HF scientific Micro200BW Turbidimeter - 0-100 NTU - Manual (Page 37)

MICRO 200 BW 0-10 & 0-100 NTU (05/05)
Rev. 3.4
3.3.2 Standardizing
The calibration standard (cuvette) supplied with the
MICRO 200 BW is a pure liquid sealed in glass. It has
a value of 0.02 NTU.
Standardization is performed in the calibration menu
see page 15 & 16 for more details. While in the
calibration menu perform the following operations:
a. Place the Calibration Standard in the Optical Well.
b. Index the Calibration Standard as previously de-
scribed.
c. Allow a few seconds for the standard to stabilize.
d. Press the F1 button to accept the frequency.
NOTE: This operation “calibrates” the .02 NTU calibra-
tion standard in the range of interest. If both
ranges maybe used this operation should be
performed on both ranges.
CAUTION: Avoid scratching the surface of the cu-
vette. Keep the cuvette surface clean and
free of dust. A scratched or dirty and
dusty cuvette will cause analysis error.
For instructions (See: V. ROUTINE
MAINTENANCE).
4.0 ROUTINE OPERATION
4.1 CONTINUOUS MONITORING FLOW
THROUGH UNIT
The standard flow through unit supplied with the instru-
ment is designed to operate at pressures up to a maxi-
mum of 60 p.s.i. (414 kPa or 4.22 kg/cm
3 ) and tempera-
tures to a maximum of 122° F (50° C) fluid temperature.
Flow rates through the unit can be adjusted from 0.5
gpm (200 ml/min) to a maximum of approximately 1.5
gpm (5.7 liters/minute). The speed of sensing turbidity
changes will depend on the length of the takeoff line, the
diameter of the takeoff line, and the flow rate or velocity
through the takeoff line. By using a high flow rate and
keeping the lines small, approximately 3/16 inch (4.8
mm) I.D. and relatively short length, the response time
is kept to a minimum. Consult HF scientific, inc. when
unusually long connections are required.
Depending on the type of fluid being monitored, a
pressure drop through the line can cause gas or air to
come out of solution and form bubbles which will create
errors in the turbidity measurements. This can be
prevented by creating a slight back pressure on the
Page 25
3.3 START UP
Before placing the MICRO 200 BW on line we recom-
mend that you standardize the instrument. The follow-
ing sections describe the required procedures.
3.3.1 Indexing
The United States Environmental Protection Agency
(U.S. EPA) recommends that cuvettes used for instru-
ment calibration or sample measurement be indexed.
To comply with U.S. EPA standards, the MICRO 200
BW includes an Indexing Ring for quick and repeatable
indexing of the reference standard.
To index the calibration standard you must be in the
calibration menu. Observe the top center (current
frequency) reading while performing the following steps:
a. Slowly rotate the standard, inside the optical well,
one complete revolution (360°). While rotating the
standard slowly, observe the measured turbidity
and locate the position of the cuvette having the
lowest reading.
b. With the calibration standard positioned at the
location having the lowest turbidity reading, install the
Indexing Ring over the cap on the standard so that the
pointer of the Indexing Ring faces directly forward.
When using the standards in the future, always insert the
standard so that the pointer of the indexing ring faces
forward. Slowly rotate the standard back and forth
about 5° to find the lowest point. The standard is now
indexed and ready for use.
Figure 10 shows a calibration standard being indexed.
NOTE: This Calibration Standard is only Indexed to the
Turbidimeter for which it was aligned.
Figure 10
Calibration Standard Indexing