Emerson SE4301T02 Low Voltage Instrumentation CHARMs

The Speed and Key Monitor is designed for high reliability for the plant’s most critical 

rotating machinery monitoring speed, phase, zero speed and direction of rotation. 

This 1-slot monitor is used together with the AMS 6500 monitors to build a complete 

API 670 machinery protection monitor. Applications include steam, gas, compressors 

and hydro turbo machinery.

The Speed and Key Monitor can be configured for redundant mode where automatic 

switchover from primary to backup tach is possible. Sensor gap voltage and pulse 

counting/comparison are monitored to trigger switchover. When the Speed and 

Key Monitor is operating in redundant mode, the main and failover key or speed 

displacement sensor must be installed in the same axial plane to ensure phase 

continuity upon failover.

Speed measurements consist of a displacement sensor mounted internally to the 

machine with the target being a toothed wheel, a keyway or gear rotating on the shaft. 

The purpose of the speed measurement is to alarm on zero speed, monitor for reverse 

rotation and provide a speed measurement to track process conditions for advanced 

analysis. Key, or phase measurements, also consist of a displacement transducer but 

must have a once per revolution target, not a toothed wheel or gear for a target. The 

phase measurement is a critical parameter when looking for machine health changes. 

The AMS 6500 is an integral part of PlantWeb® and AMS software. PlantWeb provides 

operations integrated machinery health combined with the Ovation® and DeltaV™

process control system. AMS software provides maintenance personnel advanced 

predictive and performance diagnostic tools to confidently and accurately determine 

machine malfunctions early.