cwaitang26

Hey,
I really need some serious help. I read abt using pyrosensor as passive IR detector, used for switching applications. eg. motion detector
Now, I intend to use pyrosensor in sanitary products (urinal auto flushing system). Came across some serious doubts & need to clarify:

1) Being passive IR detector, how do I control the range or sensing distance? (abt 60cm) This must be adjustable to some extend for maintenance etc

2) Another worry is can pyrosensor still work when the IR emitting body is not moving? (I've read abt motion detector circuits used to activate fluorescent lightings. They generate a delay & off light when there is no motion. IS this due to electronic circuit design or can pyrosensor also detect stationary IR emitting objects?)
3) What is the price of a pyrosensor (approximately)? (small qty buy and qty of few K's?)

I seriously need to consider the above before embarking on some serious work!

Thanks in advance.

ericgibbs

hi cwaitang,
Taking item #2, first.
On consumer, low cost PIR sensors, the design and shape of the diffuser
and lens is critical. To enable the PIR to be amplified in the receiver
without saturating the amplifier with the 'dc' IR component in the ambient light.
A way is required to give a 'fluctuation' in the PIR which can be considered
as a low frequency signal. This means that the 'dc' ambient IR component
does not get amplified, but the fluctuation is amplified.
This is where the diffuser, [the transparent front cover] of the
detector plays a part. If you examine a diffuser you see that it is not
smooth, but has a coarse patterned surface/thickness. When a PIR source is
MOVING in sight of the detector, the diffuser being patterned, causes the
PIR signal striking the detector to be modulated by the pattern on the
diffuser.
This modulated PIR is then amplified as low frequency signal, with the
background IR 'dc' being blocked.
The shape of the detectors lens is also shaped as to modulate the
MOVING PIR signal even more before it is seen by the detector.

Sensitivity can controlled electronically by varying the gain of
the detectors amplifier. Some consumer units provide semi-opaque pieces of
plastic to cover parts of the diffuser.

The dark/light detector is usually built on the same pcb as the
detector. A CDS [cad/sulph] light sensitive resistor drives a simple
amplifier. Depending upon being light or dark the CDS amplifier enables
the relay circuits driving the relay for the external light.

The output from the PIR detector drives a relay, which controls
the external light, usually a 150Watt thru 1000Watt. The light ON time
can also be adjusted.

You can buy an off the shelf consumer style PIR detector with
light/dark detection, capable of switching upto 1000Watt for about
£5.0 GBP, without the external lamp.

IMPORTANT:
If you buy an off the shelf unit, to examine/study, it will most likely
NOT be isolated from the mains supply, NO transformer. Do NOT power it up
when its dismantled, unless you are an experienced electrician.

Hope this helps

EricG