JPS6147368B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance temperature detector circuit that eliminates errors caused by the conductor resistance of a three-wire resistance temperature detector, and is particularly suitable for use in multi-channel input circuits of the same temperature measuring range. This relates to a temperature resistor circuit.

Conventional resistance temperature detector circuits include a bridge type and a constant current source type. First, an example of the bridge method is shown and explained in Fig. 1. In the figure, _A , r _B , r _C
is the conductor resistance R ₁ , R ₂ , R ₃ is the resistance, and the resistance R ₁ ~
_R3 forms a bridge circuit together with the temperature sensing resistor X. V _r is a constant voltage for the bridge, and V _CUT is the output of the bridge circuit.

In a circuit having such a configuration, a change in the resistance value of the temperature measuring resistor X due to a change in temperature can be detected as a change in voltage.

However, such a circuit has the disadvantage that the output V _OUT of the bridge circuit is affected by the conductor resistances r _A to r _C . In addition, when applied to a multi-channel input circuit with the same temperature measurement range, only one bridge reference voltage is required, but the resistor R ₁ is required for high precision and is more expensive than an analog switch.
~ _R3 is required for each input channel, and has the disadvantage that adjustment is also required for each input channel. Furthermore, since there is bridge distortion as a characteristic of bridges, there is a drawback that it is necessary to take into consideration when treating resistance value changes of the temperature-measuring resistor as voltage changes.

Next, when passing a constant current through a resistance thermometer and inputting it as a voltage, if you use a 4-wire resistance thermometer, the effect of the conductor resistance can be ignored, but if you use a 3-wire resistance thermometer, In this case, it is necessary to adopt a configuration as shown in FIG. In FIG. 2, the same reference numerals as in FIG. 1 indicate corresponding parts, I ₁ and I ₂ are constant current sources set to the same output value, and S is a suppression resistor. Here, the temperature measuring resistor has a certain specific resistance value at 0% of the temperature measuring range, for example, at a temperature of θ ₀ in the temperature measuring range of θ ₀ to θ ₁₀₀ .
The suppression resistor S is provided to eliminate this "missing part"--the live zero--and increase sensitivity. Note that v ₊ and v _- indicate the output voltage.

In a circuit with such a configuration, the output voltages v ₊ and v _- at the output V _OUT are v ₊ = (r _A +X+r _C ) I ₁ + r _C I ₂ v _- = (S+r _B + r _C ) I ₂ + r _C I ₁ Therefore, the output V _OUT is expressed as V _OUT =(XI ₂ −SI ₂ )+(r _A I ₁ −r _B I ₂ ).

And the deviation of the conductor resistance can be easily ignored,
In other words, the difference in length between the twisted pair wires can be ignored, so if r _A = r _B and I = I ₁ = I ₂ , the output V _OUT is expressed as V _OUT = (X-S) I .

Therefore, it is possible to ignore the influence of conductor resistance.

However, in such a circuit, providing two constant current sources I ₁ and I ₂ with the same output value has the disadvantage that it becomes expensive when adjustment costs are included. Furthermore, when this circuit is applied to a multi-channel input circuit with the same input range, two constant current sources I ₁ and I ₂ and a high-precision resistor S for suppression are required for each input channel, making the configuration complicated. It has the disadvantage that it is not economical, and also has the disadvantage that adjustment must be performed for each input channel.

In view of the above points, the present invention has been made to eliminate these drawbacks.The purpose of the present invention is to eliminate the number of parts that require high precision and to make the overall adjustment possible without depending on the number of channels. The object of the present invention is to provide a resistance temperature detector circuit which is convenient and low cost since it requires only a point.

In order to achieve such an objective, the present invention
This is a device in which a single constant current source is passed by changing the current path in time division using an analog switch, the generated voltage is held in a sampling hold circuit, and the difference is output.The present invention will be described below based on the drawings. Explain in detail.

FIG. 3 is a diagram illustrating the principle of an embodiment of the resistance temperature detector circuit according to the present invention. In the figure, X is a temperature measuring resistor having a first lead wire at one end and second and third lead wires at the other end, and I is a common constant current source. S ₁ and S ₂ are first and second switches that have different closing periods, and S ₃ and S ₄ are first and second switches that operate in synchronization with the first and second switches S ₁ and S ₂ , respectively. A second sampling switch, each of which is constituted by an analog switch. r _A , r _B , and R _C are conductor resistances, and S is a suppression resistance. _R11 is a resistor connected to the first sampling switch _S3 , _C11 is a capacitor connected in series with the resistor _R11 , and these constitute a low-pass filter. R ₁₂ is the resistor connected to the second sampling switch S ₄ , C ₁₂ is the resistor R ₁₂
These capacitors are connected in series to form a low-pass filter.

And this resistor R ₁₁ and capacitor C ₁₁ are the first
The _first lead wire of the resistance temperature detector X, which is generated by the current from the constant current source I flowing through the first switch _{S1 ,} is It constitutes a first signal holding means which receives as input the steady value of the voltage drop of the series circuit of the resistance temperature detector X and the third lead wire of the resistance temperature detector X. Also, resistor R ₁₂ and capacitor C ₁₂
is _the second sampling switch _S4 of the resistance temperature _sensor A second signal holding means receives as input the steady value of the voltage drop of the series circuit of the lead wire of the resistance temperature detector X, the third lead wire of the resistance temperature detector X, and the suppression resistor S. The device is configured to send out the difference between the signals held by the first and second signal holding means as an output signal.

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to FIG. 4, which shows the period during which the switches _S1 to _S4 are on. First, in this example, 1
Current is passed through the two flow paths from two constant current sources I in a time-division manner, and the generated voltage is sampled and held.

The first and second switches S ₁ and S ₂ and the first and second sampling switches S ₃ and S ₄ , which are analog switches, operate at regular intervals as shown in FIG.
Repeats ON/OFF. and,
When the first switch _S1 is turned on, the current from the constant current source I flows to GND (ground) through the flow path of the conductor resistance r _A - the resistance temperature detector X - the conductor resistance r _C. Here, since there may be a long distance wired between the resistance temperature detector , after a certain period of time has elapsed, the first sampling switch _S3 is turned on to sample the input voltage. And similarly, the second
When the second switch _S2 is turned on, the second sampling switch _S4 is turned on after a certain period of time to sample the input voltage.

At this time, the output voltages v ₊ and v _- at the output V _OUT are expressed as v ₊ = (r _A +X+r _C )I v _- = (S+r _B +r _C )I. Here, the deviation of the conductor resistance can be ignored. That is, since the difference in length between the twisted pair wires can be ignored, r _A = r _B .

Therefore, the output V _OUT is expressed as V _OUT =(X-S)I.

In this way, in the present invention, as is clear from the above explanation of the principle, the influence of the conductor resistance can be ignored in principle. Further, since only one constant current source is required, adjustment can be made by performing zero adjustment using the suppression resistor S and performing gain adjustment using the current from the constant current source I. Here, as mentioned above, the temperature measuring resistor is set at 0% of the temperature measuring range, for example, θ ₀
It has a certain specific resistance value at a temperature of θ ₀ in a temperature measurement range of ˜θ ₁₀₀ . The subreduction resistor S is provided in order to eliminate this "missing part"--the live zero--and increase the sensitivity.

FIG. 5 is a circuit diagram showing another embodiment of the present invention,
This figure shows an example of a modification of the circuit shown in FIG. 3 when the present invention is applied to a multi-channel input circuit having the same input range. In Fig. 5, the same reference numerals as in Fig. 3 indicate corresponding parts, and S _C1 ,
S _C2 is an analog switch connected between both ends of the suppression resistor S and ground.
The difference from FIG. 3 is that the sampling resistor S is inserted in a different position, and analog switches S _C1 and S _C2 are provided.

Next, the operation of the embodiment shown in FIG. 5 will be explained with reference to FIG. 6, which shows the period during which each switch is on. First, when the first switch _S1 is turned on, the analog switch S _C1 is also turned on, so
The current from constant current source I is lead resistance r _A - resistance temperature detector X - lead resistance r _C -
Flows into the GND (ground) flow path. Then, after a certain period of time, the first
The sampling switch _S3 is turned on and the input voltage is sampled. Furthermore, when the second switch _S2 is turned on, the analog switch _S2 is also turned on, so the current from the constant current source I flows into the flow path of the conductor resistance r _B - the conductor resistance r _C - the suppression resistance S - GND (ground). flows. Then, after a certain period of time, the second
The sampling switch _S4 is turned on and the input voltage is sampled.

At this time, the output voltages v ₊ and v _- at the output V _OUT are expressed as v ₊ =(r _A +X+r _C )I v _- =(r _B +r _C +S)I. Here, since the deviation in conductor resistance, that is, the difference in length of the twisted pair wires can be ignored, r _A = r _B .

Therefore, the output V _OUT is expressed as V _OUT =(X-S)I.

Here, when the analog switch S _C1 is on and when the analog switch S _C2 is on, the capacitor
The common connection point side of C ₁₁ and C ₁₂ , that is, the reference side, is connected to the reference potential via the suppression resistor S or directly to the reference potential, but the charging of the capacitors C ₁₁ and C ₁₂ is There is no problem because the voltages after the voltage is completely removed are taken out as the output voltages v ₊ and v _- .

Furthermore, if the on-resistance of analog switch S _C1 is negligible, analog switch S _C2 is not necessary, and the return line of the signal holding means, that is, the return terminals of capacitors C ₁₁ and C ₁₂ are directly connected to the common potential. However, in the case of an electronic switch, by providing an analog switch _SC2 , the first and second
The signal holding means holds a signal that does not include the voltage drop of the electronic switch.

Therefore, the on-resistance values and "variations" of the analog switches S _C1 and S _C2 are completely irrelevant.

FIG. 7 is a circuit diagram showing still another embodiment of the present invention, and shows an example in which the circuit shown in FIG. 5 is applied to a multi-channel circuit having the same input range. In FIG. 7, the same symbols as in FIG. 5 indicate corresponding parts, S ₁₁ , S ₁₂ and S ₂₁ , S ₂₂ and S _N1 ,
S _N2 are analog switches with different closing periods, X ₁ , X ₂ . . . X _N are resistance temperature sensors, r _1A ,
r _1B , r _1C and r _2A , r _2B , r _2C and r _NA , r _N
B , r _NC is the conductor resistance, S ₁₃ , S ₁₄ , S ₁₅ and S ₂₃ , S ₂₄ ,
S ₂₅ , S _N3 , S _N4 , and S _N5 are switches. Each of these switches is used to cut off the influence from other measurement points in multi-point (X ₁ , X ₂ . . . X _N ) measurement. is not necessary. R ₁₁ , R ₁₂ and R ₂₁ , R ₂₂ and R _N1 , R _N2 are resistances, C ₁₁ , C ₁₂ and C ₂₁ , C ₂₂ and C
_N1 and C _N2 are capacitors connected in series with resistors R ₁₁ and R ₁₂ and R ₂₁ and R ₂₂ and R _N1 and R _N2 , respectively, and these constitute a low-pass filter. v ₁₊ , v _1- and v ₂₊ , v ₂ - and v _N +, v _N - represent the output voltages at the outputs v _1OUT , V _2OUT and V _NOUT , respectively.

Then, depending on the desired number of measurement points, a constant current source is excluded and a plurality of resistance temperature detector circuits are provided, and the constant current source is shared, and the plurality of resistance temperature detector circuits are sequentially and selectively switched. The resistance temperature detector circuit is configured such that the resistance values of the suppression resistors are the same, and the third lead wires of the resistance temperature detectors are connected in phase to each other to form a first common switch that opens and closes in the same manner as the first switch. Also, the return lines of the first and second signal holding means are connected in phase through S _C1 , and a second switch which opens and closes in the same manner as the second switch
are led to the common potential through the common switch _S
A suppression resistor S is connected between the connection points where the return wires of the signal holding means are connected in phase.

The suppression resistor S is provided at the position shown in the figure when the suppression resistance values for multiple points (X ₁ , X ₂ . . . X _N ) are the same. However, for measurement points whose resistance value is not common to other measurement points, insert the suppression resistor at the position shown in S', cut the point marked with X, and connect it as shown by the dotted line.
In addition, the reference sides of capacitors C ₁₁ and C ₁₂ are grounded as shown by the dotted lines in the figure. That is, the suppression resistance S' and the point marked X have different suppression resistance values and cannot be used in common.

Next, the operation of the embodiment shown in FIG. 7 will be explained with reference to FIG. 8, which shows the period during which each analog switch is on. The operation of the circuit of the embodiment shown in FIG. 7 is the same as that of the circuit of the embodiment shown in FIG. 5, and since there are multiple input channels, the sampling frequency of input signals for the same channel decreases according to the number of channels. However, it does not affect the measurement results.

Now, if the deviation in the conductor resistance can be ignored, that is, if the difference in the length of the twisted pair wire can be ignored, the output V _NOUT will be V _NOUT = (X _N -S)I, so the output of each channel will be Voltage signals are not affected by conductor resistance. Further, zero adjustment of each input channel can be performed by adjusting one suppression resistor S, and span adjustment can be performed by adjusting the current from a common constant current source I.

Therefore, when the input range is the same, zero and span adjustments for all input channels only need to be performed at two points, and the number of adjustment steps can be significantly reduced.

The circuit elements that require high precision may be one suppression resistor S and one common constant current source circuit. Furthermore, since the switches used in FIGS. 3, 5, and 7 are all used in such a way that the on-resistance value does not affect the circuit operation, inexpensive analog switches can be used.

As explained above, according to the present invention, the number of parts that require high precision does not depend on the number of channels, and the entire adjustment only requires two points, zero and span adjustment, which is convenient and low cost. It is said that
It has many advantages, and is especially effective when applied to multi-channel input circuits of the same temperature measurement range. Furthermore, when using the same input temperature measuring range, zero and span adjustments for all input channels only need to be made at two points, which greatly reduces the number of adjustment steps. This is extremely effective in that it can reduce the overall price.

As described above, the present invention has great effects compared to conventional circuits of this type, and is unique as a resistance temperature detector circuit suitable for application to multi-channel input circuits of the same temperature measuring range. belongs to.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing examples of conventional resistance temperature detector circuits, FIG. 3 is a circuit diagram of an embodiment for explaining the principle of a resistance temperature detector circuit according to the present invention, and FIG. 4 is a circuit diagram showing an example of a conventional resistance temperature detector circuit. FIG. 3 is an explanatory diagram of the operation, FIG. 5 is a circuit diagram showing another embodiment of the present invention, FIG. 6 is an explanatory diagram of the operation of FIG. 5, and FIG. 7 is a diagram showing still another embodiment of the present invention. The circuit diagram, FIG. 8, is an explanatory diagram of the operation of FIG. 7. X, X ₁ , X ₂ , X _N ... Resistance temperature sensor, I ... Constant current source, S ₁ , S ₂ , S ₁₁ , S ₁₂ , S ₂₁ , S ₂₂ , S _N1 , S _N2
...Switch, S ₃ , S ₄ ... Sampling switch, S, S' ... Suppression resistor, R ₁₁ , R ₁₂ ,
R ₂₁ , R ₂₂ , R _N1 , R _N2 ...Resistance, C ₁₁ , C ₁₂ ,
C ₂₁ , C ₂₂ , C _N1 , C _N2 ... Capacitors.

Claims (1)

[Claims] 1. A resistance temperature detector having a first lead wire at one end and second and third lead wires at the other end, and a constant current source that supplies current to the resistance temperature detector. , from the constant current source flowing through the first switch via first and second switches having different closing periods and a first sampling switch that operates in synchronization with the first switch. a first signal holding means that receives as input a steady value of a voltage drop in the series circuit of the first lead wire, the resistance temperature detector, and the third lead wire caused by the current; A series connection between the first lead wire, the temperature sensing resistor, the third lead wire, and the suppression resistor is generated by the current from the constant current source flowing through the second switch. and a second signal holding means which inputs a steady value of the voltage drop of the circuit, and the difference between the held signals of the first and second signal holding means is sent out as an output signal. Resistance temperature detector circuit. 2. Depending on the desired number of measurement points, a constant current source is excluded and a plurality of resistance temperature detector circuits are provided, the constant current source is shared, and the plurality of resistance temperature detector circuits are selectively switched in sequence. A resistance temperature detector circuit according to claim 1, characterized in that: 3. The resistance temperature detector circuit whose suppression resistors have the same resistance value is connected through a first common switch whose third lead wires are connected in phase and whose opening/closing operations are the same as that of the first switch. The return wires of the second signal holding means are connected in phase and guided to a common potential through a second common switch that opens and closes in the same way as the second switch, and
3. The resistance temperature detector circuit according to claim 2, wherein the suppression resistor is connected between the phase connection points.