JPH07296288A - Composite measurement converter - Google Patents

Abstract

PURPOSE:To enable a dependable process control to be performed with a relatively simple system by easily using a composite measurement field equipment to conventional system. CONSTITUTION:The device is provided with a capacity element 21 separating the transmission signal from the composite measurement field equipment into analog signal and digital signal superimposed to the analog signal, a circuit amplifying the separated analog signal, circuit 14 performing the I/O insulation, circuit 15 outputting the standard signal, circuit 22 insulating the separated digital signal by the input and output, communication interface circuit 23 converting the transmission signal waveform, microprocessor 24 executing the various arithmetic processings and communication processings, circuit 25 outputting the output from the microprocessor 24 as a standardized signal, and power supply 10 for field equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial signal converter for receiving process quantities such as pressure, flow rate and temperature detected by a field device via a signal transmission line, converting them into a unified electric signal and outputting the same. Regarding vessels.

[0002]

2. Description of the Related Art A device called a converter receives process quantities such as pressure, flow rate, and fluid temperature of various plants from field equipment installed in the plant via a transmission line to unify the process quantities. Converted to electrical signals and transmitted to the host device.

FIG. 3 shows a conventional configuration example of a system including a converter. The field devices such as the differential pressure transmitter 1b, the pressure transmitter 1c, and the temperature sensor 2 are adapted to detect the process amount such as the flow rate, pressure, and fluid temperature of various plants, and to output the process amount as an electric signal. It is designed to be converted into and output. Differential pressure transmitter 1b,
The pressure transmitter 1c is connected to another transmitter signal converter 3b via the two-wire transmission line 5a. For example, when the temperature sensor 2 is a resistance temperature detector, the temperature sensor 2 is connected to the temperature converter 3c via a compensation lead wire 5b. The transmitter signal converter 3b and the temperature converter 3c convert the electric signals received from the differential pressure transmitter 1b, the pressure transmitter 1c, and the temperature sensor 2 into standardized electric signals, respectively, and form a two-wire transmission line. It is transmitted to the higher-level device 4 via 5a. The host device 4 performs various calculations based on the process values of the differential pressure, pressure, and fluid temperature, and also executes process control such as loop control and sequence control. The external power supply 7 supplies the drive power necessary for operating all of the above-described plural measurement field devices 1a, differential pressure transmitter 1b, temperature sensor 2, transmitter signal converter 3b, temperature converter 3c, and host device 4. , Through the power transmission line 5c.

Next, circuit configuration examples of the transmitter signal converter 3b and the temperature converter 3c will be described with reference to FIGS. 4 and 5, respectively. FIG. 4 shows an example of the transmitter signal converter 3b. The transmitter signal converter 3b generally supplies drive power to the field device and receives an output current signal 4 to 20 mA from the field device, which is proportional to the process amount, and electrically insulates between the input and output. And outputs a standardized signal. In FIG. 4, the power supply circuit 10 is supplied with drive power from the external power supply 7 via the power transmission line 5c, and each circuit in the transmitter signal converter 3b, the differential pressure transmitter 1b, and the pressure transmitter 1c. An appropriate drive voltage is supplied to each of the field device power supplies 11 for driving the.
The transmitter signal converter 3b takes in process amounts such as differential pressure and pressure converted into current signals of 4 to 20 mA via the two-wire transmission line 5a. A reference resistor 12 is connected to both ends of the input part of the transmitter signal converter 3b to convert the current signal into a voltage signal. Further, the voltage control circuit 1 is connected to the input portion of the transmitter signal converter 3b through the reference resistor 12.
3 is connected. The input impedance of the voltage control circuit 13 is very high, and part of the current signal is the reference resistance 1
By bypassing 2, the voltage signal generated across the reference resistor 12 is prevented from being attenuated. Furthermore, transmitter signal converter 3b
Includes a signal isolation circuit 14. The signal insulation circuit 14 electrically insulates the input and output signals of the transmitter signal converter 3b. The output part of the signal isolation circuit 14 is an output adjustment circuit 15.
Connected to. The output adjustment circuit 15 is the transmitter signal converter 3
The influence on the signal output value due to the electrical characteristic variation of the circuit element in b is corrected and a stable standardized electric signal is output.

FIG. 5 shows an example relating to the temperature converter 3c. When the temperature sensor 2 connected to the input section of the temperature converter 3c is, for example, a resistance temperature detector, the input section interface circuit 31 uses the temperature sensor 2 via the compensation lead wire 5b.
The amount of change in resistance value of is taken in and converted into an electric signal.
The burnout detection circuit 32 detects the disconnection of the temperature sensor 2 and scales the output signal of the temperature converter 3c. The filter circuit 33 removes disturbance noise other than the sensor signal. Amplifier circuit 34
Is amplifying a relatively small sensor signal to a level suitable for electrical processing. The linearization correction circuit 35 corrects the temperature characteristic peculiar to the temperature sensor so that an output value linearly corresponding to the temperature change can be obtained. The output section of the linearization correction circuit 35 is connected to the output adjustment circuit 15 via the signal insulation circuit 14. The functions of the insulating circuit 14 and the output adjusting circuit 15 are as described in the description of FIG.

Since the differential pressure, which is one of the process quantities to be measured, depends on the fluid temperature and pressure, in order to perform highly accurate differential pressure measurement, all process quantities of differential pressure, pressure and fluid temperature are collected. However, it is necessary to execute various arithmetic processes to calculate the true value of the differential pressure. However, the arithmetic processing has complicated function calculations of various coefficients, temperature, and pressure, and executing the arithmetic processing by a conventional field device or a microprocessor included in a conventional signal converter requires a memory. It is difficult to realize the microprocessor because the load on the microprocessor is heavy in terms of capacity and calculation speed.
Therefore, a system configuration as shown in FIG. 3 was required in order to execute the arithmetic processing in the host device. However, in order to detect one process amount, a field device, a signal converter, and a two-wire type transmission line were used. You need one each,
There was a cost problem. A composite measurement field device has been devised as a means for realizing highly accurate differential pressure measurement with a smaller device configuration. The composite measurement field device has an interface to which a temperature sensor can be connected and also has a composite sensor capable of detecting two process quantities of differential pressure and pressure. As a result, one combined measurement field device can detect differential pressure, pressure, and fluid temperature. Further, the composite measurement field device converts the differential pressure into an analog DC current signal, converts the pressure and the fluid temperature into a digital communication signal superimposed on the analog DC current signal, and outputs the digital communication signal onto a single two-wire transmission path. It is like this.

[0007]

However, since the host device does not have a function of directly receiving the digital communication signal, the digital communication signal transmitted by the composite measurement field device is directly converted into a signal converter. In the case of attempting to transmit the signal to the higher-level device via the communication device, it is necessary for the signal converter and the higher-level device to each newly include a digital communication device, which increases the cost of the system. In order to avoid this and relay between the composite measurement field device and the host device, a composite measurement converter having means for converting a digital communication signal into an analog DC signal is required. However, an analog signal and a digital communication signal superimposed on the analog signal are received through the same transmission line, signal separation and conversion processing are performed, and input / output insulation is performed on all signals. Thus, a signal converter having a function of outputting a standardized analog signal from an independent output section for each signal in a single structure has not existed in conventional signal converters.

An object of the present invention is to realize a composite measuring transducer that satisfies all the above conditions.

[0009]

In order to achieve the above object, the present invention is configured as follows.

A capacitive element for separating a transmission signal from the composite measurement field device into an analog signal and a digital signal superimposed on the analog signal, a circuit for amplifying the separated analog signal, and a circuit for performing input / output insulation. A circuit for outputting a standardized signal, a circuit for isolating a separated digital signal between input and output, a communication interface circuit for converting a transmission signal waveform, a microprocessor for executing various calculations and communication processes, A circuit for outputting the output from the microprocessor as a unified signal and a power supply for field equipment are provided.

[0011]

According to the converter having the above structure, the transmission signal from the composite measurement field device is separated into the analog signal and the digital signal by the capacitive element. The two separated
Each type of signal is processed by a functionally independent circuit system. The analog signal is output as a unified signal through an amplifier circuit, an insulation circuit, and a demodulation circuit. The digital signal is input to the microprocessor through the insulating circuit and the communication interface circuit, is subjected to various kinds of arithmetic processing, and is then output as a unified signal through the demodulation circuit. Further, when the digital communication signal includes a plurality of process signals, a multiple output control circuit is arranged between the microprocessor and the demodulation circuit and this is controlled by the microprocessor. Further, by adding demodulation circuits by the number of process signals, a plurality of process signals are simultaneously output as independent signals from independent output terminals.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows that the output of the composite measurement field device consists of an analog current signal of 4 to 20 mA, and the digital signal superimposed on this analog current signal enables communication with the composite measurement converter or communicator. The block diagram when performing is shown.

In the figure, the outline is shown in FIG.
Is the drive power required to operate all other equipment,
It is supplied via the power transmission line 5c. The composite measurement field device 1a is designed to be operated by the electric power supplied from the external power supply 7 via the composite measurement converter 3a. The composite measurement field device 1a has a composite sensor, and the composite sensor is adapted to detect a physical quantity such as differential pressure or pressure of fluid in various plants. Further, the composite measurement field device 1a has an external input terminal, and the temperature sensor 2 is connected to the external input terminal via a compensation lead wire 5b. Temperature sensor 2
Is configured to detect the fluid temperature of the portion where the temperature sensor 2 is installed, convert the fluid temperature into an electrical signal, and output the electrical signal to the compensation lead wire 5b. The composite measurement field device 1a performs various processes on the electric signals from the composite sensor and the temperature sensor 2, and among the electric signals, the differential pressure is an analog direct current signal, and the pressure and the fluid temperature are the aforesaid. Each is converted into a digital communication signal superimposed on the analog DC current signal, and is output to the composite measurement converter 3a via the single two-wire transmission line 5a. The composite measurement converter 3a includes a reference resistance between the two-wire transmission lines 5a,
By detecting the voltage between the reference resistors, the physical quantity from the composite measurement field device 1a is received. Moreover, the composite measurement converter 3a has a built-in communication device, and communicates with the composite measurement field device 1a by the digital signal to collect pressure and fluid temperature. Here, if the output signal of the communication device is a small signal of square wave or sine wave with the same amplitude in the positive and negative directions, even if a digital signal is output for communication, the output current value on the transmission line is instantaneous. However, it does not affect the indication value on the side of the composite measurement converter 3a that detects an analog signal. The composite measurement converter 3a has at least the same number of output terminals as the plurality of process quantities, and is connected to the host device 4 via the same number of 2-wire transmission lines 5a as the output terminals. The composite measurement converter 3a is configured to convert each of the plurality of process quantities into a standardized analog DC signal and output the standardized analog DC signal to the two-wire transmission line 5a. Further, the handheld communicator 6 can be connected between the composite measurement field device 1a on the two-wire type transmission line 5a and the composite measurement converter 3a. The handheld communicator 6 communicates with the composite measurement field device 1a by the digital signal, and performs processing such as monitoring of input / output signals of the composite measurement field device 1a and calibration.

The operation of the composite measurement converter 3a will be described with reference to FIG. The power supply circuit 10 is supplied with drive power from the external power supply 7 via the power transmission line 5c, and supplies appropriate drive voltage to each circuit in the composite measurement converter 3a and the field device power supply 11. There is. The field device power supply 11 is connected in series with the composite measurement converter 3a via a two-wire transmission line 5a, and the composite measurement converter 3a
It is designed to supply drive power to. Reference resistance 12
Is also connected in series with the composite measurement converter 3a, and is adapted to convert an analog current signal of 4 to 20 mA indicating a differential pressure into a voltage signal. The voltage control circuit 13 prevents a part of the analog current signal from bypassing the reference resistor 12 and attenuating the voltage signal generated across the reference resistor 12. The output end of the voltage control circuit 13 is connected to the signal isolation circuit 14
It is designed to electrically insulate signals between input and output. An example of the signal insulation circuit 14 is a flying capacitor circuit configured by a photo coupler. The output end of the signal insulation circuit 14 is connected to the output adjustment circuit 15. The output adjustment circuit 15 performs a signal correction function for outputting an accurate standardized signal. The output section of the output adjustment circuit 15 is connected to the two-wire transmission line 5a and outputs a standardized signal.

On the other hand, the pressure and fluid temperature inputted to the composite measuring converter 3a as a digital communication signal superimposed on the analog signal are separated from the analog signal by the capacitive element 21 connected in parallel with the reference resistor 12. It is then taken out and input to the communication interface circuit 23 via the input section insulating circuit 22. The communication interface circuit 23 performs a waveform conversion process on the digital communication signal and serially transmits it to the microprocessor 24 connected to the output section of the communication interface circuit 23. The microprocessor 24 cyclically digitally communicates with the composite measurement field device 1a via the communication interface circuit 23 to collect the composite measurement data, as well as execute an input signal standardization process, a pulse width modulation output process, and the like. It has become. Further, as shown in FIG. 1, the handheld communicator 6 is connected to the two-wire type transmission line 5a, and the combined measurement field device 1a
When communicating with the microprocessor 24, the microprocessor 24 constantly monitors the communication traffic state of the two-wire transmission line 5a, and when it detects the communication signal of the handheld communicator 6, it immediately performs exclusive control to perform the cyclic communication process. The handheld communicator 6 can communicate with the composite measurement field device 1a without any problem. PTM (Programmable Timer Module) 25
Are controlled by the microprocessor 24, and the digital signals pulse-width-modulated by the microprocessor 24 and containing a plurality of process quantities are respectively divided, and are simultaneously output from the prepared output units for the number of process signals. ing. The same number of demodulation circuits 26 as this are connected to the output section of the PTM 25 so as to convert the pulse width modulated process amount into an analog voltage signal. And the demodulation circuit 26 has a signal isolation circuit,
It is designed to provide electrical isolation between input and output. The output section of the demodulation circuit 26 is connected to each unique two-wire transmission path 5a so that the standardized signals of the respective process quantities are output at the same time.

Therefore, according to this embodiment, a plurality of process signals can be received via a single transmission line without any problem.
Moreover, it becomes possible to transmit a highly reliable standardized signal of each process amount to the host device.

[0018]

As described above, according to the present invention,
The composite measurement field device can be easily introduced into the conventional system, and the process control with higher reliability can be performed with a relatively simple system configuration.
Further, conventionally, the temperature converter to which the temperature sensor is connected is located relatively far from the field device group, but according to the present invention, it can be installed in a position extremely close to the temperature sensor. It is only necessary to connect a temperature sensor to the composite measuring field device, which has the additional advantage that an expensive compensating lead wire needs to be installed in a very short distance, and the cable cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a process measurement system according to the present invention.

FIG. 2 is a diagram showing a circuit configuration example of a composite measurement converter.

FIG. 3 is a diagram showing a configuration example of a conventional process measurement system.

FIG. 4 is a diagram showing a configuration example of a transmitter signal converter.

FIG. 5 is a diagram showing a configuration example of a temperature converter.

[Explanation of symbols]

1a ... Combined measurement field device, 1b ... Differential pressure transmitter, 1
c ... Pressure transmitter, 2 ... Temperature sensor, 3a ... Complex measurement converter, 3b ... Transmitter signal converter, 3c ... Temperature converter, 4 ...
Host device, 5a ... 2-wire type transmission line, 5b ... Compensation lead wire, 5c
… Transmission line for power supply, 6… Handheld communicator, 7
... external power source, 11 ... field device power source, 12 ... reference resistance, 21 ... capacitive element.

Claims (3)

[Claims] 1. A field device which detects a physical quantity to be measured (for example, temperature, pressure, flow rate, etc.), converts it into an electric signal corresponding to the physical quantity, and outputs the electric signal to a two-wire transmission path, and the two-wire transmission. Via the line, receives the electric signal and converts it into a standardized electric signal, and sends the standardized electric signal to a host device via a two-wire transmission line different from the two-line transmission line. In a system consisting of a signal converter for performing the process control based on the standardized electric signal transmitted by the signal converter, the input / output circuit of the signal converter is transmitted from the composite measurement field device. A signal separation circuit for classifying an analog DC current signal representing a main process amount and a digital communication signal superposed on the analog DC current signal and containing information representing at least one sub-process amount. In addition, one or more sub-process amounts are extracted from the digital signal extracted by the signal separation circuit, various calculations are performed on the sub-process amount, and then the sub-process amount of the sub-process amount is calculated. The above-mentioned means for converting the modulated signals output by the arithmetic circuit into a unified analog DC voltage signal and outputting the modulated signals, each of which includes an arithmetic circuit for simultaneously outputting the continuous and independent modulated signals of the same number. A composite measurement converter including at least as many output circuits as the number of process quantities. 2. The arithmetic circuit is formed by a microprocessor, and for the purpose of, for example, making a data request to the field device, the microprocessor communicates digitally with the field device via a communication interface circuit. The microprocessor sends a digital communication signal including data information, which is sent from the field device through the two-wire transmission path, as a response to the digital communication signal, by transmitting the signal on the two-wire transmission path. 2. The reception according to the communication interface circuit, and the microprocessor executes various arithmetic processing and transmission processing to a higher-level device based on information included in the digital communication signal. Complex measurement converter. 3. The digital modulation according to claim 1, wherein the analog DC current signal extracted by the signal separation circuit and one or more sub-process quantities output by the microprocessor are in a one-to-one correspondence. A composite measurement converter characterized in that a signal isolation circuit for electrically isolating the signal between the input and the output is provided on all paths with the signal.