Resonant Frequency vs. Low Frequency Noise vs. Q-Control

For low speed applications such as those in the Pulp and Paper industry and the rolling mills, the generation of low frequency noise in sensors and instrumentation is extremely critical. This is of
particular importance when the sensors are operating at elevated temperatures in the 100 to 120 °C (212 to 248 °F) range or higher. Low frequency noise is influenced by a number of factors and it is the balance of these interacting factors that is critical in sensor design. One of the more important factors is the charge sensitivity of the sensor element (crystal design). The higher the charge sensitivity, the lower the noise because less amplification is required of the sensor amplifier.

The charge sensitivity of an annular shear or compression element built from a given material depends on the size of the element. The size of the element also defines the resonant frequency, the larger the element, the lower the resonant frequency. The higher the charge output (pC/g). the lower the conversion gain required for the amplifier. Therefore, the internally generated noise is amplified less, resulting in a lower noise output of the sensor.

As can be seen from above, there is strong interaction between the various factors. The ultimate design of the “SKF Sensors” was the result of compromise of these factors in order to provide a sensor that will perform to the highest of expectations for the core segment industries of SKF.