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.