JPH0330918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of the Invention The present invention relates to a multi-point input switching device that can handle any of thermocouple, voltage, and resistance inputs.

(2) Conventional technology Conventionally, the input circuit that converts the change in resistance value of a resistance temperature sensor into voltage by flowing current and extracts it, and the input circuit that receives thermocouple/voltage as input, were configured as separate circuits. .

For this reason, it is necessary to prepare separate circuits depending on the application, which is complicated. Also, in data acquisition devices that take in a mixture of various multi-point inputs, separate circuits must be prepared depending on the type of input signal. However, it also has the drawbacks of requiring a lot of space, being complex, and being expensive.

(3) Purpose of the Invention In view of the above points, the purpose of the present invention is to provide a multi-point input switching device that can be used commonly for resistance input, thermoelectric input, and voltage input.

(4) Embodiments of the invention FIG. 1 is an explanatory diagram showing the principle of the invention.

In the figure, 11, 12, and 13 are the first, second, and third input terminals to which input signals are supplied, and _A1 is _the inverting input terminal (- ) is connected and its non-inverting input terminal (+) is connected to the second input terminal 12, R ₂ is connected between the output terminal 14 of the operational amplifier A ₁ and the inverting input terminal (-) A feedback resistor with a resistance value equal to the resistor _R1 connected to R0 is a compensation resistor connected to the third input terminal 13, _R0 is a compensation resistor connected to the third input terminal 13,
is a selection means such as a slit or a switch that selects and connects either the reference (earth) point or the constant current source I to the first input terminal 11.

Next, the operation will be explained in different cases. In Figure 2,
The connection diagram for thermocouple and voltage input is shown.

A measuring voltage E of a thermocouple or the like is connected to the first and second input terminals 11 and 12, and the selection means 2
There is a short circuit between them, and the first input terminal 11 is connected to the reference point.

In this case, the inverting input terminal (−) of operational amplifier _A1
Since zero potential is supplied to and -E is supplied to the non-inverting input terminal (+), the output voltage of output terminal 14 is
V ₀ is given by the following formula. (Note that R ₁ = R _2. ) V ₀ = (1+R ₂ /R ₁ ) (-E) = -2E (1) Next, FIG. 3 shows a connection diagram in the case of resistance input.

One end of the temperature sensing resistor (body) _Rt is connected to the first input terminal ₁₁ via the first lead wire r1, and the other end is connected to the second input terminal ₁₂ via the second lead wire r2. , and the third input terminal 1 via the third lead r ₃
Connected to 3. In the selection means 2, 20 and 22 are short-circuited, and the constant power source I is connected to the first input terminal 11.

In this case, since a constant current i flows from the constant power source I through the first lead wire r ₁ , the temperature measuring resistor R _t , the third lead wire r ₃ , and the compensation resistor R ₀ , the voltage V at the first input terminal 11 ₁ , the voltage _V2 at the second input terminal is expressed by the following equation.
Note that the resistance values of the lead wires r ₁ , r ₂ , and r ₃ are equal to r.

V ₁ = i (r ₁ + R _t + r ₃ + R ₀ ) = i (R _t + R ₀ + 2r) V ₂ = i (R ₀ + r ₃ ) = i (R + r) Therefore, the output that can be taken out from the output terminal 14 of operational amplifier A ₁ The voltage V ₀ is given by the following formula.

V ₀ = 2V ₂ -V ₁ = 2i (R ₀ + r) - i (R _t + R ₀ + 2r) = R ₀ - R _t ...(2) Here, let α be the temperature coefficient of the resistance thermometer R _t . Ba,
At a certain temperature t, R _t = (1 + αt) R ₀ (R ₀ is the resistance value at 0°C), and by substituting this into equation (2), V ₀ = R ₀ - (1 + αt) R ₀ = - αtR ₀ ...(3), and a voltage proportional to the temperature t can be obtained. The influence of lead wire (wiring) resistance is also removed.

In this manner, by using the circuit shown in FIG. 1, it is possible to easily accommodate any of thermocouple input, voltage input, and resistance input.

FIG. 4 is a configuration explanatory diagram showing an embodiment of the present invention in which the above principle is applied to a multi-point input switching device.

In the figure, 111, 112, 113,...,
1n1, 1n2, and 1n3 are a plurality of first, second, and third input terminals in a set of three to which input signals of a plurality of channels are supplied, respectively, and S is a plurality of first, second, and third input terminals in a set of four to switch input signals. Second, third, and fourth changeover switches S ₁₁ , S ₁₂ , S ₁₃ , S ₁₄ , ..., S _o1 , S _o2 ,
S _o3 , S _o4 , 5th changeover switch for short circuit zero input
Input switching consisting of S ₀₁ , S ₀₂ , sixth changeover switch S ₀₂ , S ₀₄ , S ₀₅ connected to reference resistance R _z for resistance input, and seventh changeover switch S ₀₆ , S ₀₇ for reference compensation input A is an operational amplifier A _{1 which} has an input resistance R 1 and a feedback resistance R ₂ , and the input resistance connected to this operational amplifier A ₁ is
₃ is an A _- D converter that converts the output of amplifier A into a digital signal, and 4 is a microcomputer that takes in the output of A-D converter ₃ . The central processing unit 5 is a control circuit for controlling the opening and closing of each switch of the input switch S according to instructions from the central processing unit 4.

The first and second changeover switches (S ₁₁ , S ₁₂ ), ..., (Sn ₁ , Sn ₂ ) for each channel connect constant current sources to the first input terminals 111, ..., 1n1 of each channel. I or the reference point, and connect the third and fourth changeover switches (S ₁₃ , S ₁₄ ) for each channel,
..., (S _o3 , S _o4 ) are the first and second channels of each channel.
input terminals (111, 112),..., (1n1, 1
n2) and the two input terminals of the operational amplifier _A1 (-,
+), and connect the inverting input terminal (-) of the operational amplifier A ₁ to the third changeover switch S ₁₃ of each channel.
..., an input resistor R ₁ is connected between the output terminal of the operational amplifier A ₁ and the inverting input terminal (-), and a feedback resistor R ₂ is connected between the output terminal of the operational amplifier A ₁ and the inverting input terminal (+).
is the fourth changeover switch S ₁₄ of each channel,...
S _o4 and the compensation resistor R ₀ is connected to the third
It is connected to the input terminals 113, . . . , 1n3.

Next, the operation will be explained. A thermocouple voltage input E is connected to the input terminals 111 and 112 of the first channel, and a temperature measuring resistor R t having lead wires r ₁ , r ₂ , and r ₃ is connected to the input terminals 1n1, 1n2, and 1n3 of the n- _th channel. It is assumed that there is

The input switch S is controlled by the central processing unit 4 and the control circuit 5, and since the first channel is a voltage input, the second, third, and fourth changeover switches S ₁₂ , S ₁₃ ,
_S14 is closed, the first input terminal 111 is connected to the reference point, and a connection state corresponding to that shown in FIG. 2 is established.
A voltage input is taken into a central processing unit 4 via an amplifier A and an A-D converter 3. Since the nth channel is a resistance input, the first, third, and fourth changeover switches
S _o1 , S _o3 , S _o4 are closed and the first input terminal 1n1
A constant current source I is connected to the temperature measuring resistor R _t via
The connection state corresponds to that shown in FIG. 3, and the resistance input is taken into the central processing unit 4 via the amplifier A and the A-D converter 3.

In this way, the switch of the input selector S is controlled depending on whether the input is voltage or resistance, so that a variety of inputs can be taken in by a common circuit.

In addition, in the case of thermocouple or voltage input, close the fifth changeover switch S ₀₁ and S ₀₂ and take in zero input.
The central processing unit 4 may perform calculations to correct the drift generated by the amplifier A or the like by subtracting from the measurement input.
In addition, in the case of resistance input, the sixth changeover switch S ₀₃ ,
The drift correction calculation may be similarly performed by closing S ₀₄ and S ₀₅ and connecting the constant power source I to the reference resistor R _z .
In addition, in the case of thermocouple input, the seventh changeover switch _S06 ,
Close S ₀₇ , take in the compensation voltage E ₀ corresponding to the reference junction temperature of the input terminal, add it to the measurement input,
A reference junction compensation calculation may also be performed.

(5) Summary of the Invention As described above, the present invention is a multi-point input switching device that controls an input switching device according to voltage input, resistance input, etc.

(6) Effects of the invention By simply preparing one operational amplifier, constant current source, input switch, etc., mV, voltage input, thermocouple input,
All resistance inputs can be input with a single circuit, making it possible to input a wide variety of multi-point inputs in a small space, at low cost, and with high reliability. Furthermore, various correction calculations can be easily performed.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are configuration explanatory diagrams showing one embodiment of the present invention. 111-1n3...input terminal, S...input switch,
S ₁₁ to S ₀₇ ...Selector switch, _R1 to _R4 ...Resistor, _R0 ...
Compensation resistor, _A1 , _A2 ... operational amplifier, 4... central processing unit, 5... control circuit.

Claims (1)

[Claims] 1. A plurality of channels of input terminals each having three input terminals, and a first input terminal provided for each channel that selectively connects a constant current source or a reference point to the first input terminal of each channel. a second changeover switch;
Third and fourth changeover switches provided for each channel connect the first and second input terminals of each channel and the two input terminals of the operational amplifier, and a third changeover switch of each channel and an operation switch. an input resistor connected between an inverting input terminal of the amplifier and a feedback resistor having a resistance value equal to the input resistor;
Close the resistor connected to the third input terminal of each channel and the second, third, and fourth selector switches when inputting voltage, and close the first, third, and fourth switching switches when inputting resistance.
A multi-point input switching device comprising: a control circuit that closes a fourth changeover switch. 2 Equipped with a fifth switch that takes in zero input for voltage input and thermocouple input, a sixth changeover switch that connects to a reference resistance for resistance input, and a seventh changeover switch that takes in reference point compensation input. A multi-point input switching device according to claim 1, characterized in that: