Oooh, I get it. Your current is correct, but you are assuming that it is high because of the 5.1 V. You probably have an odd resistor value(340 ohms?) at the end of the loop. It should be 250 ohms. Chris Parrish
I&C Specialist
Dekalb County, GA Water & Sewer
cjparris@co.dekalb.ga.us
Install an ultrasonic transmitter at a fixed position above the roof. Milltronics makes a simple "Probe" that works great for this kind of application. Chris Parrish
I&C Specialist
Dekalb County, GA Water & Sewer
cjparris@co.dekalb.ga.us
What other checks have you made? Have you checked the input to your retransmission device? How do you suppose you are getting 21 mA?
If the VFDs are both connected in series, make sure that their inputs are floating and not single-ended. Try removing one of them from the circuit, and check...
You are adding the potential for noise, grounding, and isolation problems. Dual power supplies are fine, but not on a single current loop, and you do have a single current loop. The theory behind current loops is that outputs are SERIAL, not parallel. Stick to established conventions, and...