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IR intensity measurement

Hi ,

Can anyone tell me a IR sensor or a logic which gives an output voltage propotional to the intensity of the incident radiation.

My transmitter is a 940nm IR LED. And i have tried many sensors like TSOP 78xx , but here it detects the radiation. The output merely says if the IR radiation is present or absent.

The basic block is as follows :

IR Transmitter -> Sample -> IR receiver -> Signal processing

The Sample is an medium which has peak absorbance at 940nm. Hence the source is IR radiation.

I have tried some alternatives like capturing the image by digital camera.., but i would like to have a simple measurement.

regards partha

Reply to
bpartha
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Any IR sensitive photodiode will do this for you. The current through the diode is proportional to the amount of IR light.

Meindert

Reply to
Meindert Sprang

For higher absorption and ambient, I'd suggest a lock-in amplifier.

Rene

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Reply to
Rene Tschaggelar

Since it seems that you're trying to measure attenuation (absorbed energy), I suggest the following very simple approach:

1) Drive LED or diode laser 940 nm source with pulsed current at any frequency well above mains frequency, say 1 kHz. 2) For receiver, use silicon PIN photodiode and shunt load resistor of about 50 ohms. Connect to oscilloscope input. 3) Conduct experiments indoors. Verify that DC voltage across load resistor is always less than 200 mV 4) Arrange photoelements for good coupling and measure peak to peak amplitude of signal. 5) Interpose sample and measure attenuation directly.

Of course, check setup using a sample with known attenuation. Double check by obscuring half of photodiode area and verify 50% attenuation, etc. If signal strength is too low, use a larger photodiode, higher source current, etc. Use of larger load resistance is also OK if DC voltage remains below 200 mV in all conditions and pulse waveform remains rectangular. With care, you can achieve accuracies on the order of 2 to 10 percent using these methods.

Paul Mathews

Reply to
Paul Mathews

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