A rapid technique for dynamic calibration of electromagnetic flowmeters

A new technique for the dynamic calibration of electromagnetic flowmeters has been developed that uses a simple transistor circuit and is suitable for both sine- and square-wave flowmeters. The magnet current is amplitude modulated using a square wave at a frequency of 1 Hz to provide a suitable input to the flowmeter. This input simulates the input that would have been generated is a square-wave oscillatory flow had been passed through a flow probe. The modulating square wave together with the square wave from the flowmeter output are sampled using a digital computer, and comparison of the Fourier transforms of the two waveforms yields a calibration of amplitude attentuation and phase lag for frequencies up to 50 Hz. The technique is very fast and thus allows multiple determinations of the calibration, which in turn lead to a more accurate calibration that has been achieved by other methods. The calibration of a Statham SP2202 flowmeter is presented providing an example of the technique.