JPH11175874A - Instrumentation interface and network system for using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an instrumentation interface of high reliability that can largely reduce an instrumentation wiring and detect on-line a failure of a line and a wrong set of a reference value by using a set reference value in a host computer. SOLUTION: This interface generates plural digital signals on the basis of a signal from a sensor for detecting quantity of physical state. At this time, a reference value set part 7 for setting plural reference values, a switch circuit 8 for comparing a signal based on a sensor signal with each of plural reference values respectively and outputting the digital signal of high level or low level, a multiplexer part 9 for fetching plural reference values and selecting one of them, an AD converter part 10 for converting the selected reference value into the digital signal and a microcomputer 11 for fetching the converted digital signal. Then, plural reference values are always monitored by software of the microcomputer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instrumentation interface and a network system using the same.
In particular, in electrical instrumentation such as boilers, it is a technology related to a suitable instrumentation interface for reliably taking sensor signals such as pressure, flow rate, temperature, etc. over a long distance from the detection end to the central control unit with high reliability. In the electrical instrumentation of boilers, boilers, etc., the interface (I / F) of the plant control unit is the same as before, and the detection end and the plant control unit are connected by digital communication to reduce the number of instrumentation cable wiring and construction. This is a technology related to an instrumentation network system that aims to reduce costs.

[0002]

2. Description of the Related Art In an electrical instrumentation of a boiler, for example, taking a pressure switch as an example, as shown in FIG.
In order to detect the predetermined pressure of
Are connected, of which two are for interlock,
Two are required for alarms, for a total of four. In a conventional device, these four signal lines are wired by four pairs of cables.
Further, a reference voltage is set for each pressure switch for each application, and the output signal from the pressure switch 15 is, for example, low (L = 0), high (H) = 1).

In a boiler, the distance from the detection end or the pipe 1 where the pressure switch 15 is located to the central control room where the control device 5 is located is several hundred meters or more. When the sensors for temperature, temperature, level, etc. are combined, the number becomes several hundreds, and the amount of wiring cables and man-hours for laying work are considerably increased. In addition, since the reference values set for the pressure switches 15 and the like differ depending on the application, maintenance work for the reference values of the pressure switches 15 distributed and installed at the site increases.

Therefore, the present applicant wired a signal line for one sensor capable of detecting a state quantity from the detection end to the control device 5 as shown in FIG. Considering outputting these outputs from a switch circuit 8 using an electronic circuit, an application for this has already been filed. When the system shown in FIG. 12 is used, the amount of wiring cables and man-hours for laying work are reduced, and the reference value setting unit 7 set in each switch circuit 8 is concentrated in the control device 5, so that the conventional system shown in FIG. The reference value maintenance work becomes easier.

However, since maintenance work cannot be performed unless the control device 5 is temporarily stopped, even if an abnormality occurs in the reference value setting unit 7 during operation or an incorrect reference value is set, Cannot be discovered until the next maintenance. For example, if the pressure of the fuel becomes abnormally high and the pressure switch exceeds the reference value and the output should be high (H), it is erroneously determined that the output remains low (L), and an interlock should be applied. You lose time. Therefore, in such a case, it is necessary to provide a configuration in which the reference value set in the switch circuit 8 can be monitored online so that the control device 5 functions safely.

Further, as shown in FIG. 13, a sensor installed at a site converts detection information (pressure, flow rate, level, temperature, etc.) into an analog electric signal, and outputs a current through a loop of an analog two-wire cable. The signal (4-20 mA) is connected to the plant controller 1077. Further, a signal for turning on / off (ON / OFF) the contact at a certain threshold value like a pressure switch is similarly connected to the plant control device 107. In such an electrical instrumentation system, the number of measurement points increases as the scale of the plant increases, and the number of transmission cables connecting the on-site measuring instruments 102 and 103 to the plant control device 7 also increases. In a plant such as a boiler, the signal wire laying distance between the measurement point and the plant control device 7 is several hundred meters,
In addition, some outdoor fuel tanks exceed 1 km, and a large number of measurement points leads to an increase in cable construction costs and a long construction period.

[0007]

In an instrumentation interface, as shown in FIG. 12, a reference value setting section 7 for setting a reference value conventionally employs a variable resistor so that a different value can be set for each application. And manually adjusted. Variable resistors are more susceptible to vibrations, temperature fluctuations, aging, and the like than electronic components such as transistors and ICs, and the reference value may be shifted due to mechanical displacement of the slider. In addition, since the adjustment is performed manually, there is a possibility that an incorrect setting is made. When the above-mentioned trouble occurs, there is a problem that an abnormality is first recognized at the next maintenance.

In the instrumentation interface according to the present invention, the reference value set in the switch circuit 8 is configured to be monitored on-line, so that the control device 5 functions safely.

In an instrumentation network system, as shown in FIG. 13, if the measurement points and the control device are separated from each other and the number of measurement points is large as in a boiler, cable construction costs increase. There is a problem that the construction period is lengthened. In recent years, in addition to the conventional analog output (4 to 20 mA), intelligent type transmitters that handle mixed analog / digital signals have begun to be widely used in transmitters installed at measurement points. Diagnosis and the like can be processed by digital communication using a communicator. However, the configuration shown in FIG. 13 has a problem in that the adjustment operation must be performed while replacing the handy-type communicator with a cable for each transmitter.

[0010] Further, with the development of digital transmission technology in recent years, the signal from the transmitter by the node 104 as shown in FIG. 14 is transmitted to the communication control station 127 and the plant control device 107 via the transmission cable 106.
A digital transmission system that is consistent up to now has been developed. Compared with the system shown in FIG. 13, the number of laid cables from the on-site measurement point to the plant control device is greatly reduced, but the interface (I / F) on the plant control device side
Needs to be changed from the conventional analog signal capturing method to the digital communication capturing method.

In the conventional system shown in FIG. 13, an analog signal and a contact signal from a sensor are directly transmitted to a plant control device 107.
14 may be connected, but in the network system shown in FIG.
Since the entire system including the communication control station 127 and the plant control device 17 is integrated by a single manufacturer's system, there is a problem that the design of the side that takes in the signal from the sensor and the design of the plant control device cannot be separated. is there.

An object of the instrumentation network system of the present invention is to digitalize an analog input and a contact input from a sensor at a node near the sensor and transmit the digitalized data.

[0013]

In order to solve the above-mentioned problems, the present invention mainly employs the following constitution.

A reference value setting section for setting a plurality of reference values in an instrumentation interface for generating a plurality of digital signals based on one signal from a sensor for detecting a physical state quantity; A switch circuit that compares a signal based on the reference signal with each of the plurality of reference values and outputs a high-level or low-level digital signal; a multiplexer unit that takes in the plurality of reference values and selects one of the plurality of reference values; An instrumentation interface, comprising: an AD conversion unit that converts the selected reference value into a digital signal; and a microcomputer that takes in the converted digital signal, wherein the plurality of reference values are constantly monitored by software of the microcomputer.

[0015] Further, a node capable of receiving signals from a plurality of sensors is installed near the sensor installed at the detection end of the plant, and analog and contact signals from the sensor are digitized at the node and installed near the plant control device. Digital transmission to the decoder in a serial manner, the decoder converts the digital signal into the original analog and contact signals and transmits the signal to the plant controller, so that the interface installed in the plant controller can be used as it is, and Instrumentation network system that can reduce the number of instrumentation cable wiring between the detection end and the plant controller.

[0016]

FIG. 1 shows a configuration of an instrumentation interface according to an embodiment of the present invention.

The instrumentation interface shown in FIG. 1 uses various types of measurement (pressure, flow rate, temperature, etc.) measured from a plurality of detection ends.
An embodiment in the case where pressure is detected from state quantities will be described. One pressure oscillator 2 is connected to each detection end, and the state quantity (for example, 4 to 20 mA) of each detection end is transmitted to the control device 5 via the process signal cable 3. The control device 5 includes an interface board 4 that compares a process value from each detection end with a reference value and outputs a switch output that replaces a conventional pressure switch.
Also, each interface board 4 has a communication cable 1
3, and can communicate with the host computer 6.

FIG. 2 shows the configuration of the interface board 4. The process amount from the detection end is input via the process signal cable 3, and is classified by application (four types in the present embodiment).
A reference value setting unit 7 for setting a reference value, a switch circuit 8 for comparing the process value with the reference value, and determining whether the process value exceeds the reference value. It comprises a multiplexer section 9 for selecting one arbitrary reference value, an AD conversion section 10 for converting the selected reference value into a digital signal, a microcomputer 11, and a communication control section 12 for controlling communication with the host computer 6. You.

Each of the reference values is stored in a multiplexer unit 9, A
Since it is taken into the microcomputer 11 via the D conversion unit 10 and constantly monitored by software, it is possible to detect a deviation of the reference value due to aging, vibration, temperature fluctuation, circuit failure, and the like. Also, a reference value to be set in each switch circuit 8 is notified in advance from the host computer 6 to the corresponding microcomputer 11 via the communication control unit 12, and the reference value is compared with an AD-converted value.
It can be determined that the reference value is incorrectly set.

By using the above configuration, it is possible to monitor the failure and erroneous setting of the reference value setting unit 7 online. Although the present embodiment shows an example implemented by software using the microcomputer 11, it can be implemented by an equivalent control circuit.

Next, FIGS. 3, 4 and 5 show the configuration of an instrumentation network system according to an embodiment of the present invention. Analog signals (for example, 4 to 20 mA) from a plurality of sensors (such as the pressure transmitter 102 and the flow transmitter 103) installed at the detection end 101 are taken into the node 104. In the node 104, analog signals from a plurality of sensors are converted into digital values, and digitally transmitted to the decoder 105 via the transmission cable 106. The decoder 105 performs D / A conversion of data received by digital transmission for each of the corresponding channels, so that the plant control device 107
From the side, the output from each transmitter is connected as it is.

As shown in FIG. 4, a single node fetches signals from a plurality of transmitters 102 at one node.
Since the transmitter 102 is often a two-wire type that supplies power from the outside, the transmitter power supply 108 and the load resistor 109 inside the node 104 are loop-wired to the transmitter 102. The output current from the transmitter 102 is converted into a voltage by a load resistor 109, and is passed through an amplifier 110 to a multiplexer 111.
To enter. A specific channel is selected by the multiplexer 111 and converted into a digital value by the AD converter 112. In addition, since the precision must not be reduced during the digital conversion, for example, the analog output precision of the transmitter is 0.1%.
The% signal is converted to a digital value by an AD converter 112 having a resolution of 1000 or more (10-bit precision or more), and the conversion result is stored in a memory 115. The conversion results of all the channels are sequentially stored in the memory 11 while sequentially switching the channels of the multiplexer 111.
5 is stored.

The CPU 114 transmits data of all channels to the decoder 105 via the communication controller 116 and the communication transceiver 117. When data is transmitted to the decoder 105, a node No. and a channel No. are added so that it can be determined from which detection end the data is. The node No is, for example, the rotary switch 1
18 is provided and the value of the rotary switch is set as the node No.
If the rotary switch is set to a different value from the other nodes, there is no double definition.

If the data transmission timing from each node is different, data collision occurs on the transmission medium, and data cannot be transferred normally.
Communication controller 116 of token passing system such as SMA system and arcnet, communication transceiver 1
17 is applied to avoid collision of data on the transmission medium.

Next, the configuration of the decoder 105 is shown in FIG. The transmission data from each node 104 is the transmission cable 1
06, the data is received by the communication transceiver 117 and the communication controller 116 in the decoder 105. C
The PU 114 takes out the received data from the communication controller 116 and stores it in the memory 115. Since the transmitted data has a node number and a channel number added thereto, the CPU writes the fetched digital value into the corresponding DA converter 119, and the signal converted into an analog voltage by the DA converter 119 is a voltage signal. The current signal is converted into a current signal by the / current conversion circuit 120 and connected to the plant control device 107. Since the precision should not be reduced when the digital value is converted back to an analog signal, the DA converter 119 has a DA having a resolution higher than the analog output precision from the transmitter, similarly to the AD converter 112 in the node 104.
A converter 119 is used.

With the configuration of the node 104 and the decoder 105 as described above, the connection from the plant control unit 107 is the same as that of the conventional system shown in FIG. Further, since only one system from the node 104 to the decoder 105 is laid from the site measurement point to the center, the cable laying work is greatly reduced and the construction cost is reduced.

Next, an instrumentation network system according to another embodiment of the present invention will be described with reference to FIGS. 6, 7 and 8. FIG. 6 shows a configuration in which the transmission path between the node 104 and the decoder 105 is duplicated. If a single transmission cable is used between the node 4 near the site measurement point and the decoder 5, the instrumentation work cost will be greatly reduced. However, if the cable is broken or the contact is poor, all data may not be able to be imported. . In the configuration shown in FIG. 6, the transmission path is duplicated, and even if an abnormality occurs on one side, the communication operation is possible on the other side, so that a more reliable system can be constructed.

FIG. 7 shows a node 10 corresponding to transmission line duplication.
4 is shown. As in the conventional case, the signal from the sensor is taken in a single system, and only the communication controller 116 and the communication transceiver 117 are duplicated. One side is used as a standby system, and the other side is used as a standby system. When an abnormality occurs in the active system, the data transmission path is switched to the standby system to prevent the system from going down.

FIG. 8 shows a decoder 1 corresponding to a transmission line duplex.
FIG. In the configuration inside the decoder 105, only the communication controller 116 and the communication transceiver 117 are duplicated similarly to the node 104. One side is a service system and the other is a standby system. When an abnormality in the service system is recognized, the transmission data is switched to the transmission path of the standby system. Therefore, the communication controller 116 and the transceiver 117 for the standby system are used.
Since the data from the node-side measuring instrument is taken in via, even if an abnormality occurs on the transmission cable, the system can continue to operate normally.

FIG. 9 shows still another embodiment in which the node 104 is a mixed analog / digital transmitter 10.
2 shows a system configuration characterized in that it can be connected to the communication system 2 and 103. In addition to outputting the process value measured at the detecting end as an analog signal (4 to 20 mA), a digital signal is superimposed, and zero point adjustment, span adjustment, self-diagnosis, etc. of the transmitter 2 can be performed by communication. What can be called intelligent transmitters has become widespread in recent years.

FIG. 9 aims at making it possible to effectively use the communication function of such an intelligent transmitter. A node 104 and a channel can be designated from the instrument management computer 121 connected to the transmission cable 106 to communicate with the corresponding intelligent transmitter 102. The intelligent transmitter 102 installed at the site can be remotely controlled. This is a system configuration characterized in that control is possible.

FIG. 10 shows the internal configuration of the node 104.
The analog signal from the intelligent transmitter 102 (4
２０20 mA) is converted into a voltage signal via a load resistor 109 similarly to the node 104 shown in FIG.
And transmit it to the decoder 105 via the communication controller 116 and the communication transceiver 117. Next, it is assumed that the instrument management computer 121 issues a self-diagnosis command to, for example, a specific intelligent transmitter 102. The self-diagnosis command of the intelligent transmitter 102 is transmitted from the instrument management computer 121 via the transmission cable 106, the communication transceiver 117, and the communication controller 116. Since the ID number (that is, node No., channel No.) of the corresponding intelligent transmitter 102 is added to the command,
The CPU 114 determines whether the received command is for the intelligent transmitter 102 connected to the CPU 114, and, if applicable, performs a self-diagnosis on the communication controller 124 (start-stop synchronization type) corresponding to the communication with the intelligent transmitter. Issue a command.

Serial start-stop synchronous data (TXD) is output from the start-stop synchronous communication controller 124, and a signal modulated by the modulation circuit 125 is transmitted to the intelligent transmitter 1.
02 is superimposed on the transmission path with the number 02. After the command is sent,
Response data (for example, no abnormality) from the intelligent transmitter 102 is transmitted to a BPF (bandpass filter) circuit 1.
At 22, only the modulation frequency used for communication is extracted,
The signal is returned to the start-stop synchronization signal (RXD) via the demodulation circuit 123, and the CPU 1
14 reads the response data from the intelligent transmitter 102. The response data is transmitted to the communication controller 116,
The data is transmitted to the instrument management computer 121 via the communication transceiver 117. By following the above procedure, a single instrument management computer 121 can remotely manage a plurality of intelligent transmitters installed at the site.

As described above, according to the embodiments of the present invention, those having the following functions and functions are included.

The problem with the instrumentation interface is that an abnormality of the reference value can be detected by taking the reference value of the individually set switch circuit 8 into a microcomputer and constantly monitoring it with software.

As shown in FIG. 1 and FIG. 2, the switch circuit 8 composed of an electronic circuit is provided with a process signal (usually 4 to 20 mA) indicating a state quantity from a sensor installed at the detection end.
The switch output is set to, for example, low (L = 0) and high (H = 1) when the reference value is set to be equal to or less than the reference value or equal to or more than the reference value. Each reference value is selected by the multiplexer unit 9, converted into a digital value by the AD conversion unit 10, and taken into the microcomputer 11. Since the reference value is always taken in by the software of the microcomputer 11, it can be detected that the reference value of the reference value setting unit 7 is shifted. Also, if the microcomputer 11 communicates with the host computer 6 via the communication control unit 12 and notifies the microcomputer 11 of a reference value to be set in each switch circuit 8 in advance, the reference value is compared with a value obtained by AD conversion. If not, it can be determined that the reference value is incorrectly set.

As described above, when the microcomputer 11 is used, it is possible to monitor an abnormality or an erroneous setting of the reference value setting unit 7 online.

A problem with the instrumentation network system is that, as shown in FIGS. 3, 4, and 5, a node 104 capable of receiving signals from a plurality of sensors is installed near the sensor, and the sensor 104 is installed in the node 104. Analog input and contact input from the plant control unit 107
This can be achieved by digital transmission to a decoder 105 installed nearby. The decoder 105 converts the digital data captured by communication back into an analog signal which is a sensor output, so that there is no difference from the conventional signal connection from the point of view of the plant control device, so that no new specification change occurs.

Further, the signal lines individually laid out perform time-division digital transmission, so that the number of signal lines from the measurement point to the decoder installed near the plant control device 107 can be reduced to one. Therefore, the construction cost can be reduced.

FIG. 3 shows a system configuration for realizing the above means, FIG. 4 shows a node 104, and FIG.
05 shows the internal configuration. 3 and 4, the current (4 to 20)
mA) A node 104 to which 16 output-type transmitters 102 can be connected is shown as an example. The current from the transmitter 102 is converted into a voltage by the load resistor 109, and the multiplexer 11
1, one of the 16 channels is selected, and the AD converter 11
In step 2, the value is changed to a digital value.

The result of the conversion is stored in the memory 115 by the CPU 114, and the data of all 16 channels are sequentially stored in the memory 115.
Take in. After storing the data of all the channels in the memory 115, the CPU 114 digitally transmits the data to the decoder 105 via the communication controller 116 and the communication transceiver 117 in a serial manner.

As the transmission medium, a cable such as a coaxial cable or a twisted pair cable, which only needs to be laid with one cable, is selected. When 16 or more transmitters 2 are connected, the nodes 104 are added and the CPU 1 on each node 104 is connected.
14 is also the decoder 1 via the communication controller 116.
05 is transmitted. When data is transmitted from each node 104, the data is transferred so that the data does not collide on the transmission medium. If the node number and the channel number are added to the transmission data, when the decoder receives the data, it can recognize where the data came from.

The decoder 105 fetches the transmission data sent from the node 104 and determines where the data came from the node No. and channel No. added to the data. The decoder 105 is provided with a D / A converter 119 and a voltage / current conversion circuit 120 corresponding to the number of input signals, and writes the received data into the corresponding D / A converter 119. The DA converter 119 is converted into an analog voltage corresponding to the written digital value, and is converted into a current signal by the voltage / current conversion circuit 120, so that the signal input to the node 104 can be reproduced.

By returning to the original current signal and connecting each to the input point of the corresponding plant control device 107, the connection specification becomes the same as that of the related art when viewed from the plant control device 107. Further, since a single transmission cable 106 can lay from the node 104 to the decoder 105 installed near the plant control device 107, the signal laying period can be significantly reduced.
Construction costs can be reduced.

[0045]

According to the present invention, the number of instrumentation wirings can be remarkably reduced, and a set reference value can be detected online using a host computer for a circuit failure or an incorrect setting of the reference value. Thus, a highly reliable instrumentation interface system can be configured.

Further, according to the present invention, the number of signals to be laid between the plant control devices located at the center can be reduced from the on-site measurement points without changing the input / output interface of the conventional plant control device. Instrumentation work costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a system configuration of an instrumentation interface according to an embodiment of the present invention.

FIG. 2 is a configuration inside the interface board of FIG. 1;

FIG. 3 is a block diagram of an instrumentation network system according to an embodiment of the present invention.

FIG. 4 is a block diagram showing the inside of the node shown in FIG. 3;

FIG. 5 is a block diagram showing the inside of the decoder shown in FIG. 3;

FIG. 6 is a configuration diagram of an instrumentation network system in which a transmission line is duplicated as another embodiment of the present invention.

FIG. 7 is a block diagram showing the inside of the node shown in FIG. 6;

FIG. 8 is a block diagram showing the inside of the decoder shown in FIG. 6;

FIG. 9 shows an analog / digital converter according to still another embodiment of the present invention.
1 is a block diagram of an instrumentation network system that also supports communication with digitally mixed intelligent transmitters. FIG.

FIG. 10 is a block diagram showing the inside of the node shown in FIG. 9;

FIG. 11 shows a configuration of a conventional instrumentation interface.

FIG. 12 shows the configuration of another conventional instrumentation interface.

FIG. 13 shows a conventional signal laying method.

FIG. 14 is a configuration diagram of a conventional network system which is fully digitized.

[Description of Signs] 1 Piping 2 Pressure transmitter 3 Process signal cable 4 Interface board 5 Control device 6 Host computer 7 Reference value setting unit 8 Switch circuit 9 Multiplexer unit 10 A / D converter 11 Microcomputer 12 Communication controller 13 Communication cable 14 Resistance Reference Signs List 15 pressure switch 101 detecting end 102 pressure transmitter 103 flow transmitter 104 node 105 decoder 106 transmission cable 107 plant control device 108 transmitter power supply 109 load resistance 110 amplifier 111 multiplexer 112 AD converter 113 CPU bus 114 CPU 115 memory 116 communication controller 117 Communication transceiver 118 Rotary switch 121 Instrument management computer 122 BPF circuit 123 Demodulation circuit 124 Asynchronous communication controller Over La 125 modulation circuit

Claims (5)

[Claims] 1. A sensor from a sensor for detecting a physical state quantity.
An instrumentation interface that generates a plurality of digital signals based on one signal, a reference value setting unit that sets a plurality of reference values, and a signal based on a sensor signal and each of the plurality of reference values. A switch circuit for comparing and outputting a high-level or low-level digital signal; a multiplexer unit for taking in a plurality of reference values and selecting one of them; an AD conversion unit for converting the selected reference value into a digital signal And a microcomputer for taking in the converted digital signal, wherein the plurality of reference values are constantly monitored by software of the microcomputer. 2. The instrumentation interface according to claim 1, wherein a connection to a host computer can be established by adding a communication control unit. 3. A node that can receive signals from a plurality of sensors is installed near a sensor installed at a detection end of a plant, and analog and contact signals from the sensors are digitized at the node and installed near a plant control device. Digital transmission to the decoder in a serial manner, the decoder converts the digital signal into the original analog and contact signals and transmits the signal to the plant controller, so that the interface installed in the plant controller can be used as it is, and An instrumentation network system characterized in that the number of instrumentation cable wires between a detection end and a plant control device can be reduced. 4. The instrumentation network system according to claim 3, wherein the digital transmission comprises a multiplex system of two or more systems for ensuring system reliability. 5. The instrumentation network system according to claim 3, wherein the node is configured to receive an analog / digital mixed signal of a sensor installed at a detection end.
F), wherein a computer is connected to the digital transmission system so that the computer can remotely manage a plurality of sensors installed at the detection end.