JPS6228627A - Temperature compensating circuit for three-wire resistance type temperature sensor - Google Patents

Abstract

PURPOSE:To make highly accurate temperature detection, by making the relation between the resistance value of a three-wire resistance type temperature sensor and the output of a temperature detecting signal detected with the sensor completely linear. CONSTITUTION:A resistance 2, 1st lead wire 4, three-wire resistance type temperature sensor 3, 2nd lead wire 5,and resistance 7 are serially connected in the described order between a constant-voltage circuit 1 and earth. A differential amplifier is constituted of a feedback resistance 11 connected between the output side and (+) input terminal of an operational amplifier 8 and the amplifier 8. The 3rd operational amplifier 15 amplifies and outputs the difference in the outputs of the 1st and 2nd operational amplifiers 8 and 12. The difference value DELTAV between the output V0 of the 1st amplifier 8 and output V1 of the 2nd amplifier 12 becomes completely proportional to the resistance value R of the three-wire resistance type temperature sensor 3. Moreover, the difference value DELTAV does not contain any element of the resistance r0 of the lead wires and no error is produced even when the fitting position of the sensor 3 is changed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a temperature compensation circuit for a three-wire resistance temperature sensor whose resistance value changes depending on temperature, such as a thermistor sensor or a platinum (PT) sensor. The present invention relates to a temperature compensation circuit for a three-wire resistance type temperature sensor that is completely unaffected by the resistance value of the lead wire of the temperature sensor and can obtain an output that is accurately proportional to the resistance value of the temperature sensor.

[Conventional technology]

Resistance-type temperature sensors are the most commonly used, and their resistance value changes depending on the temperature of the atmosphere. A temperature detection circuit using this type of temperature sensor needs to accurately detect changes in the resistance value of the temperature sensor.

Conventionally, this type of temperature detection circuit consists of a Whiston bridge circuit, to which a voltage from a constant voltage source is applied and the calculation is amplified by an operational amplifier, and the change in resistance value of the resistance type temperature sensor is detected. There are methods to obtain the corresponding voltage output. In this conventional method, changes in the resistance value of the resistance-type temperature sensor are detected as unbalanced voltage changes in the Whiston bridge, so the current value flowing through the temperature sensor changes, which makes it difficult to accurately measure the resistance value of the resistance-type temperature sensor. cannot be detected. However, in reality,
Positive feedback is added to the operational amplifier as a temperature compensation circuit, and the decrease in applied current due to an increase in the resistance value of the resistance type temperature sensor is compensated for by the increase in current due to this positive feedback. This conventional method has an extremely simple configuration that only requires the addition of a resistor for positive feedback, and achieves highly accurate linearity between the differential output and the resistance value of the temperature sensor.

[Problems to be solved by invention]

Since the temperature compensation circuit of the conventional resistance type temperature sensor is configured as described above, the linearity error is approximately 0.
Although it has a certain degree of accuracy of about 3%, there is a problem in that it is impossible to eliminate this error both practically and theoretically.Moreover, when installing a resistance type temperature sensor, the resistance of the lead wire due to positional changes is high. There is a problem in that the accuracy of this linearity changes as the value changes.

In addition, there is also a method in which the Whiston bridge is not driven with a constant voltage, but is driven with a constant current from a constant current source at each branch e of the Whiston bridge. This conventional method is
Although the resistance-type temperature sensor has the advantage of being able to convert the resistance value into a voltage value with some degree of accuracy, it requires two constant current sources with exactly the same characteristics, which increases the device price.
There were problems such as impracticality.

This invention was made to solve the above-mentioned problems.
The 3-wire resistance temperature sensor has a highly linear relationship between the resistance value and the temperature detection output, and is not affected by changes in the resistance value of the lead wire. The purpose of this study is to obtain a temperature compensation circuit for a resistive temperature sensor.

[Summary of the invention]

In order to achieve the above object, the present invention includes a voltage divider circuit that divides a predetermined voltage into a high voltage side and a low voltage side on both sides of a three-wire resistance type temperature sensor, and a voltage divider circuit that divides a predetermined voltage into a high voltage side and a low voltage side on both sides of a three-wire resistance type temperature sensor; a pair of first and second connected to the low pressure side, respectively;
an operational amplifier, a feedback resistor connected to the output side of the first operational amplifier and its non-inverting input terminal, and a feedback resistor connected to the output side of the first operational amplifier and its non-inverting input terminal; and an inverting input signal generation circuit that outputs to the inverting input terminal side of each of the second operational amplifier and an output circuit that amplifies and outputs the difference between the outputs of the first and second operational amplifiers. It is equipped with the following.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

Fig. 1 shows an embodiment of the present invention. In Fig. 1, 1 is a constant voltage circuit, 2 is a voltage dividing resistor, and 3 is a three-wire resistor type having three lead wires and whose resistance changes depending on the temperature. Temperature sensor, 4, 5.6 are lead wires of 3-wire resistance type temperature sensor 3,
7 is a voltage dividing resistor, and a resistor 2, a first lead wire 4, and a 3-wire resistance type temperature sensor 3 are connected between the constant voltage circuit 1 and the ground.
, second lead wire 5, and resistor 7 are connected in series in this order. Reference numeral 8 designates a first operational amplifier, in which a resistor 9 and a resistor 10 are connected in series between the output side and the ground, and a connection point a between the two is connected.
is connected to its (-) input terminal, and its (+) input terminal is connected to the connection point between the resistor 2 and the first lead wire 4. A differential amplifier is configured by the operational amplifier 8 and the feedback resistor 11 connected between the output side of the operational amplifier 8 and its (+) input terminal. 12 is a second operational amplifier, and the same voltage dividing resistor 13 is connected between its output side and the ground.
4 are connected in series, and the connection point C of both 5 is connected to its (-) input terminal, and that (-T) input terminal is connected to the 3-wire resistance type temperature sensor 3 and its It is connected to the connection point d with the second lead wire 5. Reference numeral 15 denotes an output circuit, for example, a third operational amplifier, which takes the difference between the outputs of the first operational amplifier 8 and the second operational amplifier 12, amplifies it, and outputs the result.

Here, resistance 14. Same 13. Same 10. Same 9. Same 2, same 1
The resistance values of 1 and 7 are respectively ``, + '2 + '!l
+'4 +'5 +'6 and ry. Also,
The resistance values of the first to third leads m4 to m6 are all r. The resistance value of the three-wire resistance type temperature sensor 3 is assumed to be R. In addition, the output voltage of the constant voltage circuit 1 is v2, the current flowing through the feedback resistor 11 is 16, the current flowing from point b through the resistance type temperature sensor 3 and resistor 7 to the ground is io, and the voltage dividing resistor The current flowing through the second operational amplifier 12 is (io-i6), the output of the first operational amplifier 8 is V(1, and the second operational amplifier 12 is
Let the output be vl. First operational term of differential amplifier @ unit 8
Since the (+) and (-) input terminals of are in an imaginary short state, the output voltage v.

Since is equal to the sum of the voltages applied to resistor 10 and resistor 11, the following equation holds true.

To + 1616” Vo ・・・・・・・・・
・・・・・・・・・(1) r3+r4 Also, since the voltage at point b is equal to the voltage at three points, −VO= (2ro + ry +R) io −−
-(2)' s + r 4 The right side of equation (2) is the current i. is the voltage at point b caused by flowing through the first lead wire 4 → three-wire resistance type temperature sensor 3 → second lead wire 5 → resistor 7. Furthermore, the voltage at point b is the current (io-
; 6) is equal to the value obtained by subtracting the voltage drop due to The current flowing through lead wire 6 of No. 3 is small, and
, resistance value rl) is also small, the voltage applied to the third lead wire 6 is assumed to be approximately O, and the point a is 1! This is because the potential at point d is equal to the potential at point d.

holds true.

By eliminating 1° from equations (2) and (5), we also obtain (4)
10 is deleted from the equation and equation (5), provided that K=-.

From equations (6) and (7), find V O−V + ”:ΔV.

Resistance value '+ + '2 + 'S! '41 '51
When '6 is selected, the formula (8) is obtained. To this, A=2B+
Substituting 1 and rearranging, Δv=B(1+B)-! −(
R-ry) ・・・・・・・・・・・・ α
0), ΔV is completely proportional to the resistance value R of the three-wire resistance type temperature sensor 3.

That is, the output V of the first operational amplifier 8. The difference value ΔV between the output V of the second operational amplifier 12 and the output V of the second operational amplifier 12 is completely proportional to the resistance value R of the three-wire resistance type temperature sensor 3 both theoretically and practically. That is, when the amplification factor of the third operational amplifier 15, e.g.
The output signal is completely proportional to the resistance value R. Moreover, since the resistance r (1) of the lead wire is not included at all in this ΔV, even if the mounting position of the 3-wire resistance type temperature sensor 3 is changed, no error will occur. Never.

Next, a case where the three-wire resistance type temperature sensor 3 is disconnected will be described. When the three-wire resistance temperature sensor 3 burns out, that is, the wire is disconnected, the output voltage V of the first operational amplifier 8. becomes very large, and the output voltage V of the second operational amplifier 12 becomes very small. Therefore, Δv=vo−v increases significantly. Also, from equation 01, Δyoc(R-r7) is obtained, and if ΔV becomes very large, it is determined that the resistance value R has become very large (in this case, the needle of the measuring instrument can swing completely). Therefore, for a three-wire resistance temperature sensor whose resistance value increases as the temperature rises, a safe side against burnout is ensured.

〔Effect of the invention〕

As explained above, the present invention has a completely linear relationship between the resistance value of the 3-wire resistance temperature sensor and the output of the temperature detection signal detected using the change in this resistance value. Since the output of the temperature detection signal is completely unrelated to the resistance value of the lead wire, highly accurate temperature detection is possible, and there is also the effect of being safe against burnout of the three-wire resistance type temperature sensor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 1 is a constant voltage circuit, 2 is a voltage dividing resistor (first resistor), 3 is a 3-wire resistance temperature sensor, 4.5.6 is a lead wire (first to third lead wire), 7 is a voltage dividing resistor, 8
is the first operational amplifier, 9 is a resistor (third resistor), 10 is a resistor (fourth resistor), 11 is a feedback resistor, 12 is a second operational amplifier, 13 is a resistor (fifth resistor), 14 is a resistor (sixth resistor), and 15 is an output circuit. Patent applicant Yamatake Honeywell Co., Ltd. (no 2 people) Procedural amendment (voluntary)

Claims (3)

[Claims] (1) A voltage dividing circuit that divides a predetermined voltage into a high voltage side and a low voltage side on both sides of a three-wire resistance temperature sensor, and a pair of voltage dividing circuits whose respective non-inverting input terminals are connected to the high voltage side and the low voltage side, respectively. a first and a second operational amplifier; a feedback resistor connected to the output side of the first operational amplifier and its non-inverting input terminal; an inverting input signal generation circuit that outputs a signal to the inverting input terminal side of each of the first and second operational amplifiers; and an output circuit that calculates and outputs the difference between the outputs of the first and second operational amplifiers. Temperature compensation circuit for 3-wire resistance type temperature sensor. (2) The high voltage side is a connection point between a first resistor connected to a constant voltage source and the three-wire resistance temperature sensor, and the inverting input signal generation circuit is on the output side of the first operational amplifier. third and fourth resistors connected in series between and ground, and fifth and sixth resistors connected in series between the output side of the second operational amplifier and ground. A temperature compensation circuit for a three-wire resistance type temperature sensor according to claim 1. (3) The resistance value of each of the fifth and sixth resistors is r_
2, r_1, the resistance values of the third and fourth resistors are r_4 and r_3, the resistance value of the first resistor is r_5, and the resistance value of the feedback resistor is r_6, then r_6/r_5. =r_4/r_3, (2r_4)/r_
3. The temperature compensation circuit for a three-wire resistance temperature sensor according to claim 2, wherein a relationship of 3-r_2/r_1+1=0 holds true.