Why do outdoor advertising machines have filters and still have clutter?

Outdoor LCD advertising cooling options have air cooling cooling, because it is for air cooling cooling treatment, so the equipment is in the flow of internal and external airflow.Double layer filter screen is used to keep out small insects and large particles of dust.After the normal operation of outdoor advertising machine for a period of time, the need for regular cleaning of the filter screen, cleaning interval specific to the local environmental quality and decided, such as 3 months, 6 months or 12 months.Although filter screen filters dust, but very small particles will still have a certain chance to enter the outdoor advertising machine, if you want to achieve a little dust do not enter, can only use air conditioning cooling scheme.