WTW 251301 Turbidity Meter, BTLS Flex/430

Nephelometric or transmittance measuring-the nephelometric measurement at 90° scattered light is advantageous for lower turbidity, whereas the transmission measurement at 180° is beneficial for medium to high turbidity values: With increasing turbidity, restray and scattering effects between particles are growing bigger. The reduction of light intensity in this case leads to a more accurate result than a 90° nephelometric measurement. Therefore, lab meters for high values are equipped with several measuring options: ratio modes calculate the final result from different measured angles. For ratiometric measurements, there is no specific standard method to be followed; rather, procedures are established by the application or industry. White light has a higher sensitivity for small particles, however, the inherent coloration of the solution has a stronger disturbing effect in this case. The IR measurement is required by DIN ISO, the white light measuring by US EPA.