JPH04315933A - Temperature measurement device - Google Patents

Abstract

PURPOSE:To provide a temperature measurement device capable of maintaining signal error and burn-out detection time in the case of receiving a plurality of input ranges in a simmilar accuracy and responsiveness to the case where the input range is one. CONSTITUTION:Changeover means changing over a time constant at the time of charging generation voltage to a capacitor C1 according to the input range of input signal from a thermocouple is provided in a temperature measurement device which has the thermocouple providing thermo-electromotive power proportional to temperature between a pair of compensation leads 2, a capacitor C1 which is connected to each lead 2 and to which thermo-electromotive power is charged, a burn-out voltage generation circuit 10 being connected to both terminals of capacitor C1 via a resistor and charging generation voltage to the condensor C1 to inform that the thermocouple is broken when it occurs.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature measuring device using a thermocouple, and more particularly to an improvement in burnout detection function.

0002

2. Description of the Related Art Conventionally, temperature measuring devices using thermocouples are provided with a burnout detection function to detect disconnection due to burnout or the like of the thermocouple.

[0003] As shown in FIG. 2, such a temperature measuring device includes a pair of compensating conductors 2a, one end of which is connected to a signal source resistor 1.
, 2b are connected to input terminals 3a, 3b of the device main body,
Thermal electromotive force Vi proportional to the temperature generated between these input terminals
is configured such that the capacitor C1 is charged via the resistor R2. The voltage charged in the capacitor C1 is converted into a digital signal by an A/D converter (not shown) and taken into the apparatus main body as temperature measurement data. Further, a power supply Vb is connected between both terminals of the capacitor C1 via a high resistance R1. This high resistance R1 and power supply Vb constitute a burnout voltage generation circuit.

In the temperature measurement device configured in this way, a bias is applied from the burnout voltage generation circuit to the input signal from the thermocouple, but the high resistance R1 is sufficiently higher than the resistance value of the signal source resistance 1. Since it is set to a large value, only the input signal from the thermocouple charges the capacitor C1.

[0005] When the thermocouple is disconnected, the signal source resistance 1
Since the resistance value becomes infinitely large, the capacitor C1 is charged with the generated voltage from the burnout voltage generation circuit. Therefore, by abnormally increasing this charging voltage, the A/D conversion data overflows, and the occurrence of burnout can be detected on the apparatus main body side.

By the way, in the above-mentioned temperature measuring device, since a bias is applied to the input signal even during normal operation, an error occurs due to this bias. This error ΔV is expressed by the following equation. ΔV=2r×Vb/R1

[0007] However, r is the resistance value of the compensation conductor, and is assumed to be sufficiently larger than the signal source resistance 1. This error ΔV becomes larger as the compensation conductor resistance value r becomes higher. For example, the error ΔV
If is 18 (μV), if the input range of the input signal from the thermocouple is 0 to 10 mV, the input error will be approximately 0.18%, and if the input range is 0 to 100 mV, it will be approximately 0.018%.
% input error. In addition, the burnout detection time is
It has an RC characteristic as shown in FIG. 3, and is determined by the constant R1×C1.

In such a measuring device, the resistor R1 and capacitor capacitance C1 must be set such that the error ΔV is minimized to improve measurement accuracy, and the burnout detection time is minimized to improve responsiveness.

When the input range is fixed and independent, the resistor R1 and capacitor capacitance C1 satisfy the above two conditions.
It is relatively easy to set , but when there are multiple input ranges, there is a problem that it is not possible to set the optimum value for each input range.

For example, 0-10mV and 0-100m
The case where an input signal of V is received will be explained as an example. 0-10
Burnout detection time in mV input range is 10
If you set the constants of R1 and C1 so that the A/D converter overflows at 10-odd mV, then 0 to
In an input range of 100 mV, burnout detection requires more than ten times that amount of time (time to reach more than 100 mV).

[0011]

[Problems to be Solved by the Invention] Therefore, in the case of a conventional temperature measuring device using a thermocouple, in the case of multiple input ranges, errors due to burnout voltage application and burnout detection time are reduced for each input range. cannot be set to the minimum and shortest values, respectively, and there is a problem that errors included in measured values are larger than in the case of a single input range, and burnout detection time becomes longer.

The present invention has been made in view of the above-mentioned circumstances, and when there are multiple input ranges of thermocouple input, it is possible to calculate the error due to the burnout voltage application and the burnout detection time in each input range by inputting the input range. It is an object of the present invention to provide a temperature measuring device that can improve accuracy and responsiveness to the same level as when using a single range.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a thermocouple that generates a thermoelectromotive force proportional to temperature between a pair of compensating conductors, and a thermocouple that is connected to each of the compensating conductors to generate the thermoelectromotive force. a burnout voltage generation circuit that is connected between both terminals of the capacitor via a resistor and that charges the capacitor with a generated voltage to notify the outside when the thermocouple is disconnected; In the temperature measuring device, the burnout voltage generating circuit includes a switching means for switching a time constant when charging the capacitor with the generated voltage according to an input range of an input signal from a thermocouple. did.

[0014]

[Operation] According to the present invention, the time constant when charging the capacitor with the voltage generated from the burnout voltage generation circuit when the thermocouple is disconnected is switched according to the input range of the input signal from the thermocouple. . Therefore, even if there are a plurality of input ranges, the error caused by the burnout voltage is kept almost constant, and the burnout detection time is also kept almost constant.

[0015]

Embodiment An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows the configuration of main parts of a temperature measuring device according to an embodiment.

In this device, one end of a pair of compensation conductors 2a, 2b extending from a signal source resistor 1 is connected to an input terminal 3a of the device main body.
, 3b, respectively. One input terminal 3a
is connected to one electrode of the capacitor C1 via a resistor Ro, and the other input terminal 3b is directly connected to the other electrode of the capacitor C1. Both electrodes of the capacitor C1 are connected to the input terminal of an A/D converter (not shown), and this A/D
The converter output is taken into the device main body as temperature measurement data.

On the other hand, the burnout voltage generation circuit 10 is
The negative side of power supply 11 is connected to the other electrode of capacitor C1. Further, on the positive side of this power supply 11, a plurality of resistors R1 to Rn each having a different value are connected to a plurality of switches 12-1 to 12-.
The other ends of the resistors R1 to Rn are connected to the signal line between the input terminal 3a and the resistor Ro. The plurality of switches 12-1 to 12-n are analog switches and are switched by a switch selection signal given according to the input range of the input signal from the thermocouple. Therefore, the voltage Vb generated by the power supply 11 is applied to the capacitor C1 via the resistor selected by one of the switches 12-1 to 12-n.

In this embodiment, the input range is determined based on the temperature measurement data taken into the device body, and a plurality of resistors R are set so that the time constant corresponds to the current input range.
One of 1 to Rn is selected. The switch selection signal input for switching the resistors R1 to Rn can be input manually by the operator, automatically input from the device itself according to the input range, or a combination of both. applies. In this embodiment, the resistance of the time constant (C1×R) that determines the burnout detection time can be changed.

In this embodiment configured as described above, a thermoelectromotive force proportional to the temperature appears between the input terminals under normal conditions, and is charged to the capacitor C1 via the resistor Ro. The charging potential of the capacitor C1 is converted into a digital signal by an A/D converter (not shown), and used as temperature measurement data for temperature measurement.

A switch selection signal determined according to the input range determined from the current measurement data is sequentially input to the burnout voltage generation circuit 10, and the switch selection signal selects one of the plurality of resistors R1 to Rn. A resistance is selected. A bias is applied to capacitor C1 via this selection resistor.

When the thermocouple is disconnected due to burnout or the like, the resistance value of the signal source resistor 1 becomes extremely large, and as a result, the generated voltage from the burnout voltage generating circuit 10 is not applied through the selected resistor. Ru. Capacitor C
1, the capacitance increases abnormally with a time constant determined by the capacitor capacitance and the selection resistor, and as a result, the output data of the A/D converter overflows and burnout is detected. When the resistance is switched as described above, the error due to the bias from the burnout voltage generation circuit 10 and the burnout detection time are as follows.

For example, the capacitance of capacitor C1 is set to 33 μF.
, Compensation conductor resistance 300Ω, Burnout applied voltage V
b is 600mV, resistance R1 is 10MΩ, resistance R2 is 1M
Let it be Ω. When the input range is 0 to 10mV, resistor R
Turn on 1. The error amount ΔV at this time is ΔV=300×
600×10-3/10×106 = 18μ
It becomes V. Therefore, the error is 0.18%. Moreover, the burnout detection time (time to reach 10.24 mV) is determined by the following equation. Vt=V(1-e-t/CR)t=-CRloge(1-Vt/V)=5.68 Therefore, the burnout detection time is 5.68 seconds. On the other hand, when the input range is 0 to 100 mV, the resistor R2 is turned on. The error amount ΔV at this time is ΔV=300×600×10-3/1×106
=180μV. Therefore, the error is 0.18%. Moreover, the burnout detection time (time to reach 102.4 mV) is 6.17 seconds.

Therefore, by changing the time constant (C×R) of the burnout detection time for each input range,
Even if the input ranges are different, the burnout detection time can be kept constant, and the influence of the error caused by the burnout detection voltage Vb can be kept constant in each input range even in normal conditions.

As described above, according to this embodiment, the resistance value that determines the time constant of the burnout detection time can be changed according to the input range, so that the burnout detection time and normal burnout detection time for each input range can be changed. Errors caused by applying an out voltage can be maintained at the same responsiveness and accuracy as when there is only one input range.

[0025]

As described in detail above, according to the present invention, even when receiving multiple input ranges, errors due to burnout voltage application and burnout detection time can be reduced.
It is possible to provide a temperature measuring device that can maintain the same responsiveness and accuracy as when there is only one input range.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing main parts of a temperature measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the main parts of a conventional temperature measuring device using a thermocouple.

FIG. 3 is a diagram for explaining the principle of determining burnout detection time.

[Explanation of symbols]

1...Signal source resistance, 2...Compensation lead wire, 3...Input terminal, 10...
Burnout voltage generation circuit.

Claims (1)

[Claims] 1. A thermocouple that generates a thermoelectromotive force proportional to temperature between a pair of compensating conductors, a capacitor connected to each of the compensating conductors and charged with the thermoelectromotive force, and a resistor between both terminals of the capacitor. and a burnout voltage generation circuit that charges the capacitor with a generated voltage in order to notify the outside when the thermocouple is disconnected, the burnout voltage generation circuit comprises: A temperature measuring device comprising a switching means for switching a time constant when charging the capacitor with the generated voltage according to an input range of an input signal from a thermocouple.