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AC current sensor with interface

Discussion in 'Electronic Repair' started by Geir Holmavatn, May 20, 2010.

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  1. Hi,

    I'm looking for non-contact current sensors for 0-60/70A AC connected to
    some digital interface (1-wire, GPIB, RS422, ethernet etc). The
    measured cable should run through a hole in the sensor and not be
    galvanically connected.

    I need to monitor and register AC current with a computer from different
    appliances...

    Thanks for comments and tips on where I can find such sensors..

    regards Geir
     
  2. Den 20.05.2010 19:38, skrev David Nebenzahl:
    I need a *digital* interface which can be read / monitored by a computer.

    The Coleparmer module does the trick, but it just goes to max 25A and I
    hoped such modules would be less expensive than those...

    Other comments?

    rgds

    Geir
     
  3. mike

    mike Guest

    You don't say exactly what you're trying to accomplish,
    so this may be tangent to your requirements....but I'll try
    not to let that stop me.

    I set out to instrument my home for the purpose of
    energy conservation. I intended to use a current probe
    and PIC processor to acquire the current data and
    send it via RS232 either directly or via RS232-Bluetooth
    adapter.

    I started with Mike's metrology rule #1:
    Never ask a question unless the answer will modify
    your future behavior.

    And a corollary: Real-time data without real-time
    control is overkill. All it gives you is worry.

    I went around the house with a RMS power meter measuring
    everything that would unplug.
    The bad news is that a bunch of things like a wireless
    telephone at 5W each really add up.
    The worse news is that I'm unwilling to give them up.
    I did unplug infrequently used vampire devices.

    Since most things are either on or off. If you know
    the consumption, you don't have to measure it in real-time.

    A Kill-A-Watt device for under $20 will measure and log
    data for you. But you have to interrupt the circuit.

    Moving on to the harder devices, I started with the
    biggest energy consumers.

    First stop was the furnace. It's gas. Hmmm.
    I determined from watching the gas meter go around
    that the 60KBTU/HR rating was pretty accurate. So, it
    was sufficient to measure the on-time. For that,
    I used a hunk of cardboard on a microswitch that
    opens when the furnace fan comes on placed over a vent.
    I used an old Palm III to plot the on-time. Calculate
    the gas cost plus the fan cost determined using a
    hand-held current clamp meter completes the calculation.

    For most things, they're either on or off. If you use
    'em less, you save. Knowing exaclty how much you're saving
    TODAY isn't useful. If your furnace thermostat is already
    as low as you can tolerate, you've done all you can.
    And you didn't need a single measurement to reach that
    conclusion.

    Next, I tackled the electric water heater. The wires
    are accessible, so I used a clamp-on probe from an old
    Triplett analog meter. It's much better than more modern
    sensors because it puts out 500mV/Amp.
    Plugged that into a Radio-shack
    DVM with RS232 output and used a laptop to log the result.
    Now, I know how much it costs to take a hot shower or
    wash a load of clothes. The thermostat is already as low
    as I can tolerate. Not much use for additional
    measurements. The plan to use a PIC to measure the sensor
    output and transmit it via RS232 or bluetooth has been aborted.

    Kitchen appliances weren't worth measuring. I'm not
    gonna stop reheating my coffee just because I have
    real-time data on the microwave. See Rule #1 above.
    I did buy an energy-efficient fridge.

    The air conditioner wiring wasn't accessible, so I
    took an alternative approach.
    Our neighborhood just got those newfangled digital
    power meters from the power company. Mine puts out
    an infrared pulse for every watt-hour consumed.

    WalMart sells individual cake slices in a plastic
    box that is a nice friction-fit over the power
    meter cylinder. It's just the right size to put
    in a PDA. The handspring visor variant of the
    Palm III works better because the IR sensor is
    on the side.

    A little bit of code and a lot of hair-pulling
    later, I have a program that graphs and logs
    power consumption. And since it measures
    exactly what the power company charges for, I
    don't have to worry about power factor, etc.

    If you control what else comes on at the same
    time, you can determine the "signature" of various
    major power consumers. That done, you can
    usually tell what's going on/off from the log.

    The PDA cake-boxed onto the power meter can do anything
    I need to monitor electricity consumption.

    Now that I have the data and have modified
    my behavior, the measurements stuff in in a
    drawer. Refinement plans have been aborted.
    I'm really glad I didn't invest a lot of $$$
    in permanent measurement and control facilities.

    Rule #1 rules...

    YMMV.
     
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