JPS59775B2 - temperature converter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a temperature converter using a 4-wire resistance temperature sensor, and in particular, parts that allow output to be out-scaled and upscaled when the resistance temperature sensor is disconnected. This invention relates to a temperature converter having an out circuit.

In general, in an automatic control system, if a resistance temperature detector is disconnected due to fatigue or damage, it must be detected and some measure taken to ensure safe operation of the control system.

Therefore, in a resistance thermometer type temperature converter, an operation is performed to swing the output signal outside the standard signal range, either the upper limit or the lower limit, so that disconnection of the resistance temperature sensor can be detected.
It is desirable to have a so-called parts-out circuit. FIG. 1 shows an example of a conventional temperature converter composed of a four-wire resistance temperature detector and an adder/subtractor.

In FIG. 1, 1 has a first current supply lead wire A1 and a first voltage detection lead wire B1 connected to one end,
It is a four-wire resistance temperature detector whose other end is connected to a second current supply lead wire A2 and a second voltage detection lead wire B2. is the equivalent resistance of each of the lead wires A1, B1, B2, A2 from the detection end to the converter. 2 is
A constant current source supplies a constant current i to the temperature measuring resistor 1 as shown by the arrow in the figure via current supply lead wires A1 and A2 and a bias resistor Rb.

Here, the bias resistor Rb has one end connected to the COM line which is the reference potential of the constant current source 2 and the adder/subtractor 3, and the other end connected to the current supply lead wire A2. With the COM line as a reference potential, the voltage generated via the voltage detection lead wire B1 is passed through a low-pass filter circuit consisting of a resistor R1 and a capacitor C1 to the first positive phase having a high input impedance of the adder/subtractor 3. It is added to the input end. Also,
The voltage generated via the voltage detection lead B2 is applied to the second negative phase input terminal of the adder/subtractor 3, which has a high input impedance, via a low-pass filter circuit consisting of a resistor R2 and a capacitor C2. . Also, bias resistor Rb
The voltage generated is applied to the third negative phase input terminal of the adder/subtractor 3 having a high input impedance. Here,
The adder/subtractor 3 sets the voltage applied to the first positive phase input terminal as e1, the voltage applied to the second negative phase input terminal as E2, and the third negative phase input terminal as the reference potential of the COM line. The voltage applied to is E3, and the output voltage is E. When, the conversion gain G for each input is equal, the calculation of equation (1) is performed. EO=G(e1-E2-E
3) 6″8゜゛゜゜゜゛″″ (1) Also, ZD is a zener diode connected to both ends of the constant current source 2, and when the resistance temperature detector 1 is disconnected, the load of the constant current source 2 is opened. This is to prevent excessive voltage from being applied to the input terminal of the adder/subtractor 3 and to protect the constant current source 2 itself. It is not necessarily necessary.

In addition, the zener voltage Vz of the zener diode ZD is set to Vz》(r1+R
t+R4+Rb)i. Here, Rt is the resistance value of the resistance temperature detector 1. The first
In the temperature converter shown in the figure, the resistance value Rt of the resistance temperature detector 1 is expressed by equation (2). Rt=Rtb+ΔRt・・・・・・
(2) Here, Rtb is a constant bias resistance value determined by the type of resistance temperature detector and the lower limit of the measurement temperature range, and ΔRt is the type of resistance temperature detector and the measurement temperature. This is the resistance change corresponding to the temperature change from the lower limit of the measurement temperature range determined by the range.

First, in a steady state, since the Zener diode ZD is in a cutoff state, each voltage applied to the adder/subtractor 3 is expressed by the following equation.

e1=(Rtb+ΔRt+R4+Rb)i...
(3) E2=(R4+Rb)i...
・・・・・・(4) E32Rb-1 ・・・
・・・・・・・・・(5) By substituting the relationships of these equations (3) to (5) into equation (1), EO=G(Rtb+ΔRt
-Rb)i... (6) In equation (6), the constant bias resistance value Rtb included in the resistance temperature sensor 1 and the value of the bias resistance Rb are equal, Rb=Rtb...・
......If you choose (7), you will get equation (8).

EO=G・ΔRt−1゜゜゜゜゜゜゛゜゜゛゛゜ (8) In such a steady state, as shown in equation (8) as the output of the adder/subtractor 3, the resistance of the resistance temperature detector is not affected by the resistance of the lead wire. A resistance change Rt in an arbitrary range can be converted into an electrical signal in a desired range.

Next, in the conventional example shown in FIG. 1, the operation of the resistance temperature detector 1 in various abnormal states will be described with reference to FIG.

In addition, the equivalent resistance R of each lead wire shown in FIG.
The value of R4 is sufficiently small compared to the values of circuit resistances Rl, R2, and Rb, and there is no problem in explaining the operation in an abnormal state. are omitted. First, when the first current supply lead wire A1 of the temperature sensing resistor 1 is disconnected, the circuit shown in FIG. 1 is represented as shown in FIG. 2a.

At this time, the constant current 1 from the constant current source 2 flows only through the Zener diode ZD, and the voltages El, e2, and E3 applied to each input of the adder/subtractor 3 all become zero. Therefore, the output E of the adder/subtractor 3. also becomes zero. Next, when the first voltage detection lead wire B1 of the resistance temperature detector 1 is disconnected, the circuit shown in FIG. 1 is represented as shown in FIG. 2b. At this time, the constant current source 1 from the constant current source 2 flows to ΔRt, Rb as shown by the arrow in the figure, and the voltages E2 and E3 are (
This is the normal voltage at steady state as shown in equations (4) and (5). However, the adder/subtractor 3 with high input impedance
The first positive-phase input terminal of is in an open state, and due to line noise, etc., the output E of the adder/subtractor 3. becomes indeterminate. Further, when the second voltage detection lead wire B2 of the temperature sensing resistor 1 is disconnected, the circuit shown in FIG. 1 is represented as shown in FIG. 2c. In this case as well, as in the case of lead wire B1 disconnection, constant current 1 flows through Rt and Rb as shown by the arrow, and voltages E and E3 are normal voltages at steady state as shown by equations (3) and (5). It is. However, the second negative-phase input terminal of the adder/subtractor 3, which has a high input impedance, is in an open state, and the output E of the adder/subtractor 3 is caused by line noise or the like. becomes indeterminate. In addition, the second current supply lead wire A of the resistance temperature detector 1
2 is disconnected, the circuit shown in Fig. 1 is changed to Fig. 2 d.
It is expressed as

Since the input impedance of the adder/subtractor 3 is very high, the constant current 1 from the constant current source 2 at this time flows only through the zener diode ZD as shown by the arrow in the figure, and generates the zener voltage Vz. This Zener voltage Vz is applied to the first positive phase input terminal of the adder/subtractor 3 via the resistor R1, and is applied to the second positive phase input terminal of the adder/subtractor 3 via the resistor Rt of the resistance temperature detector 1 and the resistor R2. Applied to the negative phase input terminal. Here, resistors Rl, R2
Since the input impedance of the adder/subtractor 3 is a very large value compared to the value of and Rt, it becomes e1-E2-Vz. Also, the voltage E3 at the third negative phase input terminal of the adder/subtractor 3
becomes zero. As is clear by substituting the values of these voltages e1 to E3 into equation (1), the output E of the adder/subtractor 3
. becomes zero. Finally, when the resistance wire Rt of the resistance temperature detector 1 is disconnected, the circuit shown in FIG. 1 is represented as shown in FIG. 2e.

In this case, as in the case where the lead wire A2 is disconnected, the constant current 1 flows only through the zener diode ZD and generates the zener voltage Vz. This Zener voltage Vz is applied to the first positive phase input terminal of the adder/subtractor 3 via the resistor R1. That is, e
1=Z. Here, the value of the Zener voltage Vz is selected to be sufficiently larger than the signal voltage e1 in the steady state expressed by equation (3). On the other hand, the voltages E2 and e3 at the other second and third negative phase input terminals of the adder/subtractor 3 are both zero. As is clear by substituting the values of these voltages e1 to E3 into equation (1), the output E of the adder/subtractor 3. swings to the positive side. Hereafter, this will be referred to as parts-out scale. As described above, in a temperature converter using a conventional 4-wire resistance temperature detector, when various abnormal conditions occur due to disconnection of the resistance temperature detector, the direction of the output cannot be determined, especially for current supply. If the lead wire A1 or A2 is disconnected, the output will be zero, and it will not be possible to distinguish it from the output when the steady state input resistance ΔRt = 0 (lower limit of the temperature measurement range).
There was a drawback that it was not possible to select the direction in which the control system would operate safely in the event of an abnormality.

The purpose of the present invention is to eliminate the drawbacks of the conventional circuit as described above, and to provide an operation that reliably swings the output of the temperature converter to the upper limit when various abnormal conditions occur due to disconnection of the 4-wire resistance temperature detector. The object of the present invention is to realize a temperature converter having a parts-out circuit with a simple configuration, which is so-called parts-out upscaling.

The gist of the present invention is that a first current supply lead wire and a first voltage detection lead wire are connected to one end, and a second current supply lead wire and a second voltage detection lead wire are connected to the other end. a four-wire resistance temperature detector connected to the resistance temperature detector; a constant current source that supplies a constant current to the resistance temperature detector via the first and second current supply lead wires; The generated voltage is
, a temperature converter comprising a second voltage detection lead wire and a high input impedance adder/subtractor inputted via the second current supply lead wire, the first voltage detection lead wire and the A first resistor is provided between the adder and subtracter, a second resistor is provided between the second voltage detection lead wire and the adder/subtracter, and a second resistor is provided between the adder and subtracter side of the first resistor and the first resistor. A first unidirectional semiconductor element is provided between the first current supply lead wire, and a second unidirectional semiconductor element is provided between the adder/subtractor side of the second resistor and the second current supply lead wire. a directional semiconductor element is provided, a third resistor and a first voltage source are provided between the first voltage detection lead wire side of the first resistor and the second current supply lead wire; A fourth resistor and a second voltage source are provided between the second voltage detection lead wire side of the second resistor and the second current supply lead wire, and a fourth resistor and a second voltage source are provided for the first current supply. If the lead wire is disconnected,
The voltage generated by passing a constant current from the constant current source to the first resistor through the first unidirectional semiconductor element, and when the second current supply lead wire is disconnected. In this case, the constant current from the constant current source is supplied to the second
Voltages generated by flowing through the second resistor through the unidirectional semiconductor element are applied to the adder/subtractor, respectively, so that the output is forced to be part-out/at-scale. be.

Hereinafter, a temperature converter having a parts-out circuit according to the present invention will be explained in detail using an embodiment shown in FIG.

In addition, in FIG. 3, the same parts as in FIG. 1 are indicated using the same symbols. The differences between FIG. 3 and FIG. 1 are as follows. A series circuit of a high impedance resistor R3 and a voltage source 4 with a voltage value a is connected between the connection point of the first voltage detection lead R1 and the resistor R1 and the reference potential COM of the adder/subtractor 3 with the polarity shown. , resistor R1 and the first of adder/subtractor 3
A unidirectional semiconductor element, for example, a diode D1, is connected with the polarity shown between the connection point with the positive-phase input terminal of the power source and the connection point between the first current supply lead wire A1 and the constant current source 2. ing. In addition, the second voltage detection lead wire B2 and the resistor R2
A series circuit of a high impedance resistor R4 and a voltage current 5 having a voltage value (-Vb) is connected between the connection point of the resistor R2 and the reference potential COM with the polarity shown, Connection point of input end and second current supply lead wire A2
The circuit configuration is exactly the same as that of FIG. 1 except that a second unidirectional semiconductor element, for example, a diode D2, is connected between the connection point of the circuit and the bias resistor Rb. Here, the forward breakdown voltage D1 of the diode D1 is:
VDl>R, ·1, and the forward breakdown voltage V of the diode D2. 2 is selected as VO2>R4·i.

Also, the value of resistor R3 is R3》(R2+Rt+R4+Rb
), and the current of Va/R3 at steady state is R2
The values of the resistor R3 and the voltage Va are selected so that Va/R3<i, so that the current does not flow from →Rt−+R4→Rb and cause a measurement error. Also, the value of resistor R4 is R4》(R3+R
4+Rb), selected as R2, and 1b/R at steady state
In order to prevent the current of 4 from flowing from R3 → R4 → Rb and causing a measurement error, the resistor R3 and the voltage (
-Vb) is selected.

In the circuit of FIG. 3 constructed as above, in a steady state, both diodes Dl and D2 are in a cut-off state,
The values of resistors R3 and R4 are also high impedance, Va/R3
, -Vb/R4 can also be ignored.

Therefore, in steady state, the diodes Dl, D2 and the resistor R
3, R4 and voltage flows 4, 5 are the same as when removed from the circuit and do not affect the measuring circuit. That is, like the conventional example shown in FIG. 1, the constant current source from the constant current source 2 flows in the direction of r1 → Rt-+R4 → Rb as shown by the arrow in the figure, and its operation and effect are also detailed in the conventional example shown in FIG. 1. Same as what I said. That is, in the steady state, the output E of the adder/subtractor 3. is given by equation (8), and measurement conversion is performed accurately. Next, referring to FIG. 3, the operation of the resistance temperature detector in various abnormal states will be explained using FIG. 4.

Here, the equivalent resistance r1 of each lead wire shown in FIG.
The value of ~R4 is a small value compared to the values of the circuit resistances R1~R4, Rb, and there is no problem in explaining the operation in an abnormal state. Therefore, in FIG. 4, the lead wire resistances r1~ R4 is omitted. In addition, adder/subtractor 3
The output E.

As is clear from the relationship between equations (1) and (8), the conditions for ensuring part-out upscaling are given by equation (9). e1-E2-E3〉ΔRts
−1 ・・・・・・・・・・・・(9) Here, ΔR
ts is the resistance change span of the resistance temperature detector 1 corresponding to the temperature change span from the lower limit value to the upper limit value of the measurement temperature range.

First, when the first current supply lead wire A1 of the resistance temperature detector 1 is disconnected, the circuit shown in FIG. 3 is represented as shown in FIG. 4a.

In this case, the input impedance of the adder/subtractor 3 and the values of the resistors R3 and R4 are much larger than the values of the resistance Rtl and the bias resistor Rb of the resistance temperature sensor, so the constant current 1 from the constant current source 2 is As in, D1→R,→Rt-+
The voltage flowing through Rb and applied to each input terminal of the adder/subtractor 3 is: ti+Rb)i}. ．． ．． ．． ．． ．．
．． ．． ．． ．． ．． ．． 00).

In addition, the zener voltage Vz of the zener diode ZD is Vz
VDl+(R1+Rt+Rb)! is selected, and the Zener diode ZD is in a cut-off state. Equation (2), (7
) and σ0) are substituted into equation (9) to obtain equation (self). (R1+ΔRt)i〉ΔRts-1...
・・・・・・・・・(self)01) As is clear from the formula,
Even when the input, which is the worst condition for parts-out operation, is the lower limit of the measurement range, that is, ΔRt-0, by selecting the value of the resistor R to be larger than the value of the measurement input gas span resistance ΔRts, the value of the adder/subtractor 3 can be adjusted. Output E.

can be swung to the positive side, allowing parts to be out-scaled instantly. Next, when the first voltage detection lead wire B of the temperature sensing resistor 1 is disconnected, the circuit shown in FIG. 3 is expressed as the fourth part (b).

At this time, the constant current 1 from the constant current source 2 flows through the resistance Rtl of the resistance temperature sensor 1 and the bias resistance Rb as shown by the arrows in the figure, as in the case of steady state, and flows through the second and third resistors of the adder/subtractor 3. The voltages applied to the negative phase input terminals are both E,2E,=Rb-1 if the lead wire resistance R4 is ignored. On the other hand, the voltage el applied to the first positive phase input terminal of the adder/subtractor 3 is the voltage Va of the voltage source 4 applied to the capacitor C, via the resistor R and R1. >>Since R1, R is ignored), and finally becomes E and Va.

Here, Z1 is the input impedance of the first positive phase input terminal of the adder/subtractor 3.

By substituting the relationship in equation (7) and the values of el to E3 above into the conditions in equation (9), an O equation is obtained. That is, by selecting the value of the resistor R and the voltage Va so as to satisfy the 0D equation, the output of the adder/subtractor 3 can be quickly made part-out upscale. In addition, the second
If the voltage detection lead wire B is disconnected, the circuit shown in FIG. 3 is represented as shown in FIG. 4c.

In this case, the constant current source flows through Rt and Rb as in the case when the main wire B1 is disconnected, and the voltages E and E3 are the same as the values in the steady state shown in equations (3) and (5). It is.
Also, the voltage E applied to the second negative phase input terminal of the adder/subtractor 3,
The voltage (-Vb) of the voltage source 5 is charged to the capacitor C2 via the resistors R, , R, with a time constant of (R, is ignored), and finally becomes.

Here, Z is the input impedance of the second negative phase input terminal of the adder/subtractor 3.

By substituting the relationship in equation (7) and the values of el to E3 above into the conditions in equation (9), equation 03) is obtained. Here, the resistance R of the lead wire
, is ignored. In equation 03), considering the worst condition for parts-out operation, the input is the lower limit of the measurement range, that is, when Rt=O (1 powder equation is (14)
It looks like the formula.

04) Resistor R4. ．． Voltage (-Vb)
By selecting the value of , the output of the adder/subtractor 3 can be quickly and reliably made part-out upscale.

Note that the voltage source 5 is not necessarily required.

In other words, as is clear from equation 04), the condition for parts out when (-Vb) is 20 is 0>(JRts- Rt
b)i...(15). In other words, even when the voltage source 5 is removed and the voltage is set to (-Vb) 2O, the value of the constant bias resistance (resistance at the lower limit of the measurement range) Rtb included in the resistance temperature detector is lower than the value of the measurement input gas span resistance ARts. If is large, the condition of equation 05) is satisfied, and the output of the adder/subtractor 3 becomes part-out upscale. The conditions for JRts and Rtb are conditions that cause almost no problems in the normal temperature measurement range. Furthermore, when the second current supply lead wire A2 of the temperature sensing resistor 1 is disconnected, the circuit shown in FIG. 3 is represented as shown in FIG. 4d.

Input impedance of adder/subtractor 3 and resistance R3, R,
The values are the resistance Rt of the resistance temperature detector 1 and the resistance (R, +Rb)
, the constant current 1 from the constant current source 2 at this time is Rt as shown by the arrow in the figure.
−? The voltages flowing through R'pass D2-+Rb and applied to each input terminal of the adder/subtractor 3 are as follows. In addition, the zener voltage Vz of the zener diode ZD is expressed as e in equation 06)
The value of l is selected to be greater than the value of l, and the zener diode is in the cut-off state. By substituting the relationship between equations (2) and (7) and equation (16) into the condition of equation (9), the (l test) is obtained.
(R,+”Rt)i>”Rts-1 ・・・07)(
17) As is clear from the equation, the input that is the worst condition for parts-out operation is the lower limit of the measurement range, that is, JRt:
Even in the case of 0, the output of the adder/subtractor 3 can be instantaneously made part-out upscale by selecting the value of the resistor R to be larger than the value of the measured gas span resistance JRts.

Finally, when the resistance wire Rt of the resistance temperature detector 1 is disconnected, the circuit shown in FIG. 3 is represented as shown in FIG. 4e.

Since the input impedance of the first positive phase input terminal of the adder/subtractor 3 and the value of the resistor R3 are very large, the constant current 1 from the constant current source 2 in this case flows only through the zener diode ZD as shown by the arrow in the figure. Generates a Zener voltage Vz. This voltage Vz is applied to the first positive phase input terminal of the adder/subtractor 3 via the resistor R1. Here, since the input impedance of the adder/subtractor 3 is very large compared to the value of the resistor R1, e1=z
becomes. On the other hand, the steady voltage applied to the second negative phase input terminal of the adder/subtractor 3 is also charged in the capacitor C2, but when the resistor wire Rt is disconnected, it is instantaneously passed through the resistors R2 and Rb. It discharges and becomes E2=o. Further, the voltage at the second negative phase input terminal of the adder/subtractor 3 also becomes E3=o. Note that a very small current of 1 Vb/R4 flows through the bias resistor Rb, but the voltage generated by this is extremely small and can be ignored. Therefore, the adder/subtractor 3 receives only the excessive Zener voltage z applied to the first positive phase input terminal, and the output becomes part-out upscale at an instant. In the embodiment shown in FIG. 3, a Zener diode ZD is provided, but this is not necessarily required depending on the circuit configuration of the constant current source 2 and the adder/subtractor 3 as described above.

The presence or absence of the Zener diode ZD is related to Figure 4 a-
As is clear from reference to e, this is only the case in FIG. 4e, that is, when the resistor wire Rt is broken.
Therefore, in the case where the resistor wire Rt is disconnected when there is no Zener diode ZD, the input impedance of the first positive phase input terminal of the adder/subtractor 3 and the value of the resistor R3 are as follows in FIG. Since it is very large, the load on the constant current source 2 becomes substantially equivalent to an open circuit, and the constant current 1 does not flow. Therefore, a power supply voltage for driving the constant current source 2 (not shown) appears across the constant current source 2, and via the resistor R1,
It is added to the first positive phase input terminal of the adder/subtractor 3. Furthermore, since the voltages E2 and e3 at the second and third negative phase input terminals of the adder/subtractor 3 are both zero, the output of the adder/subtractor 3 is also part-out upscale. In addition, in FIG. 3, a case has been described in which the resistance temperature detector 1 has a constant bias resistance Rtb, and the measurement circuit is provided with a bias resistance Rb in order to subtract this bias resistance. The presence of Rb is not necessarily required for the operation of the parts-out circuit of the present invention.

When resistance temperature detector 1 does not include a certain bias resistance (R
tb=0) necessarily requires no bias resistor Rb (RbO
), and the third negative phase input terminal of the adder/subtractor 3 is also unnecessary. In this case as well, the parts-out operation of the present invention is not restricted in any way. However, if the second voltage detection lead wire B2 is disconnected, equation (self) and equation (15), which are the conditions for parts-out upscaling, will no longer be satisfied, so upscaling will be applied. For this purpose, it is necessary to connect the voltage source 5 in series with the resistor R4. Further, in FIG. 3, a case has been described in which one of the voltage sources 4 and 5 is both connected to the reference potential COM, but both may be connected to the connection point between the lead wire A2 and the bias resistor Rb.

However, it is more convenient to connect to the reference potential COM because the power source for driving the adder/subtractor 3 (not shown) and the voltage sources 4 and 5 can be shared. In the embodiment shown in FIG. 3, the polarities of the respective input terminals of the adder/subtractor 3 are such that the voltage e1 side is the first positive phase input terminal, the voltage E2 side is the second negative phase input terminal, and so on. Although the voltage E3 side has been described as the third negative phase input terminal (to), it is also applicable to a case where the polarity is completely reversed as shown in (1) of FIG. The arithmetic expression of the adder/subtractor 3 in this case is expressed as EO-G(-e1+E2+E3), and (
The polarity is opposite to that of equation 1). Therefore, if the resistance input ΔRt of the resistance temperature sensor increases, the output E. increases on the negative side. Similarly, in all parts-out operations during various abnormal conditions due to disconnection of the resistance temperature detector 1, the output swings to the negative side, but since the direction of the output matches the direction of the output when the input ΔRt increases, the parts-out operation still occurs.・It is an up scale. Further, in the embodiment shown in FIG. 3, the negative side of the constant current source 2 is connected to the reference potential COM, but it is also possible to apply a case in which the polarity is exactly opposite to that shown in the drawing.

At this time, the polarities of the diodes Dl and D2, the voltage sources 4 and 5, and the Zener diode ZD may all be connected in opposite polarities to those shown in the drawing. In addition, in the embodiments shown in FIGS. 1 and 3,
For convenience, the operation and effects of the parts-out circuit according to the present invention have been described in the case where the connection point between the constant current source 2 and the bias resistor Rb is determined as the reference voltage of the adder/subtractor 3, but the present invention is not limited to this. isn't it.

For example, the second current supply lead wire A2 of the resistance temperature detector 1
side (in the embodiments of FIGS. 1 and 3, the third negative phase input terminal to which voltage E3 is applied) or the second voltage detection lead wire B
2 side (in the embodiments of FIGS. 1 and 3, the second negative phase input terminal to which the voltage E2 is applied) is set as the reference potential of the adder/subtractor 3, the parts-out circuit according to the present invention has the following characteristics: It can be applied as long as it does not deviate from the gist. In addition, when the lead wire A2 side is set as a reference potential, the voltage generated at the intersection of the constant current source 2 and the bias resistor Rb is applied to the voltage E3 at the input terminal, and the other settings are the same as in the embodiment shown in FIG. Then, the calculation formula of the adder/subtractor 3 is EO=G; (e1-E2+E
3) It is necessary to make the operation and polarity 1.

In addition, when the lead wire B2 side is set as the reference potential, the voltage at the input terminal to which the voltage generated at the intersection of the constant voltage source 2 and the bias resistor Rb is applied is E2, and the other parts are the same as in the embodiment shown in FIG. Then, the calculation formula of adder/subtractor 3 is E. =G1(e
1+E2-E3) It is necessary to set the operation polarity to 1. The detailed operation will be omitted because it can be easily understood by those skilled in the art from the details described in the embodiment of FIG.

As described above, according to the parts-out circuit according to the present invention,
When various abnormal conditions occur due to disconnection of the resistance temperature detector,
Since the output can always be made part-out/upscale, the control system can be operated safely.

Moreover, the circuit configuration is simple because the resistors Rl and R2 that make up the low-pass filter circuit are used together, and only two diodes, a high resistance, and a voltage source are added between both ends of the resistors and the measurement circuit. , can be realized at low cost. Further, the parts-out circuit of the present invention can be applied not only to the case of inputting a resistance temperature detector but also to the case of inputting a slip resistance, and is useful for industrial measurement.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional resistance temperature detector type temperature converter, FIGS. 2 a-e are equivalent connection diagrams of the circuit shown in FIG. FIGS. 4a to 4e are equivalent connection diagrams of the circuit shown in FIG. 3 at the time of an abnormality. 1... Resistance temperature sensor, 2... Constant current source,
3... Adder/subtractor, 4, 5... Voltage source,
R1 to R4...Resistance, Rb...Bias resistance, Dl, D2...Diode, Al, A
2... Current supply lead wire, Bl, B2...
...Lead wire for voltage detection.

Claims (1)

[Claims] 1 4 wires with one end connected to a first current supply lead wire and a first voltage detection lead wire, and the other end connected to a second current supply lead wire and a second voltage detection lead wire a constant current source that flows a constant current to the temperature measuring resistor through the first and second current supply lead wires;
A temperature converter comprising a high input impedance adder/subtractor into which the voltage generated in the temperature measuring resistor is inputted via the first and second voltage detection lead wires and the second current supply lead wire. A first resistor is provided between the first voltage detection lead wire and the adder/subtractor;
A second resistor is provided between the voltage detection lead wire and the adder/subtracter, and a second resistor is provided between the first resistor on the adder/subtracter side and the first resistor.
A first unidirectional semiconductor element is provided between the current supply lead wire of the second resistor and the adder/subtractor side of the second resistor.
A second unidirectional semiconductor element is provided between the first voltage detection lead wire side of the first resistor and the second current supply lead wire. a third resistor and a first voltage source are provided at the second resistor;
A temperature converter characterized in that a fourth resistor and a second voltage source are provided between the voltage detection lead wire side and the second current supply lead wire.