JP2817077B2 - Current output communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current output communication system for use in, for example, a process control device, which performs communication between a transmitter and a transmitter in a system in which a transmitter and a receiver are connected via a transmission line. It is about.

[0002]

2. Description of the Related Art Conventionally, in a process control device, a transmitter and a receiver are connected by a transmission line, and a signal detected by a sensor is converted into a current of 4 to 20 mA and transmitted. In this case, for example, when performing adjustment such as zero adjustment on the transmitter side, a setting unit is connected to the transmission line, a signal is transmitted from the setting unit to the transmitter to change the setting, and the transmitter side changes the setting state. Was transmitted to the setting device.

For this reason, conventionally, as shown in FIG. 5, N-bit digital data sent from a controller 5 is converted into a D / A signal.
The voltage is converted into an analog value by the converter 20, and the voltage value is converted into a current of 4 to 20 mA by the V / I conversion circuit 11 and output. The specific circuit of the D / A converter 20 is as shown in FIG. 6, and the current output from the constant current circuit is weighted by the R / 2R ladder resistance. The current switch connects and disconnects the resistor.

[0004]

However, such a conventional circuit requires an N-bit signal line at the input, and
Not only does the circuit wiring become complicated, but also the relative accuracy of R / 2R determines the accuracy of A / D conversion. Becomes large. And when it is necessary to perform not only analog communication but also digital communication using this circuit, it is very difficult to change each bit of the digital input at the same time and to take out the output. There was a problem that it would be restricted. The present invention has been made in view of such a situation, and provides an apparatus that has simple wiring and can increase the speed of digital communication.

[0005]

According to the present invention, there is provided a first voltage generating circuit for generating a first voltage, a second voltage generating circuit for generating a second voltage, A switch for switching between the output voltage of the first voltage generation circuit and the output voltage of the second voltage generation circuit, a controller for switching the switch based on communication information, and a V / I conversion circuit for converting a voltage output from the switch to a current It is provided with.

[0006]

The voltage generated by the switching voltage generating circuits 2 and 3 is switched by the switch 4 controlled by the signal from the controller 6 through the switching signal generating circuit 5, and is output as a signal having a desired duty ratio. This signal is output via LPF8 or LPF9 having different time constants. The average value of the signal passed through the filter having a large time constant is output, and analog communication is performed.

[0007]

FIG. 1 is a block diagram showing an embodiment of the present invention. In this apparatus, a reference voltage generating circuit 1 generates a necessary voltage internally based on a power supply supplied from a receiver 12 side. . The voltage generated by the reference voltage generation circuit 1 is supplied to switching voltage generation circuits 2 and 3. Here, the reference voltage generation circuit 2 generates a high voltage VH, and the reference voltage generation circuit 3 generates a lower voltage VL.

When communication is performed, a signal having a duty ratio corresponding to communication information as shown in FIG. 2B is supplied from the controller 6 to the switching signal generating circuit 5, so that the switching signal generating circuit 5 The switch 4 is controlled. As a result, the switch 4 switches the switching voltage generating circuit 2 based on the communication signal.
Alternatively, 3 is selected, and the signal shown in FIG.

The signal selected by the switch 4 is supplied to an LPF 8 or LPF 9 having different time constants and is switched by a switch 7 controlled by a controller 6. Among these two LPFs, the LPF 8 is a filter having a large time constant, for example, and outputs an average value as shown in FIG. 3C when the signal shown in FIG. 3A is supplied. The LPF 9 is a filter having a small time constant, and outputs a signal having substantially the same waveform as the input signal as shown in (b) when the signal shown in (a) is supplied.

As a result, analog communication is performed when the LPF 8 is selected, and digital communication is performed when the LPF 9 is selected. The signal output via the LPF 8 or 9 is output to the line via the V / I conversion circuit 11 and communicates with the setting device 13 connected to the line.

In addition, as shown in FIG. 4, the LPF output can be superimposed on a superimposed signal from the controller 6 to perform analog / digital communication. The superimposing circuit 10 shown in FIG. 1 has a function similar to that described above. A signal detected by an external sensor is processed by the controller 6, converted into an analog signal, and converted into an analog signal via the V / I conversion circuit 1.
1 is supplied. Therefore, the V / I conversion circuit 10 outputs a current corresponding to the sensor output to the line. When the switch 7 selects the superimposing circuit 10, the signal shown in FIG. 3A selected by the switch 4 is supplied to the superimposing circuit 10, so that the digital signal is superimposed on the one that was performing analog communication, Digital communication is performed. In addition,
Switching of the switch 7 is performed under the control of the controller 6.

Although the above embodiment has been described as operating on the power supplied from the receiver, this power may be provided in the transmitter. Although the voltage values are binary, one of them may be grounded, and may be multi-valued instead of binary.

[0013]

As described above, according to the present invention, a digital signal for communication is supplied to a V / I conversion circuit already used for transmitting a sensor signal, so that conventionally, N bits are required. Since the signal line requires only one bit, the wiring is simplified, and the digital signal can be transmitted only by switching the switching voltage generating circuit, so that high-speed communication can be performed, and the digital signal is output via a filter. Therefore, there is an effect that digital communication and analog communication can be performed by switching filters having different time constants.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of the apparatus of FIG.

FIG. 3 is a waveform chart for explaining the effect of the filter.

FIG. 4 is a circuit diagram for explaining superposition of a signal;

FIG. 5 is a block diagram showing an example of the related art.

FIG. 6 is a circuit diagram showing the internal configuration of the D / A converter of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reference voltage generation circuit 2, 3 Switching voltage generation circuit 4, 7 Switch 8, 9 LPF 10 Superposition circuit 11 V / I conversion circuit 12 Receiver 13 Setting device

Claims (1)

(57) [Claims] 1. A communication system for performing communication with a transmitter that converts a signal generated from a sensor into a digital current after converting the signal into an analog current signal and sends the analog current signal, wherein: a first voltage generating circuit that generates a first voltage; A second voltage generation circuit that generates a voltage of the first voltage generation circuit; a switch that switches between the first voltage generation circuit output voltage and the second voltage generation circuit output voltage; a controller that controls switching of the switch based on the communication information; V / that converts the voltage output from the switch to a current
A current output communication system comprising an I conversion circuit.