Mounting DS18B20s on pipework

Hi all,

 

How are we mounting our DS18B20s on pipework? I'd like the fastest possible transient response.

 

Test run was a quick and dirty jubilee clip:

https://lh6.googleusercontent.com/-6YzQe83zT_w/VDu_Y2zptfI/AAAAAAABsc0/gSsEbp6cK18/w1452-h1936-no/IMG_20141013_130233.jpg

The sensor is bare, flat side to the copper pipe, and dry. Electrical connections have heatshrink. The transient responses are attached. 80C to 15C, and 20C to 15C. The copper pipe cools in under 5 seconds; the temperature sender takes longer. The jubilee clip actually stays hot for a significant amount of time.

 

Others have used cable ties, thermal transfer paste, and aluminum tape:

http://forum.fibaro.com/viewtopic.php?t=914

http://www.raspberrypi.org/forums/viewtopic.php?t=67151&p=501538

I'm considering this or amalgamating tape, plus a cable tie over the top, then pipe insulation over the top of that. Any other suggestions, experience, or words of wisdom?

 

Thanks,

-- 

Marko

Robert Wall's picture

Re: Mounting DS18B20s on pipework

I've no experience, but just looking at the physics involved, you need a low thermal resistance between the sensor and the pipe, and a high thermal resistance between the sensor and anywhere else. I think part of your problem is the jubilee clip has a relatively high thermal mass (it's specific heat is about 20% greater, and there's more weight) and a lower thermal conductivity (about 1/9th) than copper, so it will be tending to retain its old temperature when the pipe temperature changes. I can't recollect seeing anywhere a statement about which part of the sensor is the most sensitive, so I would presume it is sensitive to the general ambient. I'd put a dab of heat transfer paste or silicone grease under and around the sensor, and tie it on with copper wire rather than steel, the idea being to get the pipe temperature to all parts of the sensor as quickly as possible. Insulation over the top will help to ensure that the sensor is close to the pipe temperature and little affected by convection currents in the air around the pipe.

ngbod's picture

Re: Mounting DS18B20s on pipework

I've been using Kapton tape to strap the sensors to the pipes and it works very well. Kapton tape is a high quality, very thin, high temperature resistant tape which is used in the aircraft industry. 

ziporah's picture

Re: Mounting DS18B20s on pipework

I've been using tie-wraps for attaching my sensors. These seem to work just fine. I also add a insulation around the tubing and the sensor so it doesn't get affected by the room temperatures.

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