9905-874

About the 9905-874

9905-874 is an overspeed protection system with three speed-sensing units that continually monitor and calculate prime mover speed. The three units are all enclosed in the same locked enclosure, which meets NEMA 4 and IP 65 standards. Each unit has its own power supply and operator interface. In model 9905-874, two of the three units have a 120 Vac/dc power supply, and the third unit has 220 Vac supply. The two 120 Vac/dc units have a voltage range of 88–132 Vac/90–150 Vdc, 7.25 W. The 220 Vac supply unit has a voltage range of 180–264 Vac, 7.25 W.

Each speed-sensing unit uses its own magnetic pickup (MPU) and performs its own speed calculation. From this, a hardware two-out-of-three vote is performed. If an overspeed condition is detected, a trip relay is activated. This method of hardware vote also permits testing or replacement of any of the three units without having to take the prime mover offline.

The three operator interfaces on the 9905-874 enclosure each have an LCD, keypad, and LEDs to indicate the functional status of the corresponding unit. There are separate LEDs to indicate different issues, and some problems, such as a tripped unit, may also be alerted with an alarm output as well.

Model 9905-874 is manufactured by Woodward as part of the company’s ProTech 203 Overspeed Protection System series. This model is one of the de-energize-to-trip versions available. More information can be found in the company’s manual 85191 (version B).