If you want to build your brewery setup using an arduino or a raspberry pi, you are likely to use the «one-wire» temperature sensor DS18B20, There is several guides on how to build 1 kettle up to 3 kettle systems, and building the temperature probe into the kettle. If you want to do the same with the one wire sensor, you should use a welded thermowell. There are some thermowell options available from amazon or ebay, but you have to make sure that the DS18B20 waterproof housing fits inside. To get you on the right track, here is the one we are using (from ebay) Its important that you check the internal diameter of the pole. The one we purchased is 8mm ID. That leaves plenty of room for the temperature sensor.
The common setup with large systems is to use RTD probes (PT100,PT1000) + mini XLR or 3pin connectors. These are available with the complete assebly (thermowell + 3pin connector) Now, this is what you want to duplicate. For the ease of cleaning and moving your brewery equipment, its nice to be able to disconnect the sensor from the kettle itself. Ideally, an XLR connector or RJ45 in the brewery controller, and a 3pin mini XLR or other types on the kettle. This gives you full flexibility when moving or cleaning etc..
I have been searching all over the internet looking for such connectors that will fit my thermowell (1/2 NPT Female) The only one ive found is this complete assembly, but its quite expensive + shipping. You can find much cheaper RTD sensors with this assembly from ebay like this one. So we bought one and did a teardown of it to use the attached 3pin connector end.
Pull out the PT100 sensor (the white pin on the picture below) and then cut off the pole (long metal tip) on the RTD thermowell.
Once the original RTD sensor is removed, you have to solder the DS18B20 in its place. We have 3 pin connector, so exactly what we need for our DS18B20. These pins you need to solder on are tiny, so make sure you dont overheat and burn them. Make sure that you check what pin goes to which color on the RTD wire. When you mount everything back, you want to know this to connect to your raspberry pi.
So, we are left with a 3pin connector on a mounting plate and a 1/2 NPT male. This will mount to our new thermowell with the 1/2NPT Female
Now, the RTD thermowell can be fitted inside the new DS18B20 thermowell, leaving you with a nice 3pin connector at the end.
So, all in all, it came to roughly $29 with free shipping from ebay.
Partlist for this;