Table of Contents
Advertisement
Macro 900 Operation Manual
15.1. PT 1551 Turbidity Probe
Turbidity can be measured by the MAP 2000/2100 using the optional PT 1551
Turbidity optical probe.
This electrode employs a Nephelometric technique in accordance with ISO
7027, which uses Formazin as a reference standard. The Macro 900 Meter
displays turbidity in Nephelometric Turbidity Units (NTU) which is nominally
equivalent to Formazin Turbidity Units (FTU).
Turbidity can be calibrated with either Formazin Turbidity Standards prepared
freshly from PT 121 Formazin Stock Solution or SDVB Turbidity Standards,
depending upon your preferred turbidity reference. Be aware, these two
standards will give very different results. Factory calibration is carried out
with a 1000 NTU Formazin Turbidity Standard in accordance with ISO 7027.
15.1.1.
About Turbidity
Turbidity is a measurement of the light scattering properties of solids
suspended within a liquid and is therefore an indirect measurement of clarity.
Turbidity is not a direct measurement of suspended solids, clarity or colour.
Particle size relative to the wavelength of the transmitted light, particle shape
and refractive index modify the distribution of scattered light. Sample colour,
(particularly dark colours) can also reduce a certain portion of the scattered
light by varying degrees.
Combined, these effects result in wide variability in the distribution and
intensity of light scattering from a turbid water sample. As a result, different
combinations of particle shape, size, colour and refractive index can produce
similar turbidity effects.
By contrast, changing only the incident light wavelength and detector distance
can dramatically change the measured turbidity of a given sample. As a result,
different model sensors from different manufacturers can measure different
turbidity values for the same sample. This highlights the qualitative nature of
turbidity measurements.
Integrated monitoring programs, where turbidity measurements from different
locations are to be compared, must use a single model of sensor and maintain
a strict QA and calibration program to accurately characterise, compare, and
interpret observed turbidity values.
15.1.2.
Precautions During Use
In common with all other submersion type Turbidity Probes, air bubbles and
stray reflections can be a problem when trying to measure low turbidity values.
In order to avoid air bubbles, keep the Turbidity probe clean, and agitate the
Probe after submersion to dislodge any air bubbles which may be clinging to
the lenses. In order to maintain a common reflective pattern between
calibration and use, always calibrate and measure turbidity with the
protective Sleeve End Cap and End Cap Plug fitted.
© 2013 Palintest Ltd.
www.palintest.com
V3
Page 54 of 147
Advertisement
Table of Contents
Troubleshooting
