Dear forum readers. .. .(the following text is extracted from Boeing Airliner magazine, OCT-DEC 1987 issue). .. . Two types of vibration pickups have been used on Boeing airplanes, the electomechanical velocity pickup and the piezoelectric accelerometer. Signals from velocity pickups are converted into vibration displacement, measured in 1/1000 of an inch, peak to peak (mils double amplitude). These units represent the physical displacement of the vibration sensor. Signals from accelerometers are converted into velocity, measured in inches per second (ips). These units represent the peak amplitude of the velovity of the vibration sensor.. . Boeing airplanes typically use a 0-5 scale for cockpit display of vibration. On earlier applications, the scale provides an indication of absolute vibration units(ips or mils da) as output from the airborne vibration monitoring (AVM) signal conditioner. This approach is not optimum in that a display of displacement units will provide relative insensitivity to low speed rotor vibration. AVM signal conditioners used on 737-300 and latter, 747, 757 and 767 provide output data in scalar units. These scalar units are uniquely tailored for each engine type to match the operating speeds and vibration characteristics of the engine rotors. The scaling used on the 737/CFM56 installation provides display sensitivity for the high speed rotor proportional to the vibration velocity. The low speed rotor vibration is displayed in units proportional to displacement, except near idle conditions where velocity scaling is used.. . . .Regards