STPM33 power offset calibration not working

[APV]

Hi ,

I have been testing STPM33 power offset calibration.It seems not working as per the Calibration application note.The document says we need to write offset values to offset register in the sensor and then the read power will be substracting that offset automatically.But when I tried ,this was not happening.The power measured found not changing even though we tried different values to the offset register.

I also tried with ST GUI application for STPM.In GUI , when I write to offset registers , the displayed power getting varied which seems correct as per calibration document. But when I checked the register values of that measured power(which is displayed in GUI itself) , the value was not changed.It seems to me the GUI displaying section substracting the offset its own!

Also to add on to that ,when I tried continuous sample mode on GUI application , the measured values are listed in another window where power data was not changed. At the same time ,if I close that window and click read once ,then displayed power is changed as per offset.

Is this a bug in the chip software ?

[Didier HERROUIN]

Hello,

Do you get this trouble with Active Power Offset or with Apparent Power Offset ?

Usually, Power offset calibration is not needed even to get high accuracy. Power offset at no current is due to ADC Sigma-Delta architecture, but its impact will disapear with higher currents.

And how do you use STPM33 ? Do you use 1 voltage input with 2 currents ?

Note that even if you see some small Power oscillation (@100Hz) during your measurements, it will not impact Energy measurement as this oscillation will be cancelled during integration.

Regards,