Most traditional viscosity measurement techniques rely on measuring the drag on a plate caused by fluid viscosity. This method is often observed in laboratory devices with moving or delicate parts, requiring a lot of maintenance. Drag measurements are impossible in a flowing fluid so an alternative technique is required. This is 'resonance'.
A brief explination of the two methods is provided below:
Drag Force Measurement
Resonant Vibration – Loss of Energy
As the surface of the sensor shears through the fluid, energy is lost due to the viscosity. The dissipated energy is accurately measured by microprocessor-controlled electronics and equated back to viscosity. Higher viscosity causes a greater loss of energy and hence a higher reading. Determining the amount of energy lost to the fluid is ideal for viscosity measurement, since it is practically independent of all other factors such as flow rate or pressure.