Using TT Electronics HM31-20050LF Current Sense Transformer with Arduino Uno.

I am using TT Electronics HM31-20050LF Current Transformer ( to detect current through a wire. I have been following primarily these two guides:

  1. CT sensors - Interfacing with an Arduino | Archived Forum

  2. Learn | OpenEnergyMonitor

I selected a burden resistor of 10 Ohms and our Current Transformer has ratio of 50:1. Therefore, in my code other than converting the 0-1023 range to the 0-5v range and taking true RMS all I should have to do is multiply by a factor of 5(÷10 and ×50). For testing purposes my load is a single lamp pulling 0.5A according to this power meter ( However, the Arduino with the help of my code is outputting 0.15A.

My current assumption is that the transformer they are using in the guides ( have some sort of built in functionality that I may need to recreate.

In practice, you need to calibrate your entire setup against a wide range of loads. 0.5 A is minimal, and you need at least 15 A in the primary circuit to properly calibrate the upper end. A 1500 W room heater would be suitable for the maximum load.

Good general tutorial on calibration here.