JPS5925002Y2 - thermal conductivity detector - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a thermal conductivity detector used as a detector for gas chromatographs and the like, and in particular to protection of its filament.

First, the operating principle of a conventionally used thermal conductivity detector will be explained based on FIG.

The four filaments la, lb, IC, and ld constitute a filament bridge 1.
A constant DC current is supplied from a constant current power supply 2 to each filament, and each filament is in a heat generating state.

For example, in the case of a gas chromatograph, one of these four filaments is placed in the flow path for only the carrier gas, and the other one is placed in the flow path for the separated component gases to flow out. When the gas flowing in both flow paths is the same carrier gas, the filament bridge 1 is in a balanced state, and the filament bridge 1
The midpoint voltage of is zero.

However, the component gas flows out into the flow path, the thermal conductivity of the gas surrounding the filament changes, and the heat dissipation state of the filament changes.

Along with this, the temperature of the filament itself changes, so the internal resistance of the filament changes, and the filament bridge 1
The balance of the filament bridge 1 is disrupted, and a voltage is generated at the midpoint of the filament bridge 1.

This voltage is amplified by an amplifier 3, and a recorder 4 records changes in this voltage over time.

From this recorded result, the type and concentration of the component gas can be known.

As long as the current supplied to the filament mentioned above is a constant current value (meaning that it is sufficient if the measurement time interval is constant), it is well known that the higher the current value, the higher the detection sensitivity. It is being

Therefore, it is desirable to use the filament at a high current value as much as possible, but using it in this high current range will overheat the filament and cause it to exceed a certain limit of internal resistance. It tends to be.

This overheating of the filament shortens its life, degrades its performance, and in severe cases leads to wire breakage.

Conventionally, to prevent this, the average resistance value (the resistance value of the entire filament bridge 1 increases as the temperature rises) is measured, and if it exceeds a certain value, the constant current is cut off. A method is being adopted.

However, according to this method, once the filament overheats, the next analysis cannot be performed unless the current setting is lowered and the current supply is restarted, and attempts are also made to set the highest current value that can be used safely without overheating the filament. The drawback was that it had to be done by mistake.

The present invention aims to provide a thermal conductivity detector that eliminates the above-mentioned drawbacks, and the main part of its configuration is that a digital counter that determines the set value of the filament heating current is connected to a constant current source. At the same time, there is a detector that detects the resistance value of the filament.The output of this detector is compared with the maximum allowable resistance value of the internal resistance of the filament, and a signal is generated when the output of the resistance value detector exceeds the maximum allowable resistance value. A pulse generator that generates a pulse signal that decrements the set value of the digital counter is connected to the digital counter, and the gate of the pulse generator is opened by the signal from the level detector. A thermal conductivity detector is characterized by the following.

The operation of the present invention will be explained below with reference to FIG. 2, which is a diagram illustrating the main parts of one embodiment.

2 is a constant current source, 1 is a filament bridge, 3 is a detector, 10 is a level detector that generates a signal when the internal resistance value of the filament exceeds the maximum allowable resistance value, and 5 is a clock pulse generator that generates a clock pulse. 6 is a gate that is opened by a signal from the level detector 10, 7 is a counter for setting the supply current value of the constant current source 1, and 8 is a counter 7.
A setting device 9 is used to change the set value in the counter 7, and a display device 9 displays the set value in the counter 7.

Note that the set value of the counter 7 is decremented by a pulse signal from the clock pulse generator 5.

The following operation in the above configuration will be explained.

First, the setting device 8 is adjusted to set the counter 7 to a set value corresponding to the current value to be supplied to the filament bridge 1.

A constant current set by the counter 7 is supplied from the constant current source 1 to the filament bridge 1.

The resistance of the filaments of this filament bridge 1 is measured by a detector 3, and if this measured resistance exceeds a predetermined maximum permissible resistance, a level detector 10 generates a signal.

This signal opens the gate 6, and when the gate 6 is opened, the pulse signal of the clock pulse generator 5 is energized to the counter 7, and the set value of the counter 7 is changed depending on the number of pulse signals applied. Decrease.

(Conversely, if the filament resistance value does not exceed the maximum permissible resistance value, the level detector 10 does not generate a signal and the gate 6 remains closed, so the pulse signal is not applied to the counter 7; The settings do not change.

) As this setting value decreases, Foramen 1 to Bridge 1
The current value supplied to the ficimen 1 decreases, and the resistance value of the ficimen 1 becomes less than the maximum allowable resistance value again, and the signal from the level detector 10 disappears. At the same time, the gate 6 is closed and the pulse signal is no longer energized to the counter 7. will be stopped.

Therefore, the set value of the counter 7 remains at the value immediately before the gate 6 closes, and the current supplied to the filament bridge 1 is also held at a value corresponding to this set value.

Then, even at this decreasing constant current value, when the filament resistance exceeds the maximum allowable resistance value, the above-described operation is repeated once again, and the current is set to a still lower value.

In other words, each time the filament resistance exceeds the maximum allowable resistance value, the constant current value supplied to the filament bridge 1 decreases in a stepwise manner.

Therefore, since the filament bridge 1 is never supplied with a current higher than the initially set current value, the filament is never damaged by overheating.

In addition, in the above example, when the filament is heated,
This simply lowers the current setting automatically, but if you add another detector to this configuration that generates a signal with a resistance slightly lower than the level detector 10 to issue an alarm. , it is possible to sense that the filament is nearing overheating before the current setting is automatically lowered due to overripeness of the filament I.

As detailed above, the present invention has a filament bridge 1
The current value to be supplied to the filament bridge is set by the counter 7, and when the filament I/resistance exceeds the maximum allowable resistance value, the set value of the counter 7 is lowered in steps. This prevents the filament from overheating even if the current setting is too high or the temperature of the detector temperature chamber is raised, and the filament can be operated at the highest allowable current value for its surrounding conditions. Therefore, it is possible to provide a detector with the highest sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the principle of a conventional thermal conductivity detector, and FIG. 2 is a diagram for explaining the main parts of the thermal conductivity detector of the present invention. 1...Filament bridge, 2...
Constant current source, 3...Amplifier, 4...Recorder, 5...Clock pulse generator, 6...
...Gate, 7...Counter, 8...
Setting device, 9...Display device, 10...Level detector, 11...Detector.

Claims (1)

[Scope of utility model registration request] A heating current is supplied to the filament, the change in resistance of the filament is measured based on the sample gas surrounding the filament, and in a detector that detects the sample gas, a digital counter that determines the set value of the heating current for the filament is controlled by a constant current. A resistance value detector of the filament is connected to the source, and the output of this detector is compared with the maximum allowable resistance value of the internal resistance of the filament, and a signal is generated when the output of the resistance value detector exceeds the maximum allowable resistance value. A level detector is provided, and a pulse generator that generates a subtraction pulse signal of the set value of the digital counter is connected to the digital counter, and the gate of the pulse generator is opened by the signal from the level detector. Features of thermal conductivity detector.