Calisense: The non invasive current sensor theory of operation
Calisense consists of 4 blocks.
1: A magnetic toroid with a hall sensor embedded inside. When current flows in the wire it creates a magnetic field which is captured by the toroid and focused on the hall sensor. The hall sensor puts out a voltage proportional to the magnetic field which itself is a function of the current flowing in the wire.
2. Analog filter circuits which clean up the raw signal from the hall sensor so that it can be digitized.
\3. An Arduino then takes the voltage and converts it to digital. The hall sensor is unbiased and will measure both positive and negative currents from +100A to -100A. The Arduino a/d is 10 bits or has resolution of 1024 thus the maximum sensor accuracy is (+100A - -100A)/1024 or roughly 0.2A. Of course there are other noise in circuit so the actual accuracy is closer to 0.3A. The Hall sensor response is non linear so it is modeled as a piece wise non linear function inside the Arduino code base.
4. From the Arduino to the PC or cell phone it is transmitted via USB to a serial terminal monitor program which displays the current. In case of a PC the serial terminal monitor can also save log of the sensor results along with a time stamp.