Adblue® Diesel Exhaust Fluid
by Refractometer or Hydrometer
In an effort to reduce environmental pollution, the European Union has established certain rules about emissions from heavy and light goods vehicles. One method adopted by vehicle manufacturers to allow compliance is SCR (Selective Catalytic Reduction), which chemically reduces NOx-emissions using a urea additive in the exhaust flow.
Adblue® (DEF in the USA) is such an additive. They are stored as a concentration in a separate tank prior to mixing with the exhaust gases as they leave the engine. In order to maintain efficiency and to be sure that systems are not compromised, it is essential that the concentration is accurately maintained. Measuring devices such as refractometers and hydrometers may perform such checks and depending on the location and accuracy required, a choice can be made from the following instruments available from Bellingham + Stanley.
Portable Devices – Hydrometer:
A hydrometer is a scaled device that measures
the specific gravity of a liquid, which in turn is proportional to
concentration. The Adblue® hydrometer is low cost and offers
excellent accuracy for measurements in the field.
Operation: Sufficient sample is syphoned from the tank using the integral suction pump. Concentration is subsequently checked against the point where the hydrometer crosses two calibrated target marks. The hydrometers are also available with an alternative Specific Gravity Scale (SG).
Portable Devices – Optical Refractometer:
A Refractometer measures the refractive index
of a liquid and requires a much smaller sample than a hydrometer. Because
the instrument is made from alloy, they are considerably robust for
use in the field.
Operation: Apply a drop of sample to the prism, look through the eyepiece and take a measurement from the scale. Conversion tables can then be used to check the concentration of the liquid under test (or other vehicle liquid such as antifreeze, windscreen wash or brake fluid!).
Portable Devices – Digital Hand Held
Refractometer:
As an alternative to the optical refractometer,
a digital hand held refractometer is available. However, due to the
light source and temperature compensation type, measurement values
may be affected if not taken at 20°C. Operation is similar to the
optical device described above.
Oil in Water Test Strips:
It is sometimes a requirement to check if there
has been contamination to the diesel exhaust fluid tank. One
method for testing if diesel has been accidentally or even purposefully
mixed with the DEF is to use simple test strips that detect oil. The
DEF is simply removed from the tank using a syphon prior to the strip
being immersed and agitated. Presence of oil causes a change
in the colour of the strip.
Laboratory Devices:
Manufacturers of Aqueous Urea Solutions (AUS)
within the European Union are required to conform to ISO22241-2 in
respect of refractive index measurement. This norm dictates that the
measurement temperature must be extremely stable (±0.02 °C)
and the refractive index resolved to 5-decimal places. Bellingham
+ Stanley has produced a specific refractometer called the RFM990-AUS32 that
meets this requirement.
Order Codes:
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Note: Accuracy of measurement is dependant on measurement method (refractive index vs. density) and temperature control type. If in doubt, contact Bellingham + Stanley. Bellingham + Stanley accept no liability for losses caused by or due to the use of this equipment.