Hi!
I have a couple of questions regarding the STPM01 energy metering circuit:
We are using it for measuring currents only with Rogowski coils. (We have 4 circuits on our board).
We are not using the voltage measuring, so it is not connected.
The microcontroller we use is a ESP32.
We are only interested in the Irms values, so after reading the registers, we take out the Irms part from the register.
The problem is that the values are not zero when nothing is connected or the sensor is connected but with no lead through the sensor.
This is measured with a Rogowski coil with 50mV/kA:
With no sensor connected the Irms part of the register reading is varying between 0x0001 and 0x0002 (the first or second bit is set (varying)).
With sensor connected but no lead throug loop the register reading is varying between 0x008 and 0x00f.
If we translate this to current, it will be (no sensor): 0.017 to 0.033A and with sensor: around 0.15 to 0.20 A.
Calculated with a voltage of 230V this makes around 5W with no sensor and 40-50W with sensor.
Even if we short the input, the reading is still not zero. (Even if we short at the circuit). It is more like the readings with the sensor connected with no lead through the loop.
We have tried both int the mode PST=1 since we have only one sensor, and PST=5
Is it possible to calibrate away the offset error? Setting bits in CHP doesn't handle the offset error at 0.
Is it possible that there is some electrical disturbance creating this offset?
Is the reading interval of STPM01 important if we only want the Irms, and not using the internal energy measuring and counting function or is it ok to take the reading when we want to (we would like 2 readings per second)?
Best regards,
Anders
