Water-Sealing a Circuit for Submersion: LM35 Temp. Sensor Tips

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Discussion Overview

The discussion revolves around methods for water-sealing an LM35 temperature sensor circuit intended for submersion in propanol. Participants explore various sealing materials and techniques, considering the effects of propanol on different substances and the implications for temperature measurement accuracy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests coating the sensor leads with clear nail polish, but expresses concern about its durability in propanol.
  • Another participant proposes hot gluing the sensor for a water-tight seal but raises issues regarding potential leaching of plasticizers from the glue.
  • A different participant mentions using silicone sealer and epoxy as alternatives, noting the importance of considering the temperature range of -50C to 0C.
  • Concerns are raised about the thickness of epoxy affecting the sensor's response time if encapsulated completely.
  • One participant warns about the risk of dendritic copper migration if contaminants are present during encapsulation.
  • Another participant shares their experience with epoxy degrading in propanol and suggests testing heat shrink tubing as a sealing method.
  • There is a suggestion to place the apparatus inside a copper tube for better sealing and thermal conductivity, while also considering the chemical interaction between copper and propanol.
  • Participants discuss the potential issues with epoxy bonding to wire insulation, particularly with teflon insulation.

Areas of Agreement / Disagreement

Participants express a variety of opinions on the best sealing methods, with no clear consensus on a single effective solution. Multiple competing views remain regarding the materials and techniques suitable for sealing the sensor in propanol.

Contextual Notes

Participants note the importance of ensuring cleanliness before encapsulation to avoid issues with electrical conductivity. The discussion highlights the challenges posed by the chemical properties of propanol on various sealing materials.

  • #31
Proton Soup said:
GND should be connected to the node where the batteries come together, plus to minus.

and they're not likely to discharge at the same rate, fwiw.

Good grief, your right Proton. I snafued again.
 
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  • #32
geseundheit ;)
 
  • #33
OK guys, so assuming I attach the GND from the sensor to the node connecting the two batteries, where should I attach the GND from the multimeter? To the same node?

And thanks a lot for the advice guys, you've been very helpful!
 
  • #34
yes, GND is the reference point, 0V
 
  • #35
Thanks proton, I'm going to wait for the parts to arrive then reassemble everything.

I'll let you guys know how it turns out.
 

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