07. Selecting Temperature Sensors - larry-athey/rpi-smart-still GitHub Wiki

There are many manufacturers of the DS18B20 temperature sensors. Dallas Semiconductor invented it, but it's not a patented design, so anybody can manufacture and sell them. This means that you will find good ones and bad ones, and you likely won't know their quality until after you buy them and put them to use.

Their specifications say that they have a range of -55C/-67F to 125C/257F, which is well within tolerance of any temperatures that you will find in an operational still. However, I have seen cheap ones crap out and stop reading after a couple distillation runs. These were HiLetgo brand units that I got from Amazon, 5 for $10. These work just fine for the temperature sensor on the hydrometer, but not anywhere on the still itself.

After replacing these three times, I finally got fed up and ordered them from Adafruit for $15 each and haven't had a single failure since then. These are built much better and have PTFE insulation and a braided shield on the cables, so you definitely will not melt the wires inside if it comes in contact with a hot surface. If there are other brands that sell a similar model for a better price, I don't know who they are. I just suggest getting these to start with to save yourself the expense and grief of having to repeatedly replace failed sensors.

If you haven't done so yet, please see my video that demonstrates the installation of these sensors. My method of attaching them to my still may come in handy for you if you don't already have temperature sensor wells on your still. All metals are great temperature conductors, so there really is no reason to drill holes in your still to install wells. They work just as accurately mounted to the outside using my method. The only exception would be if you have an oil jacketed boiler. In which case, you definitely need some kind of well into the wash vessel.

If using my installation method, the sensor on the boiler and column should be at the middle of their height. This is especially critical with the boiler so that the sensor is always in contact with an area where there is wash on the other side of the wall. You don't want to be measuring vapor temperature in the boiler. In the case of the column where you are measuring vapor temperature, you want to measure it where the vapor is still in transit. If you have bubble plates on your column, the sensor would go immediately above the top bubble plate before the dephlegmator.

In the case of the dephlegmator, you want to measure the temperature of the discharge water rather than the vapor since the dephlegmator can actually completely stop any vapor from passing through if it's running too cold. The slower the water flows through the dephlegmator, the hotter the discharge water will be and the more water vapor will pass through to your condenser. The best way to monitor this is to put a Tee on the cooling water discharge port and use the side connector to hold the temperature sensor in the water path. You can use any kind of silicone to seal it in place, food grade silicone isn't necessary since it's not in the vapor path.

NOTE: You want to make sure that there is at least part of the DS18B20 metal body on the outside of the Tee. If the sensor does fail, you will need something solid to grab onto in order to twist it out of the silicone. You may need to cut down the side connector of the Tee in order to achieve this.