Temperature compensation of resonant frequency measurements for the effects of temperature variations

A method of compensating resonant frequency measurements for the effects of variation in temperature of a measured object comprising the steps of:

• exciting a metallic or ceramic manufactured part with a transducer to obtain resonant responses;
• measuring frequency of selected resonances of metallic or ceramic the manufactured part at a reference temperature;
• heating or cooling the part or specimen to another temperature and measuring the new temperature;
• measuring the frequency of the selected resonances at the new temperature, repeating the measurements of frequency and temperature for several temperatures;
• determining a temperature function which is a mathematical relationship between each resonant frequency and temperature;
• and
• using the temperature function to adjust the frequencies measured (fm) at any temperature (Tm) to the frequency (fr) at the reference temperature (Tr) wherein the temperature function is of the form:
• f.sub.r =f.sub.m *(1+(T.sub.m -T.sub.r)/C) where f.sub.r is the resonant frequency compensated to the reference temperature f.sub.m is the measured resonant frequency, T.sub.m is the measured temperature and T.sub.r is the reference temperature.

A method for compensating the measured resonant frequency of metallic or ceramic manufactured parts whose temperature is varying with time, wherein analytical methods developed at a baseline temperature are applied to determine whether the parts are defective comprising the steps of:

• exciting the metallic or ceramic manufactured part with a transducer to obtain resonant response;
• determining at least one mathematical temperature compensation function for a specific part sample which is known to be free of defects by;
• measuring at least one response resonant frequency while the part is at a known baseline temperature,
• heating or cooling the part to a series of different temperatures,
• repeating the resonant response frequency measurement at said different temperatures, and
• fitting a relationship between baseline temperature and the different temperatures to an appropriate mathematical formula;
• measuring temperature of a part of unknown quality as its resonant frequencies are applied;
• applying at least one mathematical temperature compensation function to the measured resonant frequencies of the part of unknown quality to convert the measured resonant frequencies to the value they would have at the baseline temperature;
• and
• applying analytical techniques to the compensated resonant frequency data to determine whether the part is good or defective.