JPH0430828Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to an input switching device that switches and takes in various input signals.

[Prior Art] Switches have been used to change the range of various input signals such as resistance temperature detectors, thermocouples, mV, and large input signals. In recent years, there has been a demand for switches that can be switched using a microcomputer, and analog switches have been used as relays and ICs.

[Problems to be solved by the invention] However, relays have a limited lifespan, and problems arise when they are frequently opened and closed. Also, although analog switches solve the problem of longevity, they do not have much withstand voltage, so if you connect them directly to the input line,
There was a risk that it would be destroyed by noise, etc.

In view of the above points, the purpose of this invention is to provide an input switching device that has a long life and is resistant to noise.

[Means for Solving the Problems] This invention includes a switching element consisting of an optically isolated and driven field effect transistor that switches the input signal path according to the type of input signal supplied;
The input switching device includes a measurement circuit that measures the input signal switched by the switching element.

[Embodiment] FIG. 1 is a configuration explanatory diagram showing an embodiment of this invention.

In the figure, 11 and 12 are input terminals to which various input signals are supplied, and FET1, ..., FET9 are
A switching element 2 consisting of an optically isolated and driven field effect transistor that switches the input signal path according to the type of input signal supplied to the input terminals 11 and 12 is switched by the switching elements FET1, ..., FET9. Amplifier A ₁ which amplifies the input signal given by
Measurement circuit including A _2, etc., l ₁ and l ₂ are input terminals 11, 1
This is the input line connected to 2.

Switching element FET1 connects input terminal 11 and amplifier A ₁
An input line _L1 is provided between the drain D and the source S, and an electromotive force is generated between the gate G and the source S by the light of a light emitting element LED such as a light emitting diode, as shown in detail in Figure 2. It is composed of a high voltage field effect transistor to which the voltage of the power source _P1 of the photovoltaic element SB, such as a Si solar cell, is applied. Other switching elements FET2, ..., FET9
has a similar configuration, and is turned on when the voltage of the gate G is higher than or equal to a specified voltage with respect to the potential of the source S, and turned off when it is lower than or equal to the specified voltage.

Switching element FET2 connects input terminal 11 and amplifier A ₂
The switching elements FET3, FET4, and FET5 are provided between the input line _l2 and the ground.
l ₂ signal is divided by resistors R ₁ and R ₂ and supplied to amplifier A ₁ , and FET 6 and FET 7 are current sources.
I ₁ to input line l ₁ , input terminal 11, FET8,
FET9 has a current source on input line l ₂ and input terminal 12.
It is arranged to supply _I2 . In addition, the switching elements FET4, 5, FET6, 7, FET8, 9 are as follows:
In order to eliminate the influence of the directionality of the breakdown voltage of the high breakdown voltage field effect transistor, the transistors are configured as a set of two with their sources S commonly connected.

If the input signal is mV and a thermocouple, the switching element
The light emitting elements LED of the power supplies P ₁ and P ₂ of FET1 and FET2 are driven to emit light, a voltage is generated in the photovoltaic element SB, and this voltage is applied between the gate G and the source S to turn it on. This results in an input circuit as shown in FIG. 3a, where the input terminal 12 is grounded and is for mV and thermocouples.

If the input signal is a resistance temperature detector input, the switching element
Turn on FET1, FET6, 7, 8, and 9, and
The input circuit will be as shown in figure b, and the input terminals 11, 1
Two constant current sources are connected to the resistance temperature detector Rt connected to
I ₁ and I ₂ are connected, and amplifier A ₂ is also connected to input terminal 12 for resistance input.

When the input signal is large, the switching element FET2,
3, 4, and 5 are turned on, the input circuit becomes as shown in Figure 3c, and the input voltage at terminal 11 is divided by resistors R ₁ and R ₂ and supplied to amplifier A ₁ , which is for large input. Become.

Incidentally, since the source S of the switching element FET2 is grounded and the source potential is constant, it is sufficient to simply apply an appropriate voltage to the gate G instead of using a floating power supply as shown in FIG.

By the way, the operation of the measuring circuit using two currents in the case of the conventionally used three-wire type resistance temperature detector input shown in FIG. 3(b) will be explained.

In the figure, the resistance value of the resistance temperature detector Rt is Rt,
The resistance values of the first wiring resistance between the resistance temperature detector Rt and the input terminal 11, the second wiring resistance between the input terminal 12, and the third wiring resistance between the earth and the ground are respectively r,
Then, a constant current i is applied from the current source I1 to the input terminal 1.
1. The first wiring resistance, the resistance temperature detector Rt, the third wiring resistance, and the ground, and also the constant current i from the current source I2, the input terminal 12, the second wiring resistance, and the third wiring resistance.
Since 2i flows through the wiring resistance and the ground, and 2i flows through the third wiring resistance, the voltages V1 and V2 at the input terminals 11 and 12 are as follows.

V1 = ir + iRt + 2ir = iRt + 3ir V2 = ir + 2ir = 3ir Here, by setting the gains of amplifiers A1 and A2 appropriately and taking the difference between both V1 and V2, it is proportional to the output iRt from which the influence of wiring resistance 3ir has been removed. The following output is obtained.

[Effects of the invention] As mentioned above, this invention uses a photo-insulated and driven field effect transistor as a switching element, so it has a long life, is resistant to noise, and is easily adaptable to input signal types and ranges. A corresponding input circuit can be used.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are configuration explanatory diagrams showing one embodiment of this invention. 11, 12...Input terminal, 2...Measurement circuit,
FET1~FET9...Switching element, P1~P6...
Power supply, I ₁ , I ₂ ... constant current source, l ₁ , l ₂ ... input line.

Claims (1)

[Claims for Utility Model Registration] 1. The first terminal between the first input terminal and the first amplifier.
a first switching element provided on the input line of;
a second amplifier between the second input terminal and the second amplifier whose output side is connected to the input side of the first amplifier;
A second line provided between the input line and ground
a switching element, third, fourth, and fifth switching elements provided before and after the voltage dividing resistor that divides the signal of the first input line and supplies it to the first amplifier;
sixth and seventh switching elements provided between the current source and the first input line, and eighth and ninth switching elements provided between the second current source and the second input line.
switching elements, each of the first to ninth switching elements is composed of a field effect transistor driven in an optically insulated manner, and the input signal connected and supplied to the first and second input terminals is mV, thermoelectric In the case of a pair, the first and second switching elements are turned on, and in the case of a resistance temperature detector, the first, sixth, seventh, eighth and ninth switching elements are turned on, and in the case of a large input. An input switching device characterized in that the second, third, fourth, and fifth switching elements are turned on. 2. Each of the switching elements includes a photovoltaic element that generates an electromotive force by light from a light emitting element, and a high voltage field effect transistor to which the voltage of this electromotive force element is applied between the gate and the source, and , a fifth switching element, a sixth switching element, a seventh switching element,
2. The input switching device according to claim 1, wherein the eighth and ninth switching elements are formed by commonly connecting the sources of respective high voltage field effect transistors.