System and method for frequency measurement based on quadratic forms

A monitoring device for measuring the frequency of a waveform, the monitoring device comprising:

• an input coupled to the waveform;
• an analog to digital converter coupled to the input, the analog to digital converter measuring a plurality of data points from the waveform;
• a memory storing a point of interest from a previous cycle of the waveform;
• and
• a controller coupled to the analog to digital converter, the controller:
• referencing a point of interest from the previous cycle;
• determining four points of interest at equally spaced phase angles from the current cycle of the waveform by calculating the average of the data points around each of the respective equally spaced phase angles of the current cycle of the waveform;
• and
• determining a frequency of the waveform based on the determined four points of interest of the current cycle and the last point of interest from the previous cycle.

A machine readable medium having stored thereon instructions for determining the frequency of a waveform, the stored instructions comprising machine executable code, which when executed by at least one machine processor, causes the machine to:

• measure data points from the waveform;
• reference a last point of interest from the previous cycle of the waveform;
• determine four points of interest at equally spaced phase angles from the current cycle of the waveform by calculating the average of the data points around each of the respective equally spaced phase angles of the current cycle of the waveform;
• and
• determine a frequency of the waveform based on the determined four points of interest of the current cycle and the last point of interest from the previous cycle.

A method of calculating a frequency of a waveform measured from a monitoring device, the method comprising:

• measuring data points from the waveform;
• referencing a last point of interest from the previous cycle of the waveform;
• determining four points of interest at equally spaced phase angles from the current cycle of the waveform by calculating the average of the data points around each of the respective equally spaced phase angles of the current cycle of the waveform;
• subtracting the average value of the points of interest in the current cycle from the four points of interest and the last point of interest from the previous cycle to compensate for DC bias;
• determining a frequency of the waveform based on the determined four points of interest of the current cycle and the last point of interest from the previous cycle;
• and
• determining a sample frequency for the next cycle by multiplying the previous frequency by one plus a correction factor, the correction factor being the difference between the frequency of the current cycle and the previous cycle, and wherein the correction factor is compared to a threshold value, and the correction factor for the next cycle is reduced if the correction factor is below the threshold value.