T8842 Interface Module - ICS Triplex

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Description of T8842

The Trusted T8842 Versatile Field Termination Assembly (VFTA) is the primary interface between field devices for fire and gas detection/suppression and the Trusted TMR Zone Interface Module T8448. It features 40 individually configurable channels organized into five power groups of eight. Each channel supports a variety of analog or digital input signals and digital outputs up to 40V dc, and is protected by a 315mA field power fuse and a 50mA input signal fuse. The assembly accepts dual 24V dc supplies per group and is designed for mounting on standard TS32 or TS35 DIN rails.

Parameter

Voltage Range (Field Supply): 18 to 28V dc
Maximum Current (Field Supply): 2.52A per power group
Recommended Operating Current: 220mA per channel
Power Consumption (Field Supply): 9W maximum
Signal Input Range: 0-20mA
ESD Air discharge: 15kV
Contact discharge: 8kV
Radiated Fields: 10V/m, 27MHz to 500MHz
Transients and Bursts: 2kV, 2.5kHz for 60 seconds

FAQ

What is the purpose of the 50mA fuse on each input channel?
A: The 50mA fuse is specifically placed in series with the incoming signal path (0-20mA) to limit the current flowing through the precision 250R sense resistor. This protects the resistor and the downstream input electronics from potential damage if a field device fails or a wiring fault causes excessive current. The voltage developed across this 250R resistor is what the T8448 module measures to determine the field device status.

How are the dual 24V dc supplies configured within the VFTA?
A: Each of the five power groups receives two independent 24V dc feeds. These two supplies are combined using diodes on the VFTA, providing supply redundancy. If one 24V feed fails, the other will continue to power all eight channels within that group without any interruption. This diode "commoning" ensures high availability for critical fire and gas safety functions.

What types of field devices are compatible with the T8842?
A: The T8842 is specifically described as being suitable for both current "sinking" and current "sourcing" 3-wire field devices. This versatility allows it to interface with a wide range of detectors and actuators used in fire and gas systems, including those that require the VFTA to provide a power source and those that generate their own signal output. The configuration is managed on a per-channel basis.