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PG. 11
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Monitor battery terminal voltage. You cannot tell from terminal voltage of a lithium battery how long
the battery will last, but you can tell if it will die soon. The Low Drain Performance plot below gives
an estimate of terminal voltage for both lithium and alkaline batteries. Your measured voltage will be
2X what is shown below since there are two batteries in series within the miniPAR Logger. You can
operate batteries down to about 2.4 Volts (for two in series, 1.2 Volts on the graph below). Your
batteries are dead if the measurement of each battery adds to less than 2.4 Volts.
You may also use alkaline AA batteries such as Duracell Coppertop. They will not last nearly as
long, especially at low temperatures, but will likely be adequate for several weeks at the 10- minute
interval. Alkaline batteries may leak if severely discharged.
When replacing batteries use only fresh batteries. Do not mix battery types. If one battery differs in
type or charge level from the other and the miniPAR Logger runs them to full discharge, then one
battery may leak.
Err on the side of caution when planning your deployment.
The recommended battery is the Energizer L91 lithium battery. For more information, including the
performance at low temperatures, click this link:
http://data.energizer.com/PDFs/l91.pdf
The figure below gives a general idea
of terminal voltage vs. lifetime. Service
life in hours is incorrect since miniPAR
Logger draws far less than 50 mA
continuously, but the general shape of
the voltage vs. time gives an estimate
of life remaining. This plot is taken
from the manufacturer’s specification.
The plot is for a single battery. Double
the voltages shown to give the
terminal voltage as measured in the
picture above. The miniPAR Logger
halts operation at a total of 2.4 Volts.
C O I N C E L L B A T T E R Y L I F E
The miniPAR Logger uses a coin cell battery for backing up the clock when the AA batteries are
removed. This coin cell battery will supply many years of clock operation. Should the coin cell battery
discharge, then it must be replaced by PME. Contact PME
R E C A L I B R A T I O N
The miniPAR Logger will maintain its calibration without the necessity of
adjustment by the user. The
miniPAR Logger should be returned to PME for recalibration.
We suggest that this be done yearly.
We do not calibrate the miniPAR ourselves; we disassemble
it and send the PAR sensor to Li-Cor
for re-calibration. Follow Li-
Cor’s suggestion on how
often their sensors need to be calibrated.
