Discrete inputs can be sensed across all the usual voltage levels found in industrial facilities. The FBM207/b/c uses one of the several termination assemblies (TAs) to match to the externally powered voltage level. In cases where the inputs are integral to the plant’s control scheme, the FBM207/b/c may be installed as a redundant pair with standard control blocks used to manage the redundancy.
The FBM207/b/c Voltage Monitor/Contact Sense Input Module functions as a 16-channel DC voltage monitor or 16-channel contact sensor. Each channel accepts a 2-wire input from a DC voltage source (FBM207) or pair of contacts or solid state switches (FBM207b/ FBM207c).
Associated (TAs) support discrete input signals at voltages of 60 VDC, 120 VAC/125 VDC, or 240 VAC. For voltages higher than 60 VDC, the TAs have additional signal conditioning hardware that provides voltage attenuation and optical isolation.
The module is available in three distinct types, and each type with its associated TA supports discrete inputs as shown below:
| FBM207 | Provides voltage monitoring at:
• 60 VDC
• 120 VAC/125 VDC
• 240 VAC
Provides switch inputs with:
• External 120 VAC/125 VDC
• External 240 VAC |
| FBM207b | 24 VDC Contact Sense |
| FBM207c | 48 VDC Contact Sense |
Each discrete input is galvanically isolated from other channels and ground. Group isolated when used with external excitation.
The module performs signal conversion required to interface electrical input signals from field sensors to the redundant module Fieldbus. In addition, it executes programs for Discrete Input, Ladder Logic, Pulse Count, and Sequence of Events, with configurable options of Input Filter Time.
The module can be used as a single unit, or as a redundant pair (two FBM207s). When used as a redundant pair, the modules combine to provide redundancy at the Fieldbus Module (FBM) level, with field input signals received from one common termination assembly though a redundant adapter affixed to the baseplate of the FBM. The input current for redundant modules is doubled. A redundant digital input block in the Foxboro DCS Control Software validates each input in conjunction with information to/from the module, and selects the input with the highest quality for processing in the control strategy.
In a redundant configuration, contact sense power from each module is diode OR'd together in the redundant adapter to help assure redundant power.
A redundant contact input function block, CINR, is used for each redundant pair of inputs. The CINR block handles input reads and initialization logic for the redundant channels. On each execution cycle of the CINR block, identical reads are sent to both modules, fully exercising the fieldbus and the logic circuitry of each module.
