The active area (black part) of photodetector is much bigger and the light-to-frequency converter.
3. What for?
Now many Chinese OEM patient monitor manufacturers uses light-to-frequency converter as photodetector, such asContec, Meditech, Creative, Comen, Biolight, and their spo2 sensors usually more or less the same, for example Lemo 5 pins single notch connector spo2 sensors with digital spo2 sensor, usually works with Contec, Biolight, Meditech .... patient monitors.
So the photodetector is going to help you to decide what spo2 sensor to use. For example, Comen spo2 sensors usually 6 pins Lemo connector, single notch, however, the newer models usually use digital spo2 sensor, which is with light-to-frequency converter equipped, and the older models usually with analog spo2 sensors, so normal photodetector is equipped.
Conclusion: sometimes if you are not sure which sensor your monitor use, please take picture and send us the picture of photodetector to firstname.lastname@example.org , it will help.