If not able to read OD above a low level:
Standardize LED/Photodiode distance
If seeing noisy OD readings:
Stirring
If OD is not working at all on a single vial: Replacing Photodiodes and LEDs
Experiment Considerations
Photodiode Temperature - make sure temperature is equilibrated before calibration and before start of experiment
eVOLVER recently turned on - causes rapid change in values
Needles or other structures coming below 10mL line (close to OD PD etc)
Vial volume - a volume of 10mL will totally change OD compared to 30
Stirring with low vial volume - this will give noisy readings as the funnel created by stirring fluctuates and is more and less reflective
Pre-Calibration Considerations
od_led value in conf.yml file (PWM value)
Non-standard changes
Vial holder reflectiveness - ie white vs black vs metallic
Additional tip: if you see strange raw OD values after swapping out LEDs or photodiodes, it's possible you have the positive and negative ends switched.
Stir Bar Jumping
Fixed by increasing space between fan and vial