Hi gang, I need a bit of advice from you 4-20ma instrumentation experts. I have 4 - 4-20ma sensors that I want to input into a sitcore product (probably the portal), so I can display well and tank water depths, along with 10 or so digital values (tank float switches and misc alarms). The portal will be in the house, the sensors and float switches are in a separate building about 125 feet away. I have 2 unshielded 4 pair (no ground wire) ethernet cables connecting the house with the remote location, so I’ve got 16 (8 pair) conductors to work with. I could route the 4 4-20ma sensors to the house using one cable, which leaves me with 7 available conductors after allowing for a ground, not enough to cover off all of the digital signals.
I could install an analog to digital chip in the remote location and use I2C or SPI to read those values, but I don’t think I2C or SPI over 125 feet of wire works so well. Instead I am thinking of just using resisters in the 4 4-20 sensors at the remote location, and just measure the voltage (would require 4 wires (plus ground) instead of 8 wires). I don’t expect much signal interference on the cable as everything is 10ma or so low voltage signaling. Should this work?