4
Compact Turbimeter
34
To index a cuvette, insert the sample cuvette
with the orientation mark facing forward.
Systematically rotate the sample cuvette 45°
at a time and record the position of the lowest
value. This is the optimal cuvette alignment for
low turbidity measurement.
Total Suspended Solids
This mode will only be active if a site calibration has
been stored within the Turbimeter. Once a calibration
has been created (via the
‘Calibration’
menu) the site
ID can be used to recall the site specific relationship
between turbidity and suspended solids.
Choose
‘Reading’
mode, select
‘Total Suspended
Solids’
and press
‘OK’
. Highlight the Site ID for
the Site/Sample under investigation using the
Up/Down
arrows. The calibration data will be
recalled automatically.
Insert the sample with the orientation mark facing
forward and press
‘Read’
. A beep will occur at
the start and end of each measurement cycle.
Result is displayed on the screen in mg/l and
stored in the log with time, date, Operator ID
and Sample ID.
4.7 Calibration Menu
The Compact Turbimeter is delivered with a stored
calibration carried out on primary Formazin
standards and validated as part of the production
process. For field use, a set of calibration
standards are provided as part of the kit.
Recalibration is only required if the standards
provided show an unacceptable level of variation
from the stated values on read-back.
Two different methods of calibration are
available for the Turbimeter.
The calibration methods are:
SDVB
The use of SDVB for field calibration of turbidity
meters is preferable due to the improved stability and
handling compared to Formazin. When calibrating
turbidity instruments SDVB standards are assigned
to a specific model and cannot be transferred.
Using SDVB standards from another manufacturer
may differ greatly when applied to the
Turbimeter. This is normal behaviour and
should not cause concern.
Formazin
Freshly prepared standards can also be used for
calibration where available.
Formazin is used as the primary calibration material
for the Turbimeter and can also be used to align
the calibration of different instruments when
discrepancies occur. Preparation of Formazin
standards from 4000NTU stock solution is required
to be within the stated limits detailed below.
Total Suspended Solids
When using the Turbimeter in Total Suspended Solids
Reading mode, a calibration is required to set the
relationship between the measured turbidity values
and the ‘true’ suspended solids value, determined by
gravimetric methods. This calibration can either be
an assigned series of values from the results log
or a simple algorithm with factors provided by the
user. This relationship is typically a straight line and
hence the factors consist of a slope and intercept.
The Compact Turbimeter has two methods of
generating the data for relating the measurement
of turbidity to total suspended solids (TSS):
1 Correlation
- Using the stored turbidity data
from the instrument log and relating it to
manually entered Total Suspended Solids data
derived from elsewhere. The minimum number
of correlation points required is one, as the zero
point can be used as a second point. A maximum
number of 50 data points can be used.
2 Factor
- Using data manipulated externally,
a slope and intercept for the straight line
relationship can be entered directly. Slope
factors range from 0.1 - 50.0 and intercepts
can be set from -50.0 - +50.0
Calibrating the Compact Turbimeter
SDVB
Select Calibration and press
‘OK’
.
Choose
‘SDVB’
and press
‘OK’
.
Select the lowest (0.05 - 0.15) NTU standard and
insert into the sample chamber with the orientation
mark facing forward.
Use the
Up/Down
buttons to adjust the value on
screen to that on the standard and press
‘Read’
.
Repeat the process for the 20NTU, 100NTU
and 800NTU standards.
