Power quality analyzers measure and monitor electrical power parameters to avoid disturbances, track steady-state variations, and ensure the reliability of power distribution systems. Disturbances are measurable events that are triggered by abnormalities in voltage or current. Steady-state variations compare changes to normal values and are measured by sampling voltage and/or current levels over time. To track disturbances and steady-state variations, power quality analyzers present information as individual events, trends, or statistical summaries. Examples of individual events include voltage spikes and brownouts. Power quality analyzers can also measure transients such as primary magnitude, time of occurrence, and rate of rise. Some devices are powered by the system being tested. Others use battery power. Power quality analyzers with integral AC current clamps are also available.