ABB 4670 Series User Manual page 33

...7.2.1 Procedure
Model 7997 300
a) Shut off sample water using the isolating valve installed
upstream of the sensing unit.
b) Drain the unit by closing the inlet and opening the drain valve.
Carefully unscrew and remove the wiper unit to aid complete
drainage of the system. When the system is empty, close the
outlet valve.
c) Thoroughly dry the inner chamber using clean tissue and
wipe clean the emitter and receiver lenses. Ensure that no
greasy marks are left on the lenses and that the lenses are
dry.
Note. If the sample was cold, condensation could form on
the windows. It may be necessary, therefore, to leave the
sensor open for a short while to allow the windows to reach
ambient temperature before attempting calibration.
Dry Standard
Optical
Receiver
Inlet/Isolating
Valve
Fig. 7.3 Model 7997 300
Optical
Emitter
Flow-chamber
Drain
Valve
d) Close the drain valve and fill the chamber with high purity water.
Note the reading on the display.
If readings are out of spec. (2% FSD), repeat the procedure
from c). If reading is still out of spec., calibrate the sensor –
Section 5.2.2.
e) Insert the Dry Calibration Standard so that the turbidity value on the
label is facing the emitter. Note the reading on the display.
Fig. 7.4 Dry Calibration Standards for 7997 300 Sensors
f) Take out the Dry Calibration Standard; dry/clean off any
moisture before storing the Standard in the supplied storage
container – see also Section 7.4.1 – Care and Maintenance
of Dry Calibration Standards.
g) Fit the wiper Unit and screw it down firmly.
h) Open the inlet and outlet valves. Set the sample rate to 0.5 to
6.0 l min –1
7 MAINTENANCE...
FTU value
indication
31