Hi Roman,
In WA (AU) we use stainless steel for all food stuff, I was involved in
manufacturing industrial mixers with heaters for making fudge (think a big
(8cubic') cement mixer made of stainless steel with a second layer of
stainless steel on the outside and oil inbetween so we can get even heating)
we have drop in stainless steel temp probes with PT 100 sensors (they were
thermally epoxied after the food end was weldeded closed (with tig (mig on
SS is not very good, tig is beter)) well the first two probes died after 2
weeks, seems the heating and cooling of the epoxy ended up cracking the
sensor. now they are just slid down the tube with a good supply of thermal
grease))

Regards,

Kat.

**********************************************
K.A.Q. Electronics.
Electronic and Software Engineering.
Perth, Western Australia.
Ph +61 (0) 419 923 731
**********************************************

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Roman Black
> Sent: Thursday, 15 August 2002 6:39 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]:Measure liquids temperature with 18S20
>
>
> > On Wed, 14 Aug 2002, Claudio Martin wrote:
> >
> > >Liquid is wine stored in tanks and the range of temp. is from 10 to 30
> > >degrees. Regarding the response time isn't that important,
> because it's a
> > >huge mass of liquid. I have to check the temperature at a
> point located at
> > >the center of the mass of liquid. This point is about 3 meter
> from the top
> > >cover of the tank. I guess one stainless steel tube could be a good
> > >solution, but one point to work out is how to keep the sensor
> in contact
> > >with the end of the tube, is there any kind of glue with a good thermal
> > >conductive coeficient?.
>
>
> Wine is acidic, so it's probably best not to use
> a metal tube. Get plastic tube rated for the food
> industry, and I would use a non-toxic heatsinking
> grease like petroleum jelly in case of any leakage.
> The thermal mass of the wine is very large and the
> rate of temperature change will be slow, so the
> thermal sensor does not need any special treatment,
> ie anything buried in a 3 meter radius of water is
> going to be at the average temp! :o)
>
> I would also suspect that this being mainly water
> with normal convection etc the temperature in the
> middle probably won't be that much different than
> near the edges of the tank. You may just be able to
> put the probe near the tank wall (only about 30cm
> in?) and be close enough in temp.
>
> Be aware that there may be laws/standards related
> to the materials you can immerse in a food product...
> -Roman
>
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