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Battery Life Calculation
The PT2X has been designed for very low power consumption. When not in active use,
the unit goes into a “sleep” mode, waking only to take readings or communicate with the
host computer.
It is difficult to know how fresh particular batteries are. Just sitting on a shelf, especially
in a warm environment, will cause the batteries to lose energy. If the batteries are stored
in a cold environment, the self-discharge will be less, but the batteries won't provide as
much energy output when they're cold. Under optimum conditions, two fresh AA
alkaline batteries should provide 15,000 Joules of energy. To give yourself some margin,
INW recommends that you assume approximately 12,000 Joules.
When sleeping, the PT2X consumes approximately 150 Joules per week. Each reading
consumes approximately .075 Joules. Communicating with the sensor for one minute, to
upload data or take real-time readings, for instance, consumes approximately two Joules.
Use the following formulas to calculate your battery life:
Compute Weekly usage:
Readings usage = number of readings per hour * 24 hours * 7 days * .075 Joules
Communications usage = minutes of communication per week * 2 Joules
Sleep time usage = 150 Joules
Total weekly usage = r communi sleep usage
Compute life of batteries:
Life of batteries in weeks = 12,000 Joules / Total weekly usage
Example:
4 readings per hour, 1 minute of communication per week
Readings usage = 4 * 24 hours * 7 days * .075 Joules = 50 Joules
Communication usage = 1 * 2 Joules = 2 Joules
Sleep time usage = 150 Joules
Total weekly usage = 50 + 2 + 150 = 202 Joules
Life of battery = 12,000 / 202 = 59 weeks (approx.)
