Remote amp meter....

Discussion in 'The Projects Forum' started by Logo, Feb 22, 2011.

  1. Logo

    Thread Starter New Member

    Feb 18, 2011

    This is my first post on your website but i think that it is a really interesting site!!

    I am working as a technician for an “NGO” (like the red cross) in a 3rd word country at the moment the hospital that I work at is quite big and we are using a 250KVA generator to run it. However I am working mostly on the other side of the hospital but would like to keep an eye on the amps per phase that are coming out of the gen but I don’t what to run a cable all the way over the compound. So I was thinking if it was possible to do it wireless, as my resources here are quite limited and my electronics level quite low the only thing that I could come up with was a wireless thermometer. I was thinking that if I bought 3 of them (would have to buy different brands I guess so that they were different frequencies) taped into the temp measurea (resistor) and then used the Hall effect to measure the amps I would just need a simple circuit to go from a volts reading to measurement of resistance? I saw one post on this site form “hgmjr” about a home made amp clamp so I guess that it is possible. Oh and the other thing that I would have to do is to boost the signal as it is about 200m away………… what does anyone think?? I am not sure if you can do this with an AM radio signal as well???

    Thanks for any help :)
  2. JDT

    Well-Known Member

    Feb 12, 2009
    Sending a wireless signal of the current measurement can be done, obviously. It's not a simple project though. You could buy equipment to do this. Not cheap.

    I like your idea of measuring the temperature of something and sending the temperature measurement. Back in WW2 (not that I was there then!) there were meters that measured the current that a radio transmitter fed into the antenna that basically measured the temperature of a series resistor with a thermocouple and used that voltage to operate a meter.

    The measurement is not going to be very accurate however due to the effects of ambient temperature.

    Not sure about Hall effect. What you need are three current transformers, 1 for each phase. These are like a ring of iron with a hole in the middle. The power cable passes through the hole and is the 1-turn primary of the transformer. The secondary is wound on the ring and the whole thing is insulated. They usually have a ratio like 1000/5 which means that if the cable going through the middle is carrying 1000A then the secondary will carry 5A. It is very important that the secondary never becomes open-circuit.

    But if you connected a 1Ω resistor (say) across the secondary of each one you could measure the temperature of these. It has the advantage that your resistor is not connected to any high voltage. In fact, one side of each of your secondaries should be earthed for safety. Probably good to have each resistor and probe thermally insulated to minimise the effect of ambient temperature.
  3. n1ist

    Senior Member

    Mar 8, 2009
    What about a wireless video camera (or IP/WIFI one) pointed at the metering panel of the generator?
  4. Logo

    Thread Starter New Member

    Feb 18, 2011
    thanks for the help guys. :)