LaMotte 2020wi Portable Turbidity Meters - Manual (Page 49)

for wiping a fi lled tube before placing it in the meter chamber. Invert
tube very slowly and gently three times to mix the sample. Surround
the tube with a clean, lint-free cloth. Press the cloth around the tube.
Rotate the tube in the cloth three times to assure that all areas of the
tube have been wiped.
5. Discard tubes that have signifi cant scratches and imperfections in
the light pass zones. (Central zone between bottom and fi ll line).
6. When reading very low turbidity samples, do not use tubes or caps
that have been used previously with high turbidity samples.
7. Use the averaging option for low level measurements of turbidity.
8. The meter should be placed on a surface that is free from vibrations.
Vibrations can cause high readings.
9. Turbidity readings will be affected by electric fi elds around motors.
10. Carbon in the sample will absorb light and cause low readings.
11. Excessive color in a sample will absorb light and cause low
readings. The user should verify if a certain level of color will cause a
signifi cant error at the level of turbidity being tested.
12. Observe shelf life recommendations for turbidity standards.
13. Do not use silicone oil on tubes when testing turbidity with the
2020we/wi.
14. When testing at low concentrations use the same tube for the blank
and the sample.
15. Always insert tube into the meter chamber with the same amount of
pressure and to the same depth.
16. Occasionally clean the chamber with a damp lint-free wipe, followed
by a Windex ® dampened wipe. A clean chamber and tubes are
essential for reliable results.
17. For the greatest accuracy during the calibration procedure, be
sure that after the meter is blanked and the blank is scanned as
a sample, the reading is 0.00. If not, reblank the meter and scan
the blank again until it reads 0.00. When scanning the calibration
standards as the sample, scan the calibration standard three times
removing the tube from the chamber after each scan. The readings
should be consistent. Use the last consistent reading to calibrate
the meter. If the readings are not consistent, avoid using an aberrant
reading to calibrate the meter.
18. Calibrate the meter daily.
19. Calibrate the meter with a standard that is closest to the expected
range of the sample being tested. For example, if the sample
is expected to be less than 1.0 NTU, calibrate with a 1.0 NTU
standard and a blank (0 NTU standard). If the sample is expected
to be around 2 NTU also calibrate with the 1.0 NTU standard but
if the sample is expected to be around 8 NTU calibrate with a 10
NTU standard. If the sample is expected to be over 30 – 40 NTU
it is recommended that the meter be calibrated with a 100 NTU
standard.
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