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'[EE]:,[PIC]: How to measure level of liquids and s'
2000\05\31@213705 by Mark Willis

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Dan Michaels wrote:
{Quote hidden}

Aaah, you're thermally bonding the hot beads to the tube?  Perhaps
that'd work, might want to instead put a heater at the top of a small
rod, bond the thermistors to the rod, use them to measure along the rod,
maybe would work.

Good news is that you can use one larger PIC and run quite a few
thermistors simultaneously to get many data points simultaneously.
Sigma Delta code's not too hard to find <G>

 Mark


'[EE]:,[PIC]: How to measure level of liquids and s'
2000\06\01@115140 by Dan Michaels
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Mark  wrote:
.....
>> Not that I've ever tried this, but I figure the temperature variation
>> would distribute itself along the tube in some manner [to be measured
>> and calibrated empirically], and the math would be some weighted
>> averaging routine. Just a thought. The sorta thing you try once, and
>> immediately get a strong hunch whether it will ever work or not.
>>
>> - Dan
>
>Aaah, you're thermally bonding the hot beads to the tube?  Perhaps
>that'd work, might want to instead put a heater at the top of a small
>rod, bond the thermistors to the rod, use them to measure along the rod,
>maybe would work.
>

Yeah, that's pretty much what I had in mind. Although I am not a
thermal engineer, it seems to me there will generally be a temperature
difference between the fluid, now matter what it is, and the air
above it - due to thermal inertia - so a heater may not be required.
I'd have to try this to see how it would work. It might work with
3 thermistors this way - one at the bottom [in the fluid], one at the
top [out of the fluid], both of which act as references, and one in
between to do the actual weighted measurement - all bonded to the same
long tube.
=============

>Good news is that you can use one larger PIC and run quite a few
>thermistors simultaneously to get many data points simultaneously.
>Sigma Delta code's not too hard to find <G>
>

For production stuff, I think most companies would want to go with
as few parts as they could get away with --> costs, plus reliability
issues.

- Dan

2000\06\01@125948 by Mark Willis

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Dan Michaels wrote:
{Quote hidden}

It'd depend on situation, around here on a cold day that wouldn't work
well though - if the temp's 55F and the water pours in at 55F, you would
need to rethink - in hotter climes, 55F vs. 80F, easy to see the
difference.  Worth a try some time when you have "spare time", that
elusive thing we never have enough of <G>  I wouldn't expect
self-heating from the thermistors to work in this situation, bet you
don't either;  power resistors are cheap and plentiful though <G>  (Bond
a 5W or so resistor inside the top of the tube, use polyurethane power
cable out the top, seal the ends with PVC cement goop after scratching
the cable to give you good bonding and then using that purple MEK stuff
to prep the cable?  Seems to work pretty well in past, IME.  Run say
1-2W into the resistor so it won't be over stressed.)

> >Good news is that you can use one larger PIC and run quite a few
> >thermistors simultaneously to get many data points simultaneously.
> >Sigma Delta code's not too hard to find <G>
> >
>
> For production stuff, I think most companies would want to go with
> as few parts as they could get away with --> costs, plus reliability
> issues.

Sure - So long as it works <G>

> - Dan

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