JPH0315379B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Field of the Invention The present invention relates to an input switching circuit that switches and selects a plurality of input signals. (2) Prior Art In an input switching circuit that switches and selects a large number of input signals, various types of switch elements can be considered as the switch elements used in the input switch. In recent years, there has been a demand for higher speeds, but with the increased frequency of operation and longer life, high-voltage semiconductor switches are being used to make them contactless.
However, to drive this kind of switch,
A plurality of transformers had to be prepared and driven in isolation for each channel, making the circuit complicated, expensive, and taking up a large amount of space. (3) Purpose of the Invention In view of the above points, the purpose of the present invention is to provide an input switching circuit that is contactless and saves space. (4) Embodiment of the Invention FIG. 1 is a configuration explanatory diagram showing an embodiment of a resistance-voltage conversion circuit according to the present invention. In the figure, Rt is a resistance temperature detector, to which one end is connected the first conducting wire l ₁ and the other end is connected the second and third conducting wires l ₂ and l ₃ , and the terminals t ₁ , t ₂ , t ₃ are connected. It is connected. 1st
The constant current source I ₁ is connected to the first photocoupler PC ₁ , the first
A constant current i is passed through the conductor l ₁ , the resistance temperature detector Rt, and the second conductor l ₂ , and the second constant current source I ₂ is connected to the second photocoupler PC ₂ , the compensation resistor Ro, and the third conductor l ₃ , through the second conductor l ₂ and constant current i, and the first conductor l ₁ and the compensation resistor
Output e ₀ can be taken out from between Ro and via amplifier A, and photo couplers PC ₁ and PC ₂
The light emitting element is located in the current path, and the light receiving element is connected in series so that a disconnection detection (burnout) output e _b can be taken out. If the resistance of the conducting wires l ₁ , l ₂ , and l ₃ is r, the resistance-voltage conversion output e ₀ is expressed by the following equation, and the influence of the conducting wires is removed. e ₀ =i(Rt+2r)-i(Ro+2r) =i(Rt-Ro) (1) Note that the compensation resistor Ro is for obtaining an output from 0° C. and may be omitted. The disconnection detection status is shown in the table below.

[Table] In other words, when conductor l ₁ is disconnected, current i does not flow from the first constant current source I ₁ to the first photocoupler PC ₁ and it is turned off, and when conductor l ₃ is disconnected, the second
When the current i does not flow from the second constant current source _{I 2 to} the photocoupler PC ₂ and the conductor _{l 2 is} disconnected, the first, Current i does not flow from the second constant current sources I ₁ and I _{2 and} both are turned off. In either case, the wire breakage detection output e _b is turned off, making it possible to detect wire breakage. In this way, by providing a photocoupler in the current path, the circuit becomes simple and disconnection of the resistor can be reliably detected. FIG. 2 is a configuration explanatory diagram showing an embodiment of a multi-point input conversion circuit according to the present invention. In the figure, 1 is the reference resistance Rz, the span resistance
Rs, input switch for sequentially switching and selecting temperature measuring resistors R ₁ , R ₂ , R ₃ , R ₄ connected to terminals t ₁₁ , t ₁₂ , t ₁₃ , ..., t ₄₁ , t ₄₂ , t ₄₃ ; 2 is a drive circuit that drives the input switch 1, I is a photocoupler PC ₁ , PC ₂ , and a compensation resistor
Ro, a constant current circuit that supplies a constant current i to the reference resistor Rz, span resistor Rs, temperature measuring resistor R ₁ ,..., R ₄ via the input switch 1; A is an amplifier that amplifies the output of the input switch 1; , 3 is an isolator that insulates the output of the amplifier A, 4 is an A-D converter that converts the output of the isolator 3 into a digital signal, and 5 is an arithmetic processing of the output of the A-D converter 4, control of the drive circuit 2, etc. 6 is a detection circuit that performs disconnection detection, failure detection, etc. Constant current circuit I connects voltage V ₁ to constant voltage diode
It includes two constant current sources including two operational amplifiers A ₁ , A ₂ , two transistors Tr, Tr', etc., using the voltage made constant by ZD as a reference. The detection circuit 6 includes a first indicator L ₁ such as a light emitting diode that emits light according to the outputs of photocouplers PC ₁ and PC ₂ , and an output terminal 6 from which a disconnection detection output is taken out.
1. It consists of a second indicator L ₂ such as a light emitting diode that emits light in response to the operation (BUSY) signal of the A-D converter 4, an output terminal 62 that outputs the operation status of the A-D converter 4, etc. , first and second indicators L ₁ ,
L ₂ are placed in close proximity. The input switch 1 has three high-voltage optically driven elements such as opto-MOS/FET as switching elements for each channel, So ₁ , So ₂ , So ₃ , S ₁₁ , S ₁₂ ,
S ₁₃ ,..., S ₅₁ , S ₅₂ , S ₅₃ , and corresponding to each of these channels, the drive circuit 2 includes series-connected light emitting elements Lo ₁ , Lo ₂ , Lo ₃ , L ₁₁ , L ₁₂ , L ₁₃ ，…，
It has transistors L ₅₁ , L ₅₂ , L ₅₃ and transistors Tr ₀ , Tr ₁ ,
..., Tr ₅ is turned on by the output of the selector 20 controlled by the arithmetic circuit 5, and the voltage V ₂
By supplying the three light emitting elements to emit light at the same time, the switch elements for each channel can be turned on. In addition, as shown in FIG. 3, the optically driven element is
It is as if a switching section S such as an FET and a light emitting element L such as a light emitting diode are integrated. In this way, the drive circuit 2 can drive the switch elements in isolation with an extremely simple circuit configuration by providing a plurality of series-connected light emitting elements corresponding to each channel. In this way, the reference resistance Rz, span resistance Rs, temperature measuring resistance R ₁ ,..., selected by the input switch 1
The voltage outputs e _z , e _s , e _t of R ₄ are converted into digital signals Dz, Ds, Dt by the A-D converter 4 via the amplifier A and the isolator 3, and are sequentially stored in the memory of the arithmetic circuit 5. Ru. The calculation circuit 5 performs the following calculations for zero compensation and span compensation, and always outputs a correct output signal D. Assuming that the correct gain Ao of amplifier A, the gain error is ΔA, the offset error Δe, and the proportionality constant is k, the data of the zero reference resistance Rz, span resistance Rs, and temperature sensing resistance R ₁ ,..., R ₄ can be expressed as follows. Become. Dz=ke _z =k{i(Rz−Ro)+Δe
}(Ao+ΔA)……(2) Ds=ke _s =k{i(Rs−Ro)+Δe
}(Ao+ΔA)……(3) Dt=ke _t =k{i(Rt−Ro)+Δe
}(Ao+ΔA)...(4) From this, zero point correction is performed using the following formula. Ds−Dz=ki(Rs−Rz)(Ao+ΔA) ……(5) Dt−Dz=ki(Rt−Rz)(Ao+ΔA) ……(6) Span point correction is zero and output when there is no span error Assuming K (standard span count number), D/K=Dt-Dz/Ds-Dz... From (7), the correct output is D=Dt-Dz/Ds-Dz・K=Rt-Rz/Rs-Rz・K...
(8) is obtained. In other words, by using the reference resistance Rz and the span resistance Rs, which are not voltage sources, and performing calculations such as equation (8), offset and gain errors caused by the amplifier A, isolator 3, compensation resistor Ro, etc. are removed. A correct output D whose zero point and span point have been compensated can be obtained. In other words, according to equation (8), the accuracy is determined only by the accuracy of the resistors Rs and Rz, and other elements are not included, so the accuracy improves accordingly. The detection circuit 6 includes a first display L ₁ that detects and displays the presence or absence of a disconnection from the AND outputs of the photocouplers PC ₁ and PC ₂ , and a second display L 1 that displays the operating status of the A-D converter 4. ₂ , during normal operation, the first,
The second indicators L ₁ and L ₂ are as shown in FIG.
Repeats flashing and flashing in sync with each channel selection. If the first channel is abnormal and a disconnection detection state occurs, when this first channel is selected, the fourth
As shown in figure b, the first indicator L ₁ does not emit light;
It is easily determined that the input side including the input switch 1 is at fault. If the A-D converter 4 is out of order, in FIG. 4c,
As shown, the second indicator L ₂ does not emit any light, and A
It is easy to see that the measurement circuit including the -D converter 4 is at fault. In this way, by attaching the two indicators L ₁ and L ₂ close to a printed board, etc., and visually observing and comparing them, it is possible to easily recognize and discover faults and check the operating status. can. Note that the outputs from the output terminals 61 and 62 of the detection circuit 6 may be input to the arithmetic circuit 5 to be used for self-diagnosis by displaying the presence or absence of wire breakage and the operating state. (5) Summary of the Invention As described above, the present invention provides an input switch that includes a plurality of light-driven elements for each channel and switches between a plurality of input signals, and a plurality of light-emitting elements connected in series for each channel. The input switching circuit is provided with a drive circuit for driving the input switching device and detects disconnection using a photocoupler. (6) Effects of the invention Since the light-emitting elements connected in series for each channel simultaneously emit light to operate the light-driven element as a switch element, there is no need for a transformer, etc., and isolation and non-contact are possible. As a result, the circuit configuration is extremely simple and inexpensive, and it is possible to achieve long life, significant space savings, and miniaturization. Even if an offset voltage occurs in the optically driven element, there is no problem with the high-level high-voltage input and resistance input, and the device is usable and has extremely large practical effects. Since the disconnection is detected using a photocoupler, it can be detected easily and with high accuracy.

[Brief explanation of drawings]

1, 2, and 3 are configuration explanatory diagrams showing one embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining the operation. 1...Input switch, 2...Drive circuit, 4...A
-D converter, 5... Arithmetic circuit, 6... Detection circuit,
Ro, Rt, Rz, Rs, R ₁ ~ _{R 4} ... Resistance, I ₁ , I ₂ ...
Constant current source, PC ₁ , PC ₂ ...Photocoupler, L ₁ , L ₂
...Indicator, A...Amplifier.

Claims (1)

[Scope of Claims] 1. Switch elements of first and second light-driven elements connected to one end of each temperature-measuring resistor for each channel via first and second conductive wires, and each of these resistors. a switch element of a third optically driven element and a common compensation resistor connected to the other end via a third conductive wire;
A drive circuit that performs input switching and includes a plurality of sets of three series-connected light emitting elements that simultaneously drive the switch elements of the first, second, and third optically driven elements for each channel, and a second optically driven element. a first constant current source connected between the switch element of the third light-driven element and the switch element of the third light-driven element; a second constant-current source connected between the switch element of the third light-driven element and the compensation resistor; an amplifier for amplifying and extracting an output from between the constant current source, the switch element of the first optically driven element and the compensation resistor;
a light emitting element of the first photocoupler provided in the current path between the constant current source and a light emitting element of the second photocoupler provided in the current path between the compensation resistor and the second constant current source; , and a detection circuit that detects disconnection and includes first and second light-receiving elements connected in series to receive the outputs of the light-emitting elements of the first and second photocoupler. 2. The input switching circuit according to claim 1, wherein an opto-MOS/FET is used as the optical drive element.