Re: Pet's weight in Pet Immunity PIR sensor

["Robert L Bass" <robertlbass@xxxxxxxxxxx>]

> How Pet Immunity Sensors work according to Pet's weight?

As I'm sure you realize, PIR's don't measure the pet's weight.  The
manufacturers use weight as a guideline for installers in selecting an
appropriate pet resistant detector for the job.  The detector looks for
changes in the amount of IR (heat) energy striking various segments of a
pyrolitic transducer.  If the change is sufficient and the location of the
change meets certain criteria an alarm is generated.

There are several approaches to making a PIR pet immune.  The simplest is to
look for simultaneous IR changes (movement) in upper and lower halves of the
transducer.  That would correspond to motion in the lower and upper part of
the field of view respectively.  If the detector only "sees" motion along
the floor it's probably a pet walking on the floor.  Likewise, if the motion
is only detected up high it's possible the pet is sitting on top of  a couch
or whatever.  If motion is detected high and low at the same time that's
probably a person.

The above is the simplest type of pet resistant technology.  Microprocessors
in modern PIR detectors run complex algorithms to determine whether a given
pattern of motion (actually, changes in received IR) merits a response.
You're probably aware that there are "dual technology" detectors which
couple PIR with microwave.  Technically that isn't done so much for pet
resistance as to prevent nuisance alarms from other stimuli.

--

Regards,
Robert L Bass

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