JPH05308244A - Signal transmission circuit - Google Patents

Abstract

PURPOSE:To provide the signal transmission circuit sufficiently used even by a 2-wire instrument such as a differential pressure transducer and a device driven by a battery whose rating power is small. CONSTITUTION:The signal transmission circuit is provided with a voltage/pulse width conversion circuit 2, a leading detection circuit 3, a trailing detection circuit 4, a photocoupler 5, a photocoupler 6 and a pulse width/voltage conversion circuit 8 or the like and the leading detection circuit 3, and the trailing detection circuit 4 are used to detect a leading and a trailing of a transmission pulse signal and the pulse signal whose width is sufficiently smaller than the transmission pulse signal width is fed to the photocouplers 5, 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission circuit having a small rated power in a signal transmission circuit.

[0002]

2. Description of the Related Art For example, when connecting a computer to a peripheral device, or a central processing unit for process control, and a terminal device, a connection cable is often long, and therefore, when an analog signal is used as a transmission signal, external noise is generated. The noise margin may be lost due to picking up. In order to remove the influence of this noise, signal transmission is performed using a pulse signal, and an isolator is used to electrically insulate between a transmitter and a receiver. A photocoupler is generally used as this isolator.

[0003]

However, since the photocoupler has a limited handling current and voltage and requires a current of several mA to drive it, it consumes a large amount of power, and the photocoupler needs to be used in a differential pressure transmitter or the like. There is a problem in that it cannot be used in a wire meter or a device that operates on a battery and has a small rated power, or that it can be used for a short time.

An object of the present invention is to provide a signal transmission circuit in which a photocoupler can be used as an isolator even in a two-wire type instrument such as a differential pressure transmitter or a device which operates on a battery and has a small rated power. ..

[0005]

In order to achieve the above-mentioned object, the signal transmission circuit of the present invention comprises a detecting means for detecting the rising and falling edges of an input pulse signal and outputting a pulse, and a detecting means for detecting the rising and falling edges of the input pulse signal. It comprises a photo coupler driven by a pulse signal, and means for restoring the original pulse signal from the output of the photo coupler.

[0006]

In the present invention, the photocoupler is driven because it is provided with the detecting means for detecting the rising and falling edges of the input pulse signal and outputting the pulse, and the photocoupler driven by the pulse signal from the detecting means. Time is getting shorter,
As a result, the power consumption is small, so that it can be sufficiently used in a two-wire type instrument such as a differential pressure transmitter or a device operated by a battery. Further, since the means for restoring the original pulse signal from the output of the photocoupler is provided, the input signal can be reliably reproduced and used as the output signal.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a signal transmission circuit according to an embodiment of the present invention.

A signal is input from the voltage signal input terminal 1 and is output to the voltage signal output terminal 9.
A voltage / pulse width conversion circuit 2 is connected to the voltage signal input terminal 1, and the voltage / pulse width conversion circuit 2 proportionally scales the analog voltage signal input to the voltage signal input terminal 1 to the voltage magnitude. Converted into a pulse width signal. The voltage / pulse width conversion circuit 2 is connected to the rising edge detection circuit 3 and the falling edge detection circuit 4. The rising edge detection circuit 3 and the falling edge detection circuit 4 are composed of a one-shot multi-vibrator or the like, and
And the falling edge are detected and output as a sufficiently small pulse width.

The rising detection circuit 3 is connected to the photocoupler 5.
The fall detection circuit 4 is connected to the photocoupler 6, and the output of the photocoupler 5 is the RS flip-flop 7
The output of the photocoupler 6 is input to the reset terminal of the RS flip-flop 7. Here, the symbol S of the RS flip-flop 7 indicates a set terminal, the symbol R indicates a reset terminal, and the symbol Q indicates a positive logic output terminal. The output of the RS flip-flop 7 is supplied to the pulse width / voltage conversion circuit 8, which converts the output into a voltage signal proportional to the pulse width and outputs the voltage signal to the voltage signal output terminal 9.

Next, the operation will be described. FIG. 2 shows a time chart at points A, B, C, D, E, and F in FIG. First, when an analog voltage signal is input from the voltage signal input terminal, the voltage / pulse width conversion circuit 2 obtains a pulse width signal proportional to the magnitude of the analog voltage. For example, if the pulse width signal obtained at this time has a pulse width as shown in FIG. 2, the next rising edge detection circuit 3 detects the rising edge of the pulse indicated by and uses it as a pulse signal. The pulse signal is shown by. Further, the falling edge detection circuit 4 detects the falling edge of the pulse signal and converts it into a pulse signal, so that the pulse signal indicated by is given. , Pulse signals are supplied to the photocoupler 5 and the photocoupler 6 which serve as an isolator to drive the photocouplers. At that time, the photo coupler 5 and the photo coupler 6 are driven only during the period when the pulse train is at the high level, and the operating current of the photo coupler can be greatly reduced.

Next, the output signals of the photocoupler 5 and the photocoupler 6 are as follows, and the RS flip-flop 7 is operated. The output signal of the photocoupler 5 first sets the RS flip-flop 7 to the set state, sets the output of the RS flip-flop 7 to the high level state, and outputs the RS flip-flop 7 to the high level until the drive signal comes to the reset terminal. Is kept at.

When the output signal of the photocoupler 6 is input to the reset terminal of the RS flip-flop 7, the RS flip-flop 7 is reset and the output becomes Low level. Therefore, the output waveform of the RS flip-flop 7 is as follows.
become that way. Therefore, the signal waveform at point F is
The signal waveform at point A is restored. R
By processing the output signal of the S flip-flop 7 by the pulse width / voltage conversion circuit 8, it can be taken out from the voltage signal output terminal 9 as an analog voltage signal. By the way, the frequency of the pulse width signal at point A is usually 100
It is about Hz. For example, a duty ratio of 50 at 100 Hz
%, And if you drive the photo coupler with this pulse signal,
The driving time is 5 ms. In the present invention, if the rising and falling detection pulse widths at the points B and C are each 1 μs, the driving time of the photocoupler is 2 μs for both.
Therefore, the power consumption of the photocoupler is 1/2500
Therefore, this is a very effective method for a two-wire type instrument in which the total operating current must be 4 mA or less.

Further, the rising detection pulse width and the falling detection pulse width can be changed by changing the constants of the capacitors such as the one-shot multivibrator constituting the rising detection circuit 3 and the falling detection circuit 4. Therefore, the power consumption can be further suppressed by further narrowing the detection pulse width.

In the above embodiment, an example in which the outputs of the rising edge detection circuit 3 and the falling edge detection circuit 4 are supplied to separate photocouplers has been described, but a single photocoupler is used and a single flip-flop is used. It is also possible to use an input D-flip-flop.

[0015]

As is clear from the above description, according to the present invention, the transmission pulse signal is not used as it is to drive the photocoupler, but the transmission pulse signal rises,
Since the photocoupler is driven with a pulse width that is sufficiently smaller than the transmission pulse signal width by detecting the falling edge, power consumption is reduced, and a 2-wire type instrument such as a differential pressure transmitter or a device operated by a battery is also sufficient. It can be used and the electrical insulation effect is not lost. Further, since the means for restoring the original pulse signal is provided, it is possible to reliably reproduce the input signal and use it as the output signal.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a signal transmission circuit of the present invention.

FIG. 2 is a time chart diagram of an embodiment of a signal transmission circuit of the present invention.

Claims (1)

[Claims] 1. A detection means for detecting a rising edge and a falling edge of an input pulse signal and outputting a pulse, a photocoupler driven by the pulse signal from the detection means, and an original pulse signal output from the photocoupler. And a means for restoring the signal transmission circuit.