GENERAL DESCRIPTION The EWPC 972 is a micro-processor based digital controller specifically designed for refrigeration systems; it is particularly suited for medium or low temperature range “forced air” units. It incorporates three 12 Vdc/30 mA outputs to activate the auxiliary and external relays for (1) compressor, (2) defrost system and (3) evaporator fan control.This instrument must be used with the Din-rail mounted EWDR SLAVE (972 version) module which contains the auxiliary relays; connection is achieved through a compatible MULTILEAD CABLE, equipped on both ends with telephone type quick-disconnect and polarized connectors. This MULTI-LEAD CABLE conducts all signals, i.e. input signals from the PTC probes, output signals to energize the relays in themodule, as well as the power supply to the EWPC 972. A number of parameters are displayed alphanumerically to set up the EWPC 972 for each specific application. The EWPC 972 is supplied in the popular “32x74” ELIWELL housing and is manufactured according to VDE and UL norms. The EWDR SLAVE (972 version) is supplied in the 70x85 mm (4 modules) housing for Din-rail (Omega 3) or surface mounting and ismanufactured according to VDE and UL norms. OPERATION The temperature control is always subject to a positive temperature differential (make on rise): the compressor stops when setpoint is reached and starts again upon reaching the setpoint temperature plus the differential. A choice of two defrost types is available: electric defrost (during which the compressor stops) or hot gas defrost (duringwhich the compressor is running). Other programming options include: defrost frequency time, time count mode, defrost termination temperature, and a defrost safety limit (time-out). The evaporator probe is used to control the defrost cycle as well as the evaporator fan: a selection can be made of the temperature above which the fan is OFF, the post-defrost fan delay time and the link between fanand compressor. A number of compressor short-cycle protection solutions (i.e., delay on start, delay at switching off, delay between two successive starts) are incorporated in the system. Thanks to a wide selection of other available parameters the controller can be adapted to virtually any application requirement. FRONT KEYPAD SET: push and release to display the setpoint for 5 seconds. Duringthis period the “SET” status light is on and the setpoint can be changed with the “UP” or “DOWN” button only. The system will automatically switch to normal display after 5 seconds upon release of buttons and the new value will be memorized. UP: used to increase the setpoint value, as well as the parameter when in programming. When held down for a few seconds, the change rate accelerates. DOWN: samefunctions except to decrease a value. DEFROST: this momentary push button will start a manual defrost cycle whenever it is activated for at least 5 seconds; not accessible when in setpoint or parameter programming. The programmed interval to the next defrost cycle is automatically reset. The “DEF” goes on when the defrost is initiated, whether the defrost is manual or automatic. Led “COMP”: statuslight of the internal compressor relay. It is ON when the compressor is ON. Led “SET”: it is on during Setpoint display and programming; it blinks during parameter programming.
WHAT IT IS The EWPC 972 is a micro-processor based digital controller specifically designed for refrigeration systems; it is particularly suited for medium or low temperature range “forced air” units.
HOW IT IS MADE• Housing: black ABS plastic, selfestinguishing • Dimensions: front 74x32 mm (2.913x1.260"), depth 67 mm (2.637") • Mounting: flush panel mount with mounting bracket • Protection: the instrument frontpanel is waterproof IP65; an optional snap-on cover can be supplied to provide additional protection of the rear terminal block • Connections: telephone type receptacle for connection with the EWDR...