Where can I buy small 3-wire PT100 sensors for a PLC system?

Hello,
I’m building a smart home system based on a PLC controller, and I have an RTD6 module that supports PT100/PT1000 temperature sensors. I’d like to use this to measure the temperature in five rooms and outdoors.
Unfortunately, the distance from the RTD module will be quite long – often more than 10 metres – so I’d like to use 3-wire sensors (the third wire being for distance compensation).
Unfortunately, I can’t find any tiny 3-wire sensors anywhere… everywhere I look, there are only 2-wire ones… does anyone have access to them, or know where I can buy such sensors? Alternatively, how can I compensate for long distances with 2-wire sensors?
Best regards
V.

Hmm, I connected the extra wires directly to the sensor. It’s an SMD PT100 sensor, with two wires on each side, connected to the temperature control module.

What do you mean by ‘tiny’? Have a look at the ranges offered by companies such as Czah, Czaki and Limatherm. They have quite a wide selection. However, the sensors they offer are quite expensive (you should expect to pay around 150 zł for a Pt100). The previous speaker gave some sensible advice about soldering 3 or even 4 wires close to the sensor. With a 3-wire system, you should also ensure that the wires are of equal length, identical diameter and made of the same material. It is also possible to take measurements using a 2-wire system with cables of a known length, taking into account the temperature offset resulting from the resistance of the wires used. The problem is estimating this offset without a calibrator. You can try measuring the resistance of the wires and, using appropriate tables relating sensor resistance to temperature, estimate the corresponding temperature offset and factor this into the PLC.

In my humble opinion, the P100s won’t work in this application – it’s like using a sledgehammer to crack a nut, with far too much wiring involved.

Rethink the design: consider using 1-Wire or your own 485 modules. Alternatively, you could try ‘emulating’ the PT100 from the controller side and using digital communication with the sensors.