TE Technology TC-720 - Manual (Page 60)

The output current is measured using a resistor. However, the actual current value at any given time may
vary somewhat from the level indicated by the OUTPUT CURRENT meter due to tolerances of the resistor as
well as how quickly the controller can report the current to the computer. In the same manner, the actual
current level at which the controller may shut down output may differ slightly from the amount indicated in
the OVER CURRENT LEVEL.
NOTE: THIS IS NOT AN ANALOG CURRENT-LIMITING FEATURE!
OVER CURRENT RETRIES sets the number of times the controller will automatically attempt to restart sending output power
before disabling the output and not attempting further retries. A value of 30000 will set the retries to an infinite amount.
This allows the over current level to be set at a reasonably safe level while also allowing for momentary changes in the
apparent electrical resistance when the controller switches between heating and cooling.
It is normal to have an output current surge when the direction of current flow is instantaneously reversed to
a TE device that already has a temperature difference established across it. When this happens, the apparent
electrical resistance of the TE device is lower because the Seebeck voltage does not immediately reverse
polarity. The reversal of current will eventually reverse the temperature difference across the TE device, and
then the Seebeck voltage will likewise change polarity. As the temperature difference reverses, the current
will revert back down to a steady-state level.
If the output is disabled due to an over-current condition, the controller can be restarted by clicking the “CLEAR LATCHES”
OK button in the ALARMS section, or by cycling power to the controller, or by pressing and holding the UP arrow on the
controller itself (TC-720 only) for three seconds.
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