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SUPER soft gel sealant / silicone for pressure sensors
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DTJ:
I've starting to look around for some super soft gels for protecting the actual sensing element face on some pressure sensors.

I looking for sources of the gel like used on the Motorola MPX type pressure sensors its a fluorosilicone that is applied directly to the silicon sensor element.

1) Has anyone any recommendations on a suitable product to try?

2) What units are used to measure the hardness of these gels? They are much softer than the usual Shore A ratings. I imagine the gels in the pressure sensors are even softer than the low end extra soft OO Shore ratings.


Has anyone played with this stuff before?
coppercone2:
do they actually harden into a solid or is it paste like?

One method you might be able to measure its relative hardness if its solid and does not flow is to make a cylinder and wedge it between two plates and weigh it down and measure its bowing/deflection.

If it flows then you might just want to look at its viscosity (so rectangular tube), unless its really viscous, then you end up with a tar-drop experiment. Maybe you can do flow at increased pressures if you make a special apparatus.
e100:
The re-entrant silicone gels commonly used for potting circuits have a high hysteresis. If you disturb the surface it takes several seconds for it to return to its original shape. Presumably this would have a negative impact on the frequency response.
floobydust:
I've learned to just call application engineering for assistance. There's too many products and things to consider.
DOW Selection guide shows over 24 gels: https://consumer.dow.com/en-us/industry/ind-pcb-systems-assembly/pg-pcb-gels-encapsulants.html
coppercone2:

--- Quote from: e100 on November 17, 2018, 06:03:54 pm ---The re-entrant silicone gels commonly used for potting circuits have a high hysteresis. If you disturb the surface it takes several seconds for it to return to its original shape. Presumably this would have a negative impact on the frequency response.

--- End quote ---

I meant like to cast a small cylinder and then just weigh it down and look at it from the side with a camera or boroscope or something with a scale in the background to see how much it mushrooms, it should be a indicator of which one is softer at least.
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