JPS59204730A - Temperature detecting circuit - Google Patents

Abstract

PURPOSE:To utilize the circuit in precise temperature measurement, by connecting a highly stable fixed resistor having a specified resistance value to a thin film temperature sensor made of palladium-iron alloy or platinum-iron alloy in series, thereby correcting the dipped characteristic. CONSTITUTION:As a temperature sensor RB a thin film of palladium-iron alloy or a thin film of platinum-iron alloy is used. Resistors RA, RC, and RD, which are used for constituting a circuit, are selected so that resistance temperature coefficient is small and quality is stable for a long period. A highly stable fixed resistor RA has a resistance value, which is 2.5-5times that of the temperature sensor RB at the lowest temperature point in the temperature measuring range. By using said resistor RA, an output voltage having excellent linearity can be obtained from the sensor having a dipping characteristic. When the resistance temperature coefficient of the sensor is 6,000PPM/ deg.C, RA/RBis 2.5. When the coefficient is 4,000PPM/ deg.C, RA/RB is 4. The circuit is combined with a digital voltmeter, and a highly accurate, inexpensive thermometer can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature detection circuit using a temperature sensor.

Precise temperature measurement using a conventional thermistor with a negative resistance-temperature characteristic requires a complex linearizer, which is extremely expensive, due to the large nonlinearity of the thermistor. Also, platinum thin film temperature sensors with positive resistance-temperature characteristics have resistance in the low 6υl range? ! The jc degree coefficient is large and the convex characteristic becomes smaller in the high temperature range, and in the example of θ℃ - 50℃ - 100℃, the resistance value increases by 0913% from true 11■ at the intermediate 50℃, which is 0 in terms of temperature. .37℃ (0 for 50℃
．． 74%) error. Moreover, a stable constant current source is required for this operation, which is the case on the west side.

On the other hand, thin temperature sensors made of palladium iron alloy (PdFe) or platinum iron alloy (PtFe) have a concave characteristic in which the temperature coefficient of resistance is small in the low temperature range and large in the high temperature range, contrary to the characteristics of the platinum thin film. Therefore, it was not used for precise temperature measurement. However, in particular, thin-film temperature sensors made of palladium-iron alloy are widely used because they meet general requirements in terms of resistance, resistance-temperature characteristics, heat resistance, price, etc.

In view of the above, the present invention aims to correct the concave characteristics of thin film temperature sensors made of palladium iron alloy or platinum iron alloy so that they can be used for precise temperature measurement. be.

The feature of the present invention is that it uses a thin film temperature sensor made of palladium iron alloy or platinum iron alloy, and is highly stable and fixed with a resistance value that is 2.5 to 5 times the resistance value of these temperature sensors at the lowest temperature point of the temperature measurement range. The point is that a resistor is connected in series to these temperature sensors, and an output voltage proportional to the temperature is obtained from this connection point.

Hereinafter, the present invention will be specifically explained with reference to the drawings.

FIG. 1 shows an example of the resistance temperature characteristics of a palladium iron alloy thin film temperature sensor. Characteristic curve A.

Calculating the temperature coefficient of resistance between 25°C and 75°C for B, C, and D, the A curve is 5000 PPM/'c,
4000 PPM/'c for 8 curve, 3600 PPM/'c for c curve, 2500 P for D curve
PM/"C. From these curves, it can be seen that the larger the temperature coefficient of resistance, the greater the nonlinearity. Note that R
77' R25 is T' for the resistance value at 25°C.
The ratio of resistance values at C is shown.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

In this example, a PdFe thin film temperature sensor having resistance temperature characteristics as shown in FIG. 1 is placed on one side of the bridge circuit.

In the figure, ζ and E are applied voltage power sources and RA.

Rc and RD are resistances, RB is PdFelffi'',
IIQ jAA degree sensor, X and Y indicate output terminals. FIG. 3 is a temperature-output voltage characteristic diagram showing the results of experiments on the circuits shown in FIGS. In the experiment, E-2
, OV, and the PdFe thin film temperature sensor RB is 0℃-
A resistor with a temperature coefficient of resistance of 5000 PPM/''c at 100°C and a resistance value of l kΩ at 0°C was used. In the figure, a is when RA/RB=1, and b is when RA/RB-2. , C is RA/RB=2.5, d is RA/RB-
3, 0 is RA/Re=4, f is RA/
The respective characteristic curves when Rs=5 are plotted. however,
RA-Rp is the resistance value of each resistor, and RB is 0℃
(If the lowest temperature point in the temperature measurement range is O'C, this is the reference value.), and RA=Rc.

RB=RD at 0°C. From the 3 curves, resistance RA
If P d F 4. is selected to have the same resistance value as the resistance value RB of the PdFe temperature sensor, the degree of increase in the output voltage becomes smaller as the temperature rises. It can be seen that the resistance-temperature characteristics of the temperature sensor have a tendency opposite to that of the temperature sensor. From the b-1 curve, when the resistance value of RA is changed from 9th to It can be seen that the correction is slightly excessive.

I wanted to - C1 When the above conditions are combined, 0℃ -
The linearity error in the temperature range between 100°C and 0.1
It is possible to correct the temperature within °C, and by combining it with a digital holtometer, a highly accurate and inexpensive thermometer can be obtained. Further, by making the resistor Rc or RD variable with a potentiometer or the like, the present invention can be applied to a temperature setting section of a temperature control device. Note that the measurement temperature range can be expanded to 0° C. to 100° C. or higher if necessary, and a platinum iron alloy thin film can be used in addition to the palladium iron alloy thin film as a temperature sensor. RA+ used in circuit configuration
Each of the RC and RD resistors must be selected to have a low temperature coefficient of resistance and stable quality over a long period of time.

The above two types of temperature sensors have a variation in resistance temperature coefficient between 0℃ and 100℃ of about 5,000±1,000 PPM/'c, so if it is 6,000 PPM/'e, then RA' /Rs-2,5,4000PPM/
'C, it is effective to set RA/RB=4.

5000 PPM/”C, use RA as described above.
/Re is preferably 2.5 to 5. Outside this range, linearity deteriorates.

In the end, the resistance value of the PdFe or PtFe temperature sensor at the lowest temperature point in the temperature measurement range (O″C in the example) is 2.
By selecting a highly stable fixed resistor having a resistance value of 5 to 5 times and using -ζ, it is possible to obtain an output voltage with excellent linearity from the 61d 1 degree sensor having concave characteristics. In addition, the resistors Rc and RD can be appropriately selected depending on the application, but
As in the previous example, RA = Rc, RB = at 0'C
If it differs from RD, it can be used as a temperature detection circuit based on 0°C.

The magnitude of the output voltage can be easily changed by changing the applied voltage.
Can be adjusted. For example, to increase the output voltage in the case of FIG. 3 by 10, the resistance value of the PdFe temperature sensor at 0° C. should be set to 10Ω, and the applied voltage ratio should be set to 20V. O.V.
Using a ~20V 11J variable ta source, the sensitivity is l m
It can be changed continuously from V/'C to 20mV/'C.

According to the present invention, unlike a platinum thin film temperature sensor, a constant voltage power source and a constant current source are not required, and only a constant voltage power source is required.
The linearity error can also be improved to less than % of that of a platinum thin film temperature sensor.

Furthermore, the present invention, particularly one using a palladium-iron alloy thin film temperature sensor, has the following advantages.

In other words, the PdFe thin film temperature sensor has a large resistance value (
Because it is easy to set the circuit current to a small value, the sensitivity due to heat generation can be reduced! ■It can prevent oxidation. This is also important in reducing the current capacity of the power supply.

Generally, highly stable and constant voltage power supplies are expensive, and even if the current capacity may be slightly smaller, it will not become extremely cheap. However, in a detection circuit that can operate with an extremely small current as in the present invention, the power supply can be constructed based on a completely different concept. FIGS. 4 to 6 are circuit diagrams showing examples of such power supplies, and FIGS. 7 to 9 are voltage fluctuation characteristic diagrams corresponding thereto, respectively.

For example, in Fig. 4, the PdFe temperature sensor RB is
When Ω is set to Ω, RA is set to 80Ω, and the applied voltage is 10V, a current of 0.1mA flows through the RA, -RB series circuit, and R
Since 0.1 mΔ also flows on the C'RD side, the total e 0.2
The current consumption is mA. In the case of this level of current consumption, do you need a dedicated constant voltage IC or a temperature compensated constant? ! It has been confirmed through experiments that it is not necessary to use the Tsuji diode, and that a power supply circuit as shown in FIGS. 4 to 6 is sufficient.

In these figures, ′ζ, RK=R-Ro-1.

RN = Rp' = 500Ω + RC-RA,
RB = RD in o 'c d. In addition, the temperature coefficient of voltage between 0°C and 100'C for transistors TR
'C) It is desirable to be on the edge. This can be easily found in inexpensive commercial products. transistor TR
2. TR4 and TR5 should preferably have a voltage temperature coefficient of +'l mV/''C between 0℃ and 100℃, and diodes D1.D2゜D3.D4 should have a voltage temperature coefficient between 0℃ and 100℃. A light emitting diode with a Honjo temperature coefficient of 12 mV/'C (ordinary red light emitting diode 1.58V is available) is suitable.

In these circuits, the transistors TRI to TR5 all have their bases open and connected in the opposite direction to the input voltage Vin. However, diodes D1 to D.

is in the forward direction. Vout represents the voltage applied to the bridge (the emitter voltage of the transistor).

As can be seen from FIGS. 7 to 9 showing the experimental results, these power supply circuits can make it possible to extremely minimize fluctuations in the bridge applied voltage Vout due to fluctuations in the input voltage Vin. These power supply concave circuits use commercially available transistors with reverse polarity and suitably combine the cheapest light emitting diodes, so they are extremely cost effective and are extremely inexpensive as a whole. It is possible to do so.

Up to this point, we have described the case where a PdFe or PtFe temperature sensor RB is placed on one side of the bridge circuit, but the temperature sensor RB is connected to a highly stable fixed resistor RA with a resistance value of 2.5 to 5 times as described above. The same effect as described above can be obtained by simply connecting the terminal in series with the terminal and extracting the output voltage from this connection point.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the resistance-temperature characteristics of a PdFe thin film temperature sensor, Fig. 2 is a circuit diagram of an embodiment of the present invention, and Fig. 3 is a diagram showing an example of the temperature vs. cutting voltage of the above embodiment. Figure, Figure 4~
FIG. 6 is a circuit diagram showing an example of a power supply that can be used in the present invention, and FIGS. 7 to 9 are voltage fluctuation characteristic diagrams corresponding to each of these power supply circuits. RB...PdFe or ptFe8 film temperature sensor, sensor...The lowest point in the temperature measurement range υH. ! 4i11
A highly stable fixed resistor having a resistance value 2.5 to 5 times the resistance value of the temperature sensor at point , X, Y...output terminals.

Claims (1)

[Claims] 1. In series with the haladium iron alloy thin film temperature sensor, 2 of the resistance value of the temperature sensor at the lowest temperature point of the temperature measurement range.
．． Connect a highly stable fixed resistor with a resistance value of 5 to 5 times,
A temperature detection circuit that obtains an output voltage proportional to temperature from this connection point. 2. In series with the platinum iron alloy thin film temperature sensor, 2.5 of the resistance value of the above temperature sensor at the lowest temperature point of the temperature measurement range.
A temperature detection circuit in which a highly stable fixed resistor with a resistance value of ~5 times is connected, and an output voltage proportional to the temperature is obtained from this connection point.