In Our Plant We Measure Turbine RPM At 2 Places.

At Front Pedestal there are 84 Teeths to Complete 1 RPM & At Turning Gear ie. At Bearing no-4 There are 60 Teeths to Complete 1 RPM. In Both Places RPM is Same. Increase or Decrease in Teeths What Exactly Means?

 

Srinivas,

the number of tooth represents the number of pulses generated per revolution of shaft. The control system which is interfacing the signal from field sensor needs to be configured with number of tooth on the speed wheel (tooth wheel). So upon receipt of that many pulses it accounts one complete revolution. So the shaft rotating at same speed can have multiple speed wheels with different number of tooth and even tooth profile.

I am not sure (Someone can correct me - if I am not correct!), but the higher tooth wheel might have been designed for lower rpm measurements (during turning gear operation). So that more pulse are generated per revolution.