One example of an acoustic-wave viscosity sensor is the ViSmart by BiODE Inc. The sensor's semiconductor packaging weighs only 4 oz and is smaller than a matchbox (about 1.3 X 1.1 X 0.3 in.). Hermetic seals permit complete immersion even in harsh chemical environments. Onboard electronics control sensor operation while communicating with external readers.

A ViSmart viscosity sensor was tested recently on chemical solutions at an industrial printing site. The goal was to verify the ability of the sensor to measure viscosity of a chemical solution with different concentrations of alcohol and an alcohol substitute.

Technicians added isopropyl alcohol and an alcohol substitute in 1% increments to a chemical solution and to water. Instruments recorded viscosity data in acoustic viscosity units (AV), equal to cP s.g. All tests used a specific gravity value of 1. Testing personnel observed some shear thinning that caused slight variations from the expected lab value of 1.0 for water.

Test results confirmed the sensor's ability to measure viscosity over a wide range of temperature variations as well as changes in viscosity occurring with the addition of other liquids. Spikes appearing in the sensor's output during the injection of alcohol to the mix clearly indicate a use for the sensor in determining mixture homogeneity. Sensitivity testing demonstrated the ability to measure 1% changes in alcohol concentration as a function of viscosity.

Another in-line acoustic sensor was installed to monitor viscosity over a temperature range of 25 to 200°F in a foaming-resin application. The test held material at various temperatures in an irregular hot/cool pattern. Viscosity was seen to vary with temperature, tracking the detail of the temperature curve.

The acoustic sensors also performed well over the cool-heat cycle of foaming resin. Data tracked the solvent loss and polymerization over time demonstrating the sensor can monitor changes in the characteristics of the resin as a function of temperature.

Tests conducted in oil conditioning and monitoring showed the different, real-time behavior of new, used, and contaminated synthetic oils in a gearbox. Each oil type recorded a different viscosity value. The value of the new oil was lowest because it is subject to the most shear thinning. The value for contaminated oil was lower than that of the used sample because water had seeped into the gearbox. Note that the viscosity value of the water-contaminated oil is lower due to the high shear rate of measurement by the sensor. Depending on the rheological curve and the behavior of the non-Newtonian mixture, shear rate viscosity values are different natured than those obtained by traditional mechanical viscometers.