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PICList Thread
'[EE] : Dew Detector Reliability'
2001\01\04@135634 by Chris Carr

Forgot the Category in the Title, Second Try

In an earlier thread a remark was made that the Dew Detectors fitted to
VCR's went high resistance over a period of time causing the dew detector
come on permanently.

I took the opportunity to check this with a colleague who repairs VCR's for
a living and he expressed surprise as he could count the failures of this
type on the fingers of one hand. As far as he could remember this problem
only affected ancient recorders such as my Panasonic NV7000 (Duh).

This got me thinking that perhaps the reliability of these devices is
affected by climatic conditions and the UK is a benign climate as far as
these devices is concerned.

Anyone care to comment ?



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2001\01\04@144231 by Alice Campbell

Hello Chris,

the best description of resistive sensors ive found:

from what they say, i think the problem is that the sensor
gets irreversibly poisoned over time, mainly with silicone-
type substances (*) (not the same as silicon, BTW).
basically, the more silicone around, the faster it dies.
using a silicone lube around these sensors sounds like the
kiss of death to me.

my impression is that its better not to get too emotionally
attached to this type of sensor.

(*)Silicones are polymers in which organics groups, such as
methyl and phenyl groups are bonded to the silicone
    atoms in chains of inorganic siloxanes (-Si-O-Si-).
Possessing a host of unique properties including heat, cold
    wheather resistance, electrical insulation, release,
water repellency and defoaming properties, silicones are used
    throughout the following industries:
{Quote hidden}

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2001\01\04@145650 by David VanHorn

You can "Do the Dew" without resistive sensors.

A clean glass plate is a specular reflector, unless covered with dew (or
dirt). Then it becomes a diffuse reflector.  A diffuse reflector scatters
light in all directions (like paper). A tight IR beam can be arrainged to
bounce off the glass, and miss the target, unless there is something on the
Where's dave?

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