RE: [HoE] Sensors (was: Junker Questions )

["Patrick Phalen" <pphalen@gti.net>]

>Sensor I am a little dense on the difference between passive and active
>sensors
>Do Passive sensors only detect other things giving off the thing that it
>senses, whereas an active sensor can build a picture of its
>surroundings? Could someone give me a couple of examples of different
>sensors please?

Active Sensors Transmit as well as receive.  A Passive sensor only receives.
So, an Active Radar system sends out a radio frequency signal, which
eventually "bounces" off of an object.  The reflected energy is then
received by the radar.

A passive system would only have the ability to detect an active radar
working within its effective range.

>Is there such a thing as a passive touch sensor, or sound sensor? or are
>all sound sensors passive since they just detect sound? how bout smell
>sensors?

These, most likely, would all be passive...

>It says all active sensors must have a range but that passive mainly
>depend on the range of the active sensors they are listening for. Does
>this means that they don't buy ranges or that they have ranges, but the
>thing they are sensing for must sense within the passive sensors range?

Assuming that the sensitivity of the passive sensor is high enough, it is
*entirely* dependent on the range of the active sensor.
Technically, the detection range for a passive sensor should be
Active_range^2, but that's probably too fine a detail....


Patrick "Sensor Guy" Phalen