Watlow VPAC Solid State Relay Power Control - Manual (Page 8)

Starting Out
Watlow VPAC User's Manual
8
1. Surface must be clean and flat.
2. Use a thermal pad or a thin coat of thermal joint compound
(Dow DC-340 or equivalent).
3. Mount the SSR to the heat sink.
4. Use Belleville (spring) washers and tighten screws alternately
until the spring is deflected slightly.
з з з з з
CAUTION:
Heat sink must be mounted so that the fins are vertically aligned.
з з з з з
CAUTION:
Heat sensitive component; ambient temperature must not exceed
122°F (50°C). If overheated, unit could fail.
з з з з з
CAUTION:
Heat sensitive component; do not mount SSRs on panels that are
painted, plastic, steel or stainless steel. These materials will not
remove heat generated by the SSR. If overheated, unit could fail.
Troubleshooting
To isolate a system problem involving the VPAC, answer these
questions:
•
Are inputs to the VPAC present?
• Are outputs from the VPAC present?
• Are all connections good?
• Is the load good?
• Is line voltage within specification?
• Are temperature control signals present? If so, then the VPAC
power control itself may be the problem. The problem may be with
the VPAC's control card, transformer or solid state relay. Use the
table below to assist with troubleshooting.
Bias And Gain Adjustments
The VPAC bias and gain can be adjusted for the output of most
standard, proportional output temperature controls. Bias and gain
is factory set for an input control signal (0-5VDC or 4-20mA), but
may require minor adjustments to match the output of a specific
temperature control.
We recommend that bias and gain adjustment be performed using
a dummy load. In some applications, a dummy load may be
required if the controlled load can not be turned full ON. A dummy
load can be easily made by connecting 150 watt lamps in series to
match the operating voltage of the VPAC. Use the following steps
to make adjustments.
1. Connect an AC voltmeter across the load or dummy load of
the VPAC. Connect a DC voltmeter across, or milliampmeter
in series with, the input signal from the temperature controller.
2. Apply power to the system.
3. Set the output signal of the temperature controller to zero or
its minimum output. Adjust the bias potentiometer slowly until
the VPAC output just comes ON. Then turn it in the opposite
direction until the output is just full OFF as observed on the
output voltmeter.
4. Adjust the output of the temperature controller to full ON
(5VDC, 20mA, etc.). Adjust the gain potentiometer until the
VPAC output is just full ON.
Symptom Probable Cause Corrective Action
No output Fuses blown Check and replace fuses.
Incorrect input wiring Verify input wiring.
Incorrect input signal Check temp. control output.
Input signal reversed Verify input wiring.
Input signal not adjusted “See Bias and Gain Adjustment.”
Wrong or missing
control card Verify input wiring.
Check transformer connections.
Missing load wiring Verify load wiring
The SSR(s) will not
function without a load.
Transformer hot Incorrect transformer Check product & transformer
labels (AT+ & BT only).
Uncontrolled Bad control card, Disconnect control card, try again.
output full ON or Bias and Gain If no output, SSR is okay. Check
out of adjustment Bias and Gain Adjustment.
Bad transformer Unplug transformer wires
and try again. (AT+ & BT only.)
Bad SSR If full ON or half ON output
present with no control card
and no transformer, solid state
relay is bad; replace it.
5. Repeat Steps 3 and 4 until the VPAC turns full ON with a full
ON signal from the temperature control, and full OFF with the
minimum input signal from the temperature control. Steps 3
and 4 may need to be repeated a few times (an adjustment
made on one of the potentiometers affects the adjustment of
the other potentiometer).
6. Remove power, disconnect the meters, and reconnect the
controlled load to the VPAC if required.
Replace SSR
Solid State Relay
See Note 3.
Heat Sink (typical)
Screw, 2 ea., #8-32
See Note 4.
Belleville Washer, #8
See Note 4.
Thermal pad or
a thin coat of thermal
joint compound
(Dow DC-340)
UP
Feedback
Your comments and suggestions on this manual are welcome.
Please send them to: Technical Writer, Watlow Controls, P.O. Box
5580, Winona, MN 55987-5580, or call (507) 454-5300 or fax
(507) 45204507. The VPAC Users Manual is copyrighted by
Watlow Winona, Inc., © December 1999, with all rights reserved.
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