JPH039270A - Observation device for resistance change of heater wire - Google Patents

Abstract

PURPOSE:To acurately detect the resistance change of heater wire by holding an electromotive force compensating voltage for heat of the heater wire along with intermittently applying a constant electric power to the heater wire and detecting the change portion of a voltage between both ends of the heater wire with a current made to flow to the heater wire. CONSTITUTION:The heater wire 2 is embeded in a sample 1 of liquid or powder, etc. In a period when switches s2 and s3 are closed, a voltage equal to one generated between both ends of the heater wire 2 at the condition that the current is interrupted is generated in an integration circuit consisting of an amplifier 14 and a capacitor 15, and held also in the period when the s3 is opened. When the s1 and s2 are closed with this condition, the constant current sent out from a constant current source 12 is made to flow to the heater wire 2, and the voltage generated between both ends of the heater wire 2 is sent out from an output terminal 20 through an operational amplifier consisting of an amplifier 18 and a resistor 19. Consequently, only the voltage applied to the heater wire 2 by the constant current is observed by the terminal 20 without including an erroneous voltage according to a super electric power, etc., gener ated in the heater wire 2, thereby the accurate resistance change can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for observing changes in resistance of heating wires used, for example, in measuring the thermal conductivity of liquids, powders, etc.

A device that, when observing the thermal properties of a liquid or powder sample, embeds a heating wire in the sample, applies a heating current, and observes the temperature change of the sample by changing the resistance of the thermocouple or heating wire. is used. However, in the former method, accurate measurement is difficult because the heating power is small, and the heating current affects the thermoelectromotive force, causing errors, and the temperature at a specific point is detected. Therefore, for this reason as well, there are disadvantages such as not only being unable to perform accurate measurements but also increasing the number of lead wires. In addition, since the latter uses a division circuit to detect the resistance of the heating wire, it may cause disturbances in the baseline of the observed value at startup, and if the temperature rise is small, the heat generated at the junction between the heating wire and the lead wire may There were drawbacks such as errors occurring depending on the electric power. Therefore, the present invention provides an apparatus which does not have such drawbacks, can detect the average temperature of a sample over a wide range, and can also be used in 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 also compensates for the thermoelectromotive force of the heating wire during a part of the period when the heating wire is not in use, and at the same time maintains the compensation voltage. Changes in the resistance of the heating wire are detected by passing a constant current through the heating wire during other periods during the rest period and observing the voltage between both ends of the heating wire. Therefore, the above-mentioned drawbacks of conventional devices are eliminated, and a differential scanning calorimeter can also be constructed by embedding the heating wire in a liquid or powder sample.

FIG. 1 is a diagram showing the electrical configuration of an embodiment of the present invention, and FIG. 2 is a time chart showing the operating states of the switches so, sl, s2 and s3 in FIG. 1.

In this way, the heating wire 2 is buried in the sample l such as liquid or powder, one end of which is grounded, and the other end connected to the output amplifier 4 of the power source P through the resistor 3. Connect both ends of this resistor 3 and both ends of the heating wire 2 to the input terminals of an amplifier 5.6, add the outputs of these two amplifiers to a multiplier 7, and calculate the difference between the output and the output of the power setting device 8. The synthesis circuit 9
and is added to amplifier 4 via amplifier lO and switch sO. In other words, these constitute the power source P, and since the switch sO is closed by a pulse as shown by the same symbol in FIG. The output current of the power source P is adjusted so that the product with the voltage, that is, the power consumption, is equal to the output of the setting device 8.

In addition, the switch sl is indicated by the same reference numeral in FIG.
The switch sO is closed for a further part of the open period to apply a constant current from the current source 12 to the heating wire 2, and the switch s2 is closed each time sO is opened. In other words, these 2
When the two switches are closed at the same time, a constant current sent from the constant current source I2 is applied to the heating wire 2, and the voltage across it is applied via the amplifier 13 and the switch s2 to the amplifier 14 and the capacitor 15. The j:J synthesis circuit 16 is supplied with the output of the integrating circuit consisting of the j:J synthesis circuit 16. The output of this combining circuit 16 is applied to the integrating circuit via an amplifier 17 and a switch s3. that switch s3
As shown in Figure 2, switch s2 is closed and sl
Closes when is open. Further, the output of the amplifier 17 is sent out from an output terminal 20 via an operational amplifier consisting of an amplifier 18 and a variable feedback resistor 19.

Therefore, during the period when the switches s2 and 83 are closed, a voltage equal to the voltage generated across the heating wire 2 when the current is cut off is generated in the integrating circuit consisting of the amplifier 14 and the capacitor 15. , this voltage is maintained during the opening period of switch s3. That is, the amplifier 14, the combining circuit 16, etc. constitute a compensation circuit, and when the switches sl and s2 are closed in this state, the constant current source 12 is applied to the heating wire 2.
A constant current is sent from the amplifier 18 and the resistor 1, which generates a voltage across both ends of the heating wire 2.
The signal is sent out from the output terminal 20 via an m-arithmetic amplifier consisting of 9 and 9. Therefore, only the voltage applied to the heating wire 2 due to the above-mentioned constant current can be accurately observed through the terminal 20 without including error voltage due to electromotive force generated in the heating wire 2, and it is a constant current source! 2. Synthesis circuit I6
, amplifier 18, etc. constitute a resistance change detection circuit.

As described above with respect to the embodiments, the apparatus of the present invention is capable of measuring the voltage between both ends of a heating wire when a sufficiently large and accurate current is passed through the heating wire. Moreover, it is not affected by the heating current, etc., and the temperature of the entire heating wire is detected instead of detecting only the temperature at one point, unlike measurement using a thermal lightning pair, so an accurate value can be obtained. In addition, there is no fear that the baseline will fluctuate, thermal electromotive force, etc. at the lead wire connection portion is compensated for, and the number of required lead wires is small. Furthermore, it can also be used in a differential scanning calorimeter using internal heating.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of an embodiment of the present invention.
It is a figure which showed the open and closed state of the switch in the apparatus of a figure. In the figure, l is a sample, 2 is a heating wire, P is a power source, 7 is a multiplier, 8 is a power setting device, 11 is a controller, and 12 is a current source. 491-

Claims (1)

[Claims] a power source that applies a predetermined amount of power to the heating wire at predetermined time intervals; a current source that applies a constant current to the heating wire only for a part of the rest period of the power source; and the power source and the current source. a compensation circuit that detects and compensates for a voltage generated across the heating wire during a rest period and always holds the compensation voltage; and a voltage generated across the heating wire when the current source is in operation. A heating wire resistance change observation device consisting of a resistance change detection circuit that detects changes in