A flow cytometer (20) capable of utilizing an imaging
system including a sensor (88) to determine various properties of the flow cytometer (20). Importantly, the imaging allows for determination of a drop
delay time (154). Other characteristics that can be determined include at least the width of the
stream, pressure of the
stream, effect of charged droplets on other droplets (44), trajectory of the
stream, resonant frequency, wavelengths, change in position of droplet break-off point (150), and others. An automatic
warning system (180) can be used to alert an operator of an anomaly during setup or during normal operation. Furthermore, a mechanical
interrupter can be used to shield a sort result from
contamination by an incorrectly functioning stream. The cytometer (20) also allows for the disablement of the sort, particularly the charging and deflection systems. In addition, a more accurate
system for detecting the speed of the stream can be used. The imaging
system including a sensor (88) can allow for the removal of
background noise and the monitoring of a change in a stream characteristic.