What is the degradation in the measurement accuracy of the Vortex meter below the minimum flow specification?
The minimum flow of the meter is determined by the minimum value of signal to noise ratio at that flow. The magnitude of the signal is proportionate to the density and the square of the velocity. Consequently, the magnitude of the signal falls sharply at flows just below the minimum velocity. Since the meter basically measures flow by measuring the frequency of the signal from the sensor, if noise is predominant, it’s frequency could be anything within the signal band and would result in any value of flow rate being indicated between zero and full scale flow. To prevent this, when the signal magnitude falls below a minimum threshold, the signal is cut off and the flow will be indicated as zero.
