Fault Diagnosis
5-1
Revision 2 - 20 March, 1997
HP SERIES DIMMER
OPERATING MANUAL
5.1.2
Thermal protection
The HP12-TR / HP12-SC dimmers feature temperature-controlled fan cooling. As the
internal temperature of the dimmer increases, the fan speed also increases. The fan
begins turning at low speed at 30
°
C, and reaches maximum speed at temperatures
above 50
°
C.
The internal heatsink temperature is constantly monitored by the dimmer. If the
heatsink temperature rises above 85ºC, the dimmer will automatically shut down the
output drive and display the message
: “OVER TEMPERATURE XX
O
C”
. The
dimmer will display this message until the temperature drops below 80ºC, at which
time it will restart. The fan will continue to cool the heatsink during the shut down
period.
The electronic shutdown at 85
°
C is backed up by a 90
°
C buried cutout, which shuts
down power to all electronics other than the cooling fan.
Note that the two fans in "SC" dimmers will run slower and quieter under average
operating conditions than the single fan in "TR" dimmers, due to the increased airflow
capacity. In addition the fans in wall-mount dimmers will run slower and quieter than
the fans in rack-mount dimmers due to increased natural convective cooling.
5.1.3
Supply Power fault protection
The HP12-TR / HP12-SC dimmers will detect voltage problems generated by phase
load imbalance and a poor or missing neutral connection. A poor (resistive) neutral
connection can cause arcing and overheating of the connector, and also allows the
phase-to-neutral voltages to vary, causing overvoltage damage to components.
Bad neutral connections account for many lamp and dimmer failures. While the
internal electronics of HP12-TR dimmers can tolerate (and correct for) these fault
conditions, other equipment run from the same mains supply generally cannot.
The HP12-TR / HP12-SC dimmers will detect three types of mains supply problems:
•
Mains overvoltages
•
Mains undervoltages
•
Higher than normal neutral-earth voltages
In addition, the HP12 dimmers can correct and regulate the dimmed outputs against
variations in the mains supply voltages.
The HP12's electronic circuits will tolerate gross overvoltages and accidentally
transposed active-neutral connection with no internal damage and no damage to output
loads.
5.1.3.1
Mains Overvoltages
If the voltage on any supply phase exceeds the maximum volts for more than two
cycles the dimmer outputs are turned OFF and the following message scrolls across
the display
: “MAINS OVERVOLTAGE. PRESS NORMAL TO REACTIVATE”
.
When the overvoltage condition is removed, press the
NORMAL
button to reactivate
the dimmer. The outputs will restart according to the previous settings.
5.1.3.2
Mains Undervoltage
If voltage on any phase drops below the minimum for more than 2 cycles the dimmer
outputs for that phase are turned OFF and the following message scrolls across the
display:
“MAINS UNDERVOLTAGE. PRESS NORMAL TO REACTIVATE”
.
When the undervoltage condition is removed, press the
NORMAL
button to
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