In-Line Sensors for Urea Applications
Over the past five years Sentelligence™ has developed a flexible patent pending platform technology that can be applied to a wide range of uses for fluid condition and quality monitoring for automotive, mining, power generation, and industrial applications. The primary technology is a universal optical platform that measures the spectral or optical responses of the fluid and correlates these to the fluid composition or the presence of certain impurities. The sensor components are solid state and are selected to perform in the rigorous conditions encountered in commercial and industrial applications, under normal extremes of temperature and vibration.
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The key to the Sentelligence sensor technology is the combination of opto-electronics selected to provide the desired optical or spectral response within a given application and/or fluid environment. Almost any change in properties or fluid performance can be correlated to these optical/spectral responses with a suitable selection of sensing elements (for wavelength and/or responsivity). The primary optical function monitored is light/energy absorption in the visible, near infrared and mid-infrared (for special applications) regions of the spectrum. Measurement extensions include light scattering (for emulsified materials and particulates) and visible fluorescence (for certain additives and contaminants).
The role of the flow-through style of sensor is exemplified by the AdBlue/urea sensor that is shown in Figure 1. This sensor, with some modification, can be adapted to a range of other applications. This sensor offers the following:
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Figure 1: The AdBlue/Urea Quality Sensor, in an example flow-through configuration, designed for sub-zero operation |
- Measurement of urea concentration in SCR dosing systems over the range of 0% to 40%
- Indication of incorrect fluids, which for AdBlue might include windshield washer fluid, coolant or fuels
- Other example measurements include Bio- Diesel blends (from B5 to B100), and additive levels for replenishment systems
- Designed for operation from sub-zero (- 40°C) to elevated temperatures (60°C), and specified to 80°C.
- Configurations to accommodate coolant line heating and electrical heating (low current drain) for sub-zero applications
- Communications via CAN-Bus, with J1939 protocol – sensor powered via bus (voltage range 6VDC to 40VDC, overload protection to 200VDC)
These spectral measurement components are combined and are coupled in an optimized configuration to the optical interface, which is designed to meet the needs of a specific application in terms of geometry and fluid-light interaction. Generally, the optics are non-conventional and are highly optimized to ensure efficient coupling to the sensing element in contact with the fluid. In the standard versions of the sensors the wavelengths considered range from the short-wave visible (around 400 nm) to the end of the short-wave near infrared (around 1100 nm). The combinations of wavelengths are selected based on laboratory measurements obtained from conventional spectrometers. |
The sensor shown in Figure 1 features internal heating/cooling lines, where the temperature of the sensor is regulated and controlled by the flow of an external fluid. In the case of the AdBlue sensor, the implementation of AdBlue within Europe has required the use of the engine coolant lines to provide heat to the AdBlue tank. AdBlue freezes at 11°C (a eutectic temperature) and in arctic climates it is necessary to defrost the AbBlue tank, the delivery lines, and the sensor. This is accomplished by means of heat delivered by the hot engine coolant lines. This arrangement of the sensor can be used for any application requiring fluid based heating or cooling. The negative aspect of this design is that the fluid lines add significantly to the size and bulk of the sensor. As an alternative, a electrically heated version of the sensor is also available, and this version occupies about 50% less real-estate than the fluid heated version.
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Figure 2: Flow-through sensor designed for normal and low-temperature operation
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The flow-through sensor is not necessarily limited to a single measurement method, and multiple in-line sensors can be accommodated within the housing. Examples include the combination of spectral sensing for fluid condition and optical light scattering for particulate and emulsion/turbidity detection. The same approach can be adopted for fluid condition monitoring, such as engine oils, where the additional in-line sensing can include viscosity and electrometric measurements. The latter are used for determining oxidative breakdown or the presence of certain contaminants.
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Figure 3: An example handheld sensor designed for bio-fuel applications |
The flow-through sensors were initially designed for continuous monitoring applications on vehicles or mechanical equipment. However, with minor modification, in combination with a piston-pump (or a similar fluid transport device), the flow-through sensor can be configured for batch testing as a handheld measurement system. The example shown in Figure 3 is an infrared-based analyzer, conforming to the general ASTM method, for the compositional analysis of bio-diesel blends. The format of the sensor is quite flexible and it can be adapted to the sampling and analysis of a wide range of fluids. For further information about the products, the technology and the concepts discussed here, please contact Sentelligence at the address provided.
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