About the 9905-875
Each MPU in the 9905-875 is interfaced with one of three separate speed sensing units, which are configured for two-out-of-three voting. All three units are in the same enclosure, an enclosure that meets NEMA 4 and IP 65 standards and is key-locked to prevent unauthorized access to programming and testing.
There are several benefits to the modular design and two-out-of-three voting of model 9905-875.
- A correct output will be maintained even if one unit is tripped
- Speed-sensing units may be tested one at a time without taking the entire system offline
- The prime mover may remain online while anyone speed-sensing unit is replaced
The 9905-875 speed-sensing units are identical. Each unit has a 24 Vdc power supply (18–32 Vdc, 7.25 W voltage range) and an operator interface. The system is programmed and tested through this interface, and the current actual speed of any individual unit can be viewed on that unit’s LCD. Woodward ProTech Overspeed Protection System Manual 85191 (B) includes a programming worksheet and installation instructions for the 9905-875 system.