JPH03291543A - Detector amplifier - Google Patents

Abstract

PURPOSE:To share one optional amplifier by supplying a constant current for detection to a 3rd detection input terminal through a three-wire type resistance bulb at the time of temperature measurement processing and cutting off the constant current for detection at the time of impedance conversion processing. CONSTITUTION:At the time of the temperature measurement processing, the constant current IO for detection which is supplied from a constant current source 4 to a 1st detection input terminal A through a constant current interruption means 5 for detection forming a conduction path is supplied to the 3rd detection input terminal C through the three-wire resistance bulb Rx. The operational amplifier 1 outputs a detection output voltage which is proportional to the resistance value of the resistance bulb Rx varying depending upon the temperature of an object of measurement and released from the error based upon the resistance of a lead wire attached to the resistance bulb Rx. At the time of the impedance conversion processing, the constant current interruption means 5 for detection cuts off the constant current IO for detection. In this case, a detection input terminal A is opened, the operational amplifier 1 constitutes a voltage follower between 2nd and 3rd detection input terminals B and C, and a DC voltages Vs applied between the terminals B and C is impedance- converted by the operational amplifier 1 and outputted.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a sense amplifier used when measuring temperature depending on resistance change of a three-wire resistance temperature detector made of platinum or the like, and particularly relates to When dealing with other measurement elements expressed in voltage.

This invention relates to an improvement in which one operational amplifier can be used for temperature measurement dependent on resistance value changes and for measurement of other elements dependent on voltage values.

<Prior art> Conventionally, in this type of sense amplifier, when detecting the resistance value of a three-wire resistance temperature detector, it was necessary to pass a predetermined constant current through the resistor. .

The constant current for detection is supplied to the resistor outside the rcIl via the detection input terminal connected to the inverting input terminal of the operational amplifier. When an input signal expressed as a voltage, such as a DC voltage, is taken in with a high input impedance and outputted with a low output impedance, an operational amplifier
Usually, the wires are connected to form a voltage follower, so the inverting input terminal of the amplifier is connected to the output terminal of the amplifier via a feedback resistor, and the input signal is supplied to the non-inverting input terminal of the amplifier. be done. In this way, the operational amplifier wiring configurations are completely different between those for detecting the resistance value of a three-wire resistance temperature detector and those for converting DC voltage into impedance, so in the known circuit wiring,
Regarding these two types of signal processing, it is difficult to share an operational amplifier, and in the end, separate signal processing circuits using separate operational amplifiers are required for the above-mentioned 2s type signal processing.

Therefore, there is a problem that the number of component parts increases and the circuit configuration becomes complicated.

Means for Solving the Problems> In view of the problem of the difficulty of sharing operational amplifiers due to the above-mentioned circuit configuration constraints, the present invention provides a method for solving the problems of input resistors during temperature measurement processing, as shown in FIG. A constant current source 4 for detection is connected to the first detection input terminal A connected to the inverting input terminal of the operational amplifier 1 via 3 via constant current interrupting means 5 for detection,
This first sensing input terminal A is connected to the non-inverting input terminal of the operational amplifier l! A three-wire resistance temperature detector is connected between the three terminals of the $2 detection input terminal B and the third detection input terminal C connected to the t source return line G. On the other hand, during impedance conversion processing, the As shown in FIG. Detection input terminal B and the third detection input terminal C mentioned above
By configuring the system so that a DC voltage input signal is connected between its two terminals, the only operational amplifier can be used for temperature measurement processing and impedance conversion processing, thereby significantly reducing the number of component parts. It is an object of the present invention to provide an excellent sense amplifier with a simple circuit configuration.

Therefore, in the configuration of the present invention, during temperature measurement processing, as shown in FIG. The constant current for detection 10 supplied to the detection input terminal A flows to the detection input terminal C of @3 via the 3-wire resistance temperature detector Rx, and as a result,
Between the first detection input terminal A and the third detection input terminal C,
A voltage Va obtained by superimposing the voltage drop of the resistance value 2 of the lead wire for two trees on the voltage drop between the terminals of the resistance value Rx of the resistance temperature sensor is applied, and the voltage Va is applied to the terminals of the resistance value Rx of the resistance temperature detector. A voltage vb is applied between the input terminals C, which is the voltage between the terminals of the resistance value R1 of the resistance temperature sensor and the voltage drop of one lead wire resistance r, and these voltages Va and Vb are separately It is supplied to the inverting input terminal and the non-inverting input terminal of the operational amplifier l in that order, and from the operational amplifier l, the three-wire signal is A detection output voltage that is free from errors caused by the linear resistance attached to the RTD is output, but on the other hand, during impedance conversion processing, as shown in FIG. In this case, the detection constant current ■0 is cut off, and in this case, the first detection input terminal A is open, and the operational amplifier generates a voltage between the second detection input terminal B and the third detection input terminal C. A follower is configured, and the DC voltage Vs applied between both input terminals B and C is impedance-converted by an operational amplifier l.

It acts so that it is output.

<Embodiment> The configuration and operation of an embodiment of the present invention will be described below based on FIGS. 1 and 2.

In FIG. 1, the output terminal of a publicly known operational amplifier l is connected to the detection output terminal, and is further returned to the inverting input terminal of the amplifier at a branch midway, and is connected between the output terminal of the amplifier and the inverting input terminal. is connected to feedback resistor 2. The inverting input terminal of the operational amplifier l is connected to one end of an input resistor 3 having the same resistance value as the feedback resistor 2 through a branch in the middle.
The other end is connected to the first detection input terminal A. The non-inverting input terminal of the operational amplifier l is directly connected to the second sensing input terminal B. The third sensing input terminal C is connected to the power supply *mG of the operational amplifier l, typically to ground. The first detection input terminal A is connected to a known public constant current source 4 that is supplied with power from a predetermined power line.
is arranged so as to be connectable as a detection device, and a switch 5 as a detection constant current cut-off means is inserted between the constant current s4 and the first detection input terminal A. Regarding the constant current interrupting means for detection, other than a switch provided outside the constant current source 4 for detection, a current adjustment circuit or the like provided inside the current source 4 is used to control the constant current value. It may be adjustable to zero, and after all, any device that can adjust the current value of the detection constant current 10 to zero is included in the constant detection current interrupting means referred to herein.

In the above configuration, first, when the device operates as a detection amplifier for temperature detection during temperature measurement processing, a three-wire temperature measuring device is connected to each of the first, second, and third detection input terminals A, B, and C. ,
A wire typically made of platinum wire is connected, and the switch 5 is closed. The equivalent circuit of such a thermometer is the first
If you fill in the diagram, it will be represented by the resistance temperature detector Rx, that is, the resistance that changes depending on the temperature of the object to be measured, and the three lead wire resistances of equal value derived from three lead wires of the same shape. .

Here, for reference, a realistic numerical example regarding the above-mentioned resistance value etc. is as follows, and R is (Rx +
r) is selected to have a relatively large value.

114 temperature resistor Rx ,,, o”c knee rtoo
Q, 3500PPM/”C lead wire resistance r,,,,
1 Ω constant current for detection 10,..., 2.857 mA Ω for the resistance R,..., IO0 of feedback resistor 2 and input resistor 3. The following description will be made with reference to the currents and the like shown in the drawings.

The detection constant current 10 from the detection constant current source 4 is 11 and 12.
However, since R71CRx+r) is selected, almost all of the detection constant current 10 flows through Rx.
(i2=10), so the voltage Va at node a is Va = (r+Rx+r)I.

Therefore, the voltage vb of node b is Vb= (r+Rx)IO becomes.

Therefore, the voltage Va-Vb between the terminals of the input resistor 3 is Va
-Vb= (r+Rx+r)10 -(r+Rx)
1a = rI.

Therefore, the voltage at the output terminal of the operational amplifier l, that is, the output voltage VD at the detection output terminal, is V D =
Vb-(Va-Vb) = (r+Rx)io-r
10 = RXIO.

However, vb is also equal to the voltage at the inverting input terminal of the operational amplifier l, and (Va-Vb) is also equal to the voltage between the terminals of the feedback resistor 2.

From the above, it can be seen that the detection output voltage VD appearing at the detection output terminal is not affected by the lead wire resistance r at all.

In this way, the detection output voltage VD is directly proportional to the resistance R1 of the resistance temperature detector, which changes depending on the temperature of the object to be measured, and is free from errors caused by the lead wire resistance of the three-wire temperature detector. is an electrical signal representing the result of temperature measurement.
It is output outside the amplifier and transmitted to a display device or other instrumentation equipment not shown in the figure.

Then, when the device performs the impedance conversion process, for example,
When operating as a sense amplifier for detecting DC voltage for output signals from other measurement systems (typically DC voltage obtained by rectifying generator output linked to an anemometer), the As shown in FIG. 2, a DC voltage signal source Vs is connected between the second detection input terminal B and the third detection input terminal C, and the switch 5 is opened. In this case, as for the operational amplifier l, the switch 5 is open and the first detection input terminal A is open, so the resistor 3 becomes electrically meaningless, and as a result, the amplifier 1 , with a resistor 2 inserted between the open inverting input terminal and the output terminal, constitute a conventional voltage follower.

Therefore, the DC voltage input between the second and third detection input terminals B and C is supplied to the operational amplifier 1 with high input impedance, amplified with a gain of l, and outputted to the detection output terminal with low output impedance. be done.

Thus, for example, a DC voltage as an output signal from an anemometer or the like is impedance-converted and transmitted to a display device or other instrumentation equipment (not shown).

Effect> As described above, according to the present invention, during temperature measurement processing,
A constant current for detection 10 is supplied from the constant current source for detection 4 to the three-wire resistance temperature detector Rx via the first detection input terminal A connected to the inverting input terminal of the operational amplifier 1 via the constant current for detection interrupting means 5. The operational amplifier l outputs a detection output voltage that is proportional to the resistance value of the resistance temperature detector, which changes depending on the temperature of the object to be measured, without any error caused by the lead wire attached to the 3 & 1 type resistance temperature detector R1. , On the other hand, during impedance conversion processing,
The detection constant current interrupting means 5 interrupts the detection constant current 10, opens the first detection input terminal A, and connects the return line to the second detection input terminal B connected to the non-inverting input terminal of the operational amplifier l. By configuring the operational amplifier l to be connected to the voltage follower, the only operational amplifier l can be used in both temperature measurement processing and impedance conversion processing, which greatly reduces the number of components and reduces the circuit complexity. This has the excellent effect of making the structure itself extremely simple.

Moreover, for the switching operation between the temperature measurement processing operation and the impedance conversion processing operation, the detection constant current interrupting means 5, typically a switch, is opened and closed, and the first. A three-wire resistance temperature detector connected between the second and third detection input terminals A, B, and C; Since it is sufficient to connect and exchange the DC voltage signal source connected between the second detection input terminals B and C, there is an advantage that handling is simple.

5. Detection constant current interrupting means A, B, C, . . . 1st. Second and third detection input terminals D
,,,Detection output terminal

Claims (1)

[Claims] An operational amplifier 1; a detection output terminal D connected to the output terminal of the operational amplifier 1; and a feedback resistor connected between the output terminal of the operational amplifier 1 and the inverting input terminal of the amplifier. 2, an input resistor 3 whose one end is connected to the inverting input terminal of the operational amplifier 1, and a first detection input terminal A connected to the other end of the input resistor 3.
, a second sensing input terminal B connected to the non-inverting input terminal of the operational amplifier 1, a third sensing input terminal C connected to the power supply return line G of the operational amplifier 1, and a first sensing input terminal. A is connected to the detection constant current source 4 that can supply the detection constant current 10 to the terminal, and the detection constant current 10 supplied from the detection constant current source 4 to the first detection input terminal A is cut off. A detection amplifier comprising a detection constant current interrupting means 5.