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I am not entirely sure if this is the correct forum to ask this question so please refer me on if there is a better arena.

I am creating a small weather station and I wish to measure soil temperature. I am aware that digging a hole and then burying the sensor will alter the aeration of the soil and therefore give imprecise readings. I have therefore decided to integrate the sensor into a notch in a steel tube and then drive this tube into the ground. This means that there will be minimal disruption of the soil composition and the sensor will touch the soil both inside the tube and outside.

My concern is that the steel pole will retain heat differently to the soil (both from any showing to the sun above ground and more generally below the ground) and in doing so skew the temperature readings. Can you recommend a coating that I could put on the metal to reduce its conductivity/radiative properties and therefore minimise its impacts on the sensor?

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    $\begingroup$ How long is the tube? For modest lengths there may well be plastic tubes that work. I know there are coatings for metals that would help you, but I don't know enough to recommend one. One place you could start is by researching the epoxy coating that is sometimes used on rebar. It is thick and durable and (I assume) would have some insulating properties. $\endgroup$ – Ethan48 Jan 31 '16 at 16:26
  • $\begingroup$ Thank you, any pointers are useful as my googling so far hasn't yielded that much. The sensor needs to be 15cm deep and the tube needs to anchor 1.5m of tube above ground, but we were probably going for around 20cm. $\endgroup$ – PaulBarr Jan 31 '16 at 17:53
  • $\begingroup$ I suspect there is an ABS plastic that would work for you. $\endgroup$ – Ethan48 Jan 31 '16 at 18:44
  • $\begingroup$ To coat the steel do you mean? Thanks for your help $\endgroup$ – PaulBarr Jan 31 '16 at 20:06
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    $\begingroup$ Paul, it's easy to cut ABS or similar plastics with a hacksaw. $\endgroup$ – Carl Witthoft Feb 1 '16 at 15:03
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Instead of trying to add insulating coating to the metal tube, I would try to get rid of the tube that protrudes above ground. The tube would serve as an introduces for the sensor. The tip with the sensor could be designed such that it stays on the tube as when you push, but separates from the tube when you pull.

Or try to interrupt the thermal conduction path to the sensor. Insert a plastic section somewhere along the length of the tube. The plastic part doesn't have to be thick. It could be thinner than the tube diameter.

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  • $\begingroup$ Thank you, I was trying to think of a way of getting the sensor independent of the tube but I couldn't work it out. Essentially the tube is serving two purposes, anchoring the above ground station (for air sensors and electronics) and then putting the below ground sensors in place. Do you have any recommendations for how to achieve the sensor staying in place when pushed but separating when pulled? Essentially some sort of applicator design. $\endgroup$ – PaulBarr Jan 30 '16 at 21:14
  • $\begingroup$ Do you have a drawing or sketch or vendor and part number of the sensor? $\endgroup$ – Greg Marsh Jan 31 '16 at 13:57
  • $\begingroup$ We are going to use the DS18B20 sensor, you can buy it already waterproofed so we were going to use that: amazon.co.uk/… $\endgroup$ – PaulBarr Jan 31 '16 at 17:54

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