In a message dated 2007/07/01 11:19:30 GMT Daylight Time, Tangazazen@....... 
writes:


> The important characteristics of the LED are uniformity of the light spot 
> and linearity. The LED control feedback is dynamic i.e. both amplitude and 
> wave form are controlled, but there is a limit to how much the loop can correct 
> non-linearity before the onset of instability.
>  
>  I should perhaps point out that large quadrant silicon photo detectors are 
> a little expensive to say the least. 

Hi Martin,

       Do you use a round or a square spot and do you use a mask to define it 
accurately?

       What are the type numbers of your driver LED and the photodetector, 
please?

       Regards,
       
       Chris Chapman   
In a me=
ssage dated 2007/07/01 11:19:30 GMT Daylight Time, Tangazazen@....... writes=
:





The important characteristics o=
f the LED are uniformity of the light spot and linearity. The LED control fe=
edback is dynamic i.e. both amplitude and wave form are controlled, but ther=
e is a limit to how much the loop can correct non-linearity before the onset=
 of instability.

 

 I should perhaps point out that large quadrant silicon photo detectors are=20=
a little expensive to say the least. 




Hi Martin,



       Do you use a round or a square spot and=
 do you use a mask to define it accurately?



       What are the type numbers of your drive=
r LED and the photodetector, please?



       Regards,

       

       Chris Chapman