Calculating the operating pitch diameter of variable pitch sheaves

The operating pitch diameter of variable pitch sheaves was calculated. There is a lot of field guesswork that takes place in regard to the actual operating pitch diameter of the sheaves. Airflow is totaled with the unit complete in its normal operating configuration. The fan rpm is recorded to calculate a new rpm to satisfy design airflow requiremnts. The key to determine the operating pitch diameter is the measurement of the true speed relationship between the variable pitch sheave and a fixed pitch sheave.