Foxboro DCS Compact200 series RH916RB (16 slot horizontal bottom plate)

Foxboro DCS Compact200 series RH916RB (16 slot horizontal bottom plate)

At the Compact 200 Series site of Foxboro DCS, RH916RB is often mistaken for just a "small plug", when in fact it is a terminal matching part for the 2 Mbps Module Fieldbus backplane chain; The 16 slot horizontal bottom plate serves as the load-bearing platform for Compact 200 Series FBM and on-site I/O. Confusion between the two often leads to deviation in the direction of troubleshooting: when communication is unstable, only FBM is replaced, and it is eventually discovered that the end is not equipped with RH916RB; When expanding, only the slots were counted, ignoring the need for the bottom board to serve as the chain head or tail, and the corresponding relationship between DIP switches and letterbugs. On site maintenance should view the "chassis terminal bus power address" as a whole, rather than replacing cards in isolation.

First, distinguish between the base plate, terminal, and adapter

The Compact 200 Series 16 slot horizontal base plate can accommodate up to 16 Compact 200 Series FBMs, supporting both single and redundant modules. The base plate only supports horizontal installation and can be installed inside or outside the enclosure or on DIN rails; 19 inch rack installation requires P0930AS kit, providing an installation depth of approximately 25.4 mm. The base plate adopts a passive backplane, and the main and backup 24V DC power supplies are connected to the Primary and Secondary connectors respectively. The on-site I/O is connected to the terminal assembly through the F connector. Each pair of redundant FBMs requires a redundant adapter, non redundant FBMs can be placed in any empty space, and redundant FBMs must be placed in adjacent parity pairing positions. FBM can be replaced without dismantling the on-site terminals, power supply, and communication cables, which is an important convenience for on-site maintenance, provided that the slot, adapter, and address are correct.

RH916RB is a Fieldbus Baseplate Terminator used to terminate the CP end HDLC bus or the last baseplate of the daisy chain, suitable for situations where A/B split cables are not required. If it is necessary to divide the A/B Module Fieldbus into different cables, an RH926KW terminal/splitter should be used. The D connector on the right side of the motherboard comes from the control processor or the previous motherboard, and the E connector goes to the next motherboard; If the current is the last bottom plate, the E port should be connected to RH916RB. Common errors on site are leaving the E port of the last bottom plate empty or installing terminals incorrectly on the middle bottom plate, resulting in bus reflection and intermittent communication failures. The more terminals there are, the better, and not every motherboard is equipped with them.

Letterbug and DIP switch: Address not plugged into module

The Compact 200 Series FBM is recognized by the system software through a 6-character letterbug. The FBM on the Compact motherboard is not physically installed with letterbug, but is derived from the motherboard number and slot position. The DIP switch for the baseboard ID is used to set the baseboard number: ON corresponds to BP 0&1, OFF corresponds to BP 2&3. The first base plate number is used for the first eight slots (0 for the chain head and 2 for the chain tail), and the second base plate number is used for the second eight slots (1 for the chain head and 3 for the chain tail); The sixth character comes from the physical positions 1 to 8 of the module on the motherboard. Therefore, the first four characters of each Compact FBM in the same backplane chain are the same, the fifth character is determined by the backplane number, and the sixth character is determined by the slot position.

When troubleshooting on site, if the system displays "module not online" but the FBM light is normal, the DIP switch and the position and slot of the base plate in the chain should be checked first, rather than repeatedly changing the FBM. Especially when mixing Compact and standard 200 Series baseboards in the same chain, the Compact baseboard must be used as the first (0 and 1) or last (2 and 3) block and cannot be sandwiched in the middle. The Compact base plate only provides Compact FBM slots, while the standard base plate only provides standard FBM slots. When mixed, the slot number and letterbug derivation may change, and must be rechecked according to the chain position.

Redundant bus and terminal matching

The Compact baseboards are interconnected through a 2 Mbps HDLC redundant serial bus, and shielded twisted pair cables are used for both A/B channels to reduce noise interference. All connectors have location and function identification: A is the FBM connector, B/C is the primary and backup power supply, D is the Module Fieldbus from CP or the front backplane, E is to go to the next backplane or terminal, and F is the on-site I/O. The single section of the bus cable is allowed to be 0.125 m to 60 m, and the total allowable length of the entire bus is 60 m; the power cable is allowed to be 0.4 m to 2.1 m. On site wiring should separate the A/B buses, and the shielding layer should be treated according to the grounding specifications inside the cabinet to avoid long-distance parallel connection with the AC power line.