Vortex flowmeter electronics

A flowmeter receiving a noise contaminated input signal having a fundamental frequency varying responsively to a flow and providing an output representative of the flow, comprising:

• filter means receiving the input signal for providing a filtered signal, the filter means having a variable LP and HP frequency corner, the HP filter corner set so that when the fundamental frequency decreases the HP corner is lowered, and when the fundamental frequency increases the HP corner is raised;
• timer means for measuring a time between period boundaries of the filtered signal and measuring an elapsed time since a last period boundary of the filtered signal;
• and
• adaptive control means for controlling the HP corner frequency such that a HP filter corner higher in frequency than the current filter corner is selected when the period of the filtered signal is less than the period corresponding to a higher frequency filter characteristic and a HP filter corner lower in frequency than the current filter corner is selected when the elapsed time since a last filtered signal boundary exceeds the period corresponding to a lower frequency filter characteristic.

A method for reducing noise to signal ratio of a noise contaminated input signal which has a fundamental frequency varying responsively to a physical parameter and providing a signal with a frequency proportionally representative of the input signal fundamental frequency, the method comprising:

• measuring the output frequency to obtain a measured output frequency value by measuring time between period boundaries of the signal;
• measuring an elapsed time since an occurrence of a last period boundary in the signal;
• and
• controlling a HP filter characteristic as a function of the measured output frequency value such that the HP filter characteristic is raised when the period of the signal is less than the period corresponding to a higher frequency characteristic and the HP filter characteristic is lowered when the elapsed time since a last period boundary of the signal exceeds the period corresponding to a lower frequency filter characteristic.

A two-wire process control transmitter, comprising:

• sensing means for sensing a physical parameter and providing a noisy analog output having a fundamental frequency varying responsively to the physical parameter;
• digitizing means for generating a digital signal representative of the analog output;
• digital processing means for real-time filtering the digital signal to identify a fundamental frequency, where the filter characteristics change as a function the frequency of the fundamental frequency, the digital processing means providing an output indicating the fundamental frequency;
• and
• output means receiving the digitally processed output for providing a transmitter output representative of the physical parameter.