JPH04286219A - Method and device for analog/digital communication - Google Patents

Abstract

PURPOSE:To easily make a device into an IC formation by supplying DC power for operating a transmitter from a receiving side through a two-wire transmission line, and simultaneously, changing the output voltage of DC power source for power supply. CONSTITUTION:DC variable power supply ES to supply the DC power for operating the transmitter 1 to a receiving measuring meter 2 side through the two-wire transmission line L, and a power supply output voltage control means CNT to change the output voltage of said DC variable power supply ES by a digital signal to be sent to a transmitter 1 side are provided. Further, a voltage change extracting means 11 to extract the change of supply voltage supplied through the two-wire transmission line L is provided at the transmitter 1 side, and the digital signal sent from the receiving measuring meter 2 side is taken out by this voltage change extracting means 11. Namely, if the supply voltage supplied from the receiving measuring meter 2 to the transmitter 1 side is changed by the digital signal, the both-terminal voltage too comes to be changed according to this digital signal, and since the number of used parts can be reduced, the device can be easily made into IC formation.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an analog/digital communication method and device used in the process industry, and more particularly, to an analog/digital communication method and device for use in the process industry, and more particularly, to an analog/digital communication method and device used in the process industry. The present invention relates to an analog/digital communication method and device that performs communication using a mixture of analog and digital signals.

0002

[Prior Art] In the process industry, the process amount (
A sensor (transmitter) to detect the temperature, pressure, flow rate, etc.) is installed in the process, and the process quantity (measurement signal) is
For example, a unified signal of 4 to 20 mA is transmitted to a remote location via a wire transmission line. Figure 5 shows the sensor (
2 is a conceptual configuration diagram showing the relationship between a transmitter) and a receiving instrument (or signal converter) that receives a measurement signal via a transmission path. FIG. One side of the two-wire transmission line L is connected to a transmitter 1 such as a pressure transmitter, an electromagnetic flowmeter, a thermometer, or other sensor installed in the process, and the other side is connected to a measurement signal transmitted from the receiver side. A receiving instrument 2 is connected to receive the signal. The receiver 1 is usually equipped with, for example, a microprocessor and has a communication function. The receiving instrument 2 includes, for example, a 24V constant voltage power source Es for operating the receiver 1 via the transmission line L, a receiving resistor R for extracting the measurement signal transmitted via the transmission line L as a voltage signal, receiver 1
A transmission driver DR and a transmission line L that send digital signals to the transmission line L via a capacitor CC, for example, to check the operating state or make adjustments.
A low-pass filter circuit LPF, a high-pass filter HPF, etc., which separate the measurement signal sent via the transmission line L from the digital signal sent via the transmission line L, are included. Digital signal D1 sent from receiving instrument 2 to transmitter 1 side
Transmission is performed by supplying a current is that changes in the positive/negative direction from the transmission driver DR to the reception resistor R according to the high/low level of the digital signal. In addition, reception of the measurement signal A and digital signal D2 sent from the transmitter 1 side is performed by measuring the voltage drop vR at the receiving resistor R, and the measurement signal A is extracted through the low-pass filter circuit LPF. Then, digital signal D2 is extracted via high-pass filter HPF. A method of communicating by mixing analog signals and digital signals has already been disclosed, for example, in Japanese Patent Publication No. 63-23692.

0003

However, in the conventional device having such a configuration, it is necessary to use a power transistor in the transmitting driver DR on the receiving instrument 2 side. Furthermore, in order to prevent unnecessary low-frequency components from flowing from the transmission driver DR to the reception resistor R, it is necessary to connect a large-capacity capacitor CC to transmit the digital signal D1. If power transistors or large-capacity capacitors are used as circuit elements, converting this electronic circuit into an IC requires a very large chip area and requires consideration of voltage resistance, etc. There was a problem in that it was difficult to convert into an IC, making it impossible to reduce costs. The present invention has been made in view of these points, and provides a communication method and device that reduces the number of power transistors and capacitors and enables analog and digital communication with a circuit configuration suitable for IC implementation. The purpose is to

0004

[Means for Solving the Problems] The present invention achieves the above object by transmitting a mixture of analog signals and digital signals between a transmitter and a receiver connected to each other via a two-wire transmission line. An analog/digital communication method for communicating, in which DC power for operating the transmitter is supplied from the receiving instrument side via the two-wire transmission line, and the output voltage of the power supply DC power supply is varied. By doing so, a digital signal is sent from the receiving instrument side to the transmitter side, and the transmitter side extracts the digital signal sent from the receiving instrument side by extracting the change in the power supply voltage supplied via the transmission line. This is an analog/digital communication method characterized by the following.

[0005]

[Operation] When the power supply voltage supplied from the receiving instrument side to the transmitter side is changed by a digital signal, the voltage across the transmitter will also change in accordance with this digital signal. Therefore, on the transmitter side, by extracting the voltage change in the power supply voltage supplied via the transmission path, the digital signal sent from the receiving instrument side can be extracted, and communication can be performed.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a block diagram of the configuration of a device that implements the communication method of the present invention. In the figure, 1 is a transmitter having a communication function, and 2 is a receiving instrument connected to the transmitter 1 via a two-wire transmission line L. This receiving instrument 2 is a comprehensive representation of a device that receives signals transmitted via the two-wire transmission line L. For example, the receiving instrument 2 is a signal converter that converts the signal into a signal that can be easily handled by a computer and transmits it again to the computer side. equipment, signal conditioners, etc. are also included in this category of receiving equipment. In the receiving instrument 2, Es is a DC variable power supply configured to make its output voltage E variable, and CNT inputs the digital signal D1 transmitted from the receiving instrument 2 side to the transmitter 1 side, and This is a power supply output voltage control means that controls the output voltage E of the DC variable power supply Es accordingly. R is a receiving resistor for extracting the signal iL transmitted via the transmission line L as a voltage signal, LPF is a low-pass filter for extracting the analog signal A from the voltage signal generated at the receiving resistor R, and HPF is a voltage signal generated at the receiving resistor R. This is a high-pass filter for extracting the digital signal D2 sent from the transmitter 1 side from the voltage signal. In transmitter 1, 1
1 is the power supply voltage v supplied to the transmitter 1 via the transmission line L
This is a voltage change extraction means that extracts the voltage change of L and takes out the digital signal D1 sent from the receiving instrument 2 side. As this voltage change extraction means, for example, a high-pass filter using the voltage signal vL as an input signal is used.

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

Next, the operation of the apparatus constructed as described above will be explained based on the embodiment shown in FIG. FIG. 3 is a diagram showing voltage or current signal waveforms at each portion of FIG. 2. (a)
shows a digital signal D1 transmitted to the transmitter 1 side in the receiving instrument 2, and in this example, each bit is shown by a change in the positive/negative direction. The operational amplifier A1 is
By inputting such a digital signal D1 and a constant voltage signal Eo, the output voltage E of the DC power supply Es is adjusted according to the deviation between the two.
control. As a result, as shown in (b), the power supply output voltage E outputted from the DC variable power supply Es to the transmission line L, when the digital signal D1 (voltage amplitude is expressed by vd1) is output, is The voltage value will change 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)

[0009] The transmitter 1 is
The current iL flowing through the transmission line L is expressed as a process quantity (measurement signal) (
The transmission current iL is changed in accordance with the analog signal A), and the transmission current iL is changed in an analog manner in accordance with the process amount, for example, within a range of 4 to 20 mA, as shown in (c). This current iL is transmitted to the receiving instrument 2 via the transmission line L.
and flows to the receiving resistor R. A voltage signal vR as shown in (d) is generated across the receiving resistor R by the transmitted current iL. This voltage signal vR can be expressed by equation (2). vR=R×iL
...(2) From equations (1) and (2), the voltage (voltage at both ends) vL supplied to the oscillator 1 connected to the two-wire transmission line L can be expressed by equation (3), The voltage waveform is as shown in (e). vL=E−vR=Eo+vd1−(R×iL)
...(3)

[0010] In this way,
The voltage vL supplied to the transmitter 1 side is the digital signal D
It will change according to the voltage value vd1 of 1. Voltage change extraction means 11 provided in the oscillator 1 extracts this voltage change in voltage vL and extracts the digital signal D1 sent from the oscillator 2 side. Thereby, a digital signal can be transmitted from the receiving instrument 2 side to the transmitter 1. Note that here, the voltage vL obtained across the oscillator 1 is equal to the transmission current i
Even when L is flowing at its maximum value (e.g. 20mA),
It is assumed that a rated voltage sufficient to operate the transmitter 1 is maintained. The digital signal D2 sent from the transmitter 1 to the receiving instrument 2 side is transmitted by changing the transmission current iL, for example, in the positive and negative directions, as shown in (c). 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 taken out as a voltage signal va as shown in (f) via the low-pass filter circuit LPF. Furthermore, the digital signal D2 sent from the transmitter 1 is
It is extracted through a high-pass filter HPF as a voltage signal vd2 whose amplitude changes according to the digital signal D2.

FIG. 4 shows that in the receiving instrument 2, the DC power source E
FIG. 3 is a connection diagram of main parts showing another example of the control means CNT and the control means CNT. In this embodiment, a transistor Q1 forming a constant voltage power supply has a collector connected to a power supply Vcc and an emitter connected to a Zener diode ZD that generates a constant voltage Eo, and the output voltage of this constant voltage power supply is controlled by a digital signal D1. It is composed of 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, a case has been described in which the value E of the power supply voltage or the transmission current iL is changed in the positive and negative directions in the transmission of the digital signal, but the polarity may be changed only in one direction, or It may also be a pulse width signal.

0012

[Effects of the Invention] As explained in detail above, according to the present invention, it is possible to reduce the number of power transistors and capacitors used in the transmitter driver in the conventional device, so it is easy to integrate it into an IC. It is possible to provide an analog/digital communication method and communication device that can reduce the cost of receiving instruments.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of a device that implements the communication method of the present invention.

FIG. 2 is a block diagram illustrating the configuration of an embodiment of an apparatus that implements the method of the present invention.

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

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

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

[Explanation of symbols]

1 Transmitter 2 Receiving instrument 11 Voltage change extraction means L 2-wire transmission line Es　DC variable voltage power supply CNT Power output voltage control means R Receiving resistance LPF low pass filter HPF High pass filter

Claims (2)

[Claims] Claim 1: An analog/digital communication method for communicating by mixing analog and digital signals between a transmitter and a receiving instrument that are connected to each other via a two-wire transmission line, wherein the receiving instrument side supplying DC power for operating the oscillator from the oscillator via the two-wire transmission line, and transmitting a digital signal to the oscillator by changing the output voltage of the power supply DC power supply, An analog/digital communication method characterized in that, on the transmitter side, a digital signal sent from a receiving instrument side is extracted by extracting voltage changes in a power supply voltage supplied via a two-wire transmission line. 2. An analog/digital communication device that performs communication using a mixture of analog and digital signals between a transmitter and a receiving instrument that are connected to each other via a two-wire transmission line, wherein the receiving instrument , a variable DC power supply that supplies DC power for operating the transmitter via the two-wire transmission line;
A power supply output voltage control means for changing the output voltage of the DC variable power supply by a digital signal sent to the transmitter side is provided, and a voltage for extracting a change in the power supply voltage supplied to the transmitter via the two-wire transmission line is provided. 1. An analog/digital communication device characterized in that a change extraction means is provided, and the voltage change extraction means extracts a digital signal sent from a receiving instrument side.