Foxboro FBM204 0 to 20 mA I/O Module

Foxboro FBM204  0 to 20 mA I/O Module

DESCRIPTION

The FBM204, 0 to 20 mA Input/Output contains four 20 mA dc analog input channels and four 20 mA dc analog output channels. Each input channel accepts an analog sensor input such as a 4 to 20 mA transmitter, or a self-powered 20 mA source. Each output channel drives an external load and produces a 0 to 20 mA output. The inputs/outputs are galvanically isolated from other channels and ground.

The FBM204 performs the signal conversion required to interface the electrical input/ output signals from the field sensors to the optionally redundant fieldbus. The FBM204 executes the Analog I/O application program, which provides the following configurable options: Conversion Time, Fail-Safe Configuration (Hold/Fallback), and Analog Output Fail-Safe Fallback Data (on a per channel basis). The Fieldbus Module (FBM) may instead execute a distributed PIDA (DPIDA) application program to provide a fast control loop running in it

Features

• Four 20 mA dc analog input channels 

• Four 20 mA dc analog output channels 

• Each input and output channel is galvanically isolated 

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

• Execution of an analog I/O application program that provides conversion time and configurable options for Rate of Change Limits 

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

• Termination Assemblies (TAs) for locally or remotely connecting field wiring to the Compact FBM204 

• TA for use with Output Bypass Station to maintain outputs during maintenance operations 

• 3-tier termination assembly for per channel internally and/or externally loop powered transmitters 

• Support for DPIDA control blocks

High Accuracy

For high accuracy, the module incorporates Sigma-Delta data conversion on a per channel basis, which provides new analog input readings every 25 ms, and a configurable integration period to remove any process and/or noise and power line frequencies. Each time period, the FBM converts each analog input to a digital value, averages these values over the time period and provides the averaged value to the controller

Standard Design

FBM204 has a rugged extruded aluminum exterior for physical protection of the circuits. Enclosures specially designed for mounting the FBMs provide various levels of environmental protection, up to harsh environments, per ISA Standard S71.04

Fieldbus Communication

A Fieldbus Communications Module or a Control Processor interfaces to the redundant 2 Mbps module Fieldbus used by the FBMs. The FBM accepts communication from either path (A or B) of the 2 Mbps Fieldbus. If one path is unsuccessful or is switched at the system level, the module continues communication over the active path.

Functional Specifications

Input Channels (Four)

• Accuracy (Includes Linearity): ±0.03% of span 

• Accuracy Temperature Coefficient: ±50 ppm/ºC 

• Input Signal A/D Conversion: Each channel performs A/D signal conversion using an independent Sigma-Delta converter. 

• Input Channel Impedance: 61.5 Ω nominal 

• Integration Period: Software configurable 

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

• Normal Mode Rejection: >95 db at 50 or 60 Hz 

• Field Device Cabling Distance: Maximum distance of the field device from the FBM is a function of compliance voltage (20.2 V dc at 20.4 mA input), wire gauge, and voltage drop at the field device. 

• Loop Power Supply Protection: Each channel is channel-to-channel galvanically isolated, current limited, and voltage regulated. All analog inputs are limited by their design to less than 30 mA. If the current limit circuit shorts out, the current is limited to about 100mA.

Output Channels (Four)

• Accuracy — Analog (Includes Linearity): ±0.03% of span 

• Accuracy Temperature Coefficient: ±50 ppm/ºC 

• Output Load: 750 Ω maximum 

• Output Processing Delay: 30 ms maximum 

• Resolution: 13 bits 

• Field Device Cabling Distance: Maximum distance of the field device from the FBM is a function of compliance voltage (19.6 V dc at 20.4 mA input), wire gauge, and voltage drop at the field device.