The 3-wire RTD formula, RTD equation, 3-wire RTD working principle, 3-wire RTD advantages and disadvantages.

# 3-Wire RTD Formula

If and only if the wire resistances R1 and R3 are equal you measure the true Pt100 resistance.

As the wire L2 also is coloured red (and hard to follow) you have to keep all the wire resistances R1, R2 and R3 equal.

where

- Rpt is Resistance of RTD
- R1 is Resistance of first lead wire (Extension cable used to connect RTD)
- R2 is Resistance of second lead wire (Extension cable used to connect RTD)
- R3 is Resistance of third lead wire (Extension cable used to connect RTD)
- L1, L2 & L3 are extension cable leads
- Ω1 is the total resistance between lead wires L2 & L3
- Ω2 is the total resistance between lead wires L1 & L2