3 Wire Vs 4 Wire. The fourth wire operates similarly to the third wire, but in reverse: The electronic device you're using to interpret the rtd's resistance is usually the deciding factor here. Open neutral between the two panels would make the ground hot in the 3 wire.
If we know vs and vo, we can find rg and then solve for temperature.
The only advantage i can see is the 4 wire gives you a dedicated ground fault circuit vs sharing the neutral wire. Transmitters are available with a wide variety of signal outputs. Of course all you need is the red and black wire to run your computer fan, but if you didn't know what the extra wires are for, this video may help you out. For the 00, 000, 0000 etc. The one in the system has 2 wires on it. The only advantage i can see is the 4 wire gives you a dedicated ground fault circuit vs sharing the neutral wire. He bought a new fan for $10 and said it has 3 wires on > it. There are also faster variants with even more wires.
