HF scientific Micro200BW Turbidimeter - 0 -1000 NTU - Manual (Page 40)

Page 26
MICRO 200 BW 0 - 1000 NTU (5/05)
Rev. 3.1
discharge side of the flow through unit using the
stainless steel flow control valve (Catalog #50004)
supplied. Increasing the size of the incoming line will
also help this condition.
NOTE: Since each application is different, the amount
of back pressure required to eliminate bubbles
must be determined and modified on site during
operation by the customer.
A plastic shut-off clamp is provided on the inlet side of
the flow through unit in order to completely stop flow
to facilitate changing the cuvette. See the section on
cuvette cleaning and care for more information.
The U.S. EPA recommends that cuvettes used for
instrument calibration, standardization, or sample mea-
surement be indexed. For quick indexing of the flow
through cuvette, a rotational flow through assembly
with locking collar is supplied.
To index your flow through cuvette, slowly rotate the
flow through at least one revolution, while observing
the reading, to locate the position of the lowest reading.
Without moving the flow through, press down on it and
turn the locking collar until the flow through assembly
is securely locked in place. See figure 10.
Figure 10
Flow Through Cuvette Indexing
B. VAPORPURGE
The MICRO 200 BW is equipped with a continuous
vaporpurge system. A fan inside the sensor continu-
ously circulates heated, dry air around the optical well
and the flow through cuvette. This feature eliminates
the need for connection of a dry purge line. See Figure
11.
The desiccant beads are dark blue when dry and turn to
a light pink when expended. Check the desiccant on a
quarterly basis or if after cleaning the cuvette readings
appear erroneously high to ensure proper operation of
the vaporpurge feature. It is important to keep a cover
on the sample well if the flow through head is out for
more than a few minutes, to avoid saturating the
desiccant uselessly. A replacement desiccant tray com-
plete with foot valve is available from HF scientific or
your local representative HF part# 21555. See figure 1
on page 6 when replacing the desiccant.
Remember to dry the flow through cuvette of excess
moisture before inserting it into the optical well.
This will speed up the evaporation time.
NOTE: If it should become necessary to return the
sensor to the factory, you need only return the
upper sensor assembly and not the base. IF
RETURNING THE BASE, THE DESICCANT
TRAY MUST BE REMOVED BEFORE SHIP-
PING.
C. GRAB SAMPLES
Take extreme care when handling any sample cuvettes.
Surface scratches, dust or finger smudges will cause
analysis error. Examine each cuvette carefully before
the sample is drawn and placed in the Optical Well. We
recommend that the cuvette be wiped clean with a lint-
free laboratory tissue before the sample is drawn.
Handle Reference Standard and cuvettes by the top
portion only.
To take a reading of a grab sample:
1. Set Averaging to 1 second (see page 16).
2. Remove the flow through unit and insert grab
sample cuvette in Optical Well.
3. The turbidity value of the grab sample will now be
displayed on the readout. Allow at least two up
dates (five to ten seconds) for best accuracy before
noting the reading.
NOTE: Settling particles or air in the sample may cause
the digital reading to “hunt”. For best results
take readings before turbid particles settle but
after air bubbles have been allowed to escape.
V. ROUTINE MAINTENANCE
A. CUVETTE CLEANING & CARE
Cuvettes must be clean and free of marks or scratches
in the critical area (see figure 12 on page 28). Cleaning