JP3139502B2 - Analog / digital communication method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog / digital communication method and apparatus used in the process industry, and more particularly, to a method for transmitting and receiving signals between a transmitter and a receiver connected to each other via a two-wire transmission line. The present invention relates to an analog / digital communication method and apparatus for performing communication by mixing analog and digital signals.

[0002]

2. Description of the Related Art In the process industry, a sensor (transmitter) for detecting a process amount (temperature, pressure, flow rate, etc.) is installed in a process, and the process amount (measurement signal) is transmitted via a two-wire transmission line. For example, with a unified signal of 4 to 20 mA,
Transmission to a remote place is performed. FIG. 5 is a conceptual diagram showing the relationship between a sensor (transmitter) and a receiving instrument (or signal converter) that receives a measurement signal via a transmission line. One of the two-wire transmission lines L is connected to a transmitter 1 such as a pressure transmitter, an electromagnetic flowmeter, or a sensor such as a thermometer installed in the process, and the other is a measurement signal transmitted from the receiver. Receiving instrument 2 is connected. As the transmitter 1, for example, a device equipped with a microprocessor and having a communication function is generally used. In the receiving instrument 2, for example, a 24V constant voltage power supply Es for operating the receiver 1 via the transmission line L, a reception resistor R for extracting a measurement signal transmitted via the transmission line L as a voltage signal, for example, to check the operation state between the outgoing unit 1, a digital signal for or make adjustments capacitor CC
, A low-pass filter circuit LPF that separates a measurement signal sent through the transmission line L from a digital signal sent through the transmission line L, a high-pass filter HPF, and the like. It is included. Digital signal D sent from receiving instrument 2 to transmitter 1
1 transmits the current is that changes in the positive / negative direction according to the high / low level of the digital signal.
To the reception resistor R. The reception of the originating <br/> vessel 1 measured sent from side signal A and the digital signal D2 is performed by measuring the voltage drop voltage vR at the receiver resistor R, measured through a low-pass filter circuit LPF The signal A is extracted, and the digital signal D2 is extracted via the high-pass filter HPF. Such a method of performing communication by mixing analog and digital signals is already disclosed in, for example, Japanese Patent Publication No. 63-23692.

[0003]

In the conventional device having such a configuration, it is necessary to use a power transistor in the transmission driver DR on the receiving instrument 2 side. In addition, a large-capacity capacitor CC needs to be connected to prevent unnecessary low-frequency components from flowing from the transmission driver DR to the reception resistor R when transmitting the digital signal D1. If a power transistor or a large-capacity capacitor is used as a circuit element, when this electronic circuit is formed into an IC, a very large chip area is required and a withstand voltage must be taken into consideration. There is a problem that it is difficult to make the IC into an IC and the cost cannot be reduced. The present invention has been made in view of such a point, and a digital signal transmitted from a signal converter to a sensor.
The power supply voltage supplied to the transmission sensor is changed according to the
Digital signal transmitted from the sensor to the signal converter.
By changing the current signal supplied to the signal converter.
Between the sensor and the signal converter with a simple circuit configuration
It is an object of the present invention to provide a communication method and apparatus capable of performing analog / digital communication in one direction .

[0004]

Means for Solving the Problems To achieve such an object
The present invention has the following configuration. (Invention 1) Sensor and signal conversion connected to each other via a two-wire transmission line
Mix analog and digital signals between
An analog / digital communication method for performing communication.
An analog digital device characterized in that communication is performed according to a predetermined procedure.
Communication method. (A) From the signal converter to the sensor On the signal converter side, the power supply voltage for operating the sensor
Is supplied via a two-wire transmission line and sent to the sensor.
The power supply voltage is changed by a digital signal. Sensor
Side, the change in the power supply voltage supplied via the two-wire transmission path
By extracting, the digit sent from the signal converter
Extract the signal. (B) Communication from the sensor to the signal converter On the sensor side, the current signal is transmitted via the two-wire transmission path to the signal converter.
Send to On the signal converter side, the current signal sent from the sensor is
The signal is converted into a voltage signal by a receiving resistor and extracted. Low
The pass filter analyzes the voltage signal generated at the receiving resistor.
Extract the log signal. High-pass filter is used for receiving resistor
Extract digital signal from shear voltage signal. (Invention 2) Sensor and signal conversion connected to each other via a two-wire transmission line
Mix analog and digital signals between
An analog-digital communication apparatus for communicating, prior to
Operate the sensor to the signal converter via the two-wire transmission path.
DC variable power supply for supplying power supply voltage for
The power of the DC variable power supply is
Power supply output voltage control means for changing the source voltage, and two-wire transmission
The current signal sent from the sensor via the
The receiving resistor that is extracted and the voltage generated at the receiving resistor
A low-pass filter that extracts an analog signal from the signal,
Extract digital signal from voltage signal generated at receiving resistor
A high-pass filter, and a two-wire transmission to the sensor
Voltage change to extract the change in the power supply voltage supplied through the
Data extraction means for transmitting data from the signal converter to the sensor.
The power supply voltage supplied to the sensor is changed by the digital signal.
To the digital signal transmitted from the sensor to the signal converter.
To change the current signal supplied to the signal converter.
Characteristic analog / digital communication device.

[0005]

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration block diagram of an apparatus for realizing the communication method of the present invention. In the figure, reference numeral 1 denotes a transmitter having a communication function, and reference numeral 2 denotes a receiving instrument connected to the transmitter 1 via a two-wire transmission line L. The receiving instrument 2 generally represents a device that receives a signal transmitted through the two-wire transmission line L. For example, the receiving instrument 2 converts the signal into a signal that can be easily handled by a computer and transmits the signal to the computer again. Instruments and signal conditioners are also included in the category of the receiving instrument. In the receiving instrument 2, Es is a DC variable power supply configured to make its output voltage E variable, and CNT receives a digital signal D1 transmitted from the receiving instrument 2 side to the transmitter 1 side. This is power supply output voltage control means for controlling the output voltage E of the DC variable power supply Es accordingly. R is a receiving resistor for extracting a signal iL transmitted via the transmission line L as a voltage signal, LPF is a low-pass filter for extracting an analog signal A from a voltage signal generated in the receiving resistor R, and HPF is generated in the receiving resistor R. This is a high-pass filter for extracting the digital signal D2 sent from the transmitter 1 from the voltage signal. In the transmitter 1,
Reference numeral 11 denotes a voltage change extracting means for extracting a voltage change of the power supply voltage vL supplied to the transmitter 1 via the transmission line L and extracting a digital signal D1 sent from the receiving instrument 2 side.
As the voltage change extracting means, for example, a high-pass filter using a voltage signal vL as an input signal is used.

FIG. 2 is a block diagram showing the configuration of an apparatus for implementing the method of the present invention. In this embodiment, the DC variable power supply Es includes transistors Q1 and Q2 whose collectors are connected to the power supply Vcc and the ground, respectively, and whose emitters are connected to one of the transmission lines L.
Further, a digital signal (D1) to be transmitted to the transmitter 1 is applied to one input terminal of the power supply output voltage control means CNT, and a voltage which determines the value E of the output voltage of the power supply to the transmission line L is applied to the other input terminal. It comprises an operational amplifier A1 to which a signal Eo is applied.

Next, the operation of the apparatus having the above-described configuration will be described with reference to the embodiment shown in FIG. FIG. 3 is a diagram showing a voltage or current signal waveform in each part of FIG. (A)
Indicates a digital signal D1 transmitted to the transmitter 1 in the receiving instrument 2, and in this example, each bit is indicated by a change in the positive or negative direction. The operational amplifier A1 is
Such a digital signal D1 and a constant voltage signal Eo are input, and the output voltage E
Control. As a result, as shown in (b), when the digital signal D1 (voltage amplitude is represented by vd1) is output, the power supply output voltage E output from the DC variable power supply Es to the transmission line L The voltage value changes accordingly. The power supply output voltage E output from the DC variable power supply Es can be expressed by equation (1). E = Eo + vd1 (1)

The transmitter 1 changes the current iL flowing through the transmission line L according to the process amount (measurement signal) (analog signal A). The transmission current iL is, for example, 4 to 4 as shown in FIG. It changes in an analog manner according to the process amount in the range of 20 mA. This current iL is sent to the receiving instrument 2 via the transmission line L and flows through the receiving resistor R. At both ends of the receiving resistor R, a voltage signal vR as shown in (d) is generated by the transmitted current iL. This voltage signal vR can be expressed by equation (2). vR = R × iL (2) From the equations (1) and (2), the voltage (the voltage at both ends) vL supplied to the transmitter 1 connected to the two-wire transmission line L is
It can be expressed by the equation (3), and the voltage waveform is as shown in (e). vL = E−vR = Eo + vd1- (R × iL) (3)

As described above, the voltage vL supplied to the transmitter 1 changes according to the voltage value vd1 of the digital signal D1. Voltage change detection means 11 provided in the transmitter 1, extracts the voltage change of the voltage vL, receiving instrument 2
The digital signal D1 sent from the side is taken out. Thus, a digital signal can be transmitted from the receiving instrument 2 to the transmitter 1. Here, the voltage vL obtained at both ends of the transmitter 1 is such that the transmission current iL has the maximum value (for example, 20 V).
mA) It is assumed that a rated voltage sufficient to operate the transmitter 1 is maintained even when the current is flowing. Digital signal D2 sent from transmitter 1 to receiving instrument 2
Is transmitted while the transmission current iL is changed, for example, in the positive and negative directions, as shown in FIG. This digital signal D2
Appears in the receiving instrument 2 as a change in the voltage vR across the receiving resistor R. Here, the analog signal A corresponding to the process amount (measurement signal) sent from the transmitter 1 is extracted as a voltage signal va as shown in (f) through the low-pass filter circuit LPF. The digital signal D2 sent from the transmitter 1 is extracted as a voltage signal vd2 whose amplitude changes according to the digital signal D2 via a high-pass filter HPF as shown in (g) .

FIG. 4 shows a DC power supply E
It is a connection diagram of an important section showing another example with s and control means CNT. In this embodiment, a transistor Q1 forming a constant voltage power supply having a collector connected to a power supply Vcc and an emitter connected to a Zener diode ZD generating a constant voltage Eo, and the output voltage of the constant voltage power supply being controlled by a digital signal D1. And a transistor Q2. In this embodiment, the digital signal D1 is applied to the transistor Q2 via the capacitor C1, but the capacitor C1 used here does not need to have a large capacity. In each of the above embodiments, the case where the transmission of the digital signal changes the value E of the power supply voltage or the transmission current iL in the positive or negative direction has been described. However, the transmission may be changed to only one polarity. It may be a pulse width signal.

[0012]

According to the present invention, signal conversion is performed on a two-wire transmission line.
Digital signal transmitted from the detector to the sensor
The power supply voltage supplied to the power supply is changed. In addition, two-wire transmission
Digital data transmitted from the sensor to the signal converter on the transmission path
The current signal supplied to the signal converter is changed by the signal
I have. This allows the sensor and signal conversion with a simple circuit configuration.
Bidirectional analog / digital communication with the switch
A communication method and apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an apparatus for realizing a communication method according to the present invention.

FIG. 2 is a block diagram showing a configuration of an embodiment apparatus for realizing the method of the present invention.

FIG. 3 is a diagram showing a voltage or current signal waveform in each part of FIG. 2;

FIG. 4 is a connection diagram of main parts showing another embodiment of the DC power supply Es and the control means in the receiving instrument.

FIG. 5 is a conceptual diagram showing the relationship between a sensor (transmitter) and a receiving instrument (or signal converter) that receives a measurement signal from the sensor via a transmission path.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillator 2 Receiving instrument 11 Voltage change extraction means L Two-wire transmission line Es DC variable voltage power supply CNT Power supply output voltage control means R Receiving resistance LPF Low pass filter HPF High pass filter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-47-28451 (JP, A) JP-A-54-144117 (JP, A) JP-A-54-144119 (JP, A) JP-A 58-144 131888 (JP, A) JP-A-2-252323 (JP, A) JP-A-59-137656 (JP, U) JP-T-55-500927 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 3/00-3/44 H04B 3/50-3/60

Claims (2)

(57) [Claims] 1. A sensor connected to each other via a two-wire transmission line.
An analog-digital communication method for performing communication by mixing an analog signal and a digital signal between a signal converter and a signal converter, wherein the communication is performed in the following procedure.
Log digital communication method. (A) From the signal converter to the sensor On the signal converter side, the power supply voltage for operating the sensor
Is supplied via a two-wire transmission line and sent to the sensor.
The power supply voltage is changed by a digital signal. Sensor
Side, the change in the power supply voltage supplied via the two-wire transmission path
By extracting, the digit sent from the signal converter
Extract the signal. (B) Communication from the sensor to the signal converter On the sensor side, the current signal is transmitted via the two-wire transmission path to the signal converter.
Send to On the signal converter side, the current signal sent from the sensor is
The signal is converted into a voltage signal by a receiving resistor and extracted. Low
The pass filter analyzes the voltage signal generated at the receiving resistor.
Extract the log signal. High-pass filter is used for receiving resistor
Extract digital signal from shear voltage signal . 2. A sensor connected to each other via a two-wire transmission line.
An analog / digital communication device for performing communication by mixing an analog signal and a digital signal between a signal converter and a signal converter , wherein the signal converter operates a sensor via the two-wire transmission line. a variable DC power source for supplying a power supply voltage, Se
Digital variable power supply
Power supply output voltage control means for changing the power supply voltage ;
The current signal sent from the sensor via the transmission path is converted to a voltage signal.
The receiving resistor that is converted and taken out
Low-pass filter that extracts analog signal from pressure signal
And digital signal from the voltage signal generated at the receiving resistor.
And a high-pass filter is provided to issue Ri, to the sensor, a voltage change extraction means for extracting changes of the supplied power supply voltage via the two-wire transmission path provided by the digital signal transmitted from the signal converter to the sensor
The power supply voltage supplied to the sensor is changed, and the signal from the sensor is
The digital signal transmitted to the converter
Analog, characterized by changing the supplied current signal
・ Digital communication device.