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O&M Manual
Rev-H (8/11)
Part 6 - Operation
Turbidity monitors will start to measure aqueous samples as soon as power is applied.
Calibration of a turbidity system is normally required at start-up, but factory settings are likely to be fairly
accurate, so it is often OK to start up the montor without adjustment. Calibration requires adjustment of
both the zero and span of the instrument. Unfortunately, “true zero turbidity water” is hard to obtain, so the
factory zero setting should be used unless you are sure of your zero solution. Span adjustment should be
done either at startup or after the instrument has been in operation for a few days.
Setting Zero
Zeroing a turbidity system requires pumping “turbidity free” water through the flowcell assembly or
submerging the sensor in turbidity free water in a dark vessel. As mentioned above, the factory zero
settings are often more accurate than those obtainable in the field. However, if you wish to zero the
system, follow the procedure outlined below.
1. Disconnect the sample inlet tube and connect the calibration feed tube in its place. If using a
submersible sensor, submerge the sensor in turbidity free water after rinsing thoroughly with the same
type of water about 3 or 4 times.
2. Remove the flow control valve on top of the flowcell and allow all of the sample to drain from the
flowcell. Feed turbidity free water into the flowcell until a small amount overflows from the flow control
valve port. Let the flowcell drain and repeat 3 or 4 times. Finally, fill the flowcell with turbidity free
water until it overflows from the control valve port and then replace the flow control valve. Screw in
the flow control valve until it is shut completely. The flowcell should now be filled with turbidity free
water, and it will not drain because the outlet is sealed. Let the feed tube hang down below the
flowcell.
3. With the flowcell full of turbidity free water or the submersible sensor submerged in turbidity free
water, advance the monitor display to the D2 display (see page 17). Press the CAL key and the
display will indicate “ZERO C.: X.X%”, with the X.X value indicating the last entered zero offset,
indicated as a percentage of the operating range. Press CAL again and the unit will indicate “CAL
ZERO1: %” until it has read a stable zero value and then will indicate CAL ZERO1: X.X%”. Press
ENTER and the procedure will be repeated for ZERO2. Press ENTER again and it will again be
repeated for ZERO3. The reason for this is that you are zeroing the unit for all 3 operating ranges.
After the ZERO3 value has been recorded, the display will change to “SENS: 100%” (or some other
value depending on the last calibration).
NOTE: If the measured zero offset for any of the 3 operating ranges is greater than 10% of that
range, an error message will be displayed indicating that “ZERO >10%” and the zero for
that range will not update.
4. Press MODE to return to the turbidity value display. The zero for all 3 ranges has now been set.
(41 paginas)
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