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Pressure transducers

Discussion in 'Electronic Basics' started by Ryan, Mar 22, 2006.

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  1. Ryan

    Ryan Guest

    I'm trying to learn about pressure transducers and I've learned a tiny
    bit on the web, but not found it as fruitful as I had hoped. (Or I just
    don't understand what to look for.)

    Do they permit air to pass through them, or only into them, like a
    pressure tank?

    Is their output linear with pressure throughout its rated range? If the
    transducer is good from 0-30 psi, then does the output range from
    something like 0 to 30 volts? When their max rated pressure is reached
    and then exceeded, does the output stop changing? Is it accurate to say
    the transducer is saturated?

    Would the power supply in this example need to be 30 volts? Does the
    supply need to be steady? If the supply fluctuates, does that throw off
    the measurement? If the supply is noisy DC, does this throw off the
    measurement?

    It seems like they are always zero to X psi rating. Can the same
    transducer measure vaccuum too? If I want to guage -20 psi up to 40
    psi, can this be done with a single transducer? If not, is there a such
    thing as using two transducers to measure this range and to install one
    of them backwards?

    Thank you.
     
  2. Ralph Mowery

    Ralph Mowery Guest

    Go here and look around.

    http://www.emersonprocess.com/rosemount/products/pressure/m3051.html

    The pressure transducer usually just has air to pass into them.
    The output can be made almost any way. As you did not state what you wanted
    to do, the output in many cases is a 4 to 20 miliamp circuit.
    The output will saturate when the maximum range is exceeded. They may
    overrange a small percentage. That is if the rated output is for 20 psi
    then it may go to 21 psi.
    There are transducers that can be ranged from negative presure (gauge) to a
    positive pressure.
    BTW you can not get -20 psi. Around 14.7 psig is as low as you can get.
    That would be zero pressure absolute.
     
  3. Into or onto them. Some are made like a plug that fits in a pipe
    threaded hole. Some measure the difference between atmospheric
    pressure and applied pressure, some measure absolute pressure (have a
    vacuum on the back of the sensing diaphragm). Some have two ports, so
    they can measure the difference of two arbitrary pressures.
    Some are linearized, some produce an output directly from a strain gauge.
    There are many types.
    Most have some over range with reduced accuracy (or some sort of
    saturation) that doesn't damage the sensor.
    When additional pressure produces no additional output change, it is
    saturated.
    There are many types that operate from a wide range of supply
    voltages. Some regulate the current when a voltage is applied
    (current loop operated transmitter).
    Some do, some don't.
    See above.
    There is always at least a little bleed through from the supply. How
    much is a specification (power supply rejection).
    It may seem like that, but it is not the case, especially for the two
    port types.
    Some can. The absolute pressure types certainly can. A perfect
    vacuum is just their zero scale point.
    With the right one, sure.
    Not the best way to do it, but possible.
     
  4. Brian

    Brian Guest

    Have a look at
    http://users.pandora.be/educypedia/electronics/sensorspres.htm
    Brian
     
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