FOXBORO FBM214b HART® Communication Input Module

FOXBORO FBM214b HART® Communication Input Module

DESCRIPTION

The FBM214b HART Communication Input Module contains eight 4 to 20 mA individually isolated analog input channels. It supports any mix of standard 4-20 mA devices and HART devices. The FBM214b can serve as a HARTcommunications field device host, enabling Foxboro™ DCS to request and receive two digital messages per second from the field device. The message pass-through capability can be used to support HART universal, common practice, and device-specific commands, but it cannot support the burst communication mode. These commands are implemented using the Foxboro DCS Field Device Expert for HART. For details, see Field Device Expert for HART Devices Control and I/O (PSS 41S-10FDMHRT).The FBM214b provides individually isolated power supplies to power each of the eight channels. Optionally, the input channels can be powered by an external power supply. However, when a common external power supply is used with two or more channels, a Cable Balun module is required to help prevent HARTcommunication channel crosstalk.

Features

• 8 analog input channels, each accepting one of the following inputs: 

◦ Standard 4 to 20 mA analog sensor signal 

◦ Digital HART Frequency Shift Keying (FSK) signal superimposed on a 4 to 20 mA analog input signal 

• FSK modem dedicated to each input channel for bi-directional digital communications with a HART field device 

• Analog to digital conversion of each of the 4 to 20 mA input signals from the HART devices 

• Support for the HART universal commands necessary to interface the field device with the Foxboro DCS database 

• Per channel galvanic isolation of each of the 8 input channels from each other, ground and module logic 

• Rugged design suitable for enclosure in Class G3 (harsh) environments 

• High accuracy achieved by sigma-delta data conversions for each channel 

• Termination Assembly (TA) for locally or remotely connecting field wiring to the FBM214b 

• TA for per channel internally and/or externally loop powered transmitters

Standard Design

The FBM214b has a rugged extruded aluminum exterior for physical protection of the circuits. Enclosures specially designed for mounting the Foxboro DCS Fieldbus Modules (FBMs) provide various levels of environmental protection, up to harsh environments per ISA Standard S71.04

Fieldbus Communication

A Fieldbus Communication Module or a Control Processor interfaces the redundant 2 Mbps module Fieldbus used by the FBMs. The FBM214b module accepts communication from either path (A or B) of the redundant 2 Mbps fieldbus. If one path is unsuccessful or is switched off at the system level, the module continues communication over the active path. The use of an external power supply common to two or more loops requires a Cable Balun Module to maintain communication signal line balance.

Functional Specifications

Field Device Channels

• Supported HART Instruments: HART instruments compliant to Version 5, 6, or 7 of the HARTspecifications may be used 

• Interface: 8 individually isolated channels 

• Communication to the Device: Point-to-point, master/slave, asynchronous, half-duplex, at 1200 baud 

• Detected Error Checking: Parity on each byte, and one CRC check byte 

• Speed: 2 messages per second 

• Fastest Allowed ECB Block Period: 100 msec - However, we recommend that you see the Sizing Guidelines and Excel Workbook appropriate for your Control Processor to determine the optimal loading for a 100 msec Block Processing Cycle (BPC) 

• Maximum Distance (FBM214b to Field Device): Meets HART FSK physical layer specification HCF_SPEC-54, Revision 8.1 [up to 3,030 m (10,000 ft)] NOTE: The maximum allowable distance decreases when the loop is operated through an intrinsic safety barrier. The maximum distance of the field device from the FBM is a function of compliance voltage, wire gauge and voltage drop at the device. 

• Internal Loop Supply Compliance Voltage at Termination Assembly: 18.5 V dc minimum at 20.5 mA 

• Current Inputs: 

◦ Sense Resistor: 61.5 Ω nominal 

◦ Total Input Resistance: 280 Ω nominal 

◦ Accuracy (Includes Nonlinearity): ±0.03% of full scale 

◦ Temperature Coefficient: 50 ppm/ºC 

◦ Resolution: 15 bits 

◦ Update Rate: 100 ms 

◦ Integration Time: 500 ms 

◦ Common Mode Rejection: >100 db at 50 or 60 Hz 

◦ Normal Mode Rejection: >35 db at 50 or 60 Hz