ISO 7027 update and self-compensating turbidity sensor design are good news for data aficionados

The International Organization for Standardization (ISO) provides world-class specifications for products, services and systems, to ensure quality, safety and efficiency. On June 15, 2016, they released an update to ISO 7027-1:2016, a quantitative method for the determination of turbidity.

AquaTROLL600TurbiditySensorAdditionally, with the release of the Aqua TROLL 600 Multiparameter Sonde, In-Situ also came to market with several ground-breaking, patent-pending design updates to our ISO 7027 turbidity sensor.

The combination of updates to the ISO 7027 method and improvements to our turbidity sensor design allows water quality professionals to expand the instrument application, improve data quality, reduce the time and costs associated with calibration caused by drift and fouling, and simplify reporting.

What’s changed?

In the previous version of the standard, NTU was not considered equivalent with the same measurement as a Formazin Nephelometric Unit (FNU) made with an ISO 7027-design instrument.  However, within the Scope of the updated method, ISO now states that “There is numerical equivalence of the units NTU and formazin nephelometric unit (FNU).”

This is consistent with the Aqua TROLL 600 turbidity sensor reporting units.  Where ISO 7027 compliance is required, you can now easily convert from FNU to NTU within the accompanying VuSitu software.

Some details remain unchanged, but are important to mention:

While the presence of dissolved, light-absorbing substances that impart color in natural waters can negatively impact turbidity readings, using a spectral band-width with a range greater than 800 nm, like that utilized in the Aqua TROLL 600 turbidity sensor, minimizes the impact, with the exception of certain polluted waters or carbon remediation reagents that exhibit a black or blue color.

Aqua TROLL 600 patent-pending sensor design enhances data quality and expands application in challenging environments:

According to ISO 7027, when measuring very low turbidities, results should be corrected for stray light. With the Aqua TROLL 600’s ISO 7027 turbidity sensor, you’re now able to measure over a much wider dynamic range (i.e. 0-4000 NTU), while at the same time maintaining very low noise levels across the entire range.

At600-Turbidity-Sensor-LinearityTurbidity-Sensor-Thermal-Shock-TestingAutomatic internal compensation adjusts for shifts in LED output power over temperature during calibration and deployment, reducing inaccuracies caused by temperature changes.

The internal reference also compensates for any dimming of LED optical output, thus ensuring long-term stability and reducing instrument drift.

Improvements to calibration and maintenance regimes:

NTU and FNU are now equivalent ISO units, and ISO confirms that AMCO clear – the standard available for use with the Aqua TROLL 600 – is acceptable as a primary standard (similar to Formazin).  AMCO Clear standards are safer, easier to handle, and have a longer storage life than Formazin.

The Aqua TROLL 600 turbidity sensor is factory-calibrated across its entire range, ensuring a high degree of accuracy and decreasing the need for time-consuming and expensive user field calibrations.

For high-fouling environments, the Aqua TROLL 600 antifouling system and calibration design eliminates the need for excessive use of expensive calibration standards and complicated maintenance regimes, significantly reducing annual calibration maintenance costs.



View the ISO 7027-1:2016 update here, or, to speak with a sales consultant about the industry-leading Aqua TROLL 600 Multiparameter Water Quality Sonde, call 800-446-7488 or email


ISO 7027-1:2016(en) Water quality — Determination of turbidity — Part 1: Quantitative methods:

USGS photo: