JPH03185319A - System of temperature compensation of thermistor - Google Patents

Abstract

PURPOSE:To enable highly-precise temperature compensation by a thermistor by a method wherein an unbalance due to a difference between the constants of the thermistors for temperature detection and for ambient temperature com pensation of a Wheatstone bridge using thermistors on all of four arms is offset by using a differential amplifier circuits inserted into the other two arms. CONSTITUTION:All of four arms of a Wheatstone bridge are constructed of thermistors Ths, Thc, Th1 and Th2 respectively and an unbalance due to a difference in a thermistor constant between the thermistor Ths for temperature detection and the thermistor Thc for ambient temperature compensation is offset by using the thermistors Th1 and Th2 and a differential amplifier circuits inserted into the other two arms. The differential amplifier circuit is constructed of differential amplifiers in two stages and the resistance of the thermistors which varies exponentially in relation to a temperature T is compensated by the other thermistors having similar resistance variation characteristics. Therefore highly precise compensation for an ambient temperature is enabled, complete temperature compensation can be realized at two or more temperatures, and consequently highly precise temperature compensation for the thermistors can be realized in a wide range of temperature.

Description

[Detailed Description of the Invention] [Industrial Application Group] The present invention 1 is a Wheatstone bridge having a temperature detection thermistor and an ambient temperature compensation thermistor on one side, and an indeterminate output based on the difference in the constants of these thermistors. This invention relates to a temperature compensation method for a thermistor that uses cancellation.

[Conventional technology]

Conventionally, in a temperature measurement circuit with a handful of thermistors on each side of a Wheatstone brig, one thermistor is used to compensate for ambient temperature, etc., and the other is used as a temperature measurement thermistor. Since the thermistor constant B of the two thermistors is generally slightly different,
By inserting a small resistance in series with the thermistor on the larger side of the thermistor constant B, we can approximately make the thermistor constants ■ of the two thermistors equal, albeit within a narrow star range. Temperature compensation was performed for changes in ambient temperature.

Conventionally, there was a temperature detection circuit using thermistors on the four sides of the Wheatstone bridge.
The purpose was to double the unbalanced output of the bridge.

[Problem to be solved by the invention]

In the temperature detection path 11, in which a conventional temperature detection thermistor Ths and an ambient temperature compensation thermistor 1'hc are respectively inserted on two sides of the Wheatstone bridge, in order to compensate for the ambient temperature, for example, , as shown in Figure 1, a small series resistance was used to compensate for the slight difference in the thermistor constant by connecting the thermistor with a larger thermistor constant.Here,
E is the power supply, ■[1E1. is a resistance with an extremely small temperature coefficient of resistance.

However, since a thermistor has an exponential resistance value with respect to temperature T, it does not depend on temperature T. Compensation is essentially impossible, and the margin of error is large. The present invention can be applied, for example, from 10°C to 140°C.
When measuring the temperature of a living space such as body temperature without contact at F, which has a wide range of ambient temperature changes, weak infrared radiation is received by a thermistor and the temperature is raised. The required high precision thermistor temperature compensation method is required.

[Means to solve the problem]

In the present invention, all four sides of the Wheatstone bridge are used as thermistors, and the unbalance due to the difference in thermistor constant between the temperature detection thermistor 1'hs and the ambient temperature compensation thermistor The is replaced by thermistors Th+ inserted on the other two sides.
This is an attempt to cancel out the difference by using 'rh, 'rh, and a differential amplifier circuit. In order to completely cancel the unbalanced output at two different ambient temperatures, the differential amplifier circuit that amplifies the output of the Wheatstone bridge is configured with a two-stage differential amplifier, and the output of the one-stage differential amplifier is The amplification degree of one differential input terminal of the differential amplifier is adjusted so that it becomes zero at a certain temperature ′r, and in the second stage differential amplifier, at another temperature T, This is done by adjusting the amplification degree of one differential input terminal of the differential amplifier so that the final output v0, which is the differential output, becomes zero. In this case, one temperature T
, then the output of the two parallel differential amplifiers in the first stage is
Since both become zero, the output v0 of the differential amplifier in the second stage [j] also becomes zero. In this way, it is possible to uniquely make the final output voltage v0 Ov at the two temperatures T1 and T, and if the differential amplifier is made into multiple stages, the number of temperatures equal to the number of stages is equal to the number of stages. , independently, complete temperature compensation is I+
Becomes No.1.

[Effect]

The temperature of the thermistor configured as above
The resistance of the thermistor, which changes exponentially with respect to the temperature Tl2, is compensated by another thermistor having similar resistance change characteristics, so the circuit resistance ζ has a high accuracy.
! Temperature compensation is possible; at two or more temperatures,
Fully temperature compensated, the thermistor can be temperature compensated with very high accuracy over a wide temperature range.

Example] Examples will be described with reference to the drawings.

FIG. 2 is a conceptual circuit diagram showing the temperature compensation method of the thermistor of the present invention, and is a one-cusp embodiment in which the potentials of point ]) and point Q are both set to Ov at a certain temperature T1. It is. It consists of thermistors Ths, The, Th, , Th, without taking up the four sides of the Wheatstone bridge. 'rhs is a thermistor for detecting the temperature of the object to be measured, and 't'h and 'rht are the conventional θ thermistors for compensating the ambient temperature.
This thermistor is used to compensate for potential changes at the 0 point of the Wheatstone bridge due to the difference in thermistor constants between bs and 'I'hc. rl and r are resistances with extremely small temperature coefficients, and are used to generate the base voltage. DAl, DA2 and I) A3 are differential amplifier circuits.

As the thermistor Ths, the thermistor constant T (g =
4013, thermistor resistance Els83 when the temperature is 1゛+ = 25℃, Ω for 16, thermistor 'I'hc, thermistor constant Bc = 4020, 'r, -
Resistance Rc83.09 at 25℃, Ω, Thermist'
rh, the thermistor constant B, = 4016, T
, = resistance R1g3.03 at 25℃, Ω, thermistor 'rht, thermistor constant port, =4012,
T, resistance R at 25°C.

=83.07 using Ω, Wheatstone in Figure 2
configured the bridge. The resistance r is Ω to r1=50]
- constant resistor, ``, is a series connected resistor consisting of a fixed resistor of 40Ω and a variable resistor of 20Ω, and the DC power source E is 3V.
And so. Differential amplifier circuit DAI is 10 times, differential amplifier Aro D
A2 is an amplifier with variable amplification of 10 times,
This is a high impedance differential amplifier. Further, the differential amplifier circuit DA3 is a differential amplifier that can change the amplification degree by 10 times the voltage change of Pli and 5 to 20 times the voltage change at the Q point.

The temperature compensation path of this thermistor is adjusted as follows. First, the ambient temperature T1 (for example, if Tl=
25℃), adjust the variable resistor ``1'' so that the potential at point P, which is the output of DAI, reaches Ov.Next, adjust the amplification degree of the - side of the differential power of DA2. So, the potential at point Q is
J# coin so that it becomes Ov. At this time, I) A 3
The output v0 of is also Ov.

This is 1.I) The electric potential at point P and point Q, which are the human power of A3, is
Since both are Ov, the output V becomes Ov regardless of the amplification degree of DA3. Next, other ambient temperature 1
゛, (for example, 1", -= 85℃), C, the potential at points P and Q deviates from Ov due to the uneven voltage due to the difference in thermistor constant of the thermistor on each side of the Wheatstone Bridge, I) By A3, the generated voltage at point P is 10 times and the voltage at point Q is appropriately amplified, and DA
Adjust so that the differential output v0 of No. 3 becomes Ov. In this way, at two different temperatures T and Tt, the unbalanced output of the Wheatstone bridge due to the difference in the thermistor constant can be canceled by the differential amplification path.

According to theoretical calculations, the overall amplification degree of the differential amplifier circuit is 10
The final output voltage V, which cannot be compensated for only due to the difference in the thermistor constant when multiplied by 0, is 1 μV or less in the temperature range from 0°C to 100°C when using the thermistor under the conditions stated above. However, according to experimental results using an actual thermistor, the maximum output was 0.1 mV. The second difference between theory and experiment appears to be that the thermistor constant failure of an actual thermistor is not a constant value but is temperature dependent. However, in the case of the conventional method shown in FIG. 1, the amplification degree was 100 times that of the 101 differential amplification circuits, and the output was experimentally about 50 mV. It can be seen that this is extremely effective for temperature compensation. If thermistor constant B does not have temperature dependence or if a thermistor with very small temperature dependence is used, the theoretically very small output that cannot be compensated (
error output).

In the embodiment described above, for the sake of simplicity, the potentials at points P and Q are both amplified 1!
[Although the amplification degree of DA2 is set to 14, in reality, the differential power of the differential amplifier circuit DA3 should both be Ov at a certain temperature T (for example, T, = 25° C.). For this purpose, at a temperature of 1゛, a certain reference voltage VP+ and the potential at point P are made to have the same potential, the differential output is made to be one differential power of DA3, and a certain basic voltage VQ+ and Q It is preferable to make the potential of the point equal to the potential, and make the differential output the other differential power of DA3. Of course, these two reference voltages VPt and VQ+ may be made equal, and in the above-mentioned embodiment, only VP+ = V Q+ = OV.

In the embodiment described above, the first stage differential amplifier circuit DAI.

The potentials at point P and point Q, which are the outputs of DA2, are both O at temperature T.
At a temperature T, which is different from T,
I independently adjusted the output v0 of I) A3, which is the final differential amplifier circuit, to Ov, but I compared the potentials of point ■) and point Q with their respective reference potentials (OV may be used). Then, each differential output electric wire is set to Ov at a certain temperature T, and in the same way, the differential output of each stage of the multi-stage differential amplifier circuit 1111 connected later is is the temperature T*, 'r3. If we differentially amplify the P point side and the Q point side so that Ov is reached at different temperatures of T4..., the differential amplification [! Temperature compensation of the thermistor can be completely performed by adjusting the temperature difference by the number of stages in one path. In this way, it is possible to completely cancel out the unbalanced V-equilibrium output due to the difference in thermistor constant at many different temperatures, so the ambient temperature compensation of the thermistor can be performed with high precision over a large temperature range. be able to. Also, -
In the embodiment described above, in order to increase the output sensitivity of the Wheatstone Bridge, the differential amplifier circuit DAI, which is the first stage differential amplifier circuit, is used.

Point F was selected as the comparison reference potential of DA2, and this reference potential was made equal to the potential of point 0 at temperature T, but the comparison reference potential of differential amplifier circuits DAI and DA2 was set to the ground potential Ov. Also good. In the embodiment described above, direct current is used as the supply voltage to the Wheatstone bridge, but it is clear that there is essentially no difference even if this is replaced with alternating current.

〔Effect of the invention〕

The present invention includes the following 1-. Since it is configured as described above, an effect similar to that of 7F can be achieved.

Since all four sides of the Wheatstone bridge are made up of thermistors that exhibit an exponential μ resistance change with respect to an ambient temperature of 1°, both nominal sides will have a similar resistance change with respect to the ambient temperature. By differentially amplifying the output of the Brifuji, you can easily create a high quality thermistor around 11F! Temperature compensation is 117 functions. Also, by making the differential amplifier circuit multistage, two or more]
Unique final stage output at two temperatures ■. The uJ function is to set Ov to Ov, and it is possible to compensate the temperature of the thermistor over a wide temperature range and at high brightness.

As described above, according to the method of the present invention, the influence of ambient temperature can be extremely reduced, so that it can be applied to the following high-precision temperature measurements.

Four thermistor bolometers of the same shape with a micro air bridge structure are installed in close proximity using IG technology, and these four thermistor bolometers form a Wheatstone bridge to form an embodiment of the present invention as shown in Fig. 2. Configure the circuit to. Furthermore, if a thermistor that does not have a micro air bridge structure for directly detecting ambient temperature is formed at the same time in close proximity to these four thermistor bolometers and on the same substrate, these five thermistors can be Since the thermistor constant (or resistor) can be set close to The thermistor of the present invention is produced by irradiating the temperature detection thermistor 'rhs, which is the back side of the constructed thermistor bolometer, with weak red radiation from an object at a living space temperature such as body temperature and raising the temperature. In combination with the temperature compensation method, it becomes possible to measure the temperature of the object with high precision.

[Brief explanation of drawings]

FIG. 1 is a conventionally used temperature compensation circuit for a thermistor. FIG. 2 is a conceptual circuit diagram for explaining the temperature compensation method for a thermistor of the present invention. Ths...For temperature detection. Thermistor, The...
Temperature compensation thermistor, 'I'h, Th?・・・
・Thermistor + nl, Rf, r to r
tor...Resistance with small temperature coefficient, E...
・Power supply, DAI, DA2. DA3...Differential amplifier circuit patent distributor Wood Utility 1st week 1st week 1st week 11 I: September 14, 1990 1, -1 Table of 1 - 1 Patent application filed in 1990 No. 324683 2゜Name of the inventionRelationship with the old case of correcting the temperature compensation method of thermistor

Claims (1)

[Claims] Wheatstone, consisting only of thermistors on all four sides.
In the bridge, an unbalanced output based on the difference in the thermistor constant of the thermistors on the four sides is applied to a differential amplifier circuit that amplifies the output of the Wheatstone bridge at at least two different temperatures, and the amplification degree of the differential amplifier circuit is adjusted. A thermistor temperature compensation method characterized by having a circuit function that independently becomes zero.