Question:  

What are the main causes of problems when counting particles.

Answer:  

Particle concentration and flow have an effect on the ability to count within a certain range of particle size.  Please review the diagrams below showing the sensor response under given conditions.

985 cannot count particles larger than 10µm, and these should be avoided as they can cover or overlap with more than one smaller particle causing an increase in coincidence errors.




The flow of particles is also important for correct counting, the sensor is calibrated for a flow of 1.0 cfm (cubic feet per minute) which is 2.83 L/m (Liters per minute).