JPS61167876A - Resistance type converting device - Google Patents

Abstract

PURPOSE:To take a high-precision measurement of temperature, etc., with relatively simple circuit constitution by connecting a reference resistor which is scarcely influenced by a measured physical quantity and also has a constant resistance value in series with a converting resistor for temperature measurement, etc. CONSTITUTION:The terminal A of a temperature measuring resistor Rt is connected to a terminal 11 to which a voltage -V is applied and also connected to an amplifier 1 through a switch SW5, a terminal B is connected to the amplifier 1 through a switch SW6, and a terminal (b) is connected to a common potential point through a resistance Rs (reference resistor which is scarcely influenced by a measured physical quantity and also has the constant resistance value) and also connected to the amplifier 1 through a switch SW7. Then, the gain of the amplifier 1 is held constant, switches SW5-SW7, and SW4 are turned on successively and selectively; to measure voltages VA, VB, and Vb at the terminals A, B, and (b) and the voltage VZ at the common potential point, and measurement results are stored in an arithmetic circuit 10. The circuit 10 performs specified arithmetic on the basis of those measurement results and the value of the resistance Rs, and the calculated value of the resistance Rt is converted into a temperature signal ( deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a resistance conversion device using a conversion resistor whose resistance value changes depending on a measured physical quantity such as temperature or pressure.

(Prior art) Measurement object 11! A temperature measurement device using a temperature-measuring resistor is one type of resistance-type conversion device using a conversion resistor whose resistance value changes depending on the amount of electricity.

FIG. 2 is a structural diagram showing a main part of an example of a recorder including a conventional temperature measuring device using such a resistance temperature detector. In Figure 2, H and L are input terminals for thermocouples, DC voltage, etc., and the H terminal is for resistor R1 and switch S.
It is connected to the amplifier 1 via W+, and its L terminal is connected to a common potential point. A temperature sensor 2 outputs a temperature signal for compensating the cold junction temperature of the thermocouple, and its output terminal is connected to the amplifier 1 via a switch SW2. As such a temperature sensor 2, for example, one that utilizes a temperature change in vbe of a transistor is used. Rt is a resistance temperature detector having three terminals A, B, and b,
A constant current source 3 that applies a reference current is connected to the terminal A, and the terminal A is connected to a common potential point via a resistor R2.

4 is a signal conversion circuit that converts the resistance value (Ω) into a temperature value ('C) based on the potential difference between the terminals A and all of the measuring resistor R, and its output terminal is connected to the amplifier 1 via the switch SW3. It is connected to the. S W 4 is a switch for connecting the common potential point to the amplifier 1. These switches SW+ to SW4 constitute a multiplexer that switches the input of the amplifier 1. The output of amplifier 1 is resistor R
3 and adder 5 to, for example, an integral type A/D converter 6, where it is converted into a digital signal. 7 is a reference voltage source that outputs a reference voltage of positive polarity, and 8 is a reference voltage source that outputs a reference voltage of negative polarity. The output voltage of the reference voltage source 7 is applied to the A/D converter 6 as a reference for recommending the discharge current of the integrator of the A/D converter 6, and the reference voltage source 7 is applied as a reference for the output voltage of the reference voltage source 8. It has been added to 8. The output voltage of the reference voltage source 8 is applied to the A/D converter 6 via the resistor R4 and the adder 5, and the A/Dv
It is used as a reference for setting an offset current to make the II device 6 correspond to voltages of positive polarity and negative polarity centered on voltage zero. The digital signal converted by the A/D converter 6 is applied to an arithmetic circuit 10 made up of a microprocessor, digital circuits, etc. via a signal isolation circuit 9 such as a photocoupler. The arithmetic circuit 10 is, for example, S
Automatic zero point compensation by software for measurement results based on the digital signal output of the A/D converter 6 with W a turned on, conversion of the thermocouple output voltage into a temperature signal, linearization of the measurement signal, etc. Performs necessary calculation processing.

The results calculated in this manner are added to and recorded in a recording section (not shown).

(Problems to be Solved by the Invention) However, according to such a conventional configuration, the resistance temperature detector R
The resistance value (Ω) is calculated from the temperature value (Ω) based on the potential difference between the constant current aI3 for applying a reference current to the temperature measuring resistor R1 and the terminals A and 8 of the temperature measuring resistor Rt in a temperature measuring device using the temperature measuring device R1.
'C) Since a signal conversion circuit is provided to convert the
This has the disadvantage that the circuit configuration becomes complicated and expensive circuit components must be used to maintain high precision and high stability over a long period of time, resulting in high costs.

The present invention has been made in view of these points, and its purpose is to provide a resistive converter that can perform highly accurate measurements with a relatively simple circuit configuration.

(Means for Solving the Problems) The present invention, which achieves the above object, is a resistive conversion device using a conversion resistor whose resistance value changes depending on the measured physical quantity, which is not affected by the measured physical quantity. A reference resistor with a constant resistance value is connected in series with the conversion resistor, and a current is applied to the resistor series circuit of the conversion resistor and the reference resistor to generate a voltage in each part according to the physical quantity to be measured. means and
An A/D converter sequentially captures the voltage of each part of these resistor series circuits via a multiplexer and converts it into a digital signal, and converts it based on the voltage of each part converted by the A/DI converter and the resistance value of the reference resistor. The present invention is characterized in that it includes a calculation means for calculating the resistance value of the resistor.

(Example) Hereinafter, it will be explained in detail using the drawings.

FIG. 1 is an explanatory diagram showing the main parts of a recorder using an embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals. In Fig. 1, terminal A of resistance temperature detector R
is connected to the terminal 11 to which the voltage -■ is applied via the resistor R5, and is also connected to the amplifier 1 via the resistor R6 and the switch SWa, and the terminal B is connected to the amplifier 1 via the resistor R7 and the switch SWa. and the terminal is connected to the common potential point via the resistor R3 and the resistor R
8 and switch SW? It is connected to amplifier 1 via. Here, as the resistor R8, a highly stable resistor whose resistance value is known and whose resistance value changes little due to the measured physical quantity is used. In addition, the amplifier 1 has a switch S.
A reference voltage source 12 that generates a reference voltage VF corresponding to the full span input of the A/D converter 6 is connected via We. A terminal 13 to which a voltage of 10 V is applied instead of the conventional reference voltage 8I7 is connected to the A/D converter 6, and a changeover switch S is connected to the adder 5 instead of the conventional reference voltage source 8.
Voltage −■ through W e and resistor R@IRI O
is connected to the terminal 14 to which the voltage is applied. Here, the switches S W r -S W a constitute a multiplexer.

The operation of the device configured in this way will be explained.

First, to measure the DC voltage and the thermocouple output voltage V+, with the gain of amplifier 1 set to 1, switches S W a and S W a are sequentially and selectively turned on to measure the voltage Vz and the voltage at the common potential point. While measuring the output voltage Vp of the reference voltage source 12, the switches S W + and S W are set with the gain of the amplifier 1 set to the gain G necessary for measuring the DC voltage and the output voltage Vi of the thermocouple.
< is sequentially and selectively turned on to measure the DC voltage or the output voltage Vi of the thermal lightning pair and the voltage Vz of the common potential point for offset compensation of amplifier 1, and these measurement results Vz (
1), VF (1), Vi (G), Vz (G)!
It is stored in the calculation section 11G. Then, in the arithmetic circuit 10, these measurement results Vz(I), Vp(1), Vi
(G), Vz(G)F3, and the output voltage value ■F of the known reference voltage source 12, the calculation shown in equation (1) is performed.

Vi = [(Vi (G) - Vz (G)) / (
VF (1) Vz (1)) ] VF (+
) Here, each circuit other than the reference voltage source 12 only needs to have a relatively simple circuit configuration as long as its characteristics do not change during the period in which the voltages at these four locations are measured.

In addition, when measuring the output voltage VJ of the temperature sensor 2 to compensate for the cold junction temperature of the thermocouple, set the gain of the amplifier 1 to 1 and measure Vz(1) and Vp(1) as described above. , with the gain of amplifier 1 set to the gain G necessary for measuring the output voltage of temperature sensor 2, switches SW2 and SWa are sequentially and selectively turned on to measure the output voltage VJ of temperature sensor 2 and amplifier 1. Measure the voltage V at the common potential point to compensate for the offset of
), Vz (G) are stored in the arithmetic circuit 10. and,
The arithmetic circuit 10 calculates the cholera measurement results Vz(1) and Vp(1).
), VJ (G).

Vz (G) and the output voltage value V of the existing reference voltage source 12
An operation as shown in equation (2) is performed based on p.

VJ = [(VJ (G) - Vz (G)) / (
Vp (1) Vz (1)) ] Vp (2
) Further, the arithmetic circuit 10 converts the voltage VJ thus calculated into a temperature signal ('C).

Next, wA measurement using the resistance temperature detector Rt will be explained. A constant voltage -■ is applied to the resistance temperature detector Rt from the terminal 11.
Add. In this state, while keeping the gain of amplifier 1 constant, switch SWs, 8We, SW t
, S W a are sequentially turned on selectively, and the resistance temperature detector R
Measure the voltages at each terminal A, B, b of t, Va, Vb, and the voltage Vz at the common potential point, and record these measurement results V^
, Va +Vl), and Vz are stored in the arithmetic circuit 10. Then, in the arithmetic circuit 10, each of these measurement results V
A, VB, VIl, Vz and known resistance 1i
/IR3, the calculation shown in equation (3) is performed.

Rt = [(VA +Vb -2Va) / (V
b −Vz)IR8(3) Furthermore, the arithmetic circuit 10 converts the resistance value Rt (Ω) thus calculated into a temperature signal ('C).

With this configuration, the conventional resistance temperature detector Rt
A constant current source for applying a reference current to the resistance temperature sensor Rt, which was necessary for a temperature measurement device using the resistance temperature sensor Rt.
A signal conversion circuit that converts the resistance value (Ω) to a temperature value ('C) based on the potential difference between terminals A and 8 of There are fewer circuit components that require high stability (and costs can be reduced).

By the way, in the configuration shown in FIG. 1, the measurement voltages V^, VB, and vb during the resistance value measurement operation of the resistance temperature sensor.

The output of the amplifier 1 related to Vz will only range from zero to positive polarity. This means that if the A/D converter 6 is configured to convert full span analog input signals in both positive and negative polarity ranges into digital signals, it will convert with 1/2 resolution. Put it away. Therefore, in the device shown in FIG. 1, the resistor R9 or R
The IO is selectively connected to the adder 5 to change the amount of offset added to the A/D conversion B6. That is,
For example, when resistor R9 is connected, the A/D converter 6 has a full span of 70° with positive and negative polarity centered around zero.
For example, if a resistor RIG is connected, the A/D converter 6 can convert an analog input signal in the range of positive polarity from zero to a digital signal over a full span, and the resolution can be increased.

In the above embodiment, an example is shown in which a temperature-measuring resistor that uses temperature as a physical quantity to be measured is used as the conversion resistor, but a gauge resistor or the like whose resistance value changes depending on pressure or strain may also be used.

Further, in the above embodiment, an example was explained in which only one resistance type conversion device was incorporated into the recorder, but a plurality of systems may be provided and switched by a multiplexer.

Furthermore, the invention is not limited to recorders, and can also be incorporated into data loggers and the like.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize a resistive conversion device that can perform highly accurate measurements with a relatively simple circuit configuration.

[Brief explanation of drawings]

Fig. 1 is a configuration explanatory diagram showing the main parts of a recorder using an embodiment of the present invention, and Fig. 2 shows the main parts of an example of a recorder including a temperature measuring device using a conventional resistance temperature sensor. FIG. DESCRIPTION OF SYMBOLS 1... Amplifier, 2... Temperature sensor, 5... Adder, 6... A/D converter, 9... Signal isolation circuit, 10
...Arithmetic circuit, 12...Reference voltage source, Rt...Resistance temperature sensor, R3...Reference resistance.

Claims (1)

[Claims] In a resistive converter using a converting resistor whose resistance value changes according to a measured physical quantity, a reference resistor having a constant resistance value that is not affected by the measured physical quantity and connected in series with the converting resistor; A means for applying a current to the resistor series circuit of the conversion resistor and the reference resistor to generate a voltage in each part according to the physical quantity to be measured, and a means for sequentially capturing the voltage of each part of the resistor series circuit through a multiplexer and converting it into a digital signal. It is characterized by being provided with an A/D converter for converting, and a calculation means for calculating the resistance value of the conversion resistor based on the voltage of each part converted by the A/D converter and the resistance value of the reference resistor. Resistive conversion device.