Shaft absolute is the measure of the shaft’s motion relative to free space. Our modules calculate the absolute shaft measurement by summing the signals of both an eddy current probe (measuring the motion of the shaft relative to the case) and a seismic or velocity sensor measuring the absolute motion of the case. Monitoring absolute shaft vibration is critical for many large steam turbines where the weight of the shaft is large relative to the weight of the turbine case.
The XM® 121A Absolute Shaft Vibration Modules are XM-121 Low Frequency Measurement Modules that are loaded with XM-121A firmware. They can operate stand-alone or on DeviceNet™ networks to provide real-time data and status information to other XM modules, programmable controllers, distributed control systems, and condition monitoring systems.