Invensys Triconex Analog Input Module 3721
Description:
The Tricon is a state-of-the art controller that provides fault tolerance by means of Triple-Modular Redundant (TMR) architecture. TMR integrates three isolated, parallel control systems and extensive diagnostics in one control system.
3721 is part of Triconex fault-tolerant controller Analog Input Module. Itincludes three independent input channels. Each
input channel receives variable voltage signals from each point, converts them to digital values, and transmits the values to the three main processor modules on demand. In TMR mode, one value is then selected using a midvalue selection algorithm to ensure correct data for every scan.
Sensing of each input point is performed in a manner that prevents a single failure on one channel from affecting another channel. Each analog input module sustains complete, ongoing diagnostics for each channel. Failure of any diagnostic on any channel activates the Fault indicator for the module, which in turn activates the chassis alarm signal. The module’s Fault indicator merely reports a channel fault, not a module failure—the module can operate properly with as many as two faulty channels.
Analog input modules support hotspare capability which allows online replacement of a faulty module.The analog input module requires a separate external termination panel (ETP) with a cable interface to the Tricon backplane. Each module is mechanically keyed for proper installation in a Tricon chassis.

Model Number	3721
Voltage	0 to 5 VDC or -5 to +5 VDC1, + 6%
Type	TMR
No. of Input Points	32 differential, DC-coupled
Isolated Points	Yes
Input Update Rate	10 ms
Resolution	12 bits or 14 bits programmable
Accuracy	< 0.15% of FSR from 0° to 60° C
Input Resistance (load)	10 MΩ (DC), min.
Power-Off Resistance	140 kΩ(DC), typical
Common Mode Rejection	-85 dB (DC - 100 Hz)
Common Mode Range	-12V to +12V peak
Leg-to-Leg Isolation	420 kΩ, typical
Normal Mode Rejection	-3 dB @ 23 Hz -8 dB @ 60 Hz -14 dB @ 120 Hz
Input Overrange Protection	150 VDC/115 VAC continuous
Current Range	0-20 mA with 250 Ω shunt resistor
Diagnostic Indicators Module Status	PASS, FAULT, ACTIVE, FIELD
Color Code	Yellow