Hi,
I'm looking for some help choosing a good current sense transformer for an energy meter product I'm working on.
The device will switch on/off up to 8 IEC Outlets at UK Mains voltage. It will also monitor, and record, the current going through each outlet.
It's the current monitoring side of things I'd like to ask about.
I guess there is really two approaches to this. i)Shunt resistor ii)Current transformer. - Am I right so far?
I opened the clamp that comes with my BritishGas energy smart meter and it uses a current transformer. Some basic tests with my 'scope suggest it outputs approximately 1mV per Watt.
Now, looking at the current sense transformers available at uk.farnell.com I see there are basically two types - ones where you basically run a physical wire through the middle of a board mounted transformer, like this 
(farnell # 1454873 and similar) and ones where you form the primary circuit through pads on the board, like this : 
(farnell # 1579333).
Personally I'd prefer to use the second type if I can.
The trouble is there is quite a wide range of these on Farnell, and I need some help selecting the correct one. So here are the requirments:
Maximum of 2kW power draw, but normally each outlet will be providing only about 60W - 100W, and I still need to be fairly accurate down to low current draws of say 1W to 4W. (The client wants to be able to detect if a unit is operating, is in standby or is off/missing)
So can you help me select a transformer which can handle the maximum current, yet still be accurate at low power levels.
Or, maybe you can tell me I've got it all wrong and need a different approach completely!
