4690 Series
Turbidity systems
7 Calibration
IM/4690–EN Rev. A
21
To minimize deterioration of the secondary standard:
Carefully wipe off any residual moisture after use.
Clean the prism with lint-free cloth.
Avoid direct contact with the dry standard rod –
fingerprints on the surface may alter its stated value.
Store in the container provided when not in use and keep
in a dry place.
7.2 Performing a Calibration Verification with a
Secondary Standard
To check the calibration:
1. Close the isolating valve installed upstream of the sensor.
2. Close the sensor inlet valve and open the drain valve.
Allow the sensor to drain.
3. Carefully remove the wiper unit (7998 001, 002, 011 and
012) or the wiper plug (7998 006, 007, 016 and 017) to
aid complete drainage of the system. When the system is
empty, close the drain valve.
4. Thoroughly dry the flow chamber internally using clean
tissue.
5. Thoroughly clean and dry the emitter and receiver lenses
using clean tissue.
6. Insert the dry calibration standard with the zero NTU
indication (see Figs 7.2 or 7.3) facing the optical receiver,
ensuring the locating lug engages correctly – see Fig. 7.4.
7. Note the reading on the display.
Caution.
When removing the wiper unit
do not
put
excessive leverage on the wiper as there is a risk of
bending the wiper arm out of 90 °. On removal of
wiper, check wiper arm has not been bent.
Note.
If condensation forms on the emitter and
receiver lenses, leave the sensor open to enable the
lenses to reach ambient temperature before
attempting calibration.
Fig. 7.2 Dry Calibration Standard for Low Range Sensors
Fig. 7.3 Dry Calibration Standard for High Range Sensors
Fig. 7.4 Inserting Dry Standard
N
U
S
TA
N
D.
N
U
NTU value Indication
Zero NTU Indication
STA
N
D.
N
U
STA
N
D.
N
U
NTU value indication
Zero NTU indication
Optical
Emitter
Optical
Receiver
Locating
Lug
Zero NTU
Indication
NTU value
Indication