Hi
I'm trying to build an array of 3 OPT101 sensors side to side in order to measure daylight natural light power throughout day/evening/night hours.
The three stages do not use internal 1MOhm resistor and are configures as follows:
Stage 1: external 5.1kOhm gain resistor with 100pF feedback cap
Stage 2: external 220kOhm gain resistor with 33pF feedback cap
Stage 3: external 5.6MOhm gain resistor with 15pF feedback cap
In artificial lab light conditions the array produced an ample coverage from the most bright to quite dark
Now I'm conducting the experiment under natural light conditions outdoors. In full sunlight what I see is that all three stages are totally saturated. The VCC is 5V, all three outputs are stack at about 4.2V
I realize that even 5.1kOhm gain is way too much for full sunlight conditions. Besides, this particular stage tends to oscillate when sudden light power change occurs.
Also, right now the chip is fully exposed to the light, not only the active sensor window.
Few questions:
1. Does fully exposed chip impacts measurement reliability ? Shall I definitely to mask all but the sensor area itself ? in particular under bright illumination..
2. Are the oscillations occurring at the low gain stage (5.1k) during ligh tpower changes due to probably insufficient feedback capacitance (100pF) ?
3. Is there any limitations on minimum gain resistor value ? If yes, what ? and why ?
4. Do you think there is a configuration (gain res + feedback cap) that would work stable under full sunlight without neutral density filter on top of the sensor area ?
There is no requirement for very fast dynamic response
Thanks,
Alex
