Topic-icon VOM Voltage

9 months 2 weeks ago - 9 months 2 weeks ago #299 by Mark
Mark created the topic: VOM Voltage
The most common AC voltage systems on aircraft use 115, 26, & 5 VAC. Cycles are 400Hz. Normal power sources are 3 phase engine driven generators or inverters.

Standard checks are basically verification of power being present or not. Heavy duty components such as pumps and electric actuators use 3 phase power. One phase missing or having low voltage will cause failures of these devices. Numerous electrical and avionics related components require 115 VAC as a primary power source. Signal voltage standard is 26 VAC. Sensors and transducers modify this voltage in relationship to their position or angle as feedback to associated computers/indicators. 5 VAC is a typical voltage for instrument and panel backlighting. Some external lights use 10 VAC for power. Step-down transformers are used to change 115 VAC to the lesser voltages.

28 VDC is used for both power and control functions. Transformer rectifiers are used as a power source on AC generator aircraft. Some aircraft have DC as primary power coming directly from engine driven generators.
The majority of relays and solenoids use 28 VDC.

One helpful tip when checking power with a meter in AC or DC, is the scale at the bottom of the display. The sample rate for the digit display is not fast enough at times. If voltage is varying or intermittent, the scale is a better source for observing this problem.
Last Edit: 9 months 2 weeks ago by Mark.

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