How do zero calibrations differ between the TU5 series and legacy instruments like the 1720E and UltraTurb?

Document ID

Document ID TE9228

Published Date

Published Date 14/06/2018
Question
How do zero calibrations differ between the TU5 series and legacy instruments like the 1720E and UltraTurb?
Summary
TU5/ 1720/ UltraTurb - zero NTU calibration validation.
Answer
1. 1720E and TU5 instruments work with two different technical standards, therefore the turbidity values are not 100% comparable, especially around zero:
  • 1720E white light (EPA Method 180.1)
  • TU5 EPA red laser (EPA Method 10258)
  • TU5 ISO IR Laser (ISO Methode 7027)
2. With regards to turbidity as a physical phenomenon there is no absolute zero, as even the cleanest water will scatter light. Our instruments don’t perform a zero-point calibration, but a two point factory calibration with different standards and extrapolate down to zero at the point where the current is zero at the photodetector. Zero current would mean zero NTU.