressure reducing valve and a sample valve, and the sample gas is introduced into the column by switching the flow path of the sample valve to separate each gas component, which is detected by a detector. In the graph, the detector is a thermal conductivity element for detecting a change in resistance value caused by thermal conductivity of components of each gas separated in the column by utilizing heat generated by itself on the same substrate and the thermal conductivity element. A micro flow rate detection element is disposed at a position close to the thermal conductivity element on the gas flow path, and detects the flow rate of the gas by utilizing the temperature difference of the gas heated by the thermal conductivity element. The flow rate of the carrier gas is composed of a diaphragm sensor and is provided in the secondary pressure side flow path of the pressure reducing valve, and the flow rate of the carrier gas according to the signal detected by the flow rate detecting element. Carrier gas flow rate control means for automatically controlling the set pressure of the pressure reducing valve so as to keep the flow rate constant by the signal obtained from the pressure sensor, and the signal obtained from the pressure sensor. A gas chromatograph comprising a diagnostic means for comparing the threshold value and the column based on the comparison result.