Has anyone seen any problems with the PIR in a warm room

Wolfbrother

I'm planning on using it in a room that might hit 120F during the day. I understand it determines changes in IR, but does anyone know if it heat soaks/blinds at some temp?

Thanks

SRLM

Hi. I just got a PIR sensor for a similar environment, and have yet to test it out. After I set it up today I'll let you know how it goes. One note: the temperature where I'll test is only going to reach about 100F max. Where is it that you expect to have people in 120F temperatures?

Chris Savage

The temperature of the blinds should not increase fast enough to trip the sensor. Slow changes are allowed just for this reason. It is sudden changes in the IR patterns that trip this type of sensor.

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Chris Savage
Parallax Tech Support

Tracy Allen

It is _fluctuations_ in temperature that it detects. So when a 98.6 degF object passes in front of a 100 degrF screen, the fluctuation is not going to be as large as when the same object passes in front of a 60 degF screen, or in front of a 120 degF screen for that matter. It is more complicated than that, because the different components of longwave IR enter into the picture, emisivities of the surfaces and types of heat sources. It is as noted a matter of try it and see.

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Tracy Allen
www.emesystems.com

Wolfbrother

It's in an art gallery on the top floor of a 4 story building where the bottom floor is a fast food type resturant. I'm in California and it gets pretty warm here. We measured the ambient temp at the floor at a touch over 100. But that was this month, our hottest month is September and that is when this will be installed. At night everything cools off and that is when most of the shows are, but I guarantee if there is a design problem with high temp, that's when some important person is going to want a demo. I'd hate to have them suffer in the heat and then the thing not work.

I'll try it on a hot day and post the results.

Thanks to all.

Tracy Allen

My own experience with this was a device to assess the activity of bats emerging from old mines or abandoned buildings through relatively small openings. Also in California in the hot summer sun. In some locations the PIR sensors were at the outside entrance pointing at rocks across the way that became too hot to touch. The rocks retained heat into the evening, and I think that may have led to it missing many counts in the early evening. PIR sensors placed deeper in the cave showed many more counts, but that was due largely to bats circling many times before making their sortie.

The first time we tried this was in an abandoned house at Pt. Reyes Nat. Seashore. The house had been boarded up for years and was straight out of the Adams Family. I was inside with the PIR sensors mounted on a window frame, and hooked to an oscilloscope. And a biologist with night vision goggles and an IR iluminator was outside to do a visual count. It was spooky to see the little blips on the 'scope as bats passed by. But I did live to tell.

Under ideal conditions of a straight across motion, the pulse is biphasic, with a positive peak followed by a negative peak for one direction and the opposite phase for the opposite direction. My original plan had been to decode that into a direction of motion counter. But the pulses in reality were hardly ever ideal. The bats would circle or fly at an angle and the pulse could take any shape whatever. So we ended up with a counter correlated to activity but not an exact count. The circuit was built from a chip PIR sensor and op amps, with a large IR lens.

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Tracy Allen
www.emesystems.com