JPS59574Y2 - temperature compensation circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a temperature compensation circuit that automatically corrects a physical quantity whose measured quantity changes depending on temperature to a measured quantity at a reference temperature.

For example, the temperature characteristics of high conductivity solutions such as 10% HCI or 94% H2SO4 solutions are unique, so in order to perform precise temperature compensation, it is necessary to measure the conductivity at that temperature and calculate the conductivity at that reference temperature. Accurate temperature compensation must be performed to obtain the coefficient, and in that case, the temperature coefficient must be set depending on the type of solution.

In order to realize such temperature compensation, conventionally, signals from a temperature sensing terminal that changes in proportion to temperature, such as a thermocouple or a temperature-measuring resistor, are processed and calculated using a polygonal line approximation circuit.

Alternatively, a thermistor whose characteristics change exponentially with temperature has been used by selecting its so-called B constant.

However, the former method requires a complicated circuit and requires changing the constants of many circuit elements of the temperature compensation circuit for each solution, that is, for each temperature coefficient, which reduces the versatility of the temperature compensation circuit.

On the other hand, in the latter method, although the circuit is relatively simple, it is difficult to prepare a thermistor with a strictly limited B constant due to thermistor manufacturing technology, and it is not practical to prepare thermistors with a wide variety of B constants. It was extremely difficult.

The purpose of this invention is to provide a temperature compensation circuit that can change the temperature coefficient with a relatively simple circuit.

According to this invention, an input signal to be temperature-compensated and the output of a variable gain circuit are added in an adder circuit, and the output of the adder circuit is divided into two types: one that passes through an element that changes depending on temperature changes, and one that has its polarity inverted. Temperature compensation is performed by addition in the variable gain circuit, and the temperature coefficient of the temperature compensation characteristic can be changed by adjusting the gain of the variable gain circuit.

In this way, it is possible to compensate for the temperature of a physical quantity that changes exponentially with temperature, and also easily adjust its temperature coefficient.

If the physical quantity whose measured value changes as the temperature rises, for example the value of conductivity at toC, is a(t), then generally a(
t)=f (t-to) a (to).

The temperature is the reference temperature.

Generally, the temperature coefficient is 2 to 30%, and since the temperature compensation range is narrow, f(t(o) has a value close to 1.

Therefore a(t)[1+α(tto)−α(to)) a
It can be rewritten as (to).

In order to correct the measured value to the value at the reference temperature to, the following calculations may be performed.

This device automatically calculates the above equation (1) to correct the temperature of the physical quantity, and also allows α(1) to be arbitrarily and easily set. In other words, temperature compensation allows the temperature coefficient to be changed freely. This is a proposal for a circuit.

As shown in FIG.
is added.

That is, the input signal from the input terminal 11 is supplied to the non-inverting input terminal of the operational amplifier 15 in the adder circuit 13 through the resistor 14, and the output of the variable gain circuit 12 is supplied to the resistor 16.
It is supplied to the non-inverting input terminal of operational amplifier 15 through.

In the adder circuit 13, the non-inverting input terminal of the operational amplifier 15 is connected to a common potential point through a resistor 17, and the inverting input terminal is connected to the common potential point through a resistor 18 and to the output terminal through a resistor 19. Ru.

The output of this adder circuit 13, that is, the output of the operational amplifier 15, is supplied to an output terminal 21, and the output of the amplifier 15 is supplied to an element whose resistance value changes depending on the temperature, such as a thermistor 2.
2 and the inverted signal are sent to variable gain circuit 1.
2 is added.

That is, the output terminal of the operational amplifier 15 is connected to the inverting input terminal of the operational amplifier 23 of the variable gain circuit 12 through an element 22 whose resistance value changes depending on temperature, and the output of the amplifier 15 constitutes an inverting circuit 25 through a resistor 24. Operational amplifier 2
It is supplied to the inverting input terminal of 6.

A non-inverting input terminal of the operational amplifier 26 is connected to a common potential point, and a feedback resistor 27 is connected between the inverting input terminal and the output terminal.

The output of the inverting circuit 25, that is, the signal obtained by inverting the output of the adding circuit 13, is supplied to the inverting input terminal of the amplifier 23 of the variable gain circuit 12 through the resistor 2B.

A non-inverting input terminal of the amplifier 23 is connected to a common potential point, a variable resistor 29 is connected between the inverting input terminal and the output terminal, and the variable gain circuit 12 is configured together with the operational amplifier 23.

Now resistors 14.16, 17.1B, 19, 24, 27.
28. Each resistance value of 29 is R1, R2, R3, R4, R5
, R6, R7, R8°Rα, the resistance value of the thermistor 22 is Rt, the input voltage of the input terminal 11 is Vi, the output terminal 2
The output voltage of the operational amplifier 26 is vo, and the output voltage of the operational amplifier 26 is e2.
, and the output voltage of the operational amplifier 23 is e3, respectively.
Since the operational amplifiers 15, 23, and 26 have very large open loop gains, the gain of each amplifier is determined only by the external resistance, and the following equation is established.

Here, R2//R3 is the parallel resistance value of resistors 16 and 17,
Rt//R3 is the parallel resistance value of resistor 14.17.

In the formula for vo, the coefficient R4+R5 is the 4 gain of the adder circuit 13, and the first term in parentheses means that the input signal Vi from the input terminal 11 is divided by the resistor 14 and the parallel circuit of resistors 16 and 17. Similarly, the second term is the value obtained by dividing the output e3 of the operational amplifier 23 by the resistor 16 and the parallel circuit of the resistors 14 and 17 and reaching the input terminal of the operational amplifier 15. This is the value reached.

e3 is the sum of the output of the adder circuit through the thermistor 23 and the output of the inverter circuit 25 multiplied by their respective gains.

In the above equation, assuming that R6-R7, that is, the gain of the inverting circuit 25, is 1, e2. When e3 is deleted, it becomes.

Resistance value Rt of the thermistor 22 at standard temperature.

Furthermore Then, becomes.

When a physical quantity is proportional to temperature, a(t) [1+α(t
to )) a(to ).

Therefore, by setting β=γ(t − To ) in equation (2), a temperature-compensated output can be obtained.

Obtaining the thermistor 22 with the relationship β=γ(tto) in this manner has been conventionally performed.

Here, the temperature coefficient becomes Rαbγ, but the temperature coefficient can be changed by adjusting this Rα.

Furthermore, since the temperature coefficient is proportional to Rα, the temperature coefficient can be easily set by calibrating the variable resistor 29 in advance by attaching an equal division scale to the adjustment turning angle position.

To make β proportional to t-4o, for example, as shown in Figure 2, connect a resistor 32 in parallel with the series circuit of the thermistor 22' and resistor 31, and set the resistance values of these resistors 31 and 32. By selecting appropriate values, this circuit can be replaced with element 22 in FIG.
If used instead of , β can be made proportional to the temperature difference (t − To ).

If the physical quantity of the input measurement signal changes exponentially with temperature, a (t) = eP (t, -to) xa
It is expressed as (to).

There are various things related to this, such as electrical conductivity.

In this case, in equation (2), β=ep3t-t
It suffices to set it to 0ゝ, and in that case, equation (2) becomes.

In this case, by changing Rα, equation (3) for a coefficient q smaller than p becomes
) can be approximated as

That is, it is possible to compensate for the temperature that changes exponentially.

In order to bring this β into the relationship eP(t-to), it is sufficient to adjust the resistance values of the resistors 31 and 32 in FIG. 2, and this has been known from the past.

In Figure 3, p==Q. 04tO-10≦t≦to+10
The error between ae q (t, -t, 01 and equation (3) is shown.

In other words, the originally desired speed is expressed by equation (4), which shows the characteristics of < equation (3), and the error is less than 0.5% within the range of +/-5°C, and if compensation is taken, it is ±5°C. This can sufficiently compensate for an error of 20% or more compared to the case with a dirt floor.

In this case, although there are constraints that p is small and the temperature compensation range is narrow, it is possible to temperature compensate a physical quantity that changes exponentially with temperature.

Furthermore, since q in equations (3) and (4) is proportional to Rαp, the temperature coefficient can be easily changed by adjusting the resistance value of the resistor 29.

To adjust the gain of the variable gain circuit 12, as shown in FIG. The movable element of the variable resistor 29 may be adjusted by connecting it to the inverting input terminal.

As described above, according to the temperature compensation circuit according to this invention, temperature compensation can be performed even when the measured quantity changes in proportion to the temperature or changes in an exponential manner.

Furthermore, the temperature coefficient can be easily adjusted by adjusting the variable resistor 29.

Even if the temperature coefficient is adjusted in this way, β
-1 and ■ in equation (2).

is constant as aVi, that is, the span does not change even if the temperature coefficient is changed.

Furthermore, since the temperature coefficient is proportional to the resistance value of the resistor 29, it can be easily set to a target value by attaching an equal division scale to the rotational position of the adjustment knob as described above.

Furthermore, temperature compensation can be performed for physical quantities that change in proportion to temperature, and the temperature coefficient thereof can be changed.

In the above description, if a temperature detection terminal that outputs a signal that changes proportionally to temperature is used instead of a thermistor as the element whose resistance value changes depending on temperature, a compensation circuit for temperature characteristics that changes proportionally to temperature can be obtained.

In this case as well, by changing one type of detection terminal and one circuit element, it is possible to set an arbitrary temperature coefficient within a range smaller than the temperature coefficient of the temperature detection terminal.

[Brief explanation of the drawing]

Figure 1 is a connection diagram showing an example of a temperature compensation circuit based on this invention, Figure 2 is a diagram showing an example of an element whose resistance value changes depending on the temperature, and Figure 3 is a diagram showing an example of an element whose resistance value changes depending on the temperature. FIG. 4 is a diagram showing a partial modification of the temperature compensation circuit of this invention. 11: Input terminal, 12: Variable gain circuit, 13: Adding circuit, 25: Inverting circuit, 22: Element whose resistance value changes depending on temperature.

Claims (1)

[Scope of utility model registration request] An adder circuit is connected to the input terminal and the output side of the variable gain circuit, and adds the input signal from the input terminal and the output of the variable gain circuit; one end is connected to the output side of the adder circuit; An element whose resistance value changes, an inverting circuit that is connected to the output side of the adding circuit and outputs the output of the adding circuit by inverting the polarity, and an input side is connected to the output side of the inverting circuit and the other end of the above element. The variable gain circuit is connected to the output side of the adder circuit and is connected to the output side of the adder circuit to add the output of the inverting circuit and the output of the adder circuit supplied through the element and to change the gain. and an output terminal from which a signal is obtained, and the gain of the variable gain circuit is set according to the temperature coefficient of the input signal to be compensated.