Hallo to everyone. I have connect my raspberry with emonpi image installed to RPICT8 ( board with 8 sensor W ) My problem is that with this configuration i see 50W value with nothing connect to sensor. What is the problem ? Thanks and sorry for my bas english
Hello, and welcome to OEM. And your English is much better than my Italian. 
I do not know the RPICT8, but how big is 50 W relative to the maximum that your CT can measure? Most CTs can measure accurately down to about 1% of their rated value, below that errors inside the CT and electrical noise from the Raspberry will spoil the reading.
You can multiply the sensitivity of your CT by passing the wire though the centre a number of times. For example, when I test the 100 A CT, I use a coil of 20 turns and a current of 5 A, and the c.t. reads 100 A. If you do that, then divide the power you measure by the number of times the wire goes through, you will divide your reading of 50 W by the same number.
From the LeChacal (developer of the RPICT8) web page:
Any current sensor with current output is compatible. Note there are considerations for the burden resistor which scales the range of measured current. We recommend the sensor below to start with.
Recommended sensor:
- SCT-013-000 100A/50mA
- SCT-019 200A/33mA
- SCT-006 20A/25mA
All three CTs are listed on their Shop page.
Thankyou at all, my sensor is SCT-013-000 and the 50w respect 22KW for 100A max is only 0.3% but if i measure 200W , 50W is more important .
True, but as Robert mentioned, the anomalous readings are likely to be noise picked up
from the digital section of the board itself, or possibly from the RPi.
In addition to that, a “noisy” power supply can cause the issue you’re seeing.
Good idea i try to supply with other power supply . I will give you feedback.
Hi everyone, I update you on the situation, I proceeded to modify the file emonhub_interfacer.py. I modified this line “val = decoded [i] * float (x)” to “val = decoded [i] - float (x)”. In this way I use the scales parameter to reduce sensor reading errors.
Thankyou at all