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Benchtop and portable turbidimeters: how can turbidity be measured in NTU or FNU?

Turbidimeters quantify the turbidity by measuring light scattered by suspended particles. Essential from drinking water monitoring to biopharmaceutical processes, they deliver results in NTU or FNU according to EPA 180.1 (white light) and ISO 7027 (IR 860 nm). High-precision benchtop models and IP67 portable versions, in 90° or ratio configurations, with formazin or polymer calibration, on-board memory and GLP traceability to LIMS: the range spans ultra-low levels (?0.01 NTU) up to highly turbid matrices. 25/60 mm cuvettes, colour compensation, lamp/LED diagnostics and secure USB/Bluetooth interfaces ensure fast, repeatable and compliant measurements.

What are the different types of turbidity meters, and how do they work?

The dominant principle is nephelometry: a light source illuminates the sample and a detector measures scattering at 90°. According to the standard, the source is either a white tungsten lamp (EPA 180.1, units NTU) or an 860 nm infrared LED (ISO 7027, units FNU), the latter being less sensitive to colour. Ratio turbidimeters use multiple detectors (forward, 90°, backscatter) to compensate for colour and particle-size variation and to extend the range. For high turbidities, an attenuation (transmission) channel prevents saturation.

Two families cover the use cases: the bench-top turbidimeter, optimised for precision (fine resolution, stability, large display, traceability), ideal for analytical work and QC; and the portable turbidimeter, rugged (IP67), battery-powered for field sampling. Leading resolutions reach 0.001 NTU (drinking water), with a typical accuracy of ±2% of reading ± stray-light deviation.

Selection criteria: range and low-level resolution (<0.1 NTU), compliance with ISO 7027/EPA 180.1, cell pathlength (10/25/60 mm), management of standards (primary formazin, safer AMCO-AEPA polymers), ratio functions, memory/GLP/LIMS, battery life and ergonomics. Measurement quality also depends on preparation: remove bubbles, fill without streaks, wipe the cuvette (lint-free cloth), align and lock the cap to minimise stray light.

Comparison table (selection):
TypePrincipleApplications / Benefits
Benchtop90° nephelometry or ratio, IR/white sourceHigh precision, low-level resolution, GLP traceability
PortableCompact 90° nephelometry, IR or whiteFieldwork, rapid monitoring, IP67 housing, battery
RatioMulti-detectors (forward/90°/backscatter)Compensates colour, wide range, better linearity
EPA vs ISOWhite light (EPA 180.1) vs IR 860 nm (ISO 7027)Choice per regulation, units NTU/ FNU

In which fields is a turbidity meter used?

• Drinking water: monitoring of settling/filtration, regulatory compliance (detection down to 0.1 NTU and below).
• Wastewater: control of coagulation/flocculation, detection of shock loads.
• Environment: rivers, lakes, construction sites; turbidity/total suspended solids correlation.
• Food & beverage: brewing (EBC haze), beverages, juices; consistency and appearance.
• Pharma/bioprocess: clarification, in-process control (USP <855>), cleaning validation.
• Cosmetics: lotions (milks), emulsions, colloidal stability.
• Chemicals: dispersions, formulation and QC of raw materials.
Versions handheld are used for field sampling and on-site screening; benchtop models ensure metrology, calibration and traceability in the laboratory.

Available turbidity meters

Frequently asked questions about turbidimeters

Q : What’s the difference between ISO 7027 and EPA 180.1 ?
A : ISO uses an 860 nm IR LED (FNU), less sensitive to colour; EPA a white lamp (NTU). Choose according to regulatory requirements and the sample matrix.

Q : NTU, FNU, FTU… what do these units mean ?
A : NTU (EPA) and FNU (ISO) are conceptually equivalent; FTU is generic. In brewing, turbidity may be expressed as EBC haze. Stick to the unit required by the method.

Q : Why a ratio turbidimeter ?
A : The ratio mode combines multiple detectors to compensate for colour and particle size, improve linearity and extend the range, especially in coloured water.

Q : How to calibrate properly ?
A : Use traceable formazine or polymer standards. Allow to stabilise, mix gently, avoid bubbles. Frequency: depends on use, often monthly plus a daily check.

Q : How to avoid measurement errors ?
A : Clean, unscratched cuvette, wiped; cap in place; degas the sample; homogenise without bubbles; respect alignment and ambient temperature.

Q : Benchtop or portable ?
A : Benchtop = precision, low levels, GLP/LIMS; Portable = robustness, on-site work, rapid diagnostics. Many teams use both in a complementary way.

Q : What sensitivity to aim for in drinking water ?
A : Target a resolution of 0.001–0.01 NTU and an accuracy of ±2% or better. An ISO 7027-compliant model is often required for distribution networks.

Q : Are formazine standards safe ?
A : Formazin is a primary standard but should be handled with care. AMCO-AEPA polymer standards offer a stable, safer alternative.