Ametek Amrel PLA 2U, Operation Manual

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M470039-01 REV-F Page 19
Unregulated state (UNR):
The “UNR” message cautions that the power stage of the electronic load is operating at its minimum resistance or
equiva lent to it being shorted (ma rgina l region for the loa d). Another indica tion is tha t the loa d is being opera ted
improperly, i.e. not enough supply current/volta ge or incorrect ca libra tion da ta .
Supply Current a nd Volta ge Below Ma in Level
A common ca use for entering the unregula ted sta te is supplying the loa d with a volta ge or a current below the va lue 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
a nd the power supply is progra mmed for 2 volts. An “UNR” a la rm messa ge will a ppea r when turning the input on. The
messa ge is ca used by the la ck of volta ge needed to bring the ma in to 3 volts, a nd the volta ge a nd current rea dings will be
unsta ble during this sta te. The sa me condition will occur for CC mode, if the needed current is lower tha n the supplied
current. To fix the problem, increase the voltage or current above the needed main value. The “UNR” threshold is set as
1% devia tion from the ma ximum va lue in tha t mode a nd/or ra nge.
Re-Ca libra tion
Verify that the supply current and voltage is sufficient for the operating condition. If the “UNR” message still occurs,
check the current or volta ge rea d ba ck a nd compare it with the ma in va lue setting (CC mode: current; CV mode: volta ge)
to ma ke sure the difference is below 1%. If the difference is a bove 1% for CC/CV mode, 30% for CR mode or 0.3% for
CP mode, tha t pa rticula r mode will need to be reca libra ted. As a fa ctory defa ult, a ll loa ds a re ca libra ted to its optima l
condition. Plea se verify the ca libra tion ina ccura cy ca refully or conta ct AMETEK Technica l Support before re-ca libra ting
the unit.
CR a nd CP Mode
In CR a nd CP mode, if the volta ge or current is below the needed va lue to rea ch a certa in resista nce or wa tta ge, a n
“UNR” alarm message will appear. For example, in order to obtain 300 watts, the input current value multiplied by the
input volta ge va lue will need to equa l 300 wa tts, otherwise a n error will occur. For CR mode, the input volta ge va lue
divided by the input current va lue will need to equa l the resista nce va lue entered. To fix the problem, increa se the volta ge
or current above the needed power or resistance. The “UNR” threshold for constant power mode is set as 0.3% deviation
from the ma ximum va lue in tha t mode a nd/or ra nge. The consta nt resista nce mode ha s a higher fluctua tion in its va lue, so
it will have a higher “UNR” deviation range.
Note: When testing power supplies, a sudden current sink by the eLOAD in CP mode ma y ca use the power supply to
la tch in CC mode. At tha t time, the eLOAD will sink no current a nd displa y “UNR”. Simply power cycle the power
supply a nd repea t the a pplica tion with a higher volta ge setting to prevent the power supply from entering a n
uncontrolla ble sta te.
Preca utions for Testing Ba tteries
As a preca ution, when testing ba tteries prevent from opera ting in CV mode a nd ma ke sure tha t the loa d does not enter the
unregula ted sta te. If a ba ttery is connected to a short circuited loa d (UNR sta te), the loa d will dra w infinite current a nd
ca use perma nent da mage to the loa d, ba ttery under test a nd possibly sta rt a fire.
Under Voltage Lockout Protection (UVL):
The progra mma ble under volta ge lockout fea ture a llows the user to set a trip point between zero a nd full-sca le volta ge (V-
On Volta ge Threshold). The input will rema in off until the input volta ge is grea ter tha n the pre -progra mmed va lue or the
V-On Volta ge threshold. For the V-On (UVL) fea ture, there a re two modes tha t ca n be set. In “continuous” mode, the
UVL detection will rema in a ctive, a nd ea ch time the volta ge drops below the set threshold volta ge, the UVL protection
will shut off the input. Under “input on” mode, the UVL detection will only trigger once to shut down the input a nd will
reset ea ch time the input is cycled. The only wa y to clea r a UVL protection messa ge is to increa se the input volta ge
beyond the V-On threshold. As a recommended setting, the V-On threshold should be set equiva lent to a t lea st 1 volt.