Fieldbus control system wiring and installation - Solutions - Huaqiang

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The wiring and installation of the fieldbus control system mainly starts from the following aspects:
(1) It is rare to replace the original analog instrument control system with the fieldbus fieldbus control system, and replace the original analog 4~20mA instrument control system with the fieldbus control system. The wiring and replacement method is as follows: the analog card in the control room is replaced by the H1 card of the field bus;
• Field-installed analog meters are replaced with suitable fieldbus meters;
Use the original wiring;
Add 24V DC power supply and power regulator to meet the required line impedance requirements;
Add a terminator;
? Complete the configuration of the new system;
When implementing the replacement, attention should be paid to the constraint of line length, the matching of line impedance, the distribution of line voltage drop, etc. When the number of analog instruments is large, the original instruments should be divided into two or more groups, and multiple field bus segments should be used. It can be directly connected to the different interfaces of the H1 card by using a repeater or directly. In addition, shielding and grounding of the line should also be checked.
(2) Wiring and installation when the network segment is expanded. When a new fieldbus device needs to be added to the original fieldbus segment, the repeater can be determined according to the length of the added line. It can be added directly when the total length of the added line is less than the allowed length, otherwise a repeater can be added to extend the length of the segment. It should be noted that the added repeater acts as a fieldbus device for the fieldbus segment. In addition, two terminators must be installed on the added network segment.
To meet the conditions for the terminal to be installed at the end of the network segment, when the extended network segment is used at the end of the original network segment, the terminal device should be moved to the end of the extended network segment. If the control network segment is taken from the middle branch of the original network segment, in addition to adapting to the original junction box or installing a junction box or hub at the branch point, if the extended branch network segment has a long line length, it should be treated as a trunk. There is a line as a branch; if the line length is short, it can be treated as a branch, and the implementation should meet the constraint of the length of the branch line and the number of fieldbus devices attached to the branch. Similarly, when acting as a backbone, the terminator should be moved to the end of the line.
The expansion of the network segment will affect the voltage drop of the line. Therefore, it should be recalculated whether the power supply voltage of each field bus meets the requirements of ≥9VDC.
Sometimes, only one or several fieldbus devices need to be added. In order not to affect the work of the entire network segment, it is better to attach the newly added equipment from the nearest junction box, and check the effect of power supply and signal transmission.
For the case where there are multiple fieldbus devices on the branch line and the length of the branch line is long, the trunk line foldback criterion can be used for wiring. The mainline foldback criterion can effectively reduce the allowable cable length when there are many fieldbus devices attached to the branch line. When the main line is used to fold back the wiring, the branch line is replaced by the return of the main line, thereby eliminating the branch line and increasing the number of attached devices.
After the network segment is expanded or a new device is added, the system configuration needs to be re-executed.
(3) Wiring and installation of the fieldbus network segment of the new project. The vast majority of the bus control system projects are new projects. Therefore, the wiring should be carried out in strict accordance with the relevant provisions of the fieldbus control system wiring. The precautions for wiring are as follows:
The length of the lead wire should be 10~13mm.
The shielded wire should not be grounded at multiple points. It should be concentrated and then grounded. Typically, the shields of the branch cables are brought together and then connected to the trunk cable shield and grounded at one point (usually on the power conditioner side). For C-type cables that are not shielded, they should generally be laid with metal pipes, but it is easy to cause multi-point grounding.
The junction box should be a standard junction box with 4 ports to 12 ports.
• The fieldbus cable does not have a ground wire, but an additional ground wire can be used to connect the ground terminal of the fieldbus device to the ground point in place. The system grounding system should use the TN-S system.
• The fieldbus shielded cable must not be connected to the ground of the fieldbus device or used as a power cord.
In addition to using the DC power supply unit as the bus power supply, a power regulator is also connected to isolate the field signal and the DC power supply to prevent the power supply from being short-circuited.
In addition to the remote junction box that can be connected to the terminator, usually, the other terminator can be connected to the terminal by using a terminal that is built into the power regulator.
(4) Installation of the fieldbus device attached to the fieldbus segment. The installation of the fieldbus devices attached to the fieldbus segment includes the connection to the process pipe and the connection to the fieldbus.
Connection to the process piping: The connection of the fieldbus transmitter, test components and process piping is the same as for conventional transmitters and test components. The detection point should be close to the part to be tested. For example, to check the outlet temperature of the reactor, the detection point should be installed at the outlet of the reactor near the reactor. The installation specification should follow the installation specifications of the conventional instrument.
? Connection to the fieldbus: The connection between the field device and the field bus is different in the way of plug-in and wiring. For plug-in connections, simply connect the cable from the junction box or T-connector to the plug and then plug it into the socket of the field device. The junction box is also plugged in. When using the wiring connection method, pay attention to the polarity of the signal line. Usually, the same color code is used to distinguish different polarities. In order to quickly access and remove field devices, plug-in connectors are often used for field device connections.
(5) Installation of power supply and power conditioner. The power supply is installed according to the design requirements. Typically, the power regulator is installed as part of the system interface card or integrated system on a standard rail. The wiring should be made according to the product manual used. It should be noted that, usually, the built-in terminator of the power conditioner is used as a terminator of the network segment. Therefore, during installation, it should be checked whether the selection switch is cut to the position where the built-in terminator is selected as a terminator of the network segment. For intrinsically safe applications, it is sometimes necessary to use a safety barrier with a repeater or a multi-channel isolator. It should be noted that bus-powered power should be provided for each segment.
(6) Installation of fieldbus cable. The main contents of the cable installation project are as follows.
• Install the backbone cable (the longest cable for the fieldbus network).
• Install the terminator at both ends of the trunk cable. Usually, the terminator is not mounted on the device but mounted on the junction box. The terminator should be clearly marked; if the terminator is installed in a device, it may be inadvertently taken away with the field device at a certain repair service, thereby affecting communication throughout the network.
• Install each branch line to the main line.
• Complete the test and grounding test of parameters such as cable resistance. #p#分页头#e#
Connect the power supply, power regulator, and H1 interface card to the backbone cable.
• Complete the FOUNDATION fieldbus network/segment test procedure.
After testing the network wiring system, the equipment is connected and the control loop is put into operation.
Pay attention to the following when wiring:
• When multiple mains cables are introduced into the field junction box, the shielded wires of different networks cannot be connected together, which creates a ground loop and introduces noise into the system.
? Prevent multi-point grounding of shielded wires. The shielded wire should be grounded at one point. Usually, it is grounded at the end of the cable on the control room side (power regulator side). If an intrinsically safe grid is used, the cable shield should be grounded on the safety barrier side.
• The shielded cable of the device cable should not be connected to the ground or housing of the device.
• Use a wire stripper to remove the insulation from the cable and leave no marks on the wire.
• Using the wiring ferrule not only increases the wire contact area, but also prevents the wire from falling off.
• Cut-off conductors such as wire ends can cause short circuit in the equipment circuit. Therefore, protective measures should be taken during wiring to prevent debris such as wire ends from entering the inside of the device or the ventilation vents of the device.
• The terminal should not be installed on the device and should be installed in the terminal box of the terminal.
• Surge protectors should be installed on equipment installed in locations where lightning strikes may occur.
• Wiring should be based on the color code on the cable, blue or white (negative), brown or black (positive) and silver (shielded).