JPS6338160B2 - - 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.
Using a DC current in the range of ~20 mA, 4 mA is used as power for operating the terminal, and 16 mA 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 the 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.

An object of the present invention is to provide a two-wire signal transmission system with a simple configuration, easy insulation between power supplies and input/output, and easy multi-point integration.

In the present invention, a plurality of systems that binary-modulate electricity from an AC power source and supply it to a contact operating device of a terminal are connected in parallel to a common AC power source.

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 these units are provided depending on the number of input/output signals, but one representative column is shown here. Each unit is supplied with sufficient power from a common AC power source 11 through its respective transformer. 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 the terminals 31a to 31d of the terminal section 3 through two electric wires of the transmission section 2, respectively. here,
31a is an analog operating device, 31b is an analog detector, 31c is a contact detector, and 31d is a contact detector. These are paired with each input/output unit of the control section 1, and the paired units are indicated by a common suffix. The required number of each terminal device is provided 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 using a conversion circuit 132a, and supplies it to a modulation circuit 134a through a driver 133a, thereby modulating the output electricity (voltage or current) of the AC power supply 11. and send it out 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, a clock pulse is generated from the AC wave and used as a regulation signal for demodulation, analog conversion, etc. (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 of locations. 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 accompanying such a load change 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 131d
is input.

Such a two-wire signal transmission system uses alternating current electricity from a high-frequency alternating current power supply as a signal and power carrier, and a continuous value signal is expressed by the wave number of one state of binary modulated alternating current electricity, and a binary signal is used. Since it is expressed by the binary modulated signal itself, the configuration is simple, and insulation between power supplies and input/output is easy.
This is a two-wire signal transmission system that is suitable for transmitting high-precision signals and can be uniformly applied to transmitting both continuous value signals and binary signals. In this system,
In addition, if the AC power supply is shared by multiple signal transmission systems and clock pulses are generated and used from the AC power waves of the power supply, the operations of the multiple signal transmission systems can be synchronized with each other or have appropriate timing relationships. can be performed while maintaining

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' are provided, and output units 13a, 1
3a' 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.

Since the AC power supply is common, the input/output system for binary signals can be easily multipointed as described below. The output system of the multi-point binary signal is shown in FIG. 3, and the input system is shown in FIG. 4. The multi-point binary signal output system is shown in Figure 3a.
Or, as shown in b, a pair of a binary signal output unit that uses a switch as the modulation circuit 134c to turn on and off electricity from an AC power supply according to a binary signal, and a contact operating device that opens and closes a relay or transistor is used. , it is only necessary to connect the same number of output points in parallel to the common AC power source 11. In addition, as shown in FIG. 4a or b, the multi-point binary signal input system uses a pair of a binary signal input unit using a current detection resistor as the load detection circuit 134d and a contact detector, with the same number of common input points as the load detection circuit 134d. It is only necessary to connect it in parallel to the AC power supply 11. Conventionally, in order to isolate and input/output binary signals, special detection means and excitation means were required for each point, so when increasing the number of points, the complexity of the equipment was unavoidable. According to the invention, this point is greatly improved.

As described above, the present invention can convert electricity from an AC power source into two
The system that modulates the value and supplies it to the terminal contact controller,
Since a plurality of devices are connected in parallel to a common AC power source, a multi-point binary signal output system can be realized with a simple configuration.

[Brief explanation of drawings]

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, FIG. 3 is a block diagram of a multi-point binary signal output system, and FIG. 4 is a block diagram of a multi-point binary signal input system. 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. Signals and power source power are transmitted in parallel from a plurality of control units disposed on the power supply side to a single terminal unit disposed on the process side through a plurality of transmission lines consisting of two transmission lines. The supply system uses a single high-frequency AC power source as a power source, and each of the plurality of control units carries a signal in a format that binary-modulates the electricity of the high-frequency AC power source and converts it into a wave number of AC electricity. The terminal section includes a modulation means for demodulating the signal transmitted through the transmission line, and a demodulation means for demodulating the signal transmitted through the transmission line, and the terminal section includes a demodulation means for demodulating the signal transmitted through the transmission line, and a demodulation means for demodulating the signal transmitted through the transmission line, and a demodulation means for demodulating the signal transmitted through the transmission line. A two-wire signal transmission system comprising: power supply means for supplying electric power.