JPS62261968A - Measuring instrument for physical quantity - Google Patents

Abstract

PURPOSE:To obtain measurement temperature, etc., and to take a high-accuracy measurement by comparing a reverse integration time obtained while a switch connected to a reference resistance is closed with a reverse integration time obtained while a switch connected to a resistor for measuring a physical quantity, etc., after integrating operation. CONSTITUTION:When normal integration is performed, a switch SWD is closed and R1 is used as an integrating resistance. When reverse integration is performed, resistances are switched through switches SW1-SW4 in the order of reference resistances Ra and Rbn and a thermistor temperature sensing element RS and A/D conversion is performed continuously three times. This reverse integration time is proportional to the resistance value of the integrating resistance, so a counter controller 31 counts the reverse integration time by using a clock and inputs its counted value to a microcomputer 32. Then, the microcomputer 32 compares the value obtained by the use of the temperature sensing element RS with the counted value obtained by the use of the high-temperature side reference resistance Ra and low-temperature side reference resistance Rb and finds the resistance value of the resistor for measuring the measurement temperature and physical quantity from the comparison result.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a device for measuring temperature, resistance value, etc. using a double integration type A/D converter. I! This is the path related to the am constant circuit.

[Prior Art] Conventionally, as this type of physical FHM constant circuit, there has been one shown in FIG. 3, for example. This circuit is a thing! ffi is a temperature measurement circuit that uses a thermistor temperature sensor.

In the figure, A++A2 is an OP amplifier.

The OP amplifier A1 has a non-inverting input terminal connected to the reference voltage generation circuit 1, an inverting input terminal connected to ground via a resistor Ro, and an output terminal connected to the switch S+.

0]) The amplifier A2 has its non-inverting input terminal connected to the switch S2, and its output terminal connected to the Δ/DItIA device 2. Further, the output of the OP amplifier A2 is fed back to the inverting input terminal.

Rs is a thermistor temperature measuring element, and Ra and Rb are reference resistances, one end of which is commonly connected to the inverting input terminal of OP amplifier A+, and the other end is connected to OP amplifier A via resistor R1.
It is connected to the inverting input terminal of No.2.

The other end of the thermistor temperature sensor Rs is the switch contacts a1 and b.
1, the other end of the reference resistor Ra is the switch contacts a2 and b2.
The other end of the reference resistor Rb is connected to the contacts a3 and b3 of the switch, respectively.

When measuring temperature using such a circuit, a constant current is supplied to the reference resistors Ra, Rb, and Rs by switching the switches, and the voltage across each resistor is input to the amplifier A2.
/D converter 2 converts it into a digital value. Then, the digital value of the thermistor temperature sensing element Rs and the reference resistance Ra, Rb
The measured temperature is determined from the comparison results.

[Problem to be solved by the invention] However, in this circuit,! ! Fluctuations in the quasi-voltage and offset and drift of the OP amplifier will have a negative effect on measurement accuracy, so if you want to obtain high accuracy, use an expensive constant voltage/constant current circuit (reference voltage generation circuit or OP amplifier). There was a problem in that an equivalent item was required.

The present invention was made to eliminate the above-mentioned problems, and an object of the present invention is to realize a physical quantity measuring device that can obtain high measurement accuracy without requiring an expensive constant voltage/constant 1R current circuit. .

[Means for Solving the Problems] The present invention provides a two
I! an integral type A/D11i converter, and a resistor for physical quantity measurement, one end of which is commonly connected to the inverting input terminal of the OP amplifier, and the other end of which is connected to a reference voltage source via a switch provided for each. and a reference resistance, an inverse integration time when a switch connected to the reference resistor is closed and inverse integration is performed, and an inverse integration time when an inverse integration is performed after the integrator performs an integration operation. Control that compares the inverse integration time when the switch connected to the resistor for m measurement is closed and inverse integration is performed, and calculates the measured temperature or the resistance value of the resistor for measuring the physical quantity based on the comparison result. This is a physical meter measurement circuit characterized by comprising a circuit.

[Example] The present invention will be explained below using the drawings.

FIG. 1 is a block diagram of an embodiment of the object JJm measuring circuit according to the present invention, and here, the case of a temperature measuring circuit is illustrated. Components in FIG. 1 that are the same as those in FIG. 3 are given the same reference numerals.

In the figure, ■ is an integrator. In the integrator I, A is an OP amplifier, the non-inverting input terminal is connected to ground, and the positive reference voltage vrer is applied to the inverting input terminal via the switch S W o and the resistor FLRI. CI is an integrating capacitor connected between the inverting input terminal and the output terminal of the OP amplifier.

A series circuit of a switch SW and a resistor Rf is also connected between the inverting input terminal and the output terminal of the OP amplifier A.

A comparator C compares the output of the OP amplifier A with a predetermined reference value and outputs a 21m signal according to the comparison result.

Integrator (2) and comparator (C) constitute a double integration type A/D converter.

Rs is a thermistor temperature sensing element, and R is an approximation resistor inserted in parallel with the reference resistor in order to approximate the logarithmic characteristic between the temperature and resistance of the thermistor temperature sensing element Rs to a linear characteristic. Ra is a reference resistance on the high temperature side, and Rb is a reference resistance on the low temperature side.

A negative 3% lv lightning voltage Vref is applied to one end of these resistors R, Ra+Rb, and Rs via switches SW+, SW2, SW3, and SWa. Also,
The other end is commonly connected to one end of low bc R2.

The other end of resistor R2 is connected to the inverting input terminal to the OP amplifier.

The switch SWo=SWa, SW is, for example, an analog switch.

In the control circuit 3, 31 is a counter controller that counts the integration time of the integrator using a clock and controls the opening and closing of the switches S W o to S W a. 32 is a microcontroller (hereinafter referred to as microcomputer), which calculates the measured temperature based on the count value of the counter controller 31.

The aforementioned resistor R2 is a compensating resistor whose number is set in order to set the signal input to the counter controller 31 to a level at which the counter controller 31 can measure time.

Next, the operation of such a physical quantity measuring circuit will be explained.

FIG. 2 is a time chart for explaining the operation of the circuit shown in FIG. 1, with the vertical axis representing the output voltage of the OP amplifier and the horizontal axis representing time.

When performing normal integration, R1 is used as the switch 5Woe jump integration resistor.

During inverse integration, the resistances used during inverse integration are switched in the order of reference resistors Ra, Rb, and thermistor temperature sensing element Rs using switches SW+ to SW4 to perform A/Dt conversion three consecutive times. Since the inverse integration time is proportional to the resistance value of the integrating resistor,
The counter controller 31 counts the inverse integration time using a clock and inputs the counted value to the microcomputer 32. The microcomputer 32 compares the counted value when using the thermistor temperature sensing element Rs with the counted value when using the reference resistors Ra and R++, and determines the measured temperature from the comparison result.

Here, E≧a is the standard resistance on the high temperature side, RLI is the reference resistance on the low temperature side, and the measured temperature is determined from the temperature-resistance field characteristic curve connecting the reference resistance value on the high temperature side and the reference resistance value on the low temperature side. demand. Further, since the approximation resistor R is set in order to approximate the logarithmic characteristic of temperature-resistance value to a linear characteristic, the switch SW + is closed during each inverse integration.

In the complementary interval between each integral operation, the switch SW is closed and the integral capacitor CI is charged.

In addition, in the embodiment, a case has been described in which the object 3JJI quantity measuring device is a temperature measuring circuit, but the object 2 quantity measuring device is not limited to this, and the object II quantity measuring device may be a circuit that measures the resistance value itself or a circuit that outputs a change in resistance value. It's okay.

[Effect 1] According to the present invention, since there is no constant voltage/constant current circuit, it is not affected by the offset or drift of the OP amplifier used in the constant voltage/constant Fj1tit circuit; There is no need to use expensive constant voltage/constant current circuits to prevent this. by this,
Highly accurate measurements are possible without the need for expensive circuits. Furthermore, since the resistance value is directly input to the A/D converter, highly accurate measurement is possible.

Further, the circuit according to the present invention can simplify the configuration because two OP amplifiers and two switches can be reduced compared to the conventional circuit shown in FIG.

4. Detailed description of the invention FIG. 1 is a configuration diagram of an embodiment of the physical quantity measuring circuit according to the present invention, FIG. 2 is a time chart for explaining the operation of FIG. 1,
FIG. 3 is a block diagram of a conventional example of a substance yIA quantity measuring device.

■... Integrator, △... OP amplifier, C... Comparator, SW, SWI ~ S W a... Switch, Rs...
・Thermistor temperature sensing element, Ra, Rb...Reference resistance, 3.
...Control circuit.

Claims (1)

[Claims] A double integration type A/D converter comprising an integrator using an OP amplifier and a comparator, one end of which is commonly connected to the inverting input terminal of the OP amplifier, and the other end of which is connected in common to the inverting input terminal of the OP amplifier. A resistor for physical quantity measurement and a reference resistor are connected to a reference voltage source through switches provided for each, and after performing an integration operation in the integrator, the switch connected to the reference resistor is closed and reverse operation is performed. Compare the inverse integration time when the integration is performed and the inverse integration time when the inverse integration is performed by closing a switch connected to the resistor for measuring the physical quantity after performing the integration operation with the integrator, A physical quantity measuring circuit comprising: a control circuit for determining a measured temperature or a resistance value of the resistor for measuring the physical quantity based on a comparison result.