7
14
A microprocessor controlled special tungsten lamp emits radiation which is first optically conditioned
and beamed to the sample contained in the cuvet. The optical path is fixed by the diameter of the
cuvet. Then the light is spectrally filtered to a narrow spectral bandwidth, to obtain a light beam of
intensity
I
o
or
I.
The photoelectric cell collects the radiation
I
that is not absorbed by the sample and converts it into
an electric current, producing a potential in the mV range.
The microprocessor uses this potential to convert the incoming value into the desired measuring unit
and to display it on the LCD.
The measurement process is carried out in two phases: first the meter is zeroed and then the actual
measurement is performed.
The cuvet has a very important role because it is an optical element and thus requires particular
attention. It is important that both the measurement and the calibration (zeroing) cuvets are optically
identical to provide the same measurement conditions. Whenever possible use the same cuvet for
both. It is necessary that the surface of the cuvet is clean and not scratched. This to avoid measurement
interference due to unwanted reflection and absorption of light. It is recommended not to touch the
cuvet walls with hands.
Furthermore, in order to maintain the same conditions during the zeroing and the measuring phases,
it is necessary to close the cuvet to prevent any contamination.
1) Liquid Crystal Display (LCD)
2) Cuvet Holder
3) Cuvet alignment indicator
4) ON/OFF key
5) ZERO key
6) READ/TIMER key
7) CAL CHECK key
FUNCTIONAL DESCRIPTION
• Hold READ/TIMER for three seconds. The display
will show the countdown prior to measurement.
Alternatively, wait for 15 minutes and just press
READ/TIMER.
In both cases “SIP” will blink during
measurement.
• The instrument directly displays concentration in
mg/L of nitrogen-nitrite (NO
2
–
-N) on the Liquid
Crystal Display.
• To convert the NO
2
–
-N concentration to the nitrite
ion concentration (NO
2
–
), multiply the reading by
factor of 3.29.
• To convert the NO
2
–
-N concentration to sodium
nitrite concentration (NaNO
2
), multiply the reading
by factor of 4.93.
or
INTERFERENCES
Highly buffered samples (alkalinity above 500 ppm) or with extreme pH may exceed the buffering
capacity of the reagent: neutralize acidic samples with diluted NaOH or alkaline samples with diluted
HCl, prior to addition of the reagent.
Turbidity must be removed by prior filtration.
The following ions may cause negative errors:
cupric ions (Cu
2+
): above 5 ppm
ferrous ions (Fe
2+
): above 1 ppm
ferric ions (Fe
3+
): above 2 ppm
