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.

When long-distance or cross regional connections are required, FCM2F2, FCM2F4, and FCM2F10 fiber optic modules can be used to extend the bus between baseboards, corresponding to distances of 2 km, 4 km, and 10 km. Redundant configuration with one pair of FCM2F for each base plate; Non redundant configuration uses one FCM2F per motherboard, connected to either A or B. A maximum of two pairs of FCM2F are allowed to be connected in series; When two sets of FCM2F10 are connected in series, the total distance of the bus can reach 20 km. The fiber extension section should also pay attention to the terminal: the tail of the chain should still be installed with RH916RB according to the topology or use a splitter/terminator, and the end matching cannot be ignored just because it passes through the fiber.

When adding Compact or standard 200 Series baseboards during operation, the system must have redundant A/B buses and use A/B Module Fieldbus splitters/terminators to separate A/B, enabling expansion of cable and uninterrupted bus communication between redundant baseboards. Single bus system is not suitable for live expansion, otherwise it may cause communication interruption. Before expanding, it should be confirmed that the new base plate serves as the chain head or tail, the DIP switch is in the same position as the chain, and the terminal position is correct before connecting to the FBM.

Power supply, environment, and mechanical installation

The redundant input of the motherboard is 24 V DC+5%/-10%, and the main and backup power supplies are connected to Primary and Secondary respectively. If only one power source is connected on site, it should be confirmed that the other source is not misconnected or short circuited; If two power sources come from different power distributions, it should be confirmed that the common ground or isolation meets the system requirements. The length of the power cable is 0.4 to 2.1 meters. If it is too long, it will increase the voltage drop, especially when there are redundant FBMs and large on-site I/O loads. The base plate itself is passive, but the power consumption of FBM and on-site terminal components still needs to be calculated according to the cabinet power budget.

In terms of environment, the operating temperature of the base plate is -20 to+70 ℃, the storage temperature is -40 to+70 ℃, and the relative humidity is 5% to 95% non condensing; Operating at an altitude of -300 to+3000 meters, with a storage capacity of up to+12000 meters. Both non cabinet and cabinet installations comply with ISA S71.04 G3 harsh pollution levels, and there are also IEC 664-1 pollution level 2 requirements inside the cabinet. If the site is located in a coastal, paper-making, or chemical corrosive environment, appropriate enclosures should be prioritized, and terminal corrosion and shielding grounding should be checked regularly. The bottom plate material is PC/ABS, UL94 V0, black; The maximum weight of the 16 slot bottom plate is about 1.8 kg, and the size is about 443.6 × 214.4 × 39.8 mm. The DIN rail should be non isolated, mechanically supported, and fixed with fasteners; The P0930AS kit for rack installation should not rely solely on rail buckles to withstand cable tension.

Obstacle Tree: From Phenomenon to Root Cause

Phenomenon 1: Unstable communication in the entire or partial FBM chain. First, check if the last bottom plate E port is equipped with RH916RB; If using RH926KW splitter, confirm that the terminal switch and A/B splitter settings are correct. Further check if the A/B bus is shielded from twisted pair, if it runs parallel to the AC line, and if the connectors are tightened. Finally, verify whether the total length of the bus exceeds 60 meters, and whether the fiber segments exceed the corresponding distance and series connection limit of FCM2F.

Phenomenon 2: Address confusion after adding a new base plate. Check if the DIP switch ON/OFF is consistent with the chain head 0/1 or chain tail 2/3; Check if the Compact base plate is sandwiched in the middle of the standard base plate; Check if slots 1 to 8 correspond to the sixth character of letterbug. During operation, redundant A/B buses and splitters/terminators must be used for expansion, otherwise the machine should be shut down for expansion.

Phenomenon 3: Redundant FBMs do not switch. Check if redundant modules are installed in adjacent odd even slots and if redundant adapters are installed; Check if both the primary and backup power sources are functioning properly; Check if both A/B buses are connected. Redundant adapters are not optional decorative components, and their absence can result in the inability to recognize redundant pairs properly.

Phenomenon 4: The I/O remains unchanged after replacing the FBM. Confirm that the on-site terminal cable has not been removed and the F connector is in place; Confirm that the FBM slot position is consistent with the configuration; Confirm that the Compact FBM has not been inserted into the standard motherboard or vice versa. Compact baseboards only accept Compact FBM, while standard baseboards only accept standard FBM.

Phenomenon 5: Occasional packet loss in communication. Check if there are too many or too few terminals, if the bus cable is damaged, if the shielding layer is single ended/multi-point grounded incorrectly, and if the power cable is parallel to the bus. RH916RB should only be used for the CP end or the last bottom plate, and the middle bottom plate should not be equipped with terminals; When A/B separation is required, use RH926KW instead of forcibly twisting A/B together.

Installation and maintenance recommendations

Before installation, draw a chain: CP - first baseboard - middle baseboard - last baseboard, marking the DIP switches, slots, redundant pairs, terminal positions, and fiber segments of each baseboard. When installing, first fix the DIN rail or rack, then install the base plate, and finally insert the FBM and on-site terminals; FBM insertion is guided by connectors to avoid pin bending. During maintenance, first record the DIP switch and letterbug, and then unplug the FBM; Replacing the FBM does not require dismantling the on-site terminals, but the new FBM model, redundant/non redundant attributes, and slot matching should be confirmed. Regularly check if RH916RB is loose, if water enters the E port, and if the shielding layer is corroded. Expansion during operation must be carried out after confirming the redundant A/B buses, branch/terminal units, and power supply margins, and verifying the address and terminals in the shutdown window before connecting to production.