Metamotion C Power Consumption Verus Ambient Temperature
firmware which is working well so far.
We have found the power consumption
of the Metamotion C to ramp up unde increasing temperature. We are closely monitoring roughly 20 sensors, we
found that over the weekend when we were not in the office (and the air conditioning off) the
consumption jumped.
We hypothesised that the room temp
would have increased due to no air conditioner, so we took a sensor and measured it in the office with the air-con on, set
at about 20 degrees C. Then moved down to the factory and
noticed a jump of a couple micro amp's
Then we took it outside and saw
another increase of a couple more micro amps. Then we decided
to get serious. We used a laser temp sensor/gauge
and heat gun to measure the effects of increased temperature and
how directly they affect current consumption within the stated
operational range from Mbient Lab.
We took the Metamotion C up to 77
degrees C and idle consumption went all the way to 215uA!!! at
46 degree C we are measuring 35uA.
In many countries
that see up to 45 degrees C, storage facilities could easily exceed the ambient temperature and result in well beyond the specified idle current consumption.
Response from Matt regarding the
Cpro power consumption.
chemical potential and thus voltage will change over temperature
altering consumption, as well as the performance of active devices
in the many semiconductors. Generally this increases consumption
at higher temperatures, but depends on the component. For the
system as a whole you should not expect more than 30-50% -- idle
currents are generally affected more than active currents, because
leakage current increases with temperature. This is why the
specification is generally looser than measured in typical
conditions."
In Matt's response he states no more
than 30-50% increase in consumption with increased temps. We
have found close to a 800% increase. Under cold conditions (sensor in a freezer) we could only achieve 14.7 uA at best. In your specifications it states
idle power consumption as 10uA minimum to 25uA maximum, Heve you, in your own testing, ever been as low as 10uA?
have the thermistor turned off in idle
mode, as this sensor is clearly drawing a lot of power.
Comments
Thank you for reporting your findings.
Idle current consumption is specified at nominal operating conditions (25C). This is standard for electronic component specification. We will update the data sheet to be more clear.
My 30-50% comment was referring to your specific test at slightly elevated temperatures to possibly explain your result, not to specify performance at 80% of boiling temp.
Idle current is also strongly connected to component variation of the various sensors, which might explain why you cannot achieve 10uA. The spec is derived from equivalent reported values in sub circuit data sheets and verified by DMM.
The thermistor is only biased during active measure for a brief window (10s of us). If it were left on, it would be immediately obvious as the bias current can be as high as 300uA.
If you intend to operate at very high temperatures, please source your batteries carefully as many are not spec'd to handle the full commercial temperature range.