Current to pneumatic signal transducer 1

[maxchief]

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,

 

[tommy75]

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

 

[Ashereng]

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
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[m777182]

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

 

[KiwiMace]

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.