JPH06104802A - Communicator for field bus - Google Patents

Abstract

PURPOSE:To attain the communication with a field equipment at all times independently of the presence of interruption of an external power supply by connecting the communicator to a field bus. CONSTITUTION:Even when a host-device 3 including an external power supply 4 is inactive by incorporating a power supply supplying operating power to field equipments 1a-1c into a communicator 2' to allow the communicator 2' to supply power to a network on behalf of the external power supply 4 to set the network to a communication enable state thereby attaining communication between the communicator 2' and the field equipments 1a-1c. Thus, the dependency on the external power supply 4 having been a sole power supply means for the system is remarkably reduced and the reliability of the system is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communicator that communicates with a field device to adjust, monitor, and change the setting of the field device, and particularly to a field instrument and a communicator when the host device is not energized. The present invention relates to a communicator suitable for performing fieldbus communication between devices.

[0002]

2. Description of the Related Art Equipment called field equipment detects physical quantities such as pressure, temperature, and flow rate of various plants, converts the values into electric signals, and transmits them to a higher-level equipment through a transmission path. On the contrary, it is usual to receive the control signal transmitted from the host device and control the valve etc. 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. There is. In addition, generally, one-way communication with an analog signal is performed between the field device and the host device.

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 signal communication on the transmission line, bidirectional digital signal communication is performed, and range setting and self-diagnosis of field devices can be remotely commanded. .

Further, recently, a fieldbus system has been proposed as a system for connecting a plurality of field devices on the same transmission line and performing communication only by bidirectional digital signals, and standardization work for unifying their specifications. Is being promoted.

A typical configuration example of the fieldbus system will be described with reference to FIG. 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. Field device _1a , 1
_b and 1 _c are operated by the electric power supplied from the external power source 4 via the transmission line 5, and are sequentially detected through bidirectional communication with the host device 3 via the transmission line 5 by digital signals. Performs processing such as sending physical quantities and receiving control values. The terminators 6 _a and 6 _b are composed of resistors and capacitors connected in series, and are connected to both ends of the transmission line 5. Here, the communicator 2 is connected between the field devices 1 _a , 1 _b and 1 _c and the host device 3 and the external power source 4, and bidirectional communication is performed with the field devices 1 _a , 1 _b and 1 _c by digital signals. It is carried out.

[0007]

The main purpose of the communicator is to communicate with a field device and perform adjustment, monitoring, setting change, etc. of the field device. That is, it has no direct relationship with the operation of the higher-level device. However, conventionally, the field device does not operate unless the upper side is energized. Therefore, when performing the upper processing of the field device, it is necessary to energize the upper side irrelevantly.

In the prior art of the analog transmission system described above, the fundamental problem is that the power source is included in the form of a part of the transmission loop, so that the host device is not energized due to a power failure or the like. Has a problem that all communication functions of the system are stopped, and the field device and the communicator cannot communicate even if there is no abnormality in the transmission line or the field device itself.

Even in the conventional fieldbus system, the external power supply 4 is still the only unit that supplies power to the network, and the communication function is stopped due to a power failure or the external power supply 4 being down. Was still unresolved.

The present invention provides a communicator which solves the above-mentioned problems by incorporating a power source having a power sufficient for the network to function in the communicator and supplying power to the network from the built-in power source. The purpose is to provide.

[0011]

As a signal transmission mode of fieldbus communication, in addition to performing power supply and signal transmission on the same line, another feature is
It may be a multi-drop connection. That is, the host device including the external power supply may be basically arranged at any position on the network, and all the devices connected to the network are connected in parallel to the transmission path.

In order to achieve the above object, the present invention provides
By incorporating a power supply that supplies operating power to the field device in the communicator, even if the host device including the external power supply is not energized, the communicator substitutes power supply to the network, It makes the network available for communication and enables communication between the communicator and field devices.

[0013]

A feature of the communicator according to the present invention is that power is supplied to the network by the power source built into the communicator. Compared with the conventional communicator, the communicator has a drawback that the weight of the main body is increased by incorporating the network power supply. Further, since the capacity of the built-in power source is limited, maintenance such as replacement of the power source or charging is required after continuous use for a long period of time. However, the greatest advantage of the communicator according to the present invention is that in an emergency such as when power supply to a higher-level device is stopped due to a power failure or the like,
It is to maximize its ability as an auxiliary means for system maintenance and management. When the communicator according to the present invention is applied to a fieldbus system, fieldbus communication can be performed between the communicator and the field device even when the system is not energized. As a result, the dependence on the external power source, which has been the only power supply means in the system so far, can be greatly reduced, and the reliability of the system can be improved.

[0014]

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

FIG. 1 shows a fieldbus system using the present invention.
It is an example of a device configuration of a system.

In the figure, the field device 1 _a ,
1 _b, 1 _c is to perform two-way communication in digital signals, and transmits the pressure of the process in various plants, temperature, its value by detecting physical quantities such as mass,
Alternatively, it receives a control amount of a valve or the like. The field devices 1 _a , 1 _b , 1 _c are operated by the electric power supplied from the external power source 4 or the communicator 2 ′ via the transmission line 5, and can be connected to any place on the transmission line 5. In this embodiment, the field devices 1 _a , 1
_{An example in which b} and 1 _c are connected to a junction box (relay box) on the field side is shown, but this does not matter even if it is from the other, for example, the middle of the transmission line 5.

The host device 3 is a field device 1 _a ,
1 _b , 1 _c , communicator 2 ′ and other fieldbus compatible devices communicate digital signals via the transmission path 5, and receive various physical quantities (pressure, temperature, flow rate, etc.) detected by the field devices, Also, as plant control information, control signals are transmitted to field devices such as valves.

The communicator 2 'can be connected anywhere on the transmission line 5, by operating the display and keyboard on the main body, the field device 1 _a, 1 _b, 1
Processing such as monitoring and adjustment of the output value of _c is performed by communicating via the transmission line 5.

When the external power source 4 stops supplying power, the power source switching circuit in the communicator 2'detects the abnormality and supplies power from the power source built into the communicator 2 ', so that the communicator 2'is provided. And field devices 1 _a , 1 _b , and 1 _c can perform fieldbus communication.

The terminators 6 _a and 6 _b 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 connected on the transmission path 5 so that the communication signal depends on the connection location of the field device and the number of connected devices. The effect on Incidentally, the specifications of terminator 6 _a, 6 _b are those determined by the standard.

As a specific example for realizing the communicator 2 ', an embodiment of a power supply switching circuit will be described with reference to FIG. This circuit is located at the communicator input,
Connected to the bus. A high resistance R1 is provided between the “+” line 10 and the “−” line 11 as an analog switch SW.
1 is connected in series with the high resistance R2. The connection point of the high resistances R1 and R2 is connected to the "-" terminal of the operational amplifier OP1. On the other hand, the power supply 12 is connected to the “+” line 10 and the “−” line via the analog switch SW2.
It is connected to the line 11. The power supply terminals of the resistor R3 and the diode D1 and the operational amplifier OP1 are connected in parallel with the power supply 12, respectively, and the connection point of the resistor R3 and the diode D1 is connected to the "+" terminal of the operational amplifier OP1.

The output terminal of the operational amplifier OP1 is connected to the "-" line 11 via the light emitting diode D2 and the resistor R4, and is also connected to the control terminals of the analog switches SW1 and SW2.

Next, the operation of the present invention will be described. The analog switch SW1 has a high resistance R2 in its initial state.
The bus voltage between the "+" line 10 and the "-" line 11 is divided by the high resistances R1 and R2 and input to the "-" terminal of the operational amplifier OP1. . On the other hand, the power supply voltage of the power supply 12 divided by the resistor R3 and the diode D1 is input to the “+” terminal of the operational amplifier OP1 as the reference voltage V _REF . The operational amplifier OP1 compares and outputs two input values.

Here, by the operational amplifier OP1, the bus voltage value at the communicator connection point is changed to the reference voltage V _REF.
If it is determined that the voltage is larger than the voltage and is sufficient for the operation of the field device, the operational amplifier OP1
Outputs "L". At this time, analog switch SW
2 remains open and the communicator will operate with the power supply from the bus to which it is connected. The analog switch SW1 also maintains the initial state while being connected to the high resistance R2 side.

On the other hand, when the bus voltage value is smaller than the reference voltage V _REF , it is determined that the external power supply is cut off at the connection point of the communicator, and the operational amplifier OP1 outputs "H". At this time, the analog switch SW2 is short-circuited, and the operating power of the field device is supplied from the power supply 12. Further, the analog switch SW1 is short-circuited to the transmission line 1 ', so that the operational amplifier OP1 continues to output "H".

According to this embodiment, by switching the power source according to the magnitude of the bus voltage value at the connection point of the communicator, it is possible to always communicate with the field device regardless of whether or not the external power source is cut off. The effect is that you can do it.

[0027]

As is apparent from the above description, by connecting the communicator according to the present invention on the field bus, it is possible to always communicate with the field device regardless of whether or not the external power supply is cut off. There is an effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration example of a fieldbus system using the present invention.

FIG. 2 is a diagram showing an embodiment of a power supply switching circuit.

FIG. 3 is a diagram showing a typical configuration example of a conventional fieldbus system.

[Explanation of symbols]

_{1,1 a, 1 b, 1 c} ... field devices, 2,2 '... communicator, 3 ... host device, 4 ... external power supply, 5 ... transmission line, 6 _a, 6 _b ... terminator.

Claims (2)

[Claims] 1. A field bus for connecting a communicator to an arbitrary position on the transmission line by supplying electric power to the field device and using a pair of transmission lines to mutually communicate between the host device, the field device and the communicator. In the system, a communicator for a field bus, comprising means for supplying electric power from a power source built in the communicator to the field device via the transmission line. 2. The communicator according to claim 1, when the line voltage of the transmission line is equal to or lower than the operating voltage of the field device when the communicator is connected, the power source built in the communicator through the transmission line, A communicator for a field bus, which is provided with means for supplying electric power to a field device.