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[raytay]

Can anyone advise why the manufacturer's fitting instruction for a domestic PIR sensor recommends a minimum time setting of 3 mins when using compact flourescent energy saving lamps as the load.
The PIR in question is an Osprey Standalone Movement Sensor bought from B & Q.

[ericmark]

it takes 2 to 3 mins for a discharge bulb to reach full brightness and it would really reduce it's life if switched of before fully on regularly.
Eric

[raytay]

Thanks for your reply Eric. The answer you gave was in line with my own thinking but I wondered if there might also be an issue with 'back emf pulses' seeing as the load has an inductive choke which might affect the relay contacts adversely.
I contacted the manufacturer. The person I spoke to insisted that it was the PIR detctor that would be damaged and that if the time setting was only seconds it would soon blow the PIR sensor. They did not enlarge on this answer and I am somewhat dubious.
I have in any case set the timer to approx 3 mins.

[ericmark]

Without doing some reverse engineering I have no idea the internal switching mechanism used. It could be solid state and there may be a heat problem if switched too quickly.
Eric