Microchip has a power monitor chip, and docs on using it to monitor 3phase circuits, heard they were also coming out with a demo board but havent seen or heard anything on that for some time (it was last summer/fall timeframe). This might be exactly what you are looking for? "Peter P." wrote: Anand Dhuru vsnl.com> writes: > Its a unit that would be controlling power to a 3 phase water pump. In some > situations, the wiring would be done for a new installation, which is why I > would like to detect the right sequence as well as a dead phase. > > I would also like to incorporate a feature which tells the unit if the pump > is drawing too much or too less current (taken from a small coil wrapped > around one of the phases and fed to an adc pin), and check if the water is > in fact reaching the destination within a few seconds of the pump supposedly > starting up. > > This is why I would like to use a PIC, rather than go with an analog > solution. > > I dont think the sensing needs to be too fast. This looks like a microprocessor job then. I think that you have to monitor both current and voltage on all three phases to work around the 'generator' effect pointed out by someone else. I would probably look at a solution using three hall multipliers used as active power meters, one per phase, fed into an a/d converter each, plus a 'floating zero' meter for a fourth a/d channel (to see voltage balance between phases). Plus (remote ?) sensing of some kind for water flow. This could be expensive. Also speaking of 'not too fast', the inrush current of the motor will be huge and probably read off scale for your metering arrangement. It would probably be indistinguishable from a short circuit. Also depending on whether the pump starts primed or not there could be a second current peak later when the pump gets primed after starting. Peter P. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist