This is usually set on one or two parameters, in that the signal is only recorded if it rises above the set levels. The amplification of the signal can either be linear or logarithmic. For DNA measurements linear amplification is used, but for immunofluorescence, the use of logarithmic amplification increases the dynamic range. After conversion from analogue to digital form, the different parameters measured can be displayed on a computer screen in a variety of forms, such as a univariate or bivariate histogram, and real time dot plots. Further processing allows these to be visualised as contour plots or as three dimensional isometric plots.
Most instruments can measure at least five parameters.
As all the parameters cannot be combined for display simultaneously in a correlated fashion, a system called gating is employed. Flow cytometers can not only analyse cells but are able to physically sort them into specific populations. This is most commonly done by electrostatic deflection of charged droplets containing a cell. The flow cell is vibrated at around a frequency of 3OkHz by a piezoelectric transducer. The vibration causes the stream to break up into droplets as it leaves the exit nozzle.