JPH0620185A - Two-wire transmitter - Google Patents

Abstract

(57) [Abstract] [Purpose] A two-wire transmitter outputs a sensor signal as an analog current signal, and a modulated communication signal for digital communication is superimposed on the current signal and transmitted even if the modulation format is different. Intended to be accessible. A monitoring means monitors whether the modulated communication signal is a first modulated communication signal having a carrier or a second modulated communication signal having no carrier, outputs a monitoring signal, and a demodulation means modulates the corresponding modulated communication signal by this monitoring signal. Is demodulated and a demodulated signal is output. The processor receives the supervisory signal, decodes the corresponding demodulated signal, and outputs a response signal according to the contents of the decoding. The modulation means receives the response signal and outputs the modulated communication signal in a modulation format corresponding to the destination monitoring signal, and the adding means superimposes the modulated communication signal on the analog current signal and outputs it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention receives a power supply from a load side through two transmission lines, converts a physical quantity to be measured by a sensor into an electric signal, and converts the physical quantity into an electric signal by a signal calculation means including a microprocessor. The present invention relates to a two-wire type transmitter that performs signal processing, transmits it as a current signal to the load side through the above transmission line, and superimposes a modulated communication signal on the transmission line as necessary to perform digital communication with the outside. The present invention relates to an improved two-wire type transmitter capable of automatically distinguishing different communication modulation formats and sending a modulated communication signal to a transmission line in a corresponding modulation format.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an overall configuration including a conventional two-wire type transmitter. Reference numeral 10 denotes a two-wire transmitter that converts a physical quantity such as a process variable into an electric signal and transmits the electric signal, and electric power is supplied from a DC power supply 11 via a load 12. The electric signal is transmitted as a current signal through the transmission lines L1 and L2, and the change in voltage occurring across the load 12 is detected to know the process variable.

The current signal is, for example, 4 to 20 m from the two-wire type transmitter 10 set in a range corresponding to the pressure in the pipe.
Is transmitted is converted into a unified current I _L of A. In this case, for example, when it is desired to change or monitor the pressure range, it is convenient if it can be operated from outside the two-wire transmitter 10.

For this reason, the handheld terminal 13 is connected to the transmission lines L1 and L2 by connecting lines L1 'and L2' as required, and the two-wire transmitter 10 is connected to the handheld terminal 13. With a dedicated data communication function,
Digital data such as parameter changes is transmitted from the handheld terminal 13 to the two-wire transmitter 10.

Next, the respective constituent elements configured as described above will be described in detail. Of these, the two-wire transmitter 10
Is configured as follows. The SNR is a sensor that detects pressure / differential pressure and converts it into an electric signal. The electric signal converted by the sensor SNR is converted into a digital signal by the analog / digital converter ADC and stored in the random access memory (RAM) portion of the memory MEM through the microprocessor μP. The microprocessor μP uses the digital signal stored in the memory ME.
The digital / analog converter DA performs predetermined arithmetic operations such as linearization and damping according to the arithmetic procedure written in the read only memory (ROM) portion of M, for example.
It outputs to the output circuit OPC via C. On the other hand, the predetermined calculation result in the microprocessor μP is the built-in monitor LC.
Digitally displayed with the number of digits required for D.

The output circuit OPC converts the voltage signal converted into an analog signal by the digital / analog converter DAC into 4 to 2
Converted to a uniform current signal I _L of 0 mA and the transmission line L
1 and L2 to the load 12. Further, the output circuit OPC uses a part of the current signal I _L to transmit the 2-wire transmitter 10
Make the power supply of the internal circuit.

The IFC is an interface for data communication with the handheld terminal 13 and is connected between the transmission lines L1 and L2 and the microprocessor .mu.P, and digital signals from the transmission lines L1 and L2. Is transmitted to the microprocessor μP as parallel data, and conversely the data from the microprocessor μP is transmitted as a serial signal to the transmission line L.
1 and has a function of transmitting to the L2 side.

Further, the interface IFC modulates the data of "1" and "0" of a predetermined number of bits from the microprocessor .mu.P so that, for example, when it is "1", it does not generate the burst wave. When it is "0", the burst wave is sent out to the transmission lines L1 and L2 as a modulated communication signal associated with the burst wave, and conversely, the burst wave input from the transmission lines L1 and L2 is set to "1". ",""0" data is demodulated and transmitted to the microprocessor .mu.P.

Next, the handheld terminal 13 is constructed as follows. SER is a setting device operated by an operator and has a monitor built therein. Various settings or requests such as model request of the two-wire transmitter 10, change of display cycle, change of range, detection of abnormality, display of damping or value of current signal I _L can be made. μP ′ is a microprocessor, which receives data from the setter SER and outputs a digital signal to the two-wire transmitter 10 through the interface IFC ′ according to the processing procedure stored in the memory MEM ′. Send out. This digital signal is transmitted in the same modulation format as the interface IFC of the two-wire type transmitter, for example, as a burst wave.

Further, the microprocessor μP 'is a response data from the two-wire type transmitter 10 which is modulated in a predetermined modulation format.
Data to the memory MEM 'via the interface IFC'.
In the memory MEM 'and decodes it according to the processing procedure stored in the memory MEM' and displays it on the monitor of the setting device SER.

[0011]

However, since the two-wire type transmitter as described above is compatible with only one type of communication system, it cannot communicate at all on different communication protocols. Therefore, a user who uses this two-wire transmitter has the inconvenience of having to use the handheld terminal for each manufacturer, and the frequency of making a setting error increases.

[0012]

In order to solve the above problems, the present invention converts a physical quantity to be measured by a sensor by receiving power supply from a load side through two transmission lines into an electric signal. Then, this is signal-processed by a signal calculation means including a microprocessor and transmitted as a current signal to the preceding load side through the preceding transmission line, and if necessary, the modulated communication signal is superimposed on the preceding transmission line to the outside. A two-wire transmitter for digital communication, monitoring means for monitoring whether the preceding modulated communication signal is a first modulated communication signal having a carrier or a second modulated communication signal having no carrier, and outputting a monitoring signal, Demodulation means for demodulating the corresponding modulated communication signal by the supervisory signal and outputting the demodulated signal, and receiving the supervisory signal to decrypt the corresponding demodulated signal and outputting a response signal according to the content of the decryption. Processor And a modulation means for receiving the response signal and outputting a modulation communication signal in a modulation format corresponding to the destination monitoring signal, and an addition means for superimposing the modulation communication signal on the current signal and outputting the current signal. It is the one.

[0013]

[Operation] The monitoring means monitors whether the modulated communication signal transmitted through the transmission line is a first modulated communication signal having a carrier or a second modulated communication signal having no carrier, and outputs a monitoring signal. Next, the demodulation means demodulates the corresponding modulated communication signal by the supervisory signal and outputs the demodulated signal to the processor, and the processor receives the supervisory signal, decodes the corresponding demodulated signal, and responds to the contents of the decryption. The response signal is output to the modulation means. The modulation means receives the response signal and outputs the modulated communication signal to the addition means in a modulation format corresponding to the destination monitoring signal. The adding means superimposes the modulated communication signal on the current signal corresponding to the physical quantity measured by the sensor, and outputs it to the transmission line.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. The parts having the same functions as those of the conventional two-wire transmitter shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

In the two-wire type transmitter 14, instead of the part corresponding to the interface IFC of FIG. 5, a comparator CMP, a monitoring circuit ISP, a demodulation circuit DEM, a serial / parallel conversion circuit SPC, a modulation circuit. An interface portion including a MOD and the like is provided, and other portions are shown in FIG.
It has almost the same structure as.

Comparator CMP includes transmission lines L1 and L2.
The modulated communication signal D1 in the form of a burst wave, which is transmitted via the AC, is detected and converted into a digital signal D2 of 0 or 5 V, for example. The monitoring circuit ISP uses this digital signal D
The modulation format of No. 2 is detected and the monitoring signal D4 is output. The demodulation circuit DEM demodulates the digital signal D2 corresponding to the modulation format designated by the supervisory signal D4 and transmits the transmission data D0.
The demodulated signal D3 corresponding to is reproduced.

Demodulated signal D3 as this serial data
Is converted into parallel data by the serial-parallel conversion circuit SPC and read into the microprocessor μP. The microprocessor .mu.P decodes the read parallel data, executes a predetermined process according to the contents of the communication, and outputs the response signal D5.
Is output to the modulation circuit MOD as serial data via the serial-parallel conversion circuit SPC.

The modulation circuit MOD modulates this serial data in a modulation format based on a predetermined signal D6 designated by the microprocessor μP and outputs it as a modulated communication signal D7 to the output circuit OPC. The output circuit OPC converts the digital modulated communication signal D7 into a digital / analog conversion circuit DA.
It is added to the analog voltage output from C and output as a current signal to the transmission lines L1 and L2.

Next, the operation of the two-wire type transmitter configured as described above will be described with reference to the waveform charts shown in FIGS. FIG. 2 is a waveform diagram showing the signal waveform used in this description, and FIG. 2 (a) is a communication data used in this digital communication.
The start bit ST is 1 bit, the data part DATA is 8 bits, and the stop bit SP is 1 bit, and a total of 10 bits make up one frame.

On the other hand, as a modulation format for modulating the communication data D0, FIG. 2B shows the case of the modulated communication signal A which is output by modulating in the burst wave modulation format.
(C) shows the case of the modulated communication signal B which is output after being modulated by the FSK-like modulation format. Actually, the modulated communication signal A is, for example, 0 Hz when it is “1”,
A frequency of 2400 Hertz when "0", a frequency of 1200 Hertz when "1", and a frequency of 2200 Hertz when "0" are used as the modulated communication signal B.

As described above, in the case of the modulated communication signal A, the carrier is intermittent and there is no carrier in the period of the stop bit SP, but in the case of the modulated communication signal B, the carrier is continuous and the stop bit is stopped. There is a difference that carriers exist even during the SP period.

In the case of FIG. 3, the handheld terminal 13 is used.
2 uses the modulated communication signal A corresponding to FIG. 2B, and in the case of FIG. 4, the modulated communication signal B corresponding to FIG.
, Respectively.

First, the case shown in FIG. 3 using the burst wave will be described. When the transmission data D0 corresponding to the value set by the setting device SER of the handheld terminal 13 is output to the interface IFC ', this transmission data D0 is modulated as a burst wave, and the transmission data D0 is modulated as shown in FIG. It is sent to the transmission lines L1 and L2 as an AC modulated communication signal D1 which changes to positive and negative as shown in b).

The comparator CMP of the two-wire type transmitter 14 receives the AC modulated communication signal D1 and detects it, converts it into a digital signal D2 of 0, 5 V, for example, and this digital signal D2 is sent to the demodulation circuit DEM. It is output to the monitoring circuit ISP. The monitoring circuit ISP detects whether or not there is a carrier at the 10th bit from the stop bit, that is, the start bit ST, but in this case there is no carrier. Therefore, this modulated communication signal D1 has the modulation format shown in FIG. 2 (b). Figure 3
As shown in (e), the monitor signal D4 is output to the modulation circuit DEM and the microprocessor μP while maintaining the low level at the time of the arrow.

Since the monitoring signal D4 is low level, the modulation circuit DEM demodulates the monitoring signal D4 in the modulation format shown in FIG. 2 (b) and outputs the demodulated signal D3 (FIG. 3 (d)) in the serial-parallel conversion circuit. Output to SPC. Serial-parallel conversion circuit SPC
Converts the serial demodulated signal D3 into a parallel signal and outputs the parallel signal to the microprocessor μP. The microprocessor μP decodes this content and executes the corresponding processing, and at the same time outputs the response signal D5 to the demodulation circuit MOD via the serial-parallel conversion circuit SPC, and at the same time, the signal D6 designating the modulation format.
To the demodulation circuit MOD.

The demodulation circuit MOD modulates the response signal D5 into a modulated communication signal D7 in a modulation format designated by the signal D6, in this case the modulation format shown in FIG.
Output to. The output circuit OPC outputs the modulated communication signal D
7 is added and superimposed on the analog output of the digital / analog converter DAC, and the modulated communication signal D7 is sent to the transmission lines L1 and L2 in a form of being superimposed on the current signal.

Next, the handheld terminal 13 is shown in FIG.
Using the FSK-modulated modulated communication signal B shown in (c),
The same data as the transmission data D0 shown in FIG.
The case where (a)) is transmitted is described. The modulated communication signal D1 'received by the comparator CMP is FSK.
It is a modulated waveform, and this waveform is stop bit SP
The difference from the modulated communication signal D1 is that the carrier is present even during the period. The comparator CMP detects the modulated communication signal D1 'to obtain a digital signal D2' shown in FIG. 4 (c).

The monitoring circuit ISP uses the digital signal D2 '.
In the period of the stop bit SP, that is, whether there is a carrier at the 10th position from the start bit is detected. In this case, unlike the case of FIG. As shown, the supervisory signal D4 'is raised to the high level at the time point indicated by the arrow in the period of the stop bit SP.

The demodulation circuit DEM detects the high level of this supervisory signal D4 ', demodulates the digital signal D2' as the modulation format shown in FIG. 2C, and demodulates the demodulated signal D3.
(FIG. 4 (d)) is output. Subsequent processing by the microprocessor μP is similar to that shown in FIG.

The microprocessor μP decodes the contents read from the serial-parallel conversion circuit SPC and executes the corresponding processing, and outputs the response signal D5 to the demodulation circuit MOD via the serial-parallel conversion circuit SPC, and at the same time, the modulation format. The signal D6 ′ designating the signal is output to the demodulation circuit MOD.

The demodulation circuit MOD modulates the response signal D5 into a modulated communication signal D7 'in a modulation format designated by the signal D6', in this case the modulation format shown in FIG.
Output to PC. The output circuit OPC adds and superimposes the modulated communication signal D7 'on the analog output of the digital / analog converter DAC, and sends it to the transmission lines L1 and L2 in a form in which the modulated communication signal D7' is superposed on the current signal. As described above, the modulation format can be determined depending on whether a carrier exists during the stop bit period, and the corresponding processing can be performed.

In the above description, the FSK modulation is described as another modulation format with the burst waveform modulation format as a base, but the present invention is not limited to this, and the carrier may be, for example, a phase modulation format or a frequency modulation format. Any continuous modulation format can be applied.

[0033]

As described above in detail with reference to the embodiments, according to the present invention, even if a handheld terminal having a different modulation format is connected to the transmission line of the two-wire transmitter, the modulation format is automatically changed. Therefore, it is not necessary to use the handheld terminal properly for each communication, and the setting error does not occur. Therefore, the communication is easy to use.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram explaining the operation of the two-wire transmitter shown in FIG.

FIG. 3 is a waveform diagram showing a first communication waveform used in the 2-wire type transmitter shown in FIG.

4 is a waveform diagram showing a second communication waveform used in the two-wire transmitter shown in FIG.

FIG. 5 is a block diagram showing a configuration of a conventional two-wire transmitter.

[Explanation of symbols]

 10, 14 2-wire transmitter 11 DC power supply 12 Load 13 Handheld terminal IFC interface μP Microprocessor MEM memory CMP comparator ISP monitoring circuit DEM demodulation circuit MOD modulation circuit SPC serial-parallel conversion circuit

Claims (1)

[Claims] 1. A power supply is supplied from a load side through two transmission lines, a physical quantity to be measured by a sensor is converted into an electric signal, the signal is processed by a signal calculation means including a microprocessor, and the signal is transmitted. A two-wire transmitter that transmits a current signal to the load side via a wire and superimposes a modulated communication signal on the transmission line as necessary to perform digital communication with the outside, wherein the modulated communication signal has a carrier. Monitoring means for monitoring whether the first modulated communication signal or the second modulated communication signal having no carrier and outputting a monitoring signal; and demodulation means for demodulating the corresponding modulated communication signal by this monitoring signal and outputting a demodulated signal, A processor which receives the supervisory signal, decodes the corresponding demodulated signal and outputs a response signal according to the contents of the decoding, and a modulator which receives the response signal and corresponds to the supervisory signal Two-wire transmitter, characterized by comprising: a modulating means for outputting a modulated communication signal, wherein the adding means and outputting the superimposing the modulated communication signal to the current signal.