About the 9905-990
The 9905-990 unit was produced by Woodward Incorporated for their ProTech 203 Overspeed Protection System series. There are two different model types in the Protech series, Energize-to-Trip, and De-Energize-to-Trip; the 9905-990 model was designed as a De-Energize-to-Trip Model. De-Energize-to-Trip models are the safest to use as they will ensure that if the attached prime mover experiences a loss of power it will trip the unit.
Model 9905-990 has several features that make it an efficient choice of overspeed protection device. These three units, A, B, and C, are identical speed-sensing units that can be tested or even replaced individually. ProTech model 9905-990 uses a two-out-of-three hardware voting configuration so the overall system can remain in operation with at least two units online.
Before the hardware voting relay, the three units act independently to monitor prime mover speed (sampled every 5 ms) using magnetic pickups (MPUs) and perform a speed calculation. A trip relay is activated if an overspeed condition is met. The total response time of this process is a maximum of 40 ms.
The 9905-990 device has a speed-sensing frequency range of 100 Hz to 32 kHz and a trip-point frequency range of 250 Hz to 25 kHz. This system has an accuracy rating of 0.05% of point + 2 Hz over the operating temperature and should be installed in a location where it is protected from things, such as electromagnetic interference and vibration, in a space where there is adequate ventilation for cooling.
For more information on the functions and hardware configurations of the 9905-990 model, refer to the attached Woodward Manual 85196.