DD seawater refractometer

DD seawater refractometer

Hand-held measuring device for measuring the REAL salinity and specific gravity of seawater using the refractive index.

What is different about the DD seawater refractometer?

Although the largest percentage of salt in the sea is sodium chloride, the presence of other important ions such as magnesium and calcium in natural seawater results in a different refractive index than that of pure salt solutions.

A standard salt (brine) refractometer will therefore not provide the correct salinity for natural seawater and a conversion factor must be applied.

For example, a 35 pt solution of natural seawater has the same refractive index as a 36,5 pt solution of brine.

DD's new ATC refractometer solves this problem as the scale is calibrated for seawater and provides true salinity results for use in aquariums with great accuracy.

Our refractometers feature a copper inner body that conducts heat faster than aluminum and plastic versions, allowing for faster and more accurate automatic temperature compensation.

Easy to read

Another problem with most refractometers is that the scale usually reads from 0-100 ppt, although we are actually only interested in the 30-40 ppt range. Our new seawater refractometer is therefore specifically designed to read from 0-40 ppt, allowing 2,5 times higher resolution than a normal 0-100 scale.

Automatic temperature compensation (ATC)

There are many misunderstandings about how the ATC function works and its effects on the refractometer at different room temperatures.

Salinity is a measurement of the salt content in a quantity of water and therefore does not vary with temperature. However, a refractometer does not measure salinity directly, but rather measures the refractive index, which is then displayed as salinity. The refractive index of a solution varies with temperature, so the value measured with a refractometer is always temperature dependent.

 An ATC refractometer has a bimetallic strip inside the device that shifts the reading scale as temperature changes to compensate for the change in refractive index.

It is important to know that the temperature of the device and not the water temperature is meaningful, as the small water sample used for the test adjusts to the temperature of the refractometer within seconds.

Once the refractometer is correctly calibrated at the set calibration temperature of 20 °C, it can be used in environments where the ambient temperature and therefore the temperature of the device warm up within the ATC range, which is between 10 and 30 °C or would cool down.