Thermopile and motion detector sensors

[Jeanseb]

Hello,

Could someone tell me the difference between a motion detection sensor (as found in automatic garage light), which has a frequency range response of 7 - 13nm and which works on the principle of emissivote of a warm corpse, and thermopiles, which have about the same frequency response?

Can motion detector sensors be used for horizon sensing?

Thank you in advance!!!!

[kd7ost]

Hello,

Could someone tell me the difference between a motion detection sensor (as found in automatic garage light), which has a frequency range response of 7 - 13nm and which works on the principle of emissivote of a warm corpse, and thermopiles, which have about the same frequency response?

Can motion detector sensors be used for horizon sensing?

Thank you in advance!!!!

I don't know what kind of automatic garage light you mean. I'm aware of an infra red beam used as a safety device, but will also turn on the garage light if the door is open and the light has timed out. Breaking that beam will turn the light on for a given period. That beam is a modulated IR signal that radiates at somewhere between 850 to 980 nano meters (Depends on the device type and internal chemistry). Light at this frequency is just outside the human ability to see with normal optics. In fact Humans see light between about 380 to 750 nm. 7 to 13 nm is way out there. It's not even close to IR.

Dan

[typicalaimster]

I don't know what kind of automatic garage light you mean.

It's going to be those motion detecting flood lights. I was actually thinking about some sort of system like that yesterday. I'm sure there is a way to do it. The FMA Co-Pilot just detects difference in heat between the ground and the sky. I don't know enough about motion detectors to make a call on it.

[Jeanseb]

It's going to be those motion detecting flood lights. I was actually thinking about some sort of system like that yesterday. I'm sure there is a way to do it. The FMA Co-Pilot just detects difference in heat between the ground and the sky. I don't know enough about motion detectors to make a call on it.

Yes this is the kind of motion sensor I mean (passive infrared). there is no active beam involved. It just detects moving heat source. The movement is detected by using a fresnel lens, but the sensor only detects heat.

As explained here: http://home.howstuffworks.com/question238.htm

The "motion sensing" feature on most lights (and security systems) is a passive system that detects infrared energy. These sensors are therefore known as PIR (passive infrared) detectors or pyroelectric sensors. In order to make a sensor that can detect a human being, you need to make the sensor sensitive to the temperature of a human body. Humans, having a skin temperature of about 93 degrees F, radiate infrared energy with a wavelength between 9 and 10 micrometers. Therefore, the sensors are typically sensitive in the range of 8 to 12 micrometers.

by removing the fresnel lens, to me this kind of sensor is the same as thermopile. To the difference that they are cheaper, and can easily be found.

If anybody knows the difference, please let me know.

Thanks!!!

[kd7ost]

Well I'm no expert on that but I see what you mean. I can say that a motion detecting sensor is different than a temperature sensing unit in some ways even if they are operating in the same energy range. At least some. A thermopile like what is used in the FMA co-pilot uses just one sensor in each axis. The coupling and processing is designed to provide servo motion to keep the same temperature being sensed all around. That's differences in the processing.

The motion light seems to use two different methods. One is similar to the above description but the processing is looking for rapid temperature changes. But better units are using two sensors side by side and are looking to see variations between the two sensors to help resolve false alarms.

I don't know what to do with it. It sounds like a project to play with though if you're interested. Me?, I'll just throw on that tiny low cost co-pilot and be done with it.

To make your own you will need the thermo sensors and a housing. You will then need a buffering circuit used to power the sensors and interface variations in readings at a high resolution to a processor. Then you will need a processor with code written to act upon those variations and send suitable pulses to the servo's. You might want an enable and disable thrown in with the ability to adjust gain characteristics. Some pyro sensors are AC coupled and some are DC coupled. I don't know what Thermopiles are but I suspect you can find all that information.

Good luck

Dan