Watlow QPAC - Manual (Page 19)

QPAC User's Guide 19 Chapter 2: Install & Wire
Input Wiring
Single- and Three-Phase
DH Option Open Heater or
Shorted SCR Detector.
*1 NOTE: Interstage
transformers (16-0176)
are required for all units
150A and above.
DH Card Operation — Heater Diagnostics
The DH card uses a CT to monitor the load current and also detects when a
firing pulse is sent to the SCRs. The load current must be set by the pot on
the DH board (P1). If there is load current and no pulses to turn on the SCRs,
the "Shorted SCR" indicator light will be lit. The opto triac (U4) closes 3 or 4
seconds later and energizes an external alarm relay. If part of the load opens
(20% or more), and there are SCR pulses, the "Open Htr" indicator light is lit
and 3 to 4 seconds later, the alarm relay energizes.
This board only operates with the zero cross firing cards. For three-phase,
the CTs go in T1 and T3 lines.
Setup Procedure
1. With the DH card installed and the temperature control wired to the SCR
power control, set the temperature control output to "full on" (20mA for 4
to 20mA output, or 5V for 0 to 5V output).
2. Adjust P1 until the open heater light on the DH card is full on. No inter-
mittent cycling.
3. Slowly adjust P1 until the open heater light just turns full off. No intermit-
tent cycling.
If you are getting false alarms, adjustment is probably set too sensitive and
should be readjusted towards the off condition of the open heater light.
A shorted SCR will energize the shorted SCR light.
Single- and Three-Phase Current Transformer Wiring
Motherboard
Connector
1
2
J2
DH 08-5405
120VÅ (ac)
To Alarm or Contactor
Customer Supplied Relay
(Philips ECG PIY 1055 or equivalent)
N.C.
Momentary
Reset
Switch
U4
P1
Open heater
when lit
Shorted SCR
when lit
56 mm
(2.20 in)
30 mm
(1.20 in)
69 mm
(2.70 in)
Interstage transformer
16-0176 for 150A
and above
J3 J3
CT
T1
Load Wire
Single-Phase
T1
T3
Three-Phase
J3
Load Wires
Interstage transformer
16-0176 for 150A
and above
*1
*1
ç
CAUTION:
The shorted SCR detec-
tor feature will not work
with the manual control
input.