JPS60249441A - Two-wire data transmission equipment - Google Patents

Abstract

PURPOSE:To prevent the malfunction of mode switching due to noise by supplying a bias voltage, which is higher than that in the analog signal transmission mode, in the digital signal transmission mode. CONSTITUTION:In the analog signal mode, a power supply circuit 7 supplies 4- 20mA DC current to an analog communicator 2 and an analog communicator 8. The analog communicator 8 receives a process signal due to 4-20mA DC signal transmitted from the analog communicator 2 and outputs reception information. In the digital signal mode, a digital communicator 9 is provided with an internal power source which outputs a voltage V2 higher than a voltage V1 supplied from the power supply circuit 7, and this voltage V2 is supplied to a process variable transmitter 1. Since this voltage is higher than a set prescribed voltage, the variable transmitter 1 starts transmission and reception of digital signals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device that performs communication using a two-wire JFFI signal line. In particular, the present invention relates to a device that selects a signal mode of either an analog signal or a digital signal and performs data communication using this signal using a two-wire communication line.

[Conventional technology]

In a two-wire data transmission device, the two-wire communication line has a power of 4 mA or more.
A current of 20 mA is supplied, and analog communication is performed between analog communication devices connected to both ends of the communication line by the change in this current.

In such two-wire data transmission equipment, in order to obtain more information from communication equipment installed at a remote location,
A method of temporarily performing digital communication using two existing communication lines is being considered. To do this, the communication channel, which is in analog signal mode during normal operation, must be temporarily converted to digital signal mode by remote control.

As an example of this method, the method disclosed in JP-A-58-85649, ``Data communication device and method for alternately communicating digital data and analog data'' is known.

In this known technique, a first digital communication device connected in parallel to the communication line reduces the current flowing through the communication line to 4 m^ (minimum level). This change is rapid compared to the current change in the analog signal mode, and thereby allows the communication device installed at a remote location to detect that the communication device has been switched to the digital signal mode. As a result, communication using digital signals is started between the second digital communication device provided in the communication device installed at a remote location and the above-mentioned first digital communication device.

However, since the communication mode is switched due to sudden changes in current, it has the disadvantage of malfunctioning due to high frequency noise, and requires a bandpass filter to remove high frequency noise and pass analog signals. . Furthermore, in the digital signal mode, there is a drawback that the analog communication device on the receiving side cannot distinguish between a process signal (analog signal) and a digital signal.

[Problem that the invention seeks to solve]

The present invention solves the problem of malfunction due to noise superimposed on the two-wire communication line (also, in digital signal mode, the signal is not transmitted to the receiver's analogue tracer). The purpose is to

[Means for solving problems]

The two-wire data transmission device of the present invention includes a two-wire communication line,
A first analog communication device connected to one end of the communication line, a second analog communication device connected to the other end of the communication line and communicating with the first communication device, and a second analog communication device connected in series to the communication line. In a two-wire data transmission device, the power supply circuit is inserted in the first and second analog communication devices and supplies direct current in series through the communication lines, and the two-wire data transmission device is connected in parallel to the communication lines. First digital communication device and J-1ff
A second digital communication device is connected in parallel to the first digital communication device and communicates with the first digital communication device, and a backflow prevention II diode is connected to the output circuit of the power supply circuit. The first digital communication device includes circuit means for applying a bias voltage exceeding the DC voltage supplied from the power supply circuit between the communication lines in a mode of transmitting a digital signal to the communication line F. It is assumed that the digital communication device is provided with circuit means for detecting that the bias voltage is applied to the communication line and identifying it as a mote transmitting a digital signal.

[Effect]

In the two-wire data transmission device of the present invention, in the digital signal transmission mode, the first digital communication device supplies a bias voltage higher than the voltage of the power supply circuit for analog signals, so that the second digital communication device supplies a bias voltage higher than the voltage of the power supply circuit for analog signals. Perform transmission. At this time, the analog signal power supply circuit automatically interrupts the current supply.

〔Example〕

FIG. 1 is a block diagram of a two-wire data transmission device according to an embodiment of the present invention.

The process variable transmitter I includes a first analog communication device 2 and a first digital communication device 3, and includes a power supply circuit 7,
The second analog communication device 8 and the first digital communication device 9 are installed at locations separated by a month.

High potential terminals 101 of analog communication device 2 and digital communication device 3 are connected to the cathode terminal of diode 6 via communication line 4 . Low potential terminals 102 of the analog communication device 2 and the digital communication device 3 are connected to the analog communication device 8 via the communication line 5.

The anode terminal of diode 6 is connected to high potential terminal 701 of power supply circuit 7 . A low potential terminal 702 of the power supply circuit 7 is connected to the analog communication device 8 and to the communication wire 4.5 in series. The digital communication device 9 is connected to the communication line 4 and the communication vA5 in parallel and detachably.

The human power of the process variable transmitting device 1 is connected to a sensor (not shown in FIG. 1), and the analog communication device 2 outputs the detected state variable as a change in the amount of analog current.

Further, the process variable transmitter 1 communicates with the digital communication device 9 through the digital communication device 3 using digital signals. There are two transmission methods, analog signal mode and digital signal mode, and switching between these modes is a feature of the present invention and will be explained in detail later.

In analog signal mode, the power supply circuit 7 is connected to 4m8 to 20
A DC current of mA is supplied to the analog communication device 2 and the analog communication device 8.

The analog communication device 8 receives the 41 signal sent by the analog communication device 2.
It receives process signals in the form of DC signals from up to 20 meters, and outputs received information using a known method.

In the digital signal mode, the digital communication device 9 is connected to the communication line 4.5 when communicating with the digital communication device 3.

A feature of the present invention lies in the configuration for digital communication between the process variable transmitter 1 and the digital communicator 9.

The digital communication device 9 receives the voltage v1 supplied by the power supply circuit 7.
Equipped with an internal power supply that outputs a higher voltage ■2. This internal power supply supplies the process variable transmitter 1 with voltage for digital communication. The process variable transmitter 1 starts transmitting and receiving digital signals when the supplied voltage is higher than a predetermined voltage Vl+, which is set to a value higher than the maximum voltage in the analog signal moat. The function of the diode 6 is to prevent the current of the internal power supply of the digital communication device 9 from flowing back into the power supply circuit 7.

FIG. 2 is an equivalent circuit diagram of the tree embodiment device.

Process change transmission 2'41 is represented by resistor R5.

The digital communication device 9 is represented as a series connection circuit of a switch S, a resistor 2, and an internal power supply that outputs a voltage 2. The power supply circuit 7 is represented as a power supply that outputs a voltage v1. Analog communicator 8 is represented as resistor R1. In this equivalent circuit, the resistance of the transmission line is ignored.

The switch SW+ actually indicates connection and disconnection with the digital transmitter 97 two-wire type communication line. That is, when the digital communication device 9 is connected to the communication line, the switch SW+ is shown in a closed state, and when it is not connected, the switch SW+ is shown in an open state.

In the analog signal mode, the switch SW+ is open and the process variable transmitter 1 is supplied with current from the power supply circuit 7. The analog signal current output by the process variable transmitter 1 is transmitted to the analog communication device 8. In this state, DC communication is performed between the analog communication devices 2 and 8 using 4 to 20 m8.

In the digital signal mode, the switch SW is closed, and the process variable transmitter 1 is supplied with voltage v2 from the internal power supply. Due to the action of the diode 1''6, no current flows through the power supply circuit 7 and the analog communication device 8.

To explain the digital signal mode, that is, when the switch Sd1 is closed, when the current flowing through the process variable transmitter 1 is IL, V2 II ・R2>
The maximum values of voltages v9, V2, resistance R2, and current (2) are selected in advance so that the condition of V + --- (1) is satisfied.

- As an example, assume that ■1 is 24V, ■2 is 30V, R2 is 150Ω, and the maximum value of l is 22mA. As a result, the voltage vT between the terminals of the process variable transmitter 1 becomes V
T −V 2 1 +・R2−−−−[21,
The current flowing through the analog communication device 8 is OmA. Also,
At this time, the circuit constants of the voltage ■ are set so that V T > V ++ −−−−f31 with respect to the above-mentioned predetermined voltage vH.

In this digital signal mode, a high line bias voltage is applied between the lines 4 and 5, and for example, by changing the line voltage to two values of 27V and 29V, Transmits a digital signal of value.

FIG. 3 is a circuit diagram showing an example of the process variable transmitter 1. As shown in FIG.

Sensor 11 is connected to an analog-to-digital converter 12. Analog-to-digital converter 12 is connected to microprocessor 13. The microprocessor 13 includes a read-only memory 14, a random access memory 15,
It is connected to the digital-to-analog converter 16. [Digital/Analog Converter] One output of 6 is connected to switch S
It is connected to the input terminal of the 'ζ amplifier 17 via Wr + and a resistor R11. The other output of the digital-to-analog converter 16 is connected to both the 1ii1 potential point and the low potential terminal 102. The connection point between the resistor R'z and the amplifier 170 input terminal is connected to a common potential point via a capacitor CT1. The output of amplifier I7 is connected to high potential terminal 101.

With the above configuration, process variables are sent out as analog signals.

The high potential terminal 101 is connected to the differential amplifier 1 via a resistor RT2.
Connected to one input of 8. A connection point between the resistor RT□ and one input of the differential amplifier 18 is connected to a common potential point via a capacitor 0-2. The other input of the differential amplifier 18 is supplied with a voltage Vl.

The output of differential amplifier I8 is connected to microprocessor 13. The opening and closing of the switch Sl'lt+ is controlled by the output of the differential amplifier 18.

With the above configuration, the start of digital communication is detected.

The high potential terminal ] 01 is connected to the digital signal receiving circuit 20 . The digital signal receiving circuit 20 is connected to a universal asynchronous receiver/transmitter (IIART).

One universal asynchronous transceiver is microprocessor I
Connected to 3.

With the above configuration, digital signals are received.

Selection switch SW, □ is universal asynchronous transceiver 1
controlled by one. The non-inverting input terminal of the differential amplifier 21 is supplied with a voltage VTI or a voltage 72 (voltage with a common potential point) via a selection switch needle 2. The output of the differential amplifier 21 is connected to the base terminal of the transistor TT1. A load resistor RT3 and a load resistor RT4 are connected in series between the emitter terminal and collector terminal of the transistor `r'TI.

The emitter terminal of transistor TTI is connected to a common potential point. A connection point between the load resistance RT and the load resistance RT4 is connected to the inverting input terminal of the differential amplifier 21. The collector terminal of the transistor Air is connected to the high potential terminal 101 via the switch 5-73. The opening/closing operation of the switch SWT* is controlled by the microprocessor 13.

The values of voltage V T l and voltage V1□ are VH<V71,
V t 2 < V Z -----(4)
The sea urchin has been selected.

Digital signals are transmitted with the above configuration.

The value of the voltage Vl+ is selected to be between the lowest voltage of the digital signal and the supply voltage of the power supply circuit 7.

As a result, when the voltage between the high potential terminal 101 and the low potential terminal 102 is lower than the voltage vH, the switch SWT
, are closed and the process variable transmitter 1 sends out an analog signal. On the other hand, when the voltage between the high potential terminal 101 and the low potential terminal 102 is higher than the voltage V,
The switch SWT is opened and communication using digital signals is performed.

First, sending out analog signals will be explained.

The process variables sensed by the sensor 11 are converted into digital signals by the analog-to-digital converter 12 and processed by the microprocessor 13. Microprocessor 1
The processing sequence No. 3 is recorded 41 in the read-only memory 14 and the random access memory 15. The processed content is temporarily stored in the random access memory 15 and converted into an analog signal by the digital-to-analog converter 16. This analog signal is
High frequency components are removed by resistor RT1 and capacitor CTI, amplified by amplifier 17, and output.

The digital signal reception circuit 20 receives the digital signal.
Executed by The received take is passed through the universal asynchronous transmitter/receiver 19 and sent to the microphone 1 coprocessor 13.
sent to.

Transmission of the digital signal is started by closing the switch needle 13 under the control of the microphone TRI for one day. At this time, the universal asynchronous transceiver 19
controls the selection switch 5Wrz and sends out a digital signal by changing the voltage of the non-inverting input of the differential amplifier 21.

FIG. 4 is a circuit diagram showing an example of the digital communication device 9.

The input device 91 , the display device 92 , the read-only memory 93 and the random access memory 94 are connected to a first controller 95 . Microprocessor 95 is connected to a universal asynchronous transceiver 96. Further, the microprocessor 95 controls opening and closing of the switch SWc+. Universal asynchronous transceiver 96 is connected to digital signal receiving circuit 97 . Digital signal receiving circuit 97 is connected to one end of switch SW+.

Universal asynchronous transmitter/receiver 9 with selection switch 5Wcz
controlled by fi. A voltage VCI or a voltage V is applied to the non-inverting input terminal of the differential amplifier 98 via a selection switch 5Wcz. 2 (voltage between terminal 502) is supplied. The output of the differential amplifier 98 is the transistor 'r.

Connect to the Hose terminal. 1-A load resistor R11 is connected between the emitter terminal and collector terminal of transistor TC1.
and load resistor RC2 are connected in series. Load resistance Rr
1 and the load resistor RC2 is connected to the inverting input terminal of the differential amplifier 98. The emitter terminal of transistor TC+ is connected to terminal 902, and the collector terminal is connected to switch needle 0. is connected to the end of the switch needle through the -b f.

A resistor R2 and a power supply V2 are connected in series between one end of the switch S and the terminal 902. The other end of switch SW is connected to terminal 901.

The values of voltage VC+ and voltage VC2 are V,,<V,,,VC2<V2------(
5).

The operator operates the device of this embodiment by inputting from the input device 91. The operating status of the device of this embodiment is displayed on the display device 92.

When this digital communication device 9 communicates with the process variable transmitter 1, the switch SW1 is closed (connected to a two-wire communication line). As a result, the voltage ■2 is output from the terminal 901 and supplied to the process variable transmitter 1. After this, the digital communication device 9 starts sending out digital signals.

Transmission and reception of digital signals by the digital communication device 9 is as follows:
The process variable transmitter 1 performs the same operation as the transmission and reception of digital signals.

In the above example, in the analog signal mode, the first analog transmitter was used only for transmission, and the second analog communication device was used only for reception. Also, in digital signal mode, both digital communicators can be dedicated to transmit or receive.

〔Effect of the invention〕

The two-wire data transmission word A of the present invention is that in the digital signal mode, the DC voltage supplied to the communication line in the analog signal mode is high. Since such a high voltage is not generated due to noise, mode identification becomes reliable, and malfunction of mode switching due to noise can be prevented. Therefore, there is an effect that the device operates stably.

Furthermore, since no current flows through the analog communication device on the receiving side during digital communication, there is an effect that the communication mode can be determined at L-1 by monitoring the signal received by the analog communication device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a two-wire data transmission device according to an embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the device of this embodiment. FIG. 3 is a circuit diagram showing an example of a process variable transmitter. FIG. 4 is a circuit diagram showing an example of a digital signal communication device. DESCRIPTION OF SYMBOLS 1... Process variable transmitter, 2... Analog communication device, 3... Digital communication device, 4.5... Communication line, 6
... Diode, 7... Power supply circuit, 8... Analog communication device, 9... Digital communication device, 11... Sensor, 12... Analog-digital converter, 13...
・Microprocessor, 14...Read-only memory, 1
5... Random access memory, ]6... Digital-to-analog converter, 17... Amplifier, 18... Differential amplifier, I9... Universal asynchronous transceiver, 20
...Digital signal receiving circuit, 21...Differential amplifier, 91...Input device, 92...Display device, 93...
・Read-only memory, 94...Rung l, access memory, 95...Microprocessor, 96...Universal non-uniform gJ] transceiver, 97...Digital signal-
signal receiving circuit, 98 differential amplifier, 101... high potential terminal, 102... low potential terminal, 701... high potential terminal, 702... low potential terminal, 9fll, 902...
terminal. Patent originator Yokogawa Hokushin Electric Co., Ltd. agent Patent attorney Takashi Ide 112 ; ¥) 2 (2

Claims (1)

[Claims] (1) A two-wire communication line, a first analog communication device connected to one end of the communication line, and a first communication device connected to the other end of the communication line; A power supply circuit inserted in series with a second analog J signal device that performs communication and the communication line and supplies direct current to the first and second analog communication devices in series via the communication line. A two-wire data transmission device comprising: 1- a first digital communication device connected in parallel to the output line; and a first digital communication device connected in parallel to the communication line and communicating with the first digital communication device A backflow prevention 1F diode is connected to the output circuit of the power supply circuit, and the first Digicle 1Jr1 signal transmits the digital signal to the communication line. The second digital communication device includes circuit means for applying a bias voltage exceeding the DC voltage supplied from the power supply circuit between the lines, and the second digital communication device detects each time the high-ass voltage is applied to the communication line. 1. A two-wire data transmission device, comprising circuit means for identifying that the mode is for transmitting digital signals.