How far can I run a 10k2 thermistor wire before I have to calibrate? 500 feet ok?

Google was my friend on this, there’s a cable resistance tool here:

https://www.omnicalculator.com/physics/wire-resistance

Plugging in some numbers for length of 500 ft and assuming 18 gauge (1mm diameter) copper wire we get a resistance of 3 ohms. Then checking the temperature versus resistance curve of a 10k thermistor we get 450 ohms for each degree C in the 20DegC neighborhood. So 3 ohm/ (450 ohms/deg C) = 0.0003 DegC . Had to check my math twice to believe that but it looks to be correct. The conclusion is you can use pretty much any cable length with 10k type temperature sensors.

With 1000 Pt sensors on the other hand, these sensors have a change of resistance of ~5 ohms per deg C in this same 20deg region so the 3 ohms would have an offset of over ½ DegC =~ 1Deg F. This is why our T3E-Pt12 expansion modules have an option to connect with 3 or 4 wires which can compensate for the cable resistance.

My suggestion is use a 4-20mA transmitter instead. You are looking for a world of troubles with 500 feet of wire with a thermistor.

Just my experience over the last 30 years.

Jim

If noise is the problem you’re thinking about JD, you could consider using shielded cable, right… ! Just be sure to attach the shield to earth at one end only.

No not noise but 500’ resistive is not how you do it

Typos happen…

Now I’m curious. I’ll run a short one foot run and another long 500 foot run and see how it works and I’ll report back.