Electronic viscosity measurement systems

The BiODE ViSmart acoustic wave resonance based electronic viscosity sensor and measurement systems provide a solution oriented product for the coating industry quality and process control

Viscosity control for product quality and process control is a crucial aspect of manufacturing operation in the paints and coatings industry.

As suppliers focus on customer satisfaction and consistency of product, viscosity becomes more important to measure and directly influences cost efficiency and quality in most processes.

In the coating industry, viscosity is a measurement that has challenged process engineers and quality control departments, since it can be affected greatly by physical variables, namely temperature and shear rate.

Additionally in OEM applications, there is a need for the solution provider to deliver a valued-added feature for constant monitoring of viscosity, for example in the dispense control of solvents.

Viscosity management can result in significant savings of the coating consumable while at the same time minimise the downtime in the process.

Historically, costly and inflexible mechanical products have been used.

Up until now there has been no viable "electronic" way to measure viscosity, and processors have been forced to measure infrequently or utilise a wide range of methodologies with repeated cost/benefit trade-off.

The BiODE ViSmart acoustic wave resonance based electronic viscosity sensor and measurement systems changes all this: they provide a solution oriented product for the coating industry.

The BiODE ViSmart sensor system can measure viscosity from 0 to 10,000 cP ranges (can measure higher ranges and is material dependent) with +/-1% repeatability, in operating temperature environments of -20C to 135C.

The ViSmart sensor has no moving parts, uses semiconductor technology and is housed in a hermetically sealed four-ounce package.

The ViSmart sensor measures temperature at the same time, hence relieving the customer of providing a separate temperature measurement device.

PRINCIPLE OF OPERATION.

The coating industry is familiar with kinematic viscosity (centistokes) and dynamic or absolute viscosity (centipoise), which are related according to the formula.

centistokes = centipoise/specific gravity.

The BiODE instrument introduces a third class of viscosity, called acoustic viscosity.

Acoustic viscosity has units of centipoise × specific gravity.

Knowledge of the specific gravity allows conversion between these three units at a fixed shear rate and temperature.

This method of measuring viscosity employs a shear acoustic wave resonator in contact with the liquid.

The viscosity of the liquid determines how thick a layer of fluid is hydro-dynamically coupled to the surface.

The loading of the acoustic resonator caused by this viscously-entrained liquid is determined by the thickness and density of the entrained film.

The response of an acoustic viscometer is thus proportional to the product of the viscosity, the density and the radian frequency of the vibration in the limit of low frequencies.

The acoustic wave resonator supports a standing wave through its thickness.

The wave pattern interacts with electrodes on the lower surface (hermetically sealed from the liquid) and interacts with the fluid on the upper surface.

The bulk of the liquid is unaffected by the acoustic signal and a thin layer (of the order of microns or micro-inches) is moved by the vibrating surface (the vibration amplitudes are of the order of a single atomic spacing).

BiODE ViSmart can be immersed in a fluid and can also accept a droplet sample as little as 100 micro-liters.

The overall dimensions of the BiODE sensor are approximately 1.3 × 1.1 × 0.3 inches (smaller than a matchbook).

The BiODE system is inherently network-enabled (including provisions for wireless data transfer) and allows data analysis on a system other than the computer physically connected to the sensor.

The BiODE system is readily extensible to distributed process control or to field-portable measurements.

The display of measurement information is immediate and continuous and is a marked improvement over current technology.

IN-PROCESS MEASUREMENTS.

Most existing in-line viscometers are large and bulky and response is slow and inaccurate, while many units have difficulty measuring fluids with high or variable shear rates.

They also present challenges in cleaning, operating and most only provide analogue outputs and are therefore difficult to interface to modern process control equipment which accept more flexible digital inputs.

The benefits of the BiODE digital design is that it is inherently much smaller, much faster, much more durable and reliable, much lower cost, and much more scaleable than existing products.

Its design is much more flexible than existing systems, and much easier to connect to a wide selection of process control devices because it outputs digital rather than analogue signals For in-process measurements, the ViSmart can be mounted directly in the reactor tank for batch applications, or in the pipe for in-stream applications on multiple customer specific custom options.

The ViSmart is unaffected by static, laminar or turbulent flow since the operating shear rate of the ViSmart is several orders of magnitude higher than fluid flow characteristics.

Also it is immune to vibration and orientation effects.

As long as the fluid is in contact with the sensor surface, viscosity will be measured.

Additionally, no customer calibration is required (it is factory calibrated to NIST traceable mineral oils).

The ViSmart has the ability to integrate other off-the-shelf products for pH, conductivity and RTD measurements and can be deployed for full integration for Intranet viewing or host plant control software.

Finally, since the ViSmart is a high shear rate viscometer a 1:1 correlation with current low-shear viscometer methods is material dependent and can be generated as a library database for customers.

For plant-wide scalability, up to eight ViSmart units can be connected to the industrial plant control hub product, ViscNet which can deliver outputs (4-20 mA, TCP/IP, etc) for integration and control of solenoid valves and pumps.

APPLICATIONS.

Recently, a customer in the automotive coating industry evaluated the ViSmart as part of its product quality procedures.

Data was taken continuously and the ViSmart was proven to be sensitive to viscosity as a function of different products and various process conditions At another customer for proprietary foaming resin applications a ViSmart sensor was installed for in-line viscosity monitoring.

The ViSmart indicates solvent loss and/or polymerisation with increasing time demonstrating that the ViSmart can adequately monitor the change in the characteristics of the resin as a function of temperature.

For a customer in an OEM coating process with a non-homogenous blend, the ViSmart is able to continuously show the behavior of the blend in real-time.

It was clearly seen that the level of agitation was introducing changes in the structure of the samples.

It is possible that there is a non-homogenous mixing of the solid content in the carrier fluid as the sample is agitated and there was no quick 'bulk equilibrium' obtained.

As the agitation is stopped equilibrium of settling is reached.

The ViSmart on-board electronics and communication protocols provide the necessary interface for integration to OEM product platforms such as dispensing, pumping and coating station equipment, allowing the equipment manufacturers to provide value-added features of viscosity monitoring and control.

For another customer in the coating industry, who desired to verify that the BiODE ViSmart has the accuracy to detect different dilution concentrations and perform tasks as a QC tool at installation, a test was performed with a glycerin-water mixture.

Data was taken starting with 50 ml of glycerin, to which 50 ml of water was added.

A series of 10 ml additions of water were made down to a 25% final concentration.

An aliquot was removed and mixed with 20 ml of glycerin.

This solution was added to verify scale stability.

The ViSmart was able to track the changes in viscosity.

Finally, at another customer, Penmor Lithographers in Lewiston, Maine, head pressman James Bissonette has been using the ViSmart to measure the coating that is used to laminate the pages and covers of brochures and magazines on a lithography coater machine.

Applying the laminate is a final step and viscosity must be closely monitored.

If it is too viscous, the covering could result in pages sticking together and could ruin a print run.

Bissonette installed the sensor at the point where the coating is drawn from the barrel.

Viscosity and temperature data are provided in real-time to a laptop computer, which he monitors without having to take manual samples.

BiODE customised the software to provide the data in a format that Bissonette required.

BiODE ViSmart, eCup and ViscNet products are viable in-line measurement techniques for process control in manufacturing environments, especially in tandem with end-point analysis for a variety of different viscosity and measurement needs.

They are designed to provide instantaneous, real-time in-process viscosity measurements, providing customers with a continuous digital audit trail.

The ViSmart small size and lack of any moving parts using state of the art semiconductor sensor technology, coupled with the eCup and/or ViscNet provides the process operator with a cost-effective and flexible tool to reduce operating costs, minimise process errors, and improve final product quality while increasing productivity and enabling increased control of process parameters.

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