Conventional mechanical and electromechanical viscometers designed primarily for laboratory measurements are difficult to integrate into the control and monitoring environment. As a consequence, many companies rely on decisions based on intermittent “snapshot” data acquired from periodic sampling where conventional instrumentation can be affected by temperature, shear rate, and other variables.

Acoustic wave sensors offer a number of advantages over conventional mechanical and electromechanical viscometers as they are small, solid-state devices that can be completely immersed in the oil, providing an instantaneous viscosity data stream for embedded OEM or end-user spot-check applications. The sensors are unaffected by shock, vibration, or flow conditions so they can be used in harsh operating conditions to measure viscosity of oil from 0 to 500 cP with a temperature range of -25°C to 125°C. At the same time, sensor measurements are not affected by particulates.

Acoustic wave sensors measure viscosity by placing a hermetically packaged quartz crystal chip with an abrasionresistant, hard-coat surface in contact with the oil. The oil’s viscosity determines the thickness of the oil hydrodynamically coupled to the surface of the sensor. As the acoustic wave penetrates the oil, viscosity is calculated by measuring the power loss. Because an acoustic wave sensor is a solid-state device no bigger than a matchbox, it requires no calibration, contains no moving parts, and can be completely embedded for hardware integration to any control platform.

The effectiveness of acoustic wave sensors in military equipment is illustrated through testing done by a global leader in the automotive and trucking industry. The company integrated acoustic wave sensors into its engines to continuously monitor the condition of the engine oil as a function of the fuel dilution. The sensors provided current, accurate, and reliable viscosity data to ensure and extend the warranty period on the engines.