The PR3 range of thyristor stacks provides full seamless control of three phase resistive
loads, using two thirds control technique. Signal control is by a dc signal or manual control
is via a 5k potentiometer. These burst firing control stacks use fast pulse zero volts
switching technology, to minimise flicker and eliminate RFI problems. They also incorporate
an automatic resetting temperature trip, integral semiconductor fuses and heatsink.
Suitable for 3-wire, 3-phase floating-star or closed-delta configured resistive loads. This
includes the Heating, Ventilating and Air Conditioning (HVAC) market for air curtain
applications, but also for furnaces, ovens, dryers and hot plates.
* Alarm relay functions (3-way terminal – V/free alarm “NO_NC_C”)
The alarm circuit has ‘voltage free’ relay contacts and are rated up to 2A @ 125V
ac (RMS) load. Connection is via the PCB terminal.
For alarm relay status options see SPECIFICATIONS.
Note: The internal supply to the relay is obtained from the transformer via two 20mm 1A fuses. These are
connected to the Black (L2) and Grey (L3) phases and therefore the relay and LED can only energise when
there is an over-temperature condition, a sensor fault, or a phase loss on L1 phase. See Remote Supply option section.
* Over temperature protection
When a heatsink temperature of above 90ºC is detected by the sensor, the alarms relay changes state and the status LED indicator flashes
continuous rapid pulsing. The power to the load will be disconnected and will not return until the temperature drops to 85ºC.
* Temperature sensor loss
The Status LED indicator changes to continuous equal ON/OFF pulsing if the sensor fails.