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7.
If the verification fails, a verification failure message
(Procedure Failed) is displayed:
Verification
PV
1400 NTU
STD
1000 NTU
Procedure Failed
Exit
This may indicate that the sensor requires calibration.
6.3 Turbidity calibration
Used to calibrate the sensor to measure turbidity. There are two
possible calibration modes:
— 1-Point calibration, refer to Section 6.3.2, page 15
— 2-Point calibration, refer to Section 6.3.3, page 16
A 1-point calibration adjusts the Calibration Slope and is
suitable for general operation.
A 2-point calibration is recommended when measuring low
turbidity values (below 50 NTU). The Offset and Slope are
adjusted resulting in improved accuracy at low turbidity
concentrations.
When performing calibrations for measuring low turbidity
values (below 50 NTU), ensure the sensor reading is not affected
by light scattered by the calibration solution container. Use a
large container (minimum 1 litre) and ensure that the sensor is
immersed by no more than 5 cm below the solution surface and
is at least 5 cm from the container walls.
For low level applications that use the ABB Flowcell
(ATS4000741), use the Calibration Pot (part no. ATS4000740) to
calibrate the sensor. See Section 6.3.1.
DANGER – Formazin
Formazin is a polymerisation of 2 hazardous
constituents. Please conduct a full risk assessment
based on the supplier's safety datasheet for formazin
before use.
When calibrating using high NTU values of formazin, stir the
solution continuously throughout the procedure. If the
calibration is performed outside, shield the calibration vessel
from direct sunlight.
Before starting the calibration process, ensure that the vessel
and the sensor are cleaned and dried thoroughly to avoid
contaminating calibration solutions. Before adding formazin to
the vessel, ensure the solution is mixed thoroughly by rocking
(not shaking) the bottle gently.
6.3.1 Calibration using optional calibration pot ATS400740
The calibration pot (part no. ATS4000740) is recommended for
use in the following situations:
—
When performing a calibration in direct sunlight.
The calibration pot excludes ambient light that can affect
the measurement.
—
For low level applications (less than 50 NTU) that use the ABB
flowcell (ATS4000741)
The interior properties (dimensions and surface finish) of
the flowcell and calibration pot are comparable, resulting in
a matched calibration.
—
For high concentration calibrations, when the use of large
quantities of formazine solution is not desirable.
The calibration pot requires only 200 ml of calibration
solution.
Do not use the calibration pot in low level applications (less than
50 NTU) that either do not use the flowcell or where the sensor
is mounted more than 5 cm away from any surface, as the
surface light scattering in the calibration pot could result in an
offset in the reading.
IMPORTANT (NOTE)
— When inserting the sensor into the calibration
solution take care not to trap air bubbles in the front
face of the sensor. For sensors with wiper, perform
a wipe before proceeding with calibration.
— Sensors with accessories connected:
— sensor
B
(Fig. 6.2, page 14:) is shown with a
standard cable attached. If accessories (such as
dip pole, chain adaptor) are connected the
calibration can still be performed with them in
place.
Referring to Fig. 6.2, page 14:
1.
Slide cap
A
onto sensor
of the sensor.
2.
Hold cap
A
and press sensor
anti-clockwise twisting motion until sensor
IMPORTANT (NOTE)
Cap
A
has 2 sprung-loaded ball screws
engage with 2 holes
Confirm correct alignment by checking that 2
grooves
E
on the top face of cap
holes
D
/ ball screws
For sensors installed in a flow cell, the flow cell thread
adaptor can be used instead of the calibration pot cap.
Alternatively, unscrew the adaptor and slide back to allow
the cap to fit onto the sensor.
3.
Carefully pour 200 ml (6.76 ounce [US, liquid]) of formazin
F
into calibration pot
4.
Carefully slide sensor / cap assembly
pot
G
until fully inserted.
Aztec ATS430 | Turbidity sensor | OI/ATS430–EN Rev. H 13
B
until the cap is close to the top
B
down using an
B
connects.
C
D
in the top ring of sensor
A
align with
C
when cap is connected.
G
.
H
into calibration
that
B
.
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