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pyroelectric detectors

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rudie

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Hello,

I am trying to detect some materials in oil with infrared light. As a receiver I am probably going to use a pyroelectric detector. On the internet I couldn't find any sufficient information about the output of such a detector. Does anyone know how this detector reacts to wavelengths? for example were in the output signal can i see the wavelength of the received light and what happens the the output if the receiver receives more than one wavelength?

An other solution would be to use a photodetector. But in my appilication i will need to detect wavelenght up to 16um. Are there any photodetectors that can detect this wavelength?

I hope someone can help me.

greets Rudie
 

Hello,

basically pyroelectric detector are well suited for IR measurements up to e. g. 16 µm. Semiconductor photodetectors are more sensitive, but would need cryo cooling for mid IR. Pyrodetectors (basically thermal detectors) have no wavelength selectivity at all, execept for what's defined by the window (if any).

Spectral photometers with pyrodetectors, common in gas detection, are generally using optical bandpass interference filters for wavelength selection. For some "popular" wavelengths, detectors with mounted filters are available from manufacturers. Also usual IR motion sensor have a filter, but it's 8-14 µm wideband and the detectors are measuring difference between two areas.

Regards
Frank
 

First of all, thanks for your reply.

But hoe does the output of a pyroelectric detector look like. Especially why it receives more frequencies how can i filter them (electrically) or is that impossible.

But as you say it is possible to detect these kind of wavelengths with photodetectors. But what is cyro cooling? And how can i make it? Do you have some information about that?

Greets Rudie
 

Sounds like you would need some basic literature on optical sensors and measurement before effectively proceeding with the project.

Basically nearly all spectrometric measurements are using a modulated source, e. g. by a mechanical chopper. With pyroelectric detector, this is mandatory, cause it is only measuring AC. Having a 10 Hz modulated source, you get's (small) 10 Hz AC voltage at the pyrodetector output, proportional to intensity at the detector, that's all. Would be postprocessed to get a maximum accurate intensity measurement, but's still a single value, representing a total optical power at the detector, without any spectral information. You need an optical spectral selection to get spectral information.
 

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