Comparison of long-term stability of AM versus FM gyroscopes

A vibrating ring gyroscope is operated in AM and FM mode to demonstrate improved long-term stability of FM operation. Both bias and scale-factor (SF) accuracy were tested over a one-month period with devices power cycled between measurements. Bias and SF improve by more than two orders-of-magnitude from 335mdps to 2.86mdps and from 518ppm to 4.31ppm in the AM and FM modes, respectively. The temperature coefficients decrease from over 700dph/°C to less than 3dph/°C for the bias and 105ppm/°C to 1.25ppm/°C for the SF. The in-run bias improves from 19dph to less than 1.5dph. AM and FM tests use the same transducer with no additional trimming, demonstrating the fundamental advantage of FM over AM readout.