How can you tell for sure whether a vibrator is delivering enough energy?
Vibrators that are in poor condition may operate at lower frequencies than normal. The frequency can be measured by an inexpensive vibrating reed tachometer. Measurements should be made when the vibrator is operating at full depth in the concrete. If this frequency is substantially lower than when the vibrator operates in air, or lower than it has been known to operate in the concrete previously, it is not doing as much work as it should. It may need a more adequate supply of electric or air power or it may need repair.