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Theory of Operation
4-46.
Current Transformer.
4-47.
A separate Current Transformer exists for each output current rating in the DPA-1 PHASE/AMP
Series. The transformer provides a current step-down ratio such that the maximum rated output current of a
given DPA-1 unit will result in a full scale deflection of the Current Indicator (ammeter).
Transformer is connected across the primary winding of power transformer T2 in the Current Limit Module. The
load line connected to terminal X1 on the unit must pass through the transformer (doughnut) for proper
operation of the Current Limit. A standard current transformer is rated 2 Volt amperes (5 amperes, 0.4 Volt)
which is sufficient for the standard current limit, Option A. If a remote meter is connected into the circuit or
other options are used, it may be necessary to use a current transformer with a 5 Volt ampere (Option X) or
greater capacity.
4-48.
Current Indicator.
4-49.
The Current Indicator is an AC 0 to 5 ampere ammeter with an accuracy of (+5) percent of full scale
deflection. The function of the meter is to measure and display the output current supplied to the load by the
unit. The meter is connected across the primary winding of power transformer T2 in the Current Limit Module
and the Current Transformer.
4-50.
OPTIONAL HEAT SINK THERMOSTATS.
4-51.
When used, a Heat Sink Thermostat is mounted on each heat sink in close proximity to the power
SCR. The thermostat is of the bi-metal type and is available with either N.O. or N.C> contacts. The contacts
change at a temperature of approximately 200°F (93°C). This temperature is safely below the maximum
permissible junction temperature of the neighboring power SCR.
resistance 100 megohms at 500 V dc, dielectric strength 1500 VAC at 60 HZ for one minute) from the heat
sink. Any standard alarm device or circuit may be connected to the contacts on the thermostat. Maximum
ratings for the contacts are as follows: Voltage, 250 Volts AC, Current, 7 amperes AC.
30
AMETEK HDR Power Systems
Phase/AMP Series DPA1/DCPA1
The contacts are insulated (insulation
Document 9100030
The Current
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Troubleshooting
