mA to mV conversion circuit
mA to mV conversion circuit
(OP)
I need to make a simple circuit to convert mA to mV. I have a Fluke 789 Processmeter that will source 4-20mA for calibration. I have a need for a 0-30mV signal that the meter cannot provide. My initial thought was to place a resistor in parallel to the load, but the math works out to a 0.0006 ohm resistor.
Anyone have any ideas?
Thanks,
Todd
Anyone have any ideas?
Thanks,
Todd





RE: mA to mV conversion circuit
So, if you need 30 mV at 20 mA, just use a 1.5 ohm resistor. Offset the 6 mV caused by the 4 mA. And there you are.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: mA to mV conversion circuit
Phoenix Contact and quite a few others have ready-made converters for 4-20 mA ==> 0-1 mA. Pass it through 30Ω of resistance and you're golden.
30Ω is not a standard value except at 5 percent tolerance. You might want to work with a 50Ω pot or else grab a decade box. Or make your own.
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: mA to mV conversion circuit
4-20mA -> 6-30mV
My instinct says to aim for a much higher initial voltage, and then knock it down with a voltage divider adjacent to the input. One would need to be cognizant of the available voltage within the 4-20mA output, and be aware of the input Z for the input.
The higher intermediate voltage may allow easier use of a DVOM to help confirm correct operation at the mid point. It might also help avoid the usual millivolt problems of noise and thermal offsets.
Think about calibration, perhaps with selected values and parallel pots to tweak. One should be able to combine normal values.
RE: mA to mV conversion circuit
RE: mA to mV conversion circuit
A current signal can pass unmolested through crappy connectors and lots of unshielded wire; a tiny voltage signal cannot.
Mike Halloran
Pembroke Pines, FL, USA
RE: mA to mV conversion circuit
OR There are lots of ten turn precision pots on ebay with direct reading dial. Try for a pot under 500 ohms. About a 10 ohm resistor would give you 100mv for 10ma. You could adjust the current up or down to give 100mv full scale. Staying down at the bottom range of the pot would give you a readable 0-30mv
RE: mA to mV conversion circuit
I'll say it again - THANKS FOR ALL OF YOUR SUGGESTIONS!!!
Todd