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Current to pneumatic signal transducer

Current to pneumatic signal transducer

Current to pneumatic signal transducer

(OP)
Hello all!
For anyone who may be interested,
I wish to demonstrate a P/I transducer which receives an input signal of 4-20mA and uses a 20 psig air signal to produce an air signal out of 3-15psig to some pneumatic actuator, such as a damper
motor or a modulating valve.
Is there an inexpensive device for generating a 4-20mA signal?
I am told that 10volts and a 500ohm resistor will produce 20mA
but how do I feed this to the transducer?
It does not have to be a smooth modulation, although that would be preferable, I would be willing to make four set-ups,
one for 5mA,10mA,15mA, and 20mA each.Possibly someone may know of some purchasable device for under a gazillion dollars!
Does a rheostat and some sort of resistance device make any sense?
Thanks for any help and Happy Thanksgiving,

RE: Current to pneumatic signal transducer

  Transcat model MS-420, you can see it in the online catalog at transcat. This should work just fine for your Demo. and its only $215.00

RE: Current to pneumatic signal transducer

maxchief,

A 4-20mA to 3-15 psig transducer is usually spelled I/P.

Anyhoot. If you have a Fluke, most have a 4-20 mA signal source/generator. You can use that to generate the various 4-20 mA signal you need. Most instrumentation techs have one - maybe you can borrow one? Flukes come in a wide range, some up to $10,000 - so I wouldn't suggest you buy one unless you need it for something else.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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RE: Current to pneumatic signal transducer

If you accept "modulation by hand" then a 1,5 V battery source in series with a rheostat 75-375 Ohms (neglecting the inner resistance of the battery) will produce a 4-20mA current through your transducer. Turning your rheostat up and down you "modulate" the signal. With a selector switch and fixed resistors you can set your current to preselected values.
m777182

RE: Current to pneumatic signal transducer

I'm thinking that the I/P will have a coil that requires closer to 24-40vdc to operate.  Building on the above, using a 24V supply, you need resistors or a potentiometer to wind through this range:

0%    6k    4mA
25%   3k    8mA
50%   2k    12mA
75%   1k5   16mA
100%  1k2   20mA

and 0.5W or bigger.  Use a decent ammeter to dial the pot into your actual desired mA.

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