I found this site while googling and am pleasantly surprised that it is covering a lot of things that I have been working on.

For the last few months I have been developing a sensor and associated collector to measure the parameters of electricity supply.

My sensor uses a PIC micro and 433 MHz radio to send to a Pi where the data is stored in RRD databases and displayed via a web page, data is stored for a year before being overwritten. There is normally one connected here but as that is my home IP it is often not there or the sensors are not connected.

It is very much a work in progress but currently has a minimum measurement of about 100 ma and a resolution of 15 ma with a maximum current of about 150 amps. The range and resolution are related to the coil that is installed, I have coils that will go up to about 2000 amps but will not resolve below about 5 amps, horses for courses and all that.

There is little on here about Rogowski coils, it seems people consider them to be too difficult and needing integrators but that is not the case, they are very easy to wind and you do not need an integrator if you use the rate of change of the output to calculate the current.

Interesting to note that certainly on my LV supply in the UK the third harmonic is huge, my incoming waveform hasn't seen a sine wave for eons. For this reason I measure the voltage at 3.33 ms past zero cross over, this removes the third harmonic.

Interesting link if you are UK based. My sensor will track that frequency which was a real buzz.

I made a LinuxCNC based machine to wind the Rogowski coils best use for an inkjet printer ever.

The Raspi has problems for this sort of use. If power is lost it trashes the SD card (or USB stick) so I made a board with battery backup to auto start and shutdown the Pi.

The PCB and schematic files are here if you want them

Also on that PCB are a RTC and a temperature/humidity sensor, RTC using I2C and the DTH11 using one wire comms

Sample coil

Some coils being tested

That copper bar is two turns on a transformer, it allows me to make a maximum of about 300 amps. 

Prototype sensor


Main problems currently are related to calibrating the measurements. My LV supply is not stable enough to allow accurate calibration so I am currently making a PIC based 50 Hz oscillator to provide stable voltage, current and phase in order to allow me to finalise the equations for accurate measurements. Phase is a real sticky one as the phase shift through the Rogowski coil and associated opamp circuit is dependent on current, a really horrible thing to solve.

Anyway, enough for now, off to read the forum.