I am not a thermistor advocate for industrial work.
Thermistors have two problems
- the entire thermistor market is aimed at OEM business, embedded temperature sensing in a product. So the packaging tends to be tiny and unprotected. Process mfg like United Electric do offer packaged thermistors, packaged in a stainless sheath, like an industrial RTD or thermocouple, if you really want to go there.
- You have to deal with the non-linearity of a thermistor's curve, and its range. When you're talking 1° that can be an issue and you've already run into the issue as to whether a standard resistance I/O card can handle a given thermistor and even trying to find a thermistor.
Most, if not all PLC's offer an RTD card or a thermocouple card or a universal temp card that routinely handles either RTD or thermocouple, but when it comes to a thermistor, you're on your own: getting a resistance card with a fixed current output and then doing a polynomial or look-up table to convert to temperature. While that design effort can be amortized over thousands of units for an embedded thermistor in a consumer production item, in most industrial projects, it can't. It's a whole lot of work to implement a thermistor for an industrial job, but it isn't for an RTD.
Process instrumentation distributors can handle RTD's for you. Someone's recommended one, there are dozens, if not hundreds of others. Personally, I'd stay away from Grainger, because no one there knows an RTD from a pipe wrench, but that's my experience.
You definitely want a 3 wire, 100 ohm, DIN standard, platinum RTD. On the PLC end, all modern RTD I/O cards do 3 wire with compensation. There are very FEW RTD inputs that handle true 4 wire RTD's that are not priced for lab work; besides, the practical difference in accuracy between 3 wire and 4 wire outside of a laboratory environment is negligible so it isn't worth shooting for 4 wire accuracy. You do not want a 2 wire RTD because the offset error over 100' of copper wire is substantial. A 3 wire RTD is the perfect avenue with its compensated lead resistance.
If they're indoors, you might not need a 'head' (although a head serves as a junction box), you might be able to use the leads coming out of a stainless steel sheath.
above: RTD with a 'head' that's used as a junction box (terminal strip inside).
above: An RTD in the sheath with some lead wire attached. A coiled spring serves as a strain relief
Sometimes you need a compression fitting to hold it in place:
Either buy RTD extension wire (color coded) from the distributor who sells you the RTDs or use dual twisted pair cable and leave one wire open. Do not use twisted pair and the shield, because the 3rd wire compensation is out the door.