Instrument Loops - 4 -20ma vs. 1-5 VDC

  • Thread starter Sergio Toledano
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Thread Starter

Sergio Toledano

Is soo easy, remember Ohm's law:
V= I*R.
For best exactitude use 1% resistors or better.
Ohm Law works well here:
E = I x R
E = .004Ma x 250 ohms =1 volt
E = .020Ma x 250 ohms =5 volts
Calculated as a series circuit
I need help understanding how placing a 250 ohm resistor across a 4 - 20 ma load will change it to a 1 - 5 vdc signal.
I usually use a 250 ohm resistor to measure a loop that I don't want to break to get in sereies with. Of course you use ohms law to obtain the resistor value. I use that resistor as a regular "tool".

Current stay the same in series. Voltage stays the same in parallel. It really isn't a "stupid" question. You would be suprised how many rookies right out of school do not know this.