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Looking for a signal conditioner

Discussion in 'Electrical Engineering' started by BIGEYE, Sep 1, 2005.

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  1. BIGEYE

    BIGEYE Guest

    I've got a level transducer that I want to use on a project. The transducer
    has a 4/20 mA output equivalent to 0 to 5 metres. Unfortunately the range of
    the transducer is too large for what I need. I only need about 4 to 9.8 mA =
    0 to 1.8 metres. The receiving instrument is 4/20 mA input = 0 to 100%. My
    100% is 1.8 metres and not the 5 metres of the tx.
    Is there a signal conditioner available where I could input the 4 to 9.8 mA
    and get 4 - 20 mA output, or is there another way (apart from buying a new
    tx to the range I require).
    TIA
     
  2. You don't indicate what sort of receiving instrument you are using. or what
    sort of control you have on your level transducer. You basically need to
    change the slope parameter on one of them. If your receiver is a dcs, an
    sldc, or a plc, there is a decent chance that you could redefine the
    bandwidth in the receiver without a lot of trouble.

    There are some signal available which convert between various protocols.
    One of these might have a range which works for you. Setting your initial
    signal up as a voltage (0 to 10 volts) using a resistor might let you change
    from 0 to 10 v to 4 to 20 mA, which would give you your range.
    Unless you absolutely need the extra precision or absolutely must have the
    full 16mA bandwidth, I'd either get a transducer which fits the right range,
    or just go with the 9.8 mA maximum signal, rather than modify it.

    I'm not so concerned about your ability to fool with it. It's avoiding the
    headache for the next guy who has to deal with non standard equipment.

    Michael
     
  3. BIGEYE

    BIGEYE Guest


    It is an analogue readout 0 - 100%
     
  4. Iain

    Iain Guest

    You sure it doesnt have a zero and a span adjustments to let you set the 0
    to 100 percent to twhatver loop current you need? Most I've seen have,
    rather than rigid 4-20 = 0 to 100.
     
  5. Jerry Avins

    Jerry Avins Guest

    Draw a new card for the meter. Your intended use is nearly full scale;
    that ought to leave you with enough accuracy.

    Jerry
     
  6. Dave Slee

    Dave Slee Guest

    Without hesitation, I'd reccomend to anyone who plays with 4-20mA loops,
    +/-10V command signals, valve drivers and so on to have one of these in
    their toolbox...

    Weidmuller WAS4 PRO DC/DC part no. 8560740000

    http://www.weidmuller.co.uk/docs/do...&m1=20177&m2=20287&m3=24448&m4=26245&m5=28604

    (go to the website for Weidmuller, Downloads, Catalogues & Brochures,
    Product Information, Electronics, Analogue signal conditioning, page 28
    onwards). Sorry, its big at about 3MB of PDF, but it is well worth having
    for reference.

    OK, why do I think they are so good? Apart from pulling me out of the brown
    smelly just recently, these things will take more or less any voltage or
    current signal and linear scale it to more or less any other voltage or
    current signal with true three port isolation. They do standard calibrated
    ranges like 4->20mA or -10->+10V. They do bipolar current like a +/-10mA
    command signal. They run off just about any auxillary supply to hand either
    AC or DC. They have span and zero pots for weird sub-ranges of either input
    or output. And a killer feature... 10kHz bandwidth with a switchable filter
    to slug that to 10Hz bandwidth.

    For signal conditioners they are quite pricey (£130 or so each in the UK).
    But the beauty is they bodge anything to anything.

    As for the brown smelly I mentioned? I'm using some to actually drive
    hydraulic servo valves directly. The old controller I have wants to send
    +/-50mA PWM current with 500Hz dither and my modern replacement valves with
    on-board electronics expect +/-10mA. Yes, I could try setting up a current
    divider with parallel resistors across the input to the new valve, but it
    was easier just to put one of those conditioners in and set the appropriate
    input and output ranges, 10kHz bandwidth and off I went. Got a ground loop
    isolation which turned out to be beneficial as a lucky side effect too.

    Hope this saves you trawling through many, many catalogues.

    Best Regards,
    Dave Slee
     
  7. BIGEYE

    BIGEYE Guest

    Thanks, these look very useful.
     
  8. luke

    luke

    15
    0
    Sep 1, 2009
    TURCK also makes level transducers
     
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