Optical Density (OD) Readings

Optical Density

Flow Chart

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

Variables

Experiment Considerations

• Ambient light

• Photodiode Temperature - make sure temperature is equilibrated before calibration and before start of experiment

• eVOLVER recently turned on - causes rapid change in values

• Vial to Vial Sleeve Distance - Second Forum Post

• 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

• LED to photodiode angle

• Depth of photodiode and OD LED into the vial

• od_led value in conf.yml file (PWM value)

• Resistor pack value

Non-standard changes

• Low (~10mL) culture volumes ONLY - readings are affected by stirring

• Vial holder reflectiveness - ie white vs black vs metallic