9905-989

About the 9905-989

ProTech overspeed protection model 9905-989 monitors prime mover speed for overspeed conditions. This is done through the use of three magnetic pickups (MPUs) that are interfaced with three individual, identical speed-sensing units. Speed is sampled every 5 ms and units A, B, and C performs separate speed calculations. The subsequent hardware two-out-of-three vote determines whether or not a trip relay is activated. If only one of the units detects an overspeed condition, that unit will trip but the other two will remain in operation and continue to provide an accurate output.

The current speed of each unit can be viewed on an LCD for that unit, located on the front panel. The peak speed of each unit can also be viewed here. When an overspeed condition is detected, if the speed exceeds the previously recorded peak speed for that unit, a new peak speed is updated and stored in non-volatile memory.

Each unit also has a keypad, LED indicators, and a potentiometer. Model 9905-989’s speed-sensing units are all contained in the same locked, IP 65 (similar to NEMA 4) certified enclosure. Units A, B, and C all come with their own 2Vdc power supply.

Some features of the 9905-989 system are made possible by the modular design of the device. The ability for this system to function when one of the units is offline permits continued operations during unit testing (for which there is a built-in self-test), troubleshooting of any unit, and unit replacement. A few additional features of this ProTech model are remote reset, alarm outputs, and LED indicators. Full product specifications for this de-energize-to-trip device are in Woodward ProTech manual 85196.