The objective that has to be achieved hereby is to change the velocity (preset velocity) to the

measured velocity. You measure the velocity by moving the red cross into the right maximum

within the time chart. If the gas density of your measured aerosol doesn't change you do not have

to calibrate the velocity. However, during a calibration procedure one should always compare the

old particle velocity with the new particle velocity as a large deviation gives also an indication for a

leakage in your suction tubes or a problem with your suction pump. In case you have a pressure‐

resistant sensor, e.g. welas? sensor 2070 P, or a pressure‐resistant and heatable sensor, e.g. we‐

las? sensor 2070 HP, and if the pressure or temperature conditions change, you have to calibrate

and adjust the particle velocity as well. Always try to calibrate your sensor with CalDust 1100 at

the same pressure and temperature conditions as your subsequent measurements. However,

sometimes it is not possible to calibrate your sensor with a calibration dust at the same thermo‐

dynamic conditions. For this reason, you can also adjust the velocity without re‐adjusting the pho‐

tomultiplier amplification and without using a calibration dust. However, the particles have to be

larger than 0.4 μm. If you adjust the PM amplification, the velocity should not change. Alternative‐

ly you can activate the automated gas density correction.