Chapter 2 - Introduction; Overview - Honeywell UDC2800 Product Manual

Chapter 2 - Introduction

Overview

12
Function
UDC2800 Limit Controllers accept input signals from any of several
types of external sensors such as Thermocouples (T/Cs) and
Resistance Temperature Detectors (RTDs). It conditions these
signals, as necessary, to derive the equivalent Process Variable (PV)
value that drives various circuits in the controller.
The equivalent PV signal is compared with the Limit control set point
and any error signal from the differential amplifier de-energizes the
coil of an electromechanical, single-pole, dual-throw (SPDT) limit
output relay.
When de-energized, the output relay "Locks Out" and remains that
way until the PV input signal drops below the High Limit Set Point or
goes above the Low Limit Set Point and the controller is reset
manually via the keyboard or from a remote location (Contact Input
Option).
The contact of the output relay terminates at the rear terminal of the
controller to which you make the appropriate field wiring
connections.
A flashing "LIMIT" in the lower display indicates that the output relay
is de-energized.
Features
90 – 264 Vac or 24 Vac/dc Power Supply
n
Input/Output Isolation
n
Isolated Auxiliary Current Output / Digital Input
n
Modbusâ RS-485 or Ethernet TCP/IP Communications
n
High Limit Controller
When the PV input signal is below the limit set point, the output relay
energizes. If the PV signal exceeds the limit set point, the output relay
de-energizes and the flashing "LIMIT" display is turned on.
When the PV signal returns to a value below the limit set point, the
controller can be reset manually using the RESET key or Contact
Input Option.