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Router
Participant

Join Date: Feb 2008
Posts: 2

Electronics

02/12/2008 11:50 AM

hi all I need a circuit diagram to provide a 4 to 20 ma source. This is part of a college assignment. I wanting to biuld a mains powered 4 to 20 ma source. The input to the module can be either 12/24 DC via a power supply and ideally the circiut will be conventional using an op-amp and transistors. I would also like to incorperate a digital current display.

Thankyou in advance
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bhankiii
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Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: El Lago, Texas, USA
Posts: 2639
Good Answers: 65
#1

Re: Electronics

02/12/2008 3:30 PM

It would be helpful if you specified at what voltage you need your current, and under what conditions you need 4 vs 20, but look at the data sheet for the LM317 voltage regulator. It can be easily used as a series current regulator - using one external resistor - 62 ohms will get you 20mA, IIRC.
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Router
Participant

Join Date: Feb 2008
Posts: 2
#2
In reply to #1

Re: Electronics

02/12/2008 5:02 PM

The supply voltage is 24v dc and the mA's have to be variable between 4 and 20. It is to be used simulate instrument signal loops.
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bhankiii
Guru
Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: El Lago, Texas, USA
Posts: 2639
Good Answers: 65
#3
In reply to #2

Re: Electronics

02/12/2008 5:09 PM

You can use the LM317 with a variable resistor to set the current, or a digital potentiometer if you need automatic control.
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