Foxboro 0 to 20 mA Output Interface Module (FBM44)

I/A Series® Hardware

 Dual Baud Rate Intelligent Transmitter/

 0 to 20 mA Output Interface Module (FBM44)

 The Dual Baud Rate Intelligent Transmitter (IT)/0 to 

20 mA Output Interface Fieldbus Module contains 

four individual Intelligent Transmitter interface 

channels and four 0 to 20 mA dc analog output 

channels. The module is a main type and 

independently connects to the redundant Fieldbus.

 Intelligent Transmitter (IT) Interface Channels

 Each IT interface channel provides internally isolated 

power and communication capabilities to an IT over a 

single twisted-pair wire. The module also allows the 

use of an external power supply to power the IT.

 The use of an external power supply common to two 

or more loops requires the use of a Cable Balun 

Module to maintain digital communication line 

balance. The baud rate is software-selectable with all 

channels at the same baud rate. Each module 

provides bi-directional digital communications at 

4800 baud rate between the IT and the system 

redundant Fieldbus or provides bi-directional digital 

communications at 600 baud rate while allowing 

simultaneous 4 to 20 mA analog signal for use in 

other applications (for example, to an emergency 

shutdown system)

The module is an IT host, enabling the system to 

receive digital messages from the transmitter in 

engineering units. Each message is received ten 

times per second at 4800 baud and two times per 

second at 600 baud and contains:

 • Two measured variables (that is, primary 

pressure and transmitter temperature) in IEEE 

32-bit floating-point

 • Security information

 • Diagnostics

 • Message checking.

 This information is available to all elements of the 

system.

 Since the communications are bi-directional, the 

system can display the output, transmitter 

temperature (°C and °F), and continuous self

diagnostics. Additionally, the following information can 

be displayed or reconfigured from the console or a 

Hand-Held Terminal (PSS 2A-1Z3 A):

 • Output in engineering units

 • Fail-safe state

 • Tag number, name and location

 • Device name (letterbug)

 • Last calibration date

 • Two levels of upload/download capabilities.

 The IT interface portion of the module executes the 

Intelligent Transmitter application program. The 

configurable options for this program are Fieldbus 

Switching Enable and Fieldbus Switching Time.

 Output Channels

 Each output channel drives an external load and 

produces a 0 to 20 mA output. Each output channel 

performs the signal conversion required to interface 

the electrical output signals to field actuators from the 

redundant Fieldbus.

 The output channel portion of the module executes 

the analog I/O application program. The configurable 

options for this program are Fail-Safe Configuration 

(Hold/Fallback), Analog Output Fail-Safe Fallback 

Data (on a per channel basis), Fieldbus Switching 

Enable and Fieldbus Switching Time.

 An optional style of termination cable assembly which 

is available includes built-in bypass jacks for each 

output channel on the front connector of the Fieldbus 

Module. Jacks accept a bypass plug from the 

I/A Series Output Bypass Station or other external 

20 mA source. This option should be considered for 

applications where maintaining output is desired 

during maintenance operations, for example, when 

replacing a failed module.

 Common Characteristics

 POWER REQUIREMENTS

 Input Voltage (Redundant)

 26 to 42 V dc (nominal)

 Consumption

 11 W (maximum)

 Heat Dissipation

 8 W (maximum)

 ISOLATION

 FUNCTIONAL SPECIFICATIONS

 Transmitter Channels (Cont.)

 MAXIMUM DISTANCE (INTERFACE TO 

TRANSMITTER)* (SHIELDED TWISTED-PAIR 

WIRES, OR AT MINIMUM TWISTED-PAIR WITH 

OVERALL SHIELD)

 The module can withstand, without damage, a 

potential of 600 V ac applied for one minute 

between any channel and earth (ground), or 

between a given channel and any other channel.

 NOTE

 This does not imply that these channels are 

intended for permanent connection to hazardous 

voltage circuits. Connection of these channels to 

voltages greater than 30 V ac or 60 V dc violates 

electrical safety code requirements and may 

expose users to electric shock.

 COMMUNICATION

 Via a redundant Fieldbus

 Transmitter Channels

 INTERFACE

 4 isolated and independent channels

 ERROR CHECKING

 CCITT 2 byte CRC

 COMMUNICATIONS

 Non-redundant, point-to-point, master/slave, 

asynchronous, half-duplex at a software-selectable 

baud rate of 600 or 4800 baud. All 8 input channels 

must be configured at the same baud rate 

(600 baud for 4 to 20 mA transmitters or 4800 baud 

for digital transmitters).

 SPEED

 10 messages per second at 4800 baud, or 

2 messages per second at 600 baud

 610 m (2000 ft) (shielded twisted-pair wires) at 

4800 baud, or 1800 m (6000 ft) at 600 baud

 MAXIMUM LOOP RESISTANCE

 500 Ω (not including the transmitter). The 

maximum resistance between the Hand-Held 

Terminal (HHT) and the transmitter is 350 Ω.

 TRANSMITTER INTERNAL POWER

 24 V dc +4%, -2%, source resista