MechE needs Elec.Cir advice
MechE needs Elec.Cir advice
(OP)
Hello all,
To anyone who may be interested.
I wish to demonstrate a P/I Transducer which when fed an input
of 4-20mA will output to a pneumatic actuator an air signal of
3-15psig. I need to be able to generate a signal of 4-20mA.
I seem to recall that 10volts and a 500ohm resistor will produce 20mA but how do I feed this to my transducer?
It does not need to be a smooth modulation(although that would
be nice) but I would be willing to make four set-ups one each
for 5mA, 10mA, 15mA, and 20mA if that is easier.
Possibly there is a ready made device which I can purchase for
under a gazillion dollars.
Does a rheostat through some sort of resistance device make
any sense?
Thanks for any help and Happy Thanksgiving,
To anyone who may be interested.
I wish to demonstrate a P/I Transducer which when fed an input
of 4-20mA will output to a pneumatic actuator an air signal of
3-15psig. I need to be able to generate a signal of 4-20mA.
I seem to recall that 10volts and a 500ohm resistor will produce 20mA but how do I feed this to my transducer?
It does not need to be a smooth modulation(although that would
be nice) but I would be willing to make four set-ups one each
for 5mA, 10mA, 15mA, and 20mA if that is easier.
Possibly there is a ready made device which I can purchase for
under a gazillion dollars.
Does a rheostat through some sort of resistance device make
any sense?
Thanks for any help and Happy Thanksgiving,





RE: MechE needs Elec.Cir advice
For a slightly more professional ready-made unit which you can connect a potentiometer to, try http://www.prelectronics.co.uk/filer/5111uk.pdf. Cost is about £100 but it has everything you'll need (except the potentiometer) built in including power supply. PR in the UK will supply it factory configured F.o.C if you tell them what config you want at time of order.
Does you I/P converter have any details on it? Specifically look for a resistance. If you know that resistance then it would be possible to calculate the additional resistance required so you can use (e.g.) a 12V battery with a series resistor to drive the desired current through the I/P. To do calculate the external resistance we'll need the coil resistance of the I/P. Can you borrow a multimeter and measure it?
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Sometimes I only open my mouth to swap feet...
RE: MechE needs Elec.Cir advice
RE: MechE needs Elec.Cir advice
RE: MechE needs Elec.Cir advice
Set the pot visually to maximum resistance.
Close the circuit.
Turn down the pot.
Note the current increase and the I/P change.
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If you need some protection. Set the pot to achieve 22mA. Then read its resistance. Procure a resistor that is the measured value or slightly less. Add this in series with everything else. Now if the the pot is run all the way down to zero you can't exceed 20mA plus a few mA.
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Definition: You have stated that you send 4-20mA to a device and it puts out a corresponding pressure.
This makes it an "I to P" not a "P to I".
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com