JP2874763B2 - Observation device for resistance change of heating wire - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for observing a change in resistance of a heating wire used for measuring the thermal conductivity of, for example, a liquid or a powder.

When observing the thermal characteristics of a liquid or powder as a sample, a heating wire is buried in the sample, a heating current is applied, and a temperature change of the sample is observed by a resistance change of the thermocouple or the heating wire. Is used. However, in the former case, precise measurement is difficult because the heating power is small, and the heating current affects the thermoelectromotive force to cause an error, and the temperature at a specific point is detected. Therefore, there are drawbacks such that accurate measurement cannot be performed and the number of lead wires increases. In the latter case, the resistance of the heating wire is detected using a division circuit.Therefore, when the baseline of the observed value is disturbed at startup and the temperature rise is small, the heat generation at the junction between the heating wire and the lead wire is performed. There are drawbacks such as an error caused by power. Accordingly, the present invention provides an apparatus which does not have such a drawback and can detect a wide range of average temperature in a sample and can be used for a differential scanning calorimeter or the like.

That is, the present invention intermittently applies a certain amount of power to the heating wire at certain time intervals, and furthermore, during the rest period, further increases the error voltage caused by the thermoelectromotive force at the junction between the heating wire and the lead wire. , The error voltage is held, and a constant current is applied to the heating wire during another period during the pause, and the error voltage is subtracted from the voltage between both ends of the heating wire. The heating voltage is observed, and thereby the resistance change of the heating wire is detected. Therefore, the above-described disadvantages of the conventional apparatus can be eliminated, and the differential scanning calorimeter can be constituted by embedding the heating wire in a liquid or powder sample.

FIG. 1 is a diagram showing an electrical configuration of an embodiment of the present invention, and FIG.
The figure is a time chart showing the operating states of the switches s0, s1, s2, s3 in FIG. As described above, the heating wire 2 is buried in the sample 1 such as liquid or powder, one end of which is grounded, and the other end is connected to the output amplifier 4 of the power source P by the resistor 3. Both ends of the resistor 3 and both ends of the heating wire 2 are connected to the input terminals of the amplifiers 5 and 6, respectively.
Is calculated by the synthesizing circuit 9 and added to the amplifier 4 via the amplifier 10 and the switch s0. That is, these constitute the power source P, and the switch s0 is closed by the pulse indicated by the same symbol in FIG. 2, so that the current flowing through the heating wire 2 and the voltage The output current of the power source P is adjusted so that the product of the voltage, that is, the power consumption becomes equal to the output of the setting device 8.

Also, the switch s1 has the same sign as shown in FIG.
The switch s0 is closed only for a part of the open period, a constant current is applied from the current source 12 to the heating wire 2, and the switch s2 is closed each time s0 is opened. That is, when the two switches are closed at the same time, a constant current sent from the constant current source 12 is applied to the heating wire 2 and the voltage across the heating wire 2 is supplied to the amplifier 14 via the amplifier 13 and the switch s2. Also, the output of the integrating circuit including the capacitor 15 is applied to the synthesizing circuit 16. The output of the synthesis circuit 16 is applied to the integration circuit via the amplifier 17 and the switch s3. The switch s3 is closed when the switch s2 is closed and the switch s1 is open as shown in FIG. Further, the output of the amplifier 17 is transmitted from an output terminal 20 via an operational amplifier including an amplifier 18 and a variable feedback resistor 19.

Therefore, during the period when the switches s2 and s3 are closed,
When the current of the heating wire 2 is cut off, a voltage equal to the voltage generated between both ends of the heating wire 2 is generated in the integrating circuit composed of the amplifier 14 and the capacitor 15, and this voltage is maintained even during the open period of the switch s3. . That is, the amplifier 14 and the synthesis circuit 16
Constitute a compensation circuit, in which state switches s1 and s2
Is closed, a constant current sent from the constant current source 12 flows through the heating wire 2, and a voltage generated between both ends of the heating wire 2 by the current flows through an operational amplifier including an amplifier 18 and a resistor 19. From the output terminal 20. Therefore, only the voltage applied to the heating wire 2 by the above-mentioned constant current can be accurately observed by the terminal 20 without including an error voltage due to the thermoelectromotive force at the junction between the heating wire 2 and the lead wire. The constant current source 12, the combining circuit 16, the amplifier 18 and the like constitute a resistance change detecting circuit.

As described above with reference to the embodiment, the device of the present invention can measure the voltage across the heating wire in a state where a sufficiently large and accurate current is applied to the heating wire.
Moreover, since the temperature of the entire heating wire is detected without being affected by the heating current and detecting only one temperature as in the measurement using a thermocouple, an accurate value can be obtained. In addition, there is the effect that there is no possibility that the baseline fluctuates, the thermoelectromotive force at the junction between the heating wire and the lead wire is compensated, and the required number of lead wires is small.
Furthermore, it can also be used for a differential scanning calorimeter by internal heating.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG.
It is the figure which showed the opening and closing state of the switch in the apparatus of the figure. In the drawing, 1 is a sample, 2 is a heating wire, P is a power source, 7 is a multiplier, 8 is a power setter, 11 is a controller, and 12 is a current source.

Claims (1)

(57) [Claims] 1. A power source for applying a predetermined power to a heating wire at a predetermined time interval, a current source for applying a constant current to the heating wire only for a part of a rest period of the power source, and A voltage (that is, an error voltage) generated between both ends of the heating wire during a rest period of the power source and the current source is detected and maintained, and at the time of operation of the current source, a voltage generated between both ends of the heating wire is detected. A compensating circuit for subtracting the error voltage, and detecting a voltage resulting from the resistance of the heating wire based on a voltage obtained by subtracting the error voltage from a voltage generated between both ends of the heating wire when the current source is operating. A heating wire resistance change observation device comprising a resistance change detection circuit.