The Condensation Particle Counters (CPCs) 5420 and 5421 are the result of continuous development of GRIMMs world-wide appreciated technology. Signal processing was considerably improved to achieve a high concentration range at essentially zero false counts; and excellent linearity. These universal butanol CPCs are designed for mounting in 19’’ racks, e.g. in the GRIMM EDM665 Wide Range Aerosol Spectrometer for outdoor measurements. Notably, these CPCs are equipped with rugged pumps and fully suitable for long lasting continuous measurements. The CPC may be ordered with (5420) or without (5421) SMPS options; an upgrade is possible.