Hach-Lange 2100 N IS Laboratory Turbidimeter User Manual - Manual (Page 27)

Measurement techniques
Measurements may be made with different operation mode settings and
optional accessories.
Calibrate the instrument whenever the sample cell pathlength is
changed.
Manual or automatic ranging
The manufacturer recommends that ranging be set to automatic for most
measurements.
The setting can be changed at any time during sample measurement.
Push RANGE repeatedly to step the instrument from automatic ranging
to manual ranging and then scroll through the manual range settings.
The Manual Range light turns on when manual ranging is selected. The
Auto Range light turns on when automatic ranging is selected.
Notes:
• When manual ranging is selected, the display flashes all 9s when the
sample being measured is greater than the selected range. The
display flashes all 0s when the sample measured is less than the
selected range.
• When automatic ranging is selected, the display flashes 9s when the
sample is greater than the maximum range of the instrument.Refer to
Measure over-range samples on page 22.
• When automatic ranging is selected, the display flashes all 0s when
the measurement is less than the range of the instrument or a
negative value. Calibrate the instrument.
Signal averaging on or off
Signal averaging corrects for reading fluctuations that are caused by
random drifting particles in the sample. When signal averaging is on, an
average reading is calculated every 3 seconds and shown on the
display.The last ten measurements are used to calculate the average
reading.
The manufacturer recommends that signal averaging be on for most
measurements.
Push UNITS AVG to turn signal averaging on or off. The UNITS AVG
light turns on when signal averaging is on.
Push ENTER when signal averaging is on to erase data in the signal
averaging buffer and provide an immediate update on the display as
necessary. This is especially useful when measuring samples with large
differences in turbidity.
Using the air purge system
The air purge system is used to keep condensation off the external
surface of the sample cell when cold samples are measured.
The air purge system pushes dry air through the optical compartment to
keep the outside the sample cell dry. The connection is made at the air
purge fitting on the back of the instrument
Figure 2 on page 8.
Use dry nitrogen or instrument grade air (ANSI MC 11.1, 1975) at no
greater than 138 kPa (20 psig). The manufacturer recommends an air
consumption rate of 3 to 10 SCFH (standard cubic feet/hour).
When the sample temperature is about or less than 2 °C (35 °F), use a
desiccant dryer and particle filter to make sure that the dew point of the
air purge is less than the sample temperature. The air dryer contains
silica gel desiccant that turns pink. Replace the desiccant when it turns
pink.
If only shop air is available, use a coalescing filter with an automatic
drain and a dryer and particle filter to get instrument quality air. Use a
coalescing filter that typically operates for greater than 2000 hours.
Replace the particle filter when the air dryer is replaced.
Figure 7 and Figure 8 show the methods for connecting the two types of
air supply to the instrument.
Note: The dryer and filter are not necessary if dry nitrogen is used.
Figure 7 Instrument quality air
1 Particle filter (Balston DFU 9933-
05-BQ or equivalent)
3 Pressure regulator
2 Air dryer (Balston DAU 9933-
05-101 or equivalent)
4 Instrument air
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