JPH0211960B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to an isolated signal conversion device used in the field of industrial measurement such as process control, and particularly to obtain a stable control system that is not affected by disturbances such as noise. The present invention relates to an isolated signal converter.

TECHNICAL BACKGROUND OF THE INVENTION Conventionally, an isolated signal converter used in a process control system has a configuration roughly as shown in FIG. That is, this device includes a modulation circuit 2 that amplifies an input signal V _IN with an input amplifier 1 consisting of an operational amplifier, modulates it, and transmits it to a remote location, and a demodulation circuit 3 that demodulates the modulated signal to obtain an input signal V _IN . Between,
A signal isolation circuit 4 such as a photocoupler or isolation transformer is inserted, and power is supplied separately to the transmitting system such as the input amplifier 1 and modulation circuit 2, and the receiving system such as the demodulating circuit 3 and output amplifier 5. In order to achieve this, a power supply circuit 6 such as a DC-DC converter is provided which is insulated from each other. Although not shown, the output signal V _O of the output amplifier 5 is sent to a control system such as a controller. In the figure, V _P
is a DC power supply.

Problems with the Background Art However, in the above device, since it is necessary to supply power to the transmitting system and the receiving system separately, one of the power supply lines, for example 7, must be connected over a long distance. However, the cost and construction work are difficult. In addition, in order to avoid the influence of noise etc. that enters one power supply line 7, it is necessary to insulate the electric wire circuit 6 for each system.
The drawback is that a complicated and expensive device such as a DC-DC converter must be used.

Purpose of the Invention The present invention has been made in order to eliminate the above-mentioned drawbacks, and it is possible to supply power to a transmitting/receiving system using one DC power supply without requiring an insulated power supply circuit, and to transmit signals using a signal isolation circuit. It is an object of the present invention to provide an isolated signal conversion device that can improve efficiency.

Summary of the Invention The present invention includes a transmission system circuit that converts an input signal into a pulsed signal proportional to the input signal, converts this pulsed signal into two mutually contradictory waveform signals, and outputs the two waveform signals, and a DC power supply that supplies power to the transmission system circuit. , a signal isolation transformer whose primary winding is supplied with each signal of the transmission system circuit and whose intermediate terminal is supplied with the DC power; and each signal obtained from both ends of the secondary winding of this signal isolation transformer. By providing a receiving system circuit that demodulates the signal and converting it into a signal proportional to the input signal, and a rectifier circuit that rectifies the output voltage of this signal isolation transformer and uses it as a power source for the receiving system circuit, a single DC power supply can be used. The above object is achieved by making the receiving system circuit also serve as a power source and transmitting the signal to the secondary winding of the signal isolation transformer without causing magnetic saturation.

Embodiment of the Invention FIG. 2 is a block diagram showing an embodiment of the present invention, in which an input amplifier 11 comprising, for example, an operational amplifier, etc.
amplifies the process input signal V _IN and then supplies it to the signal conversion circuit 12 for facilitating circuit isolation.
The signal conversion circuit 12 is, for example, a voltage-pulse width conversion circuit that is composed of an integrating amplifier, a comparator, etc., and converts the input signal V _IN into a pulse width duty cycle signal proportional to the input signal V IN, or a voltage-pulse width conversion circuit that converts the input signal V _IN into a frequency signal. A voltage-frequency conversion circuit is used.
A pulse width-biphase conversion circuit 13 is connected to the output side of the signal conversion circuit 12. The pulse width-biphase conversion circuit 13 converts the pulse width duty cycle signal and the clock CLK into two waveform signals that are opposite to each other so that the same signal can easily pass through the signal isolation transformer 14 used in the next stage, and The purpose is to simplify the configuration of the signal isolation transformer 14. This signal isolation transformer 14 is 1
Both the next winding and the secondary winding have an intermediate terminal,
Both ends of the primary winding are connected to both output ends of the pulse width-biphase conversion circuit 13, and the intermediate terminal of the primary winding is connected to the input amplifier 11 and the signal conversion circuit 1.
2 and a DC power supply 15 for powering the pulse width-biphase conversion circuit 13 and the like.
The secondary winding of the signal isolation transformer 14 is connected to an output amplifier consisting of an operational amplifier, etc. via a biphasic-pulse width conversion circuit 16 and a signal conversion circuit 17 having a demodulation function that converts the pulse width into voltage to obtain an input signal. 18 are connected. In addition, a diode is installed at both ends of the secondary winding of the signal isolation transformer 14.
D ₁ and D ₂ are connected, and the voltage appearing at both ends of the secondary winding is rectified and supplied to the biphase-pulse width conversion circuit 16, signal conversion circuit 17, output amplifier 18, etc. The intermediate terminal of the secondary winding is used as a zero potential line for circuits 16, 17, 18, etc. Although not shown, the signal V _O output from the output amplifier 18 is sent to a process control system or the like.

Next, the operation of the isolated signal converter configured as above will be explained. The input amplifier 11 amplifies the input signal V _IN of the process etc. to obtain a signal A=V _IN ·K (where K is the amplification degree) as shown in FIG. 3A.
This is supplied to a subsequent signal conversion circuit 12 such as a voltage-pulse width conversion circuit. This signal conversion circuit 12 converts it into a pulse width duty cycle signal as shown in FIG.
supply to. At this time, the circuit 13 has a clock.
CLK is supplied. Here, the pulse width-biphase conversion circuit 13 converts T ₁ of the signal B
A pulsed signal C that rises at the falling edge of the clock CLK input within the period T2, and a pulsed signal C that rises at the rising edge of the clock CLK inputted within the _T2 period, and a pulsed signal exhibiting a waveform completely opposite to that of the signal C.
C' and supplies the respective signals C and C' to both ends of the primary winding of the signal isolation transformer 14. Therefore, when focusing on the signal waveform obtained from the secondary winding of the signal isolation transformer 14, the time axis direction is voltage -
This is a biphase waveform after pulse width modulation, and the amplitude becomes the signals D and D' obtained by the voltage V _P of the DC power supply 15. Note that the DC power supply V _P is set to a voltage (for example, 15V) that can be used as a circuit power supply after the secondary winding. Therefore, the signals D and D' obtained from the secondary winding are connected to the diodes D ₁ and D ₂
If rectified by , one DC power supply 15 can be used as a power source not only for the transmission system circuits 11 to 13 but also for the reception system circuits 16 to 18 after the secondary winding.

On the other hand, the signal D output from both ends of the secondary winding,
D' is converted into a pulse width by a biphase-pulse width conversion circuit 16 (see Fig. 3E), and then demodulated by a signal conversion circuit 17 that includes a pulse width-voltage conversion means using a filter or the like, and is proportional to the input signal. The signal F shown in FIG. 3 is extracted.

Note that the present invention is not limited to the above embodiments. Although the above embodiment has been described as a digital signal transmission circuit, it can also be used as an analog signal transmission circuit. That is, in the configuration shown in FIG. 2, for example, transmission system circuits 11 to 15 are installed on the local side, and analog signals output from the signal isolation transformer 14 are demodulated by reception system circuits 16 to 18 installed on the center side. A configuration may also be used in which the input signal is obtained by An example of this is shown in FIG. In this case, it is effective to use twisted wires for the signal circuits H and L connected to the secondary winding of the signal isolation transformer 14 in order to strengthen the nozzle resistance. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

Effects of the Invention As described in detail above, according to the present invention, since the pulse width-biphase and biphase and pulse width conversion means are provided between the input and output terminals of the signal isolation transformer, the transformer can be miniaturized. It is possible to prevent magnetic saturation and improve signal transmission characteristics and input/output accuracy. Furthermore, one DC power supply can be used not only for the transmission system but also for the reception system, thereby eliminating the need for a complicated and expensive insulated power supply. Further, it is possible to provide an isolated signal conversion device that can provide signal isolation and power supply isolation with one signal isolation transformer.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional device, FIG. 2 is a block diagram showing an embodiment of the isolated signal converter according to the present invention, FIG. 3 is a waveform diagram explaining the operation of the device of the present invention, and FIG. 4 FIG. 2 is a configuration diagram showing another embodiment of the present invention. 12... Signal conversion circuit (voltage-pulse width conversion circuit), 13... Pulse width-biphase conversion circuit, 14... Signal isolation transformer, 15... DC power supply, 16... Biphas-pulse width conversion circuit, 17... ...Signal conversion circuit, _D1 , _D2 ...Diode.

Claims (1)

[Claims] 1. Converting into a pulsed signal proportional to the input signal,
A transmission system circuit that converts this pulsed signal into two mutually contradictory waveform signals and outputs it, a DC power supply that supplies power to this transmission system circuit, and each signal of the transmission system circuit that is supplied to both ends of the primary winding. a signal isolation transformer whose intermediate terminal is supplied with the DC power, and a receiving system circuit which demodulates each signal obtained from both ends of the secondary winding of the signal isolation transformer and converts it into a signal proportional to the input signal. and a rectifier circuit that rectifies the output voltage of the signal isolation transformer and uses it as a power source for a receiving circuit. 2. The isolated type according to claim 1, wherein the means for converting into a pulsed signal uses a voltage-pulse width conversion circuit that converts into a pulse width duty cycle signal proportional to the input signal. Signal converter. 3. The isolated signal conversion device according to claim 1, wherein the means for converting into a pulsed signal uses a voltage-frequency conversion circuit that converts into a pulse signal with a frequency proportional to the input signal. 4 The transmission system circuit includes a voltage-pulse width conversion circuit,
2. The isolated signal conversion device according to claim 1, further comprising a pulse width-biphase conversion circuit. 5. The isolated signal converter according to claim 1, wherein the reception system circuit includes a biphase-pulse width conversion circuit and a pulse width-voltage conversion circuit.