BMS 631 - LECTURE 1 Flow Cytometry: Theory J.Paul Robinson Professor of Immunopharmacology School of Veterinary Medicine, Purdue University

Page 10

High Voltage on PMTs

•The voltage on the PMT is applied to the dynodes

•This increases the “sensitivity” of the PMT

•A low signal will require higher voltages on the PMT to measure the signal •When the voltage is applied, the PMT is very sensitive and if exposed to light will be destroyed

•Background noise on PMTs is termed “dark noise”

•PMTs generally have a voltage range from 1-2000 volts •Changing the gain on a PMT should be linear over the gain range •Changing the voltage on the PMT is NOT a linear function of response