Re: Refrigerator monitor ideas?

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message
news:45c4ade0.1223264953@xxxxxxxxxxxxxxxx
> "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
> >Anyway, IIRC there were lots of variations in coil temperature due to
door
> >openings, defrost cycles, power blips and more.  I'm assuming that your
idea
> >is to look for constant 32F readings on the coil indicating that it's a
> >block of ice.  That implies a control system of some complexity, doesn't
it?
> >If I could find a cheap used pen recorder I'll bet that coil freeze-ups
> >would appear distinctly differently after a few days of icing but that's
> >still too late.  The ideal time to stop it is before an ice dam forms.
>
> Actually, I was thinking more of monitoring the condensor coil temperature
> which should rise steadily as the efficiency of the evaporator coil is
> degraded by the ice.
>
> I would think that if the temperature stays above some (unknown) point for
> some (unknown) time it's a fairly strong indicator that something is
amiss.
> You might even simulate this by leaving the door ajar for awhile to get a
> temperature profile to compare with a normal profile.
>
> Then the logic is fairly simple. Measure the temperature every n minutes
and
> increment a variable if its above some (unknown) level and reset the
> variable to zero if it's below that (unknown) level. If the variable
reaches
> x, sound an alarm. You might be able to do this with the logic in an
Ocelot
> (or CPU-XA) although I have to confess I'm not all that familiar with its
> variables and timers. You might get help on the ADI forum.

I was hoping for something a lot simpler than an Ocelot!  The problem is
complicated by the fact it's not frequently used for human food.  It might
take a week before a human would notice something was suddenly "too warm" or
at least warmer than usual.

Since this is the dog/science fridge, only my food, my science projects and
the dog's food live in there.  The great "Active-Eye Cold-Soaking Battery
Test" in the kitchen unit banished all science projects to the basement.  By
the time I drank a canned soda from the downstairs unit and noticed it was
too warm, it was too late.

I think you're on the right track, though.  What *may* work is a simple LCD
thermo with a remote probe and a "max temp" alarm feature.  I see them
around for $10-15.  If I placed the thermistor inside a jug of water at the
back of the unit, its location and thermal mass should insulate it from all
but the most severe open door or defrost cycle temperature swings.  If I set
it to just slightly warmer than what it reads as the MAX recorded temp after
a few weeks, it should pick up coil anomalies quite fast.  When those
aluminum tubes and fins get covered with ice, their efficiency plummets.

> I realize this doesn't provide the early warning you desire but I doubt
you
> are going to find any early warning methodology as the condensation will
be
> affected by relative humidity.

That's a good point.  The unit's in a position where I can easily extend the
drain tube beyond the floor pan and into a floor drain.  That might reduce
the humidity in the summer and give me a visual indication of water flow but
unless I armored it, the dogs would eat it.  (-:

How do they detect wing icing on airplanes?  I remember reading about one
design that used an inflatable rubber wing surface that flexed and allowed
the ice crack off but I don't recall how they determine wing icing depth.  I
do seem to recall that Palm 90 crashed here a while back because the pilots
didn't know how badly iced they were at the moment of takeoff.  I believe
someone used diluted deicer that actually froze up on the wing surfaces.

If I really wanted to figure this out, I'd put a temp probe AND an
intervalometer camera in the coil area and another temp probe in a water
bottle and then correlate various bad events like a plugged drain or a
propped open door with coil appearance.

--
Bobby G.