Ametek Amrel PLA Series Operation Manual page 20

Unregulated state (UNR):
The "UNR" message cautions that the power stage of the electronic load is operating at its minimum resistance or
equivalent to it being shorted (marginal region for the load). Another indication is that the load is being operated
improperly, i.e. not enough supply current/voltage or incorrect calibration data.
Supply Current and Voltage Below Main Level
A common cause for entering the unregulated state is supplying the load with a voltage or a current below the value set
for electronic load's main level. For example, if the input is off in CV mode and the main level of the load is set at 3 volts
and the power supply is programmed for 2 volts. An "UNR" alarm message will appear when turning the input on. The
message is caused by the lack of voltage needed to bring the main to 3 volts, and the voltage and current readings will be
unstable during this state. The same condition will occur for CC mode, if the needed current is lower than the supplied
current. To fix the problem, increase the voltage or current above the needed main value. The "UNR" threshold is set as
1% deviation from the maximum value in that mode and/or range.
Re-Calibration
Verify that the supply current and voltage is sufficient for the operating condition. If the "UNR" message still occurs,
check the current or voltage read back and compare it with the main value setting (CC mode: current; CV mode: voltage)
to make sure the difference is below 1%. If the difference is above 1% for CC/CV mode, 30% for CR mode or 0.3% for
CP mode, that particular mode will need to be recalibrated. As a factory default, all loads are calibrated to its optimal
condition. Please verify the calibration inaccuracy carefully or contact AMETEK Technical Support before re-calibrating
the unit.
CR and CP Mode
In CR and CP mode, if the voltage or current is below the needed value to reach a certain resistance or wattage, an
"UNR" alarm message will appear. For example, in order to obtain 300 watts, the input current value multiplied by the
input voltage value will need to equal 300 watts, otherwise an error will occur. For CR mode, the input voltage value
divided by the input current value will need to equal the resistance value entered. To fix the problem, increase the voltage
or current above the needed power or resistance. The "UNR" threshold for constant power mode is set as 0.3% deviation
from the maximum value in that mode and/or range. The constant resistance mode has a higher fluctuation in its value, so
it will have a higher "UNR" deviation range.
Note: When testing power supplies, a sudden current sink by the eLOAD in CP mode may cause the power supply to
latch in CC mode. At that time, the eLOAD will sink no current and display "UNR". Simply power cycle the power
supply and repeat the application with a higher voltage setting to prevent the power supply from entering an
uncontrollable state.
Precautions for Testing Batteries
As a precaution, when testing batteries prevent from operating in CV mode and make sure that the load does not enter the
unregulated state. If a battery is connected to a short circuited load (UNR state), the load will draw infinite current and
cause permanent damage to the load, battery under test and possibly start a fire.
Under Voltage Lockout Protection (UVL):
The programmable under voltage lockout feature allows the user to set a trip point between zero and full-scale voltage (V-
On Voltage Threshold). The input will remain off until the input voltage is greater than the pre-programmed value or the
V-On Voltage threshold. For the V-On (UVL) feature, there are two modes that can be set. In "continuous" mode, the
UVL detection will remain active, and each time the voltage drops below the set threshold voltage, the UVL protection
will shut off the input. Under "input on" mode, the UVL detection will only trigger once to shut down the input and will
reset each time the input is cycled. The only wa y to clear a UVL protection message is to increase the input voltage
beyond the V-On threshold. As a recommended setting, the V-On threshold should be set equivalent to at least 1 volt.
M470039-01 REV-F Page 19