OBS501 Smart Turbidity Meter with ClearSensor
®
Technology
25
AMCO Clear
®
SDVB turbidity standards are used to calibrate an OBS501
sensor. SDVB standards are made for individual instruments. Standards made
for one model of turbidity meter cannot be used to calibrate a different model.
TABLE 8-4. Calibration Materials and Volumes
Sidescatter 90-Degree Materials
Calibration Cup Diameter
(mm/inches)
8594 – 20 TU
100 (~4)
8595 – 40 TU
100 (~4)
8596 – 125 TU
100 (~4)
8597 – 250 TU
100 (~4)
8598 – 500 TU
100 (~4)
8599 – 1000 TU
100 (~4)
OBS Sensor Material
8600 – 125 TU
200 (~7.9)
8601 – 250 TU
200 (~7.9)
8602 – 500 TU
200 (~7.9)
8603 – 1000 TU
100 (~4)
8604 – 2000 TU
100 (~4)
8605 – 4000 TU
100 (~4)
The GFS item numbers, standard values, and volumes required for the standard
low ranges are given in TABLE
. SDVB standards have a shelf life of two
years provided that they are stored in tightly sealed containers and evaporation
is minimized.
The TU values of the standards will remain the same as long as the ratio of
particle mass (number of particles) to water mass (volume) does not change.
Evaporation causes this ratio to increase and dust, bacteria growth, and dirty
glassware can also cause it to increase. Therefore, take the following
precautions. 1) Always use clean glassware and calibration containers.
2) Don’t leave standards on the bench in open containers or leave the standard
bottles uncapped. Perform the calibration as quickly as possible and return the
AMCO solutions to their bottles. 3) Clean dirty sensors with a clean, alcohol-
soaked cloth to sterilize them before dipping them into the standards.
4) Transfer entire bottles between containers. To avoid aeration, do not shake
excess fluid off the glassware.
Because of the intrinsic errors in the TU value of formazin used by the SDVB
manufacturer (GFS Chemicals) and the dilution procedures, the uncertainty in
the TU value of an SDVB standard is ± 1% of the value indicated on the
standard bottle. Consequently, the TU value of one liter of standard in an
uncovered 100-mm calibration cup will increase ~1% in 10 hours on a typical
summer day (relative humidity = 90% and air temperature = 18 °C). For
example, the TU value of a 2000 TU standard in a 100-mm cup will increase
by about 2 TU (0.1%) per hour. TABLE
gives the increases for some other
commonly used standards.
