efigalaxie
Member
I just was hit with something that threw me for a loop.
With a three wire 4-20ma loop, another tech simply placed his Fluke meter (set for measuring DC ma current, leads on the meter correctly) across the negative and signal lines for the sensor and read current. I broke the loop and inserted the same meter into the loop and it read the same. He told me on 2 wire loops that this would blow the meter fuse, but on the 3 wire, it wouldn’t. This is really bothering me. Why can we get an accurate reading both through the meter and placing the meter across the loop - in a 3 wire loop?
With a three wire 4-20ma loop, another tech simply placed his Fluke meter (set for measuring DC ma current, leads on the meter correctly) across the negative and signal lines for the sensor and read current. I broke the loop and inserted the same meter into the loop and it read the same. He told me on 2 wire loops that this would blow the meter fuse, but on the 3 wire, it wouldn’t. This is really bothering me. Why can we get an accurate reading both through the meter and placing the meter across the loop - in a 3 wire loop?