9905-872

About the 9905-872

Woodward model 9905-872 is an overspeed protection system that continually monitors for overspeed conditions. This model is comprised of three separate speed-sensing units, all fitting together inside one, locked IP65-certified enclosure. The 9905-872 speed-sensing units are each interfaced with a magnetic pickup (MPU) and each performs its own speed calculations. These calculations are put to a two-out-of-three hardware vote.

Like other overspeed protection devices in this ProTech 203 series, each speed-sensing unit has its own power supply. In the 9905-872 system, Unit A and Unit B are 24 Vdc, while Unit C is 120 Vac/dc. Model 9905-872 is a de-energize-to-trip version. This model samples prime mover speed every 5 ms and has a max overall system response time of 40 ms.

The three-unit design and two-out-of-three voting configuration minimize overall system downtime in a few ways:

• The prime mover can remain online if a single unit is tripped
• The prime mover can remain online during the testing of individual units
• Speed-sensing units can be replaced while the prime mover is online

Details on how this works can be found in Woodward ProTech 203 Overspeed Protection System Manual 85191 (version B).

Additional features of the ProTech 203 99050872 model include LED indicators for a failed MPU, an incorrectly functioning CPU, and a tripped speed-sensing unit (there is also an alarm output for a tripped unit); a key lock for the enclosure; and remote reset.