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If SampleTime + 0.025 > TXInterval then we need to make SampleTime =
TXInterval - 0.025
Also note that we cannot use a TXInterval of less than 0.041 if we are in low power mode as this will cause
unpredictable results.
Calculate measurement current
LoadCellCurrent = ((5000 / LoadImp) * 2)
If in Low Power Mode
'fixed block
U1 = 0.5 / TXInterval * 1
'Measurement block
U2 = (FixedMeasurementCurrent + LoadCellCurrent) / TXInterval * 0.006
'fixed block
U3 = (FixedMeasurementCurrent + LoadCellCurrent) / TXInterval *
SampleTime
AwakeCurrent = (U1 + U2 + U3) * HoursUsage / 24
If not in Low Power Mode
AwakeCurrent = (FixedMeasurementCurrent + LoadCellCurrent) * HoursUsage /
24
Calculate currents
Now calculate sleep current
SleepCurrent = 30 / WakeInt * 0.008
SleepCurrent = SleepCurrent * (24 - HoursUsage) / 24
Calculate total current
TotalCurrent = AwakeCurrent + SleepCurrent
Calculate battery life in hours
BattHours = (BattAH / TotalCurrent) * 1000
Allow a safety margin
BattHours = BattHours * 0.9
The calculated battery life in hours is BattHours
Acquisition Module Battery Life – Non Strain Gauge Input
Accurate Guide
The following shows how to more accurately calculate battery life. This does rely on an estimate of usable
battery capacity which is not as high as manufacturers state their battery capacity to be except for batteries
where the cuttoff voltage above the minimum voltage for the device.
To estimate usable capacity you will need to refer to manufacturers discharge graphs and find a curve closest to
around 30mA and estimate the capacity as Amps X Time where time is the point where the battery falls below
where the device would be supplied with 2.1V. This will be 1.05 in the case of 1.5V cells as we use two in series.
TXInterval = TXInterval Parameter / 1000
SampleTime = SampleTime Parameter/ 1000
HoursUsage = How many hours the device is NOT asleep in a 24 hour period
BattAH = Usable battery capacity in Amp Hours (Ah)
WakeInt = WakeChkInt parameter
FixedMeasurementCurrent = 45 plus current in milliamps drawn from the 5V
excitation supply for connected sensors.
Internally the device will adjust SampleTime if it is too long for the TXInterval so we need to take this into
account for our calculations:
If SampleTime + 0.025 > TXInterval then we need to make SampleTime =
TXInterval - 0.025
Also note that we cannot use a TXInterval of less than 0.041 if we are in low power mode as this will cause
unpredictable results.
Mantracourt Electronics Limited T24 Technical Manual
92
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