The viable cell density measurement is based on permittivity. Viable cells behave like little capacitors and their polarization and depolarization in an alternating electrical field is measured. The signal can be correlated to the bio-volume, resp. the viable cell density. Only viable cells can be polarized so this method is insensitive to cell debris as well as to microcarriers. A measuring loop consists of an Incyte sensor that is available in different dimensions and different conductivity range, an Incyte pre-amlifier and an Arc View controller. The Arc View can display both parameters at once using the 2 (Arc View 265) or 4 (Arc View 465, 465 XL) channel inputs. Additionally Arc pH and DO sensors with a wireless module can be displayed on the controller giving the user the ability to regard all relevant parameters of a cell culture or fermentation on one screen. Incyte sensor and pre-amplifier are sold as calibrated Incyte Unit but are also available as spare parts.