JPH05260568A - Field bus system - Google Patents

Abstract

PURPOSE:To easily detect a communication abnormal part and to reduce power consumption by stopping a reception operation while a transmission operation is being performed in a field bus system. CONSTITUTION:Field equipment 1a, 1b, and 1c are operated by a power supplied from an external power source 4 via a transmission line 5, and the communication of a duplex 1 digital signal with high-order equipment 3 is performed. Each field equipment is provided with an analog switch to immediately return a signal made into standard outputted from an encoder circuit to a decoder circuit, and performs a loop-back test for only the field equipment and a loop- back test including the transmission line 5, and identifies abnormality whether it is the one of field equipment itself or the one including the transmission line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fieldbus system for transmitting a signal on a two-wire type transmitter, and more particularly to a transmission line including field devices which detects an abnormality on the fieldbus by a loopback test. The present invention relates to a fieldbus system suitable for increasing the reliability of the entire fieldbus system.

Further, the present invention relates to a field bus system suitable for keeping the power consumption of the entire system low.

[0003]

2. Description of the Related Art A so-called field device detects a physical quantity such as pressure, temperature, and flow rate of various plants, converts the value into an electric signal, and transmits the electric signal to a host device through a transmission line. On the other hand, on the contrary, it is usual to receive a control signal transmitted from a host device and control valves and the like of the plant.

The transmission of the electric signal is standardized when the transmission signal is an analog signal, and an analog current signal of 4 to 20 mA is transmitted between the field device and the host device. ing. Further, generally, the field device and the host device are unidirectionally unidirectionally transmitted with an analog signal, and the host device and the field device have a one-to-one correspondence.

However, in recent years, field devices with a built-in microprocessor have been developed and put into practical use due to improvements in semiconductor integrated circuit technology. According to this, in addition to unidirectional analog communication on the transmission path, bidirectional digital signal communication is performed to set the range of field devices,
It has become possible to remotely issue a self-diagnosis or the like, and known techniques include JP-A-58-48198 and JP-A-59.
−201535, etc. Also in this case, there is a one-to-one correspondence between the host device and the field device. Also, recently, a fieldbus system has been proposed as a system in which a plurality of field devices are connected on the same transmission line and communicates only with bidirectional digital signals, and standardization work for unifying their specifications has been promoted. There is.

A typical configuration example of the fieldbus system will be described with reference to FIG. In the figure, a plurality of field devices and a host device describe a transmission path. The figure shows an example of a device configuration in which a plurality of field devices and host devices are connected in a tree form via a transmission path. The field devices 1a, 1b, 1c are connected to the external power source 4 via the transmission line 5.
It operates by the electric power supplied from, through the transmission line 5,
Bidirectional communication is performed with the host device 3 by digital signals in order, and processing such as transmission of detected physical quantities and reception of control values is performed. The upper communication device 2 includes field devices 1a, 1b,
1c is connected between the host device 3 and the external power source 4, and bidirectional communication is performed with the field devices 1a, 1b, 1c and the like by digital signals. In addition, the terminators 6a, 6
b is composed of a resistor and a capacitor connected in series, and is connected to both ends of the transmission line 5.

This terminator is set to a value much smaller than the input impedance in the communication frequency band of the field device connected on the transmission path 5, so that the terminator of the field device and the number of connected devices can be used. The influence on communication signals is kept low.

Further, there are a voltage driver and a current driver as a method of a transmission circuit (hereinafter referred to as a driver) for performing communication, and the transmission signal thereof is defined by a transmission voltage value in a state in which a terminator is connected. ing.

[0009]

In the above-mentioned conventional technique, the host device and the field device correspond one-to-one, and it was relatively easy to determine where the cause of the abnormality was.

However, in the field bus, the number of host devices and field devices connected to the transmission line is plural.
When an abnormality occurs, it is difficult to identify the cause. In addition to communication, the field bus externally supplies operating power to each field device via a transmission line. The field device itself is often used in an explosive hazardous area where the installation environment is severe. Therefore, it is necessary to establish a power supply method that takes the explosion-proof structure into consideration, and it is an issue to reduce power consumption in terms of reliability. The present invention is
It is an object of the present invention to provide a fieldbus system capable of determining whether the field device itself has an abnormality or an external abnormality by simply improving the structure of the field device.

Another object of the present invention is to provide a fieldbus system which can reduce the power consumption of each field device by the above-mentioned structural improvement.

[0012]

In order to achieve the above object, the present invention immediately returns a standardized signal output from an encoder circuit in a field device to a decoder circuit, and loops the field device itself. An analog switch that can be switched between when performing a back test and when performing a loop back test of the entire system including the transmission line is provided, and self-diagnosis is performed periodically to instantly detect an abnormality in the field device itself. ..

When an abnormality occurs, the same operation is immediately performed to instantly detect the abnormality of the field device itself.

Further, by using the above-mentioned analog switch that disconnects the decoder circuit when the encoder circuit is performing the transmission operation, the transmission operation and the reception operation do not occur at the same time, and the power consumption during communication is reduced. Is the minimum necessary increase.

[0015]

In the fieldbus system according to the present invention, an analog switch is provided for immediately returning the standardized signal output from the encoder circuit in the field device to the decoder circuit, thereby performing the loop bat test of the field device itself. Loop back test including transmission line can be performed.

As a result, these two cases can be compared and it is possible to determine whether the field device itself is abnormal or an external abnormality.

Further, if the receiving circuit is cut off by the analog switch at the time of signal transmission, only the transmitting operation is performed, so that the power consumption is increased only by the power consumption of the transmitting circuit.

As a result, the transmitting circuit and the receiving circuit do not operate at the same time, so that it is possible to reduce the increase in power consumption due to communication.

[0019]

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

FIG. 2 shows an example of the device configuration of the fieldbus system used in the present invention.

In the figure, field devices 1a, 1
b and 1c are used for two-way communication with digital signals, and process pressure, temperature,
It detects a physical quantity such as a flow rate and transmits the value, or receives a controlled quantity such as a valve. The field devices 1a, 1b, 1c are operated by the electric power supplied from the external power source 4 via the transmitter 5, and can be connected to any place of the transmission line 5. In the present embodiment, an example is shown in which the field devices 1a, 1b, 1c are connected to the field side junction box (relay box). However, this is a problem even if it is from the middle of another transmission line 5, for example. Absent.

The host device 3 includes field devices 1a, 1b,
Various physical quantities (pressure, temperature, flow rate, etc.) detected by the field device by performing digital signal communication with the field bus compatible device such as 1c and the host device 2 via the transmitter 5.
In addition, the control signal is transmitted to a field device such as a valve as plant information.

The upper communication device 2 can be connected to any place on the transmission line 5, and the field device 1 can be operated by operating a display or a keyboard in the upper communication device 2.
Processes such as monitoring and adjustment of the output values of a, 1b, and 1c
Communication is performed via the transmission line 5 and the communication is executed.

The terminators 6a and 6b are composed of resistors and capacitors connected in series, and are connected to both ends of the transmission line 5. This terminator has a value that is considerably smaller than the input impedance in the communication frequency band of the field device or the like connected on the transmission path 5, so that the communication signal depending on the connection location of the field device and the conditions such as the number of connected devices. The effect on The specifications of the terminators 6a and 6b are determined by the standard.

Next, referring to FIG. 1, as a typical example thereof,
The operation of the field device will be described in detail. Figure 1
In the above, the DC-DC converter 107 creates a voltage V _DD for operating the field device 1 itself from the voltage applied from the external power source through the transmission line, and the constant current circuit 1
The control unit 10 controls the current consumption of the entire field device 1 to be constant. Each output of the composite sensor 108 is input to the multiplexer 109. The multiplexer 109 includes an I / O interface 106.
The input switching signal from is input, and the signal is input to the A / D converter 105. Further, there is a microprocessor 101, and this microprocessor 1
Reference numeral 01 is a correction calculation using the outputs sequentially sent from the A / D converter 105 and various coefficients stored in the ROM 103 and the RAM 102 to obtain a true value,
The value is stored in 02. FIG. 3 is a flowchart showing the operation of this system, and the detailed contents will be described below.

When the field device communicates, the following operation is performed. In the transmission operation, first, in response to a command from the microprocessor 101, the data stored in the RAM 102 is output from the transmission / reception circuit 104 as a serial digital signal sequence. This signal becomes a signal encoded by the encoder circuit 113. Normally, in the communication state, the analog switch 115 is connected to B, and the driver 11
The signal coded 1 is input and output from the driver 111 to the transmitter as a communication signal. Here, the coding is, for example, “1” or “0” of a digital signal.
There are two types of frequency coding methods corresponding to the above, and a method of coding the baseband signal into Manchester code. The driver system includes a voltage signal output system and a current signal system. In the present embodiment, a current signal system is available, and the output current of the driver 111 is an instruction from the I / O interface 106. Can be switched by.

In the reception operation, the communication signal from the transmission line is taken out by the decoder circuit 114 into the serial digital signal string, and the digital signal "1",
It is output as data consisting of "0". Transmitter / receiver circuit 1
The signal input to 04 is taken out as received data by the microprocessor 101.

Here, the microprocessor 101 is
Analog switch 11 via O interface 106
A loopback test is performed in a state in which 5 is connected to B, that is, in a state including a transmission path, and transmission / reception digital signals are stored in the RAM. Next, microprocessor 10
Reference numeral 1 connects the analog switch 115 to A via the I / O interface, performs a loopback test of the field device itself, and stores a digital signal for transmission / reception in the RAM. These two cases are handled by the microprocessor 10
According to 1, comparison and processing are performed to determine whether the field device itself has an abnormality or the abnormality is external.

If there is no abnormality, the microprocessor 101 passes through the I / O interface 106,
The analog switch 115 is returned to B. If there is an abnormality, the abnormality is transmitted as a communication signal to other field devices and higher-level devices, and the microprocessor 101 returns the analog switch 115 to B via the I / O interface 106.

Further, the signal level detection circuit 112 receives the same signal as the decoder circuit 114 receives the communication signal on the transmission line, and if the amplitude of the signal is larger than a specified value, it is determined that there is an abnormality, and the abnormal signal is detected. Is output to the I / O interface 106. Microprocessor 101 is I
The abnormality signal is received via the I / O interface 106, the above-mentioned two loopback tests are performed, the location of the abnormality is determined, and the abnormality is transmitted as a communication signal to other field devices and host devices. Then
The analog switch 115 is connected to B.

The cases where the abnormal signal is output include i) the case where excessive noise enters the transmission path, and ii)
There are cases where the terminators connected to both ends of the transmitter come off, and iii) the field device itself is abnormal. i)
Most of them are transient, and if a loopback test is performed at periodic intervals, only essential abnormalities such as ii) and iii) can be detected as abnormalities.

During the transmission operation, the microprocessor 101 connects the analog switch 115 to C through the I / O interface 106, and when the transmission operation is not in progress, the analog switch 115 is set to B.

According to this embodiment, it is possible to detect an abnormality on the fieldbus and identify where the cause of the abnormality is.
The reliability of the entire transmission line including each field device can be improved. Further, since the receiving operation is not performed at the same time during the transmitting operation, there is an effect that the power consumption of the entire fieldbus system can be reduced.

[0034]

As is apparent from the above description, according to the present invention, the standardized signal output from the encoder circuit in the field device is converted into an analog signal for immediately returning the signal to the decoder circuit. By providing a switch and adding a loopback test function, it is possible to immediately determine whether the abnormality of the transmission line is the field device itself or an external abnormality with a normal communication signal.
Since the abnormality information is transmitted as a communication signal, there is an effect that the abnormality countermeasure can be easily performed before the abnormality occurs in the system.

Further, the fieldbus system according to the present invention has an effect that the power consumption of each field device can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a field device according to the present invention.

FIG. 2 is a device configuration diagram showing an embodiment of a fieldbus system according to the present invention.

FIG. 3 is a flowchart showing an embodiment of the fieldbus system according to the present invention.

[Explanation of symbols]

1, 1a, 1b, 1c ... Field device, 2 ... Host communication device, 3 ... Host device, 4 ... External power supply, 5 ... Transmission path, 6a,
6b, 7 ... Terminator.

Claims (3)

[Claims] 1. In a system for communicating between a field device and a host device connected on a field bus transmission line, an analog signal detected by a field device itself from a sensor is digitized by an A / D converter and digitized. And a decoder circuit for converting the standardized reception signal into a digital signal for the field device itself to receive, and a microprocessor as the signal processing means. In a field device with a built-in
An analog that can be switched between when the standardized signal output from the encoder circuit is immediately returned to the decoder circuit and the loopback test of the field device itself is performed, and when the loopback test of the entire system including the transmission path is performed. A field bus system in which each field device is provided with a switch and a control means for switching the analog switch under the control of the microprocessor. 2. The fieldbus system according to claim 1, wherein when an abnormality occurs on a transmission path including the field device, a loopback test of the field device itself,
Loopback test of the entire system including the transmission line
2. A fieldbus system, wherein the analog switch according to claim 1 is switched and compared according to the control of a microprocessor, and an abnormal signal is transmitted to other field devices and host devices. 3. The fieldbus system according to claim 1, wherein each field device is provided with means for stopping the reception operation by using the analog switch according to claim 1 during a transmission operation. Fieldbus system to be.