JPH01109497A - System for inputting analog signal of insulating type - Google Patents

Abstract

PURPOSE:To send data to a secondary side without any influence to an input signal by utilizing a magnetic core as an insulating circuit and using a direct current sensor which can measure a current even while an input and output are not connected. CONSTITUTION:An analog measuring signal for current delivery flows to a primary coil 1 and a magnetic flux is generated. In proportion to this magnetic flux, a voltage is generated in a Hall element 2. Then, this voltage is amplified up to a desired value by an amplifier 4 and outputted. On the other hand, in order to execute the correction of accuracy, a reference power source of a reference coil 5 is turned on and off and the output of the Hall element 2 is detected. At such a time, an input is turned off by a switch 6 and a detected value and a theoretical value are compared by a microcomputer 10. Then, the amplifier 4 is adjusted by a gain off-set adjusting circuit 9. Thus, the input of a remote supervision control device, etc., can be transmitted cyclically at 1/10 second around for respective points. Then, when a correction processing is executed at <=1/100sec, there is no influence to an external part.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to input insulation of analog measurement signals of remote monitoring and control equipment, measurement control equipment, etc., and is particularly applicable to controlled facilities that require measures against surges and high voltages. The current passing on the side is usually 4~20
This invention relates to an isolated analog signal input method suitable for (mA).

[Conventional technology]

Especially slave station devices such as remote monitoring control devices and measurement control devices. (
Controlled stations) are often installed in areas prone to lightning such as mountainous areas or in high voltage environments such as power plants.

In addition to installing arresters on transmission lines, dielectric strength is also required for digital, analog, and other signal input/output terminals. “Conventionally, elements such as relays or photocouplers have been used to insulate signal input/output terminals for digital signals, as shown on page 113 of ``Tele Control System'' (published by Denkishoin in 1978). . Furthermore, isolation of analog signals has been performed using an isolation amplifier or a flying capacitor system as shown in FIG. The flying capacitor method is made of two transfer contacts and a capacitor, and the terminal side and the internal circuit side are connected alternately, and the charged voltage of the capacitor is transferred between them.

[Problem that the invention seeks to solve]

Each of the above conventional techniques has the following problems.

In the isolated amplifier method, when providing isolation between channels, it is necessary to supply power to each isolated amplifier independently, which increases the board area and cost. Recently, there are also isolated amplifiers with built-in isolated power supplies, but since the accuracy depends on the accuracy of each IC, there is a lot of variation and the price is high.

On the other hand, in the flying capacitor method, voltage (potential accumulated in the capacitor) is transferred using two transfer contacts, but this involves problems with reliability because a mechanical element called a contact (usually a mercury relay) is used. . Also 1
Since the signal goes through the process of being stored in a capacitor, there are problems in terms of accuracy and response speed.

An object of the present invention is to provide an analog isolation method that can reduce the circuit scale and cost without reducing the accuracy of analog signal input values.

[Means for solving problem 8] The above purpose is achieved by using a DC current sensor as an insulating circuit that can measure current with the input and output disconnected (insulated state) using a magnetic core. can. However, although this type of current sensor has excellent linearity, since it is conventionally used for large currents (on the order of amperes), the drift becomes large for 4 to 20 mA. Therefore, in order to further improve the characteristics, an insulated circuit with good characteristics can be obtained by winding a coil having a reference and a power source around the magnetic core and incorporating a calibration microcomputer. - [Function] - In other words, the primary side (input) and secondary side (output) exchange by magnetic flux and are separated by an insulating film, so almost perfect insulation cannot be achieved. can.

Further, the theoretical output value and the actual output for the reference coil having the reference power source are periodically compared by a microcomputer, and the gain and offset can be automatically adjusted.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. ff
An analog measurement signal (typically 4 to 20 mA) flows through the primary coil 1 and generates magnetic flux.

A voltage is generated in the Hall element 2 in proportion to this magnetic flux.

Em is amplified to a desired value by amplifier 4 and output.

On the other hand, in order to correct the accuracy, the reference power source 8 of the reference coil 5
is set to 0N-0 and FF, and the output of the Hall element 2 is detected. At this time, the input is turned off by the switch 6.Next, the detected value and the theoretical value are compared by the microcomputer 10, and the gain/offset adjustment circuit 9 is used to control the amplifier 4.
Adjust. Inputs from a remote monitoring and control device etc. need only be transmitted macyclically for about 1710 seconds at each point, and if processing is performed within 1/100 seconds (actually on the μSeC order), there will be no effect on the outside. Also, let's explain accuracy correction using a mathematical formula.

V,=ΔV V,. =20X 1O-3X A + ΔV, and ■
. , V2° is fixed at '18, the offset error and gain are known, and the gain and offset of the amplifier 4 can be adjusted accordingly.

According to this embodiment, various currents can be handled by changing the number of turns of the coil. Furthermore, regardless of the input, the accuracy can be increased as much as possible by using the reference power source.

In addition to this embodiment, instead of the Hall element TIE current sensor, a Cramer transformer (with two secondary coils) type DC current sensor or a servo Hall element current sensor (with a secondary coil to keep the magnetic flux at zero) can be used. It goes without saying that there is a device (controlling the current). Further, as a method of detecting the gain offset error, the primary coil may be divided into two and the cases where the number of turns is n and 2n may be compared, that is, as shown in the following equation.

V, = AI ten Δ■−■ v8: Volume I! Output V when n times =
2AI+ΔV-■ Output when v2 2 turns is 2n times ■×
If you do 2-■, you can find out ΔV from the actual measurement value, and if you measure another point using the reference coil, you can also find out A.

【Effect of the invention〕

As explained above, the present invention has the following effects.

1. Data can be sent to the secondary side without any effect on the input signal.

2. Dielectric strength can be easily increased by simply increasing the insulation between the primary and secondary coils.

3. The offset and gain are constantly (cyclically) adjusted, resulting in a highly accurate isolation circuit.

4. There is no need to provide a DC-DC converter for each channel, allowing for a compact and inexpensive configuration.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, and Fig. 2 is a conventional analog insulation example (flying capacitor method).
FIG. DESCRIPTION OF SYMBOLS 1...Primary coil, 2...Hall element, 3...Magnetic core, 4...Amplifier, 5...Reference coil, 6...Semiconductor relay. 7...Relay switch, 8...Reference power supply. 9... Gain/offset adjustment circuit, 10... Microcomputer.

Claims (1)

[Scope of Claims] 1. An isolated analog signal input method characterized in that a DC current sensor is used as input insulation means for analog measurement signals in a remote monitoring control device or a measurement control device. 2. The isolated analog signal input method according to claim 1, wherein a coil equipped with a reference power source is wound around the magnetic core of the DC current sensor to calibrate the output.