There exists a critical need in the mobile and fixed asset market to empower field units to determine oil quality on demand and provide complementary oil condition information that has been traditionally obtained from oil analysis labs. The current methodology of testing in off-site labs is non-optimal and costly due to the logistical challenges of shipping samples and the time delay in getting information back to personnel to be able to make quick and informed decisions. Determining oil quality in real time with embedded and portable oil assessment devices operated by mechanic personnel provides the operational flexibility and rapid means of screening oil quality that is key to establishing a program to provide real-time condition-based monitoring products for the care of all assets.

Measuring the viscosity of oil is a rapid method of determining oil condition, and is considered an important parameter in assessing asset readiness. The SenGenuity ViSmart viscosity sensor, which can compliment IR spectroscopy and other bulk property sensors, can provide instantaneous on-line viscosity and temperature data, has no moving parts with an extremely wide operating range and offers universal plug-and-play connectivity for integration with and into other handheld products. The sensors have been on the market for close to a decade and are currently installed in markets ranging from oil condition monitoring in machine tool and rotating equipment industries to process control in coating applications. It is in these rigorous environments where ROI benefits have been realized, and are now been evaluated for mobile and fixed assets where oil condition monitoring is of paramount importance.

SenGenuity’s acoustic wave (AW) 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 or vibration or by flow conditions, so they can be used in harsh operating conditions to measure viscosity from zero to 500 cP with a temperature range of minus-15 degrees to 125 degrees Celsius with a high degree of accuracy. At the same time, sensor measurements are not affected by particulates in the oil.

Conventional mechanical and electro-mechanical 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.

Given that contaminants in oil (water, solvents and fuel) are known to degrade viscosity and cause damage to internal components of diesel assets, whether they are trucks or construction equipment or military vehicles or power gen equipment, it is important to not just rely on snapshot data. High water contamination levels in diesel fuel have been shown to be the reason for corrosion and pitting, leading to increased metal wear particle counts. The presence of residual cleaning solvents and fuel contamination has caused seals to swell and create less-than-ideal engine operating situations. Knowledge of viscosity in real time provide a significant benefit to measure aging of oil, ingress of contaminants during commercial operations and prevent incipient mechanical failure due to loss of oil lubrication properties.

This case study, together with customer data, shows the SenGenuity ViSmart viscosity threaded bolt sensor (Figure 2) that is targeted at embedded integration to fi xed and mobile diesel assets.

Product technology
SenGenuity has developed a unique method to offer a viscosity sensor with a wide dynamic range (air to several thousand cP) in a single sensor (Figure 1).

Figure 1. The SenGenuity sensor uses an acoustic waveguide with electrical transducers on one surface and being in contact with the fluid on the other surface.

The ViSmart is a commercially available, robust, reliable and cost-effective surface acoustic wave solid-state viscometer for integration into in-line, real-time monitoring and process control systems for scalable applications (Figure 2).

Figure 2. SenGenuity Solid-state Low-shear Bolt Viscosity Sensor

The sensor has no moving parts (other than the atomic scale vibration of the surface) and, due to the high frequency of the vibration, several millions of vibrations per second, is independent of flow conditions of the liquid and immune to vibration effects of the environment. High-temperature electronics are utilized that allow a very wide operating temperature range for the sensor.

The importance of these acoustic sensors lies in the distinctly different measurement principle. Whereas one class of mechanical devices measures kinematic (flow) viscosity and the other class measures intrinsic (friction) viscosity, the acoustic wave (AW) sensors measure acoustic impedance, (ωρη)1/2, where ω is the radian frequency (2πF), ρ is the density and η is the intrinsic viscosity.

The viscosity measurement is made by placing the quartz crystal wave resonator in contact with liquid. The liquid’s viscosity determines the thickness of the fluid hydro-dynamically coupled to the surface of the sensor. The sensor surface is in uniform motion at frequency, ω=2πF, with amplitude, U. The frequency is known by design and amplitude is determined by the power level of the electrical signal applied to the sensor. As the shear wave penetrates into the adjacent fl uid to a depth, d, determined by the frequency, viscosity and density of the liquid as d=(2η/ωρ)1/2, as depicted in Figure 3.

Figure 3. This figure depicts a cross-section of the sensor showing transducers on the lower surface and liquid molecules (gold balls) on the upper surface.

Acoustic viscosity is calculated using power loss from the quartz resonator into the fluid. The unit of measure is acoustic viscosity (AV) and is equal to ρη, (g/cm3 • cP) (density times dynamic viscosity).

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 (on the order of microns or micro inches) is moved by the vibrating surface. Also present is a proprietary hard coat surface that is scratch proof and abrasion resistant which allows the sensor to be operable in extreme environments and enabling the ViSmart sensor to be a suitable candidate for oil condition- and fuel quality-based monitoring applications in mobile and fixed asset markets.

Customer Application and Data
A customer in a third-world country in the telecom and data enterprise industry has strategic and critical power generation equipment in far-flung locations. Challenges of logistics are such that they would rather not have to conduct frequent site visits. Due to the remoteness of the sites, they are not part of power or telecommunications grid, and as such are susceptible to weather damage, equipment malfunction, vandalism and asset theft.

Partnering with remote site monitoring solution providers, the ViSmart sensors, as part of an overall solution package, can provide secure and reliable monitoring for the quality of the oil and fuel present in the power generator sets that present in these telecom and data enterprise infrastructures.

The goal of the customer was two-fold. First, they wanted to be able to identify if the quality of oil was within the nominal operating performance parameters over time and to determine if oil change intervals could be improved (currently oil is changed every 150 to 200 hours). Viscosity reading was identified as the key indicator parameter (it is important to note that the ViSmart sensor also measures temperature). A secondary goal was to ensure that the sensor would identify an event wherein a non-specified oil was introduced to the power-gen set.

Second, the customer had a requirement of identifying if there was contamination in the fuel line, either due to the water or kerosene. Again, viscosity reading was identified as a key indicator parameter.

Test conditions were set up and actual oil samples were obtained from a power-gen set supplying continuous electrical power (at variable load) in lieu of commercially purchase power (output rating of 22 kVA, 18 kW at 220V/60 Hz). In Figure 4, the relationship between viscosity of virgin and used 15W40 oil as a function of temperature is observed. The used oil has a run time of 150 hours; it is clearly observed that the shift in viscosity in nominal and there is no need to change the oil.

Figure 4. Viscosity-temperature Data for New and Used 15W40

As part of the same set-up, different grades of oil were checked for viscosity values in order to confirm the ability of the ViSmart sensor to differentiate between types of oil. Furthermore, the different types of oil were introduced to the power-gen set equipment specified 15W40 to determine if the sensor can notify the customer of an event when incorrect oil is present. The data is shown in Figure 5, acquired at a temperature of 40 degrees C, and clearly shows the differentiation in the condition of oil.

Figure 5a. Different Viscosity Values for Various Oil Condition States at 40 Degrees Celsius

Figure 5b. Different Viscosity Values for Various Oil Condition States at 40 Degrees Celsius (in detail)

Viscosity data also was acquired at 100 degrees C; and again, the differentiation in the different oil condition states is observed (see Figure 6). With viscosity data acquired at multiple temperatures, determining the condition of the oil and verifying if it is within its operational parameters is possible.

Figure 6. Different Viscosity Values for Various Oil Condition States at 100 Degrees Celsius

As part of the same set-up in the power-gen equipment, viscosity of diesel fuel, combined with contamination in the fuel was measured at various temperatures. The contamination consisted of water and kerosene, and all conditions were measured at 25 degrees and 40 degrees Celsius. As the data in Figure 7 clearly shows, the ViSmart is capable of monitoring the fuel viscosity and ensuring that it is within performance parameters.

Figure 7. Different Viscosity Values for Various Fuel Quality States at 25 and 40 Degrees Celsius

All of the data above indicates that with simple logic employed at the remote monitoring station, together with warning and alarm conditions, the viscosity and temperature of oil and fuel acquired can monitor the proper conditions needed for the power-gen equipment to function reliably without downtime.

The ViSmart viscosity sensor can be readily applied in field operations or installed directly on the equipment for continuous monitoring of viscosity to enable the mechanic personnel to test the oil or fuel in minutes. It would be complementary to lab oil analysis test burden by providing real-time viscosity data and would enable streamlining of logistic costs. And given no calibration is required for the rugged vibration and shock proof sensor, once it is installed in a harsh industrial environments, maintenance costs are extremely low.

The sensors are currently used in 24/7 applications in the commercial sector, with real-time data transfer for decision making abilities. The real-time in-line threaded bolt sensor can be fully immersed in the oil and/or fuel and be simply used for spot-checking or continuous monitoring. Providing real-time viscosity data and using the sensor continuously would provide the necessary information to personnel to make critical decisions in actual field applications leading to extension of machine life and maintenance schedules while complimenting the other oil quality parameter data stream obtained from the labs.

About the author:
This article was provided by SenGenuity, a strategic business unit of Vectron International ( SenGenuity’s mission is to bring to market highly differentiated sensor solutions based on Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) technologies. If you would like to learn more about sensors, e-mail, call 603-578-3025 or visit