JPH1048191A - Gas chromatograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas chromatograph in which a refrigerant can be supplied to a thermostat more stably than in conventional cases. SOLUTION: A flow control valve 12 whose opening is changed according to a voltage applied to a solenoid is arranged and installed in the halfway part of a refrigerant supply pipe 26. A computing device 14 outputs a voltage instruction signal according to the difference between a temperature inside a thermostat monitored by a platinum sensor 36 or the like and a set temperature, and a flow-control-valve drive circuit 16 applies a voltage instructed by the signal to the solenoid at the flow control valve 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas chromatograph, and more particularly to a low-temperature control device therefor.

[0002]

2. Description of the Related Art In a gas chromatograph, a column for separating a sample is stored in a thermostat. The thermostat is provided with a heating means, and during the analysis, the heating means appropriately heats the thermostat so that the temperature in the thermostat is maintained at a constant temperature corresponding to the sample. The temperature in the thermostat that can be set and maintained by the heating means is room temperature + 5 ° C to 400 ° C
The degree is generally. However, depending on the sample, the separation must be performed at a temperature lower than room temperature. Therefore, in order to cope with a low temperature that is not included in the above temperature range, a gas chromatograph provided with a low temperature control device for appropriately cooling a constant temperature bath has also been developed.

[0003] As one of low-temperature control devices for gas chromatographs, a device for controlling the temperature in a constant-temperature bath at a low temperature by introducing a refrigerant such as liquefied carbon dioxide gas or liquid nitrogen into a constant-temperature bath has been conventionally known. I have.

FIG. 5 is a partially cutaway view showing a schematic configuration of a low-temperature control device using a refrigerant. In this low temperature control device,
The refrigerant sealed in the cylinder 22 is supplied through a refrigerant supply pipe 26 into a thermostat 24 in which the column 23 is stored. An electromagnetic valve 28 is provided on the way of the refrigerant supply pipe 26. The operation of the solenoid valve 28 is controlled by the electric control unit 30. The fan 32 is for stirring the gas in the thermostat 24 to make the temperature distribution uniform. Further, a thermosensitive body 34 composed of a platinum sensor or the like is arranged in the thermostat 24. The heat sensitive body 34 is connected to the electric control unit 30.

FIG. 6 is a block diagram showing a configuration of an electric system of the low-temperature control device. The platinum sensor 36 included in the thermal element is grounded. A constant current is always supplied to the platinum sensor 36 by a constant current source 38. When the electric resistance of the platinum sensor 36 changes according to the temperature in the thermostat, the potential difference between both ends of the platinum sensor 36 also changes. After this potential difference is amplified by the amplifier 40, A
The data is converted into digital data by the / D converter 42 and input to the arithmetic unit 44. The arithmetic unit 44 obtains the temperature in the constant temperature bath based on the input data, and determines the duty ratio (sets the solenoid valve 28 to the open state (ON) by a predetermined method according to the difference between the temperature and a preset temperature. The ratio between the holding time and the holding time in the closed state (OFF) is determined, and a drive signal is output to the solenoid valve drive circuit 46 so that the solenoid valve 28 is opened and closed at the duty ratio. The solenoid valve drive circuit 46 that has received the drive signal opens and closes the solenoid valve 28 at the above timing.

A method for determining a duty ratio for opening and closing the solenoid valve 28 will be described with reference to FIG.

First, the time when the cooling is started is defined as t0, and t0
, A time tn (n = 1, 2,...) For monitoring the temperature in the thermostat at predetermined time intervals θ, and the solenoid valve is turned ON / OFF a predetermined number of times during each time θ. I do. Now, assuming that the temperature in the thermostatic chamber at each monitor time tn is Tn and the set temperature is T, the difference en between the two at each monitor time tn is obtained by the equation en = Tn-T, and the operation variable yn is calculated as follows. The equation yn = K ｛en + (θ / TI) Σen + (TD / θ) (en−
en-1)} (where K, TI and TD are constants, {en = e1 + e2 +
.. + En). Yn obtained in this way
At the time θ from time tn to tn + 1.
The duty ratio for performing the N / OFF control is set. According to this method, for example, when the monitor temperature Tn is sufficiently higher than the set temperature T, the solenoid valve is always in the ON state, but when Tn becomes a value sufficiently close to T, the solenoid valve is turned on / off at a stable duty ratio. OFF is repeated.

[0008]

However, when the temperature in the thermostatic chamber is controlled by the above method, the state of the solenoid valve is switched between ON / OFF as shown in FIGS. 8 (a) and 8 (b). The temperature in the thermostat is set to the set temperature T
It is inevitable that it fluctuates around. Further, the pressure and temperature distribution in the thermostatic chamber are disturbed in accordance with the sudden blowing / stopping of the refrigerant from the refrigerant supply pipe, thereby causing, for example, the column to vibrate due to wind pressure or the column temperature to decrease locally. Or When the column is subjected to various kinds of disturbances as described above, the influence appears in the form of disturbance or fluctuation of the baseline of the detector, and the accuracy of the measurement is impaired.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a gas chromatograph for controlling a low temperature of a thermostat using a refrigerant such as liquefied carbon dioxide or liquid nitrogen. It is another object of the present invention to provide a gas chromatograph which can supply a refrigerant to a thermostat more stably than before.

[0010]

A gas chromatograph according to the present invention, which has been made to solve the above-mentioned problem, controls the temperature in a constant temperature bath by supplying a refrigerant into a constant temperature bath in which a column is stored. In the gas chromatograph provided with a low-temperature control unit, the low-temperature control unit includes: a) a flow rate control having a continuously variable opening provided in the middle of a refrigerant flow path for supplying a refrigerant into the constant temperature bath. A valve; b) temperature monitoring means for monitoring the temperature in the thermostatic chamber; c) a predetermined temperature corresponding to a difference between the temperature in the thermostatic chamber monitored by the temperature monitoring means and a preset temperature. The refrigerant which changes the flow rate of the refrigerant into the constant temperature bath by continuously changing the opening degree of the flow control valve in the method described above, thereby stabilizing the temperature in the constant temperature bath at the preset temperature And control means. It is characterized by a door.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preparation stage for analysis, when a refrigerant control means opens a flow control valve, a refrigerant sealed in a refrigerant supply source such as a cylinder flows out of the refrigerant supply source and passes through a refrigerant flow path to a constant temperature. It is supplied into the tank. The temperature monitoring means monitors the temperature in the thermostat and sends data indicating the value to the refrigerant control means. The refrigerant control means continuously changes the opening of the flow control valve by a predetermined method according to the difference between the monitor temperature and the set temperature, thereby gradually reducing the difference between the monitor temperature and the set temperature. The monitor temperature is stabilized at the set temperature.
Then, when the temperature in the thermostat is stabilized, the analysis is started.
Through the analysis, the refrigerant control means performs feedback control of the opening of the flow control valve so that the monitor temperature is always maintained at the set temperature.

[0012]

According to the gas chromatograph of the present invention having means for continuously changing the flow rate of the refrigerant, the temperature of the column can be more stably maintained than the conventional gas chromatograph which controls the time ratio of supplying / stopping the refrigerant at a constant flow rate. Not only can control be performed, but the disturbances or fluctuations in the detector baseline do not occur due to various disturbances caused by sudden blowing / stopping of the refrigerant, so that the accuracy of data obtained by analysis is higher. It will be.

The present invention can be applied to low-temperature control of a sample injection port (injection unit) of a column.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a gas chromatograph equipped with a low-temperature control device according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an electric system of a low-temperature control device for a gas chromatograph according to this embodiment. In this electric system, the configurations and operations of the platinum sensor 36, the constant current source 38, the amplifier 40, and the A / D converter 42 are the same as those in FIG. On the way of the refrigerant supply pipe 26, a flow control valve 12 whose opening degree can be changed by changing a voltage applied to a solenoid (not shown) is provided. The arithmetic unit 14 determines the temperature in the thermostatic chamber based on the data input from the A / D converter 42, and changes the flow rate of the flow control valve 12 in accordance with the difference between the temperature and the set temperature. A voltage instruction signal is output to the control valve drive circuit 16. The flow control valve drive circuit 16 applies a voltage corresponding to the voltage instruction signal to the solenoid of the flow control valve 12.

The method of changing the opening of the flow control valve 12 according to the difference between the monitor temperature in the thermostat and the set temperature is, for example, as follows. First, when the monitor temperature is higher than the set temperature, the opening degree of the flow control valve 12 is increased to increase the flow rate of the refrigerant. Conversely, when the monitor temperature is lower than the set temperature, the opening of the flow control valve 12 is made smaller to reduce the flow rate of the refrigerant. The amount by which the opening is increased or decreased is proportional to the magnitude of the temperature difference. By such feedback control, the opening of the flow control valve 12 is adjusted at minute time intervals to stabilize the temperature in the thermostat at the set temperature.

FIG. 2 is a schematic configuration diagram showing various examples of a flow control valve used in the low temperature control device of the present embodiment. FIG.
The flow control valve (a) has a flapper 51 having one end fixed.
Is elastically deformed by the electromagnetic force of the solenoid 52 to change the opening degree of the flow path 53. In the flow control valve of FIG. 2B, the valve body 56 is supported by the electromagnetic force of the solenoid 54 and the elastic force of the spring 55. When the electromagnetic force by the solenoid 54 is changed, the valve body 5
The position of No. 6 changes, so that the opening of the flow path 57 also changes.

FIG. 3 is a schematic configuration diagram showing various examples of a flow control valve drive circuit used in the low temperature control device of the present embodiment.

First, the circuit shown in FIG.
0 is used. In this circuit, the arithmetic unit 14
D / A converter 60 receiving the voltage instruction signal output from
Applies the voltage indicated by the voltage instruction signal to one end of the solenoid 13 of the flow control valve. On the other hand, the potential at the other end of the solenoid 13 of the flow control valve is maintained at a constant value by a DC voltage generation circuit (DC) 62. According to this circuit, the voltage between both ends of the solenoid 13 changes according to the change of the voltage instruction signal, and therefore, the opening of the flow control valve can be continuously changed.

Next, the circuit of FIG. 3B utilizes a pulse width modulation circuit (PWM) 64. Generally, when a pulse voltage that is periodically turned on / off is applied to an inductive load such as a solenoid, the current flowing through the load is as shown in FIG.
As shown in (a) and (b), it exhibits a saw-like waveform that increases and decreases between an upper limit and a lower limit. Here, if the ratio of the ON time in one cycle is reduced, both the upper limit and the lower limit of the current decrease (FIG. 4A), and if the ratio of the ON time is increased, the upper limit and the lower limit of the current are both increased. (FIG. 4B). Utilizing this phenomenon, the pulse width modulation circuit 6
The principle of the circuit in FIG. 3B is to control the amount of current flowing through the solenoid 13 using the control circuit 4.

The pulse width modulation circuit 64 that has received the voltage instruction signal from the arithmetic unit 14 applies a pulse voltage having a duty ratio corresponding to the voltage instruction signal to one end of the solenoid 13. Here, the frequency of the pulse voltage is set to a sufficiently high value (for example, about 1 kHz) so that the flapper or valve body of the flow control valve does not respond to ON / OFF of the pulse voltage. In addition, Schottky
By using the barrier diode 66, it is desirable to reduce the difference between the upper and lower limits of the current, that is, the fluctuation of the current. Even with such a circuit, it is possible to control the opening of the flow control valve in the same manner as in a circuit using a D / A converter.

[Brief description of the drawings]

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

FIGS. 2A and 2B are schematic configuration diagrams showing various examples of a flow control valve used in the low-temperature control device of the embodiment.

FIGS. 3A and 3B are schematic configuration diagrams showing various examples of a flow control valve drive circuit used in the low-temperature control device of the embodiment.

FIGS. 4A and 4B are diagrams showing current waveforms when a pulse voltage is applied to an inductive load.

FIG. 5 is a partially broken view showing a schematic configuration of a low-temperature control device using a refrigerant.

FIG. 6 is a block diagram showing a configuration of an electric system of a conventional low-temperature control device.

FIG. 7 is a view for explaining a method of determining a duty ratio for opening and closing a solenoid valve.

8 (a), (b) ON / OFF state of solenoid valve
The figure which shows a mode that the temperature in a thermostat fluctuates according to switching between.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Flow control valve 13, 52, 54 ... Solenoid 14, 44 ... Calculation device 16 ... Flow control valve drive circuit 22 ... Cylinder 23 ... Column 24 ... Constant temperature bath 26 ... Refrigerant supply pipe 28 ... Solenoid valve 30 ... Electric control part 34 ... Heat sensitive body 36 ... Platinum sensor 40 ... Amplifier 42 ... A / D converter 46 ... Solenoid valve drive circuit 60 ... D / A converter 62 ... DC voltage generation circuit 64 ... Pulse width modulation circuit

Claims (1)

[Claims] 1. A gas chromatograph comprising low-temperature control means for controlling a temperature in a constant-temperature bath by supplying a refrigerant into a constant-temperature bath in which a column is stored, wherein the low-temperature control means comprises: A flow control valve having a continuously variable opening disposed on the way of the refrigerant flow path for supplying the refrigerant to the b.) B) temperature monitoring means for monitoring the temperature in the constant temperature bath; c. By continuously changing the opening of the flow control valve in a predetermined manner according to the difference between the temperature in the thermostatic chamber monitored by the temperature monitoring means and a preset temperature, And a refrigerant control means for changing the flow rate of the refrigerant to the thermostat so as to stabilize the temperature in the thermostatic chamber at the preset temperature.