Calibration Checks; Procedure - ABB 4670 Series User Manual

...7 MAINTENANCE

7.2 Calibration Checks

The system uses LED technology and very stable electronics
which avoids the risk of electronic drift. Therefore, routine
calibration is normally unnecessary. However, it may be
necessary to routinely check the system accuracy (particularly
after cleaning). This should then be considered as a calibration
check and not a calibration adjustment.

7.2.1 Procedure

Model 7997 200 Series
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 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.
Note. The dry calibration procedure for the 7997 300 and
7997 400 requires the use of demineralized water for zero
calibration.
Flow Chamber
Inlet/Isolating valve
Fig 7.1 Model 7997 200 Series
30
Dry
Standard
Optical
Emitter
Optical
Receiver
Drain
Valve
d) Insert the Dry Calibration Standard with the zero on the label
facing the receiver.
NTU value
indication
Fig 7.2 Dry Calibration Standards for
7997 200 Series Sensors
e) Rotate the Dry Calibration Standard so that the turbidity
value on the label is facing the receiver.
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.
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 Sensor Unit top cap (7997 202) and screw it down
firmly, or fit the wiper unit (7997 200 and 201).
h) Open the inlet valve. Ensure that the flow through the sensor
–1
is 0.5 to 6.0 l min
Zero NTU
indication