Negative Results
The 2020e and 2020i turbidity meters will display
negative results if the sample water is less turbid
than the blank reading. This is possible in ultra-
low turbidity waters, where the sample turbidity is
at or near the detection limit of the meter.
Negative readings can also indicate a problem
when the meter was blanked. If the meter is
accidentally blanked to a 1.0NTU standard,
subsequent tests may negative, in response to
the high blank reading. Correct this problem as
follows:
1. Reset the meter to the factory calibration
settings: with the meter turned OFF, hold down the
*OK button and press ON. Release both buttons
at the same time. Press *OK to select the default
settings. Press *OK again and the meter will turn
off. The factory settings will be restored.
2. Follow the instructions on how to properly fill
the turbidity tubes with the standard solutions (see
below).
3. Once the tubes are filled with standard, turn
the turbidity meter on and enter the measurement
mode. Scan the blank tube (0.00 NTU). Then
leave the blank tube in the meter and press *OK to
scan the blank as a sample. It should read 0.00.
If not, press the UP button and reblank the meter
again. Then scan the blank as a sample again
until it reads 0.00. This may take at least three
tries.
NOTE: a small negative number will be observed
if the reading is slightly less than the reading
used as a blank. This is expected due to minute
variations between readings. A reading of -0.02 or
even -0.04NTU is not uncommon. Once 0.00 or a
very small negative number is achieved, the meter
is ready to be calibrated.
Filling Turbidity Tubes
It is important to use the proper test tube designed
for use with the 2020e and 2020i turbidity meters,
LaMotte code 0475. Tubes must be clean and free
from fingerprints, lint, dried spills and significant
scratches. Use lint free tissue to wipe your tubes
clean.
When filling a tube with standard solution, rinse the
vial with a small amount of the standard solution,
three times, then fill to the line. This will assure
that no dust, debris or dirt will contaminate the
standard solution that you pour into the vial. Put
a dry tube positioning ring on the tube. The tube
positioning ring has two tapered notches and one
squared-off notch. Place the ring on the tube so
that the one squared-off notch is aligned with the
vertical, white indexing line that extends 90° from
the horizontal fill line on the tube. This will assure
that you properly index the tube inside the light
chamber each time. Wipe any liquid that may
have leaked between the positioning ring and tube
surface. Cap the tube and apply an Avery label
marked with the corresponding NTU value.
Unstable Readings
Unstable readings can occur when excessive
physical change occurs in the sample at the time
that the sample is scanned in the meter. Settling
and sedimentation can cause this in high turbidity
waters and even microscopic air bubbles and
submicron particulates can cause this in low
turbidity waters. The ERR4 “Processing Error”
may be triggered in response to these situations.
To obtain the most accurate and stable readings
possible, utilize the signal averaging feature
of the meter. Turn the meter on and select
Options, then Averaging. Choose between 2, 5
or 10 measurements. Press OK, then press the
back button to return to the main menu. Signal
averaging of 5 measurements is usually sufficient
and provides optimal balance of the signal
averaging benefits, with minimal stress to the
battery.
Power Problems
Be sure to use brand name 9V alkaline batteries.
Heavy Duty, Rayovac and store brand batteries
do not have enough sustained power to keep
the meter on and power the lamp. We suggest
Duracell Alkaline 9V batteries. Rechargeable
batteries can be used; we suggest Duracell or
Energizer 9V NiMH rechargeable batteries. If
using the meter in a lab setting, remove the
battery altogether and operate exclusively with the
TC-3000 Meter Troubleshooting Guide
