JPS6338159B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-wire signal transmission system. More particularly, the present invention relates to a two-wire signal transmission system that uses high-frequency alternating current electricity as a carrier of information and power.

In process control, two-wire signal transmission systems are used to exchange information between each point in the process and the control unit. The two-wire signal transmission system also has the function of supplying operating power from the control unit to terminal devices such as detectors and operating devices located at various locations in the process. Conventional two-wire signal transmission systems typically use direct current electricity as an information and power carrier, e.g.
A DC current in the range of -20mA is used to generate 4mA of power for operating the terminal, and 16mA above that is used for information.

Terminals are distributed throughout the process, but the control section is centralized in a control room or the like. Power is supplied to each two-wire signal transmission system from a common DC power source or commercial power source in a control room or the like. It is desirable that each two-wire signal transmission system be isolated from each other and between the input and output within each system, so if power is supplied from a common DC power supply, each system must be isolated from DC/ It is necessary to isolate the power supply and input/output using a DC converter, etc., and if the power is supplied from a commercial power source,
Although the power supply is isolated by the power transformer, since the transformer's power is converted to direct current and used, a DC/DC converter is still required for input/output isolation. For this reason, the conventional two-wire signal transmission system inevitably has a complicated configuration when insulation is required. Furthermore, since the transmitted signal is a signal in which the amplitude of the current represents information, it is easily affected by noise and has the drawback that highly accurate information is difficult to obtain.

There are two types of signals exchanged between the control unit and the process: signals whose values change continuously (hereinafter referred to as continuous value signals) and signals whose values change only in binary terms (hereinafter referred to as binary signals), and For each, there is a signal (input signal) that is input from the process to the control unit and a signal (output signal) that is output from the control unit to the process. Conventional two-wire signal transmission systems are used for inputting and outputting continuous value signals, and separate systems are used for inputting and outputting binary signals. Therefore, in order to comprehensively transmit process signals, two systems with completely different configurations are required, which complicates the system configuration. In particular, since input/output of binary signals is often performed at multiple points, the complexity of the system is doubled.

In order to improve the reliability of process control, the control units for one terminal are duplicated, one is on the active side and the other is on the standby side, and when the active side fails, the standby side is backed up. In that case, the standby side must be prepared to monitor the input/output signals of the active side to maintain continuity of control during backup. To achieve this, a two-wire signal transmission system must be able to easily exchange signals between different systems, but conventional two-wire signal transmission systems do not have a configuration suitable for this. If we try to make this possible, the configuration will inevitably become complicated. In particular, if it is attempted to enable alternating current between systems while maintaining insulation between systems, the configuration becomes significantly complicated.

The purpose of the present invention is to have a simple configuration, easy insulation between power supplies and input/output, suitable for transmitting high-precision signals, and uniformly applicable to the transmission of both continuous value signals and binary signals. It is an object of the present invention to provide a two-wire signal transmission system that can easily be multipointed and can easily perform alternating current between systems for duplication.

In the present invention, a high frequency AC power source is used as a power source provided on the control unit side, and a signal is added to the wave number of the output electricity of the AC power source so that the energy is used as power for operating the terminal device.

Hereinafter, the present invention will be explained in detail with reference to the drawings.
FIG. 1 is a conceptual block diagram of an embodiment of the present invention.
In FIG. 1, 1 is a control section, 2 is a two-wire transmission section, and 3 is a terminal section. In the control unit 1, 11
is a high frequency AC power source. Here, "high frequency" means that the frequency is such that a continuous value signal, which will be described later, can be expressed with necessary and sufficient resolution. The waveform of the output electricity from the AC power supply may be a rectangular wave, a sine wave, a triangular wave, or any other arbitrary waveform. 12a to 12d are transformers, 13a to 13d are input/output units of the control section, where 13a is shown as a continuous value signal output unit, 13b is shown as a continuous value signal input unit, and 13c is a binary signal output unit. 13d is shown as a binary signal input unit. A required number of each of these units is provided depending on the number of input/output signals, but one representative example is shown here. Each unit has a common AC power source 1
1 through each transformer with sufficient power. Each transformer performs functions such as power supply isolation, step-up or step-down, and impedance conversion.

The input/output units 13a to 13d are connected to each terminal device 3 of the terminal section through two electric wires of the transmission section 2, respectively.
1a to 31d, respectively. Here, 3
1a is an analog operating device, 31b is an analog detector, 31c is a contact operating device, and 31d is a contact detector, respectively. These are paired with each input/output unit of the control section 1, and the paired units are indicated by a common suffix. Each terminal device is provided with a required number according to the number of points of each input/output signal.The continuous value signal output unit 13a converts the output signal of the continuous value output circuit 131a into a pulse width signal with a conversion circuit 132a, and modulates it through a driver 133a. The output voltage (voltage or current) of the AC power supply 11 is modulated and sent onto the transmission line. The output signal form of the continuous value output circuit 131a may be either an analog signal or a digital signal. Modulation methods include amplitude modulation, phase modulation,
Any modulation method such as FSK/PSK can be used.
Due to this modulation, the alternating current electricity applied to the analog controller 31a through the transmission section 2 changes in amplitude, phase, etc. in a binary manner corresponding to the logic value of the pulse width signal. The wave number of the portion corresponding to the value "1" represents the value of the continuous value signal. That is, since the value of the continuous value signal is expressed by the number of pulses, it is less susceptible to noise, and if the frequency of the alternating current electricity is made high enough, highly accurate signal transmission can be achieved.

The analog operating device 31a receives the alternating current electricity modulated in this way through the transformer 311a,
The pulse width signal is either left as AC or converted to DC by the rectifier circuit 312a and then demodulated by the demodulation circuit 313a, and the obtained pulse width signal is converted into an analog signal by the conversion circuit 314a and given to the operation circuit 315a.
operate the process through a. transformer 311
The AC electricity received by a is also passed through the rectifier circuit 312.
a, and is supplied as operating power to each circuit of the analog operating device 31a. Also, if necessary, clock pulses are generated from AC waves and used as regulation signals for demodulation and analog conversion (not shown). The transformer 311a provides insulation between the continuous value signal output unit 13a and the analog operating device 31a, and performs functions such as voltage step-up, voltage step-down, and impedance conversion as required. In addition,
The transformer 311a is not limited to the illustrated position, but may be provided anywhere on the transmission line, and may be provided in any number. The same holds true for any of the following terminals.

The continuous value signal input unit 13b is connected to the transformer 1.
2b of alternating current electricity is sent out onto the transmission line through the load state detection circuit 134b. This alternating current electricity is transmitted to the transformer 311 by the analog detector 31b at the terminal part.
The electric power is received through the rectifier circuit 312b, and is converted into direct current by the rectifier circuit 312b, and is used as a power source for operating each circuit of the analog detector 31b. Clock pulses are generated as needed from alternating current electricity (not shown). Analog detector 3
1b converts the process analog measurement signal detected by the detection circuit 315b into a pulse width signal by the conversion circuit 314b. The clock pulse is converted by the conversion circuit 31.
4b is used for regulating the operation. This pulse width signal is applied to a load control circuit 313b, which changes the load amount of the rectifier circuit 312b or transformer 311b in a binary manner corresponding to the logical value of the pulse width signal. At this time, the wave number of the AC electricity included in the load state corresponding to the logical value "1" of the pulse width signal represents the value of the analog measurement signal. Since the transmission current changes in response to such changes in load, this is detected by the load detection circuit 134b of the continuous value signal input unit 13b, the pulse width signal is restored by the reception circuit 133b, and the pulse width signal is restored by the conversion circuit 132b. It is converted into a continuous value signal and applied to the continuous value input circuit 131b. The form of this continuous value signal is an analog signal or a digital signal depending on the configuration of the continuous value input circuit 131b.

The binary signal output unit 13c outputs the binary signal generated by the binary signal output circuit 131c to the driver 133.
c to the modulation circuit 134c, which modulates the output electricity of the AC power supply 11, and transmits it to the contact operating device 31c through the transmission line. Modulation circuit 1
Although amplitude modulation (on-off modulation) is suitable for the modulation by 34c, it is not necessarily limited to this.

The contact operation device 31c receives the transmitted signal through the transformer 311c, demodulates it (simply rectifies it in the case of on-off modulation) in the demodulation circuit 313c, restores the binary signal, and operates the relay etc. 315 according to this signal.
Operate c.

The binary signal input unit 13d sends out AC electricity from the AC power supply 11 onto the transmission line through the load detection circuit 134d. This AC electricity is transmitted to the contact detector 3
1d receives power through the transformer 311d,
Rectified by the rectifier circuit 312d and connected to the contact circuit 315d
given to. The contacts of the contact circuit 315d are opened and closed by external operations, and the load of the transformer 311d changes in a binary manner due to the opening and closing of the contacts, so the change in current due to such load changes is binary. It is detected by the load detection circuit 134d in the signal input unit 13d, and the receiving circuit 133
d, the binary signal is restored and the binary input circuit 133d
is input.

Such a two-wire signal transmission system uses AC electricity from a high-frequency AC power source as a signal and power security, and a continuous value signal is expressed by the wave number of one state of binary modulated AC electricity, and a binary signal is used. is expressed by the binary modulated signal itself, so it has a simple configuration, easy isolation between power supplies and input/output, and is suitable for transmitting high-precision signals, and is suitable for transmitting both continuous value signals and binary signals. It also becomes a two-wire signal transmission system that can be uniformly applied. In this system, if the AC power supply is shared by multiple signal transmission systems and clock pulses are generated and used from the AC electricity waves of the power supply, the operations of the multiple signal transmission systems can be synchronized or synchronized with each other. This can be done while maintaining an appropriate timing relationship.

With such a signal transmission system, the reliability can be easily increased by duplicating the input/output units of the control section. Figure 2 shows an example of duplication. In FIG. 2, one set of analog operations at the terminal, two sets of continuous value signal outputs for the detectors 31a and 31b, and input units 13a, 13b, 13 are shown.
a'13b' is provided, and the output units 13a, 13
A' and input units 13b and 13b' are connected in parallel to a common transmission line. With this arrangement, the continuous value input signal, ie the pulse width modulated load state, generated by the analog detector 31b is commonly input to the continuous value input units 13b, 13b'. Then, the operation output of the same value based on this input signal is output from the continuous value output units 13a, 1.
3a' and applied to a common analog controller 31a. Since the AC power source 11 is common, the two pulse width modulated operation outputs can be provided synchronously. In such a state, even if one of the input/output unit pairs goes down due to a failure, the input/output operations by the other pair will continue normally.
Service to the process is uninterrupted. That is, by simply connecting the transmission lines of two input or output units in parallel to a common terminal, a duplex system can be easily constructed, and input/output insulation can be maintained. Moreover, when mutual isolation between duplicated systems is desired, a transformer may be inserted at an appropriate position. The above is an example in which the continuous value signal transmission system is duplicated, but the binary signal transmission system can also be duplicated in the same manner.

An example of a continuous value signal output system is shown in FIG. In FIG. 3, the modulation circuit 134a is constituted by a parallel circuit of a switch S and a resistor R, and the switch S is opened and closed by a driver 133a in accordance with a pulse width signal. As the switch S opens and closes, the amplitude of the AC voltage applied from the AC power source 11 to the transmission line is modulated into two values, large and small. The alternating current voltage modulated in this way is taken out to the secondary side of the transformer 311a, rectified by a rectifier circuit 312a, and given to the demand circuit 310a. Demand circuit 310a
1 includes a demodulation circuit 313a, a conversion circuit 314a, and an operation circuit 315a in FIG. The output power of the rectifier circuit 312a is
The capacitor C is charged through the capacitor C, and this charged power is given to the demand circuit 310a as operating power.

FIG. 4 shows the configuration of another example of a continuous value signal output system, in which a high frequency AC power source is connected to both ends of the primary coil with center tap of the transformer 12a'.
1 output electricity is applied alternately in half cycles, 2
The AC voltage induced on the next side is applied to the demand side through a transmission line. transformer 12
The center tap of the primary coil a' is connected to the common point through a parallel circuit of a resistor R and a collector-emitter circuit of a transistor Q. Transistor Q is turned on and off by a pulse width signal applied to its base. As the transistor Q is turned on and off, the voltage applied to the primary coil of the transformer 12a' is modulated into two values, large and small, so that the demand side is supplied with an AC voltage whose amplitude is modulated according to the pulse width signal. Such an AC voltage passes through a transformer 311a, is rectified by a rectifier circuit 312a, is applied to a parallel circuit of a Zener diode Z and a capacitor C through a resistor r, is made constant by the Zener diode, and is charged to the capacitor C. The voltage drop across resistor r and the voltage across capacitor C are provided to demand circuit 310a as a signal and a power supply voltage, respectively. Since the voltage drop across the resistor r is amplitude modulated in accordance with the pulse width signal, the process operation signal can be obtained by restoring continuous values from the pulse width signal.

An example of a continuous value signal input system is shown in FIG. In FIG. 5, the voltage of an AC power source 11 is amplitude modulated by opening and closing a switch S, and a timing signal of a constant period is superimposed on it, and then sent to a signal line. Note that the superimposition of the timing signal may be omitted depending on the case. Such a voltage passes through a transformer 311b, is rectified by a rectifier circuit 312b, is applied to a detection conversion circuit 310b, and is charged to a capacitor C through a diode D. Rectifier circuit 31
A series circuit of a resistor r and a transistor Q is provided between the output terminals of the transistor 2b. The voltage of capacitor C is given to detection conversion circuit 310b as a power supply voltage.
The detection conversion circuit 310b includes the conversion circuit 314b and the detection circuit 315b shown in FIG.
The detection conversion circuit 310b operates under the control of a timing signal included in the DC voltage applied from the rectification circuit 312b, converts the analog detection signal into a pulse width signal, and uses this pulse width signal to drive the transistor Q.
Turn on and off. As the transformer Q turns on and off, the load of the rectifier circuit 312b, that is, the transformer 31
1b changes binary, and the corresponding change in the transmission current is detected by the receiving circuit 133b that observes the voltage drop across the resistor R' on the power supply side, and based on this, the pulse width signal and the The corresponding continuous value signal is restored.

The configuration of another example of the continuous value signal input system is shown in FIG. In FIG. 6, the output voltage of the high frequency AC power supply 11 is the center tap 1 of the transformer 12b'.
A half cycle is alternately applied to both ends of the secondary coil, thereby causing an AC voltage induced on the secondary side to be sent out through the transmission line. The center tap of the transformer 12b' is connected to a common point through a resistor R and a collector-emitter circuit of a transistor Q. Transistor Q is turned on and off by a timing signal applied to its base. As the transistor Q is turned on and off, the voltage applied to the primary coil of the transformer 12b' is modulated into two values, large and small, so that an alternating current voltage on which a timing signal is superimposed by amplitude modulation is sent to the transmission line. Such AC voltage passes through the transformer 311b and is then connected to the rectifier circuit 3.
The voltage is rectified by 12b, applied to a parallel circuit of a Zener diode Z and a capacitor C through a resistor γ', is made constant by the Zener diode Z, and is charged to a capacitor C. The voltage drop across resistor r' and the voltage across capacitor C are provided to detection conversion circuit 310b as a timing signal and a power supply voltage, respectively.

The detection conversion circuit 310b includes a preamplifier circuit A,
It consists of an integrating circuit I, a comparing circuit H, and a flip-flop circuit F for pulse width conversion. The preamplifier circuit A inputs the analog voltage to be converted to the integrating circuit I. The integrator circuit I receives this analog signal either alone or when the switch K is closed, using the reference voltage e.
The difference between the two is calculated and integrated, and the integrated output is provided to the comparison circuit H. Comparison circuit H detects whether the integral output has become zero, and uses the output signal to reset flip-flop circuit F. Flip-flop circuit F
is set by a timing signal included in the voltage drop across the resistor r', and the set output signal turns on the switch K of the integrating circuit I. Integrator circuit I, comparator circuit H, and flip-flop circuit F
is known as an integral type voltage/pulse width converter, and by means of such a converter, the analog output voltage of preamplifier circuit A is converted into a pulse width signal every time a timing signal is applied. is converted to Therefore, if the transistor Q is turned on and off using this pulse width signal, the receiving circuit 133b which observes the voltage drop across the resistor R on the power supply side
The pulse width signal can be detected by

As described above, in the present invention, a high frequency AC power source is used as a power source provided on the control unit side, and a signal is added to the wave number of the output electricity of the AC power source, and the power for operating the terminal device is added to the energy. Therefore, according to the present invention, the configuration is simple, the insulation between power supplies and input/output is easy, and it is suitable for transmitting high-precision signals, and can be uniformly used for transmitting both continuous value signals and binary signals. It is possible to realize a two-wire signal transmission system in which alternating current between systems is easy due to duplication.

[Brief explanation of the drawing]

Fig. 1 is a conceptual configuration diagram of an embodiment of the present invention;
The figure is a conceptual block diagram of a duplex system, Figures 3 and 4 are concrete block diagrams of a continuous value output system, and Figures 5 and 6 are concrete diagrams of a continuous value input system. This is a configuration diagram. 1...Control unit, 11...AC power supply, 12a-1
2d...Transformer, 13a...Continuous value signal output unit, 13b...Continuous value signal input unit, 1
3c...Binary signal output unit, 13d...Binary signal input unit, 2...Transmission section, 3...Terminal section, 31a...Analog operation device, 31b...Analog detector, 31c...Contact operation device , 31d...
Contact detector.

Claims (1)

[Claims] 1. A system for supplying signals and power from a control section located on the power source side to a terminal section located on the process side through two transmission lines, using a high frequency AC power source as the power source. , the control section has a modulation means for binary-modulating the electricity of the high-frequency AC power source and converting it into a wave number of AC electricity, and transmitting the signal to the transmission line, and the terminal section is configured to transmit the signal to the transmission line via the transmission line. A two-wire signal transmission system comprising demodulation means for demodulating the signal transmitted via the transmission line, and power supply means for supplying the energy of the signal transmitted via the transmission line as power for operating the terminal section. . 2. The two-wire signal transmission system according to claim 1, wherein in the terminal section, the signal demodulated by the demodulating means becomes an operation signal for operating a process.