User's Manual

7
Photometric chemical analysis is based on the possibility to develop an absorbing compound from a
specific chemical reaction between sample and reagents. Given that the absorption of a compound
strictly depends on the wavelength of the incident light beam, a narrow spectral bandwidth should be
selected as well as a proper central wavelength to optimize measurements.
The optical system of Hanna's HI 95 series colorimeters is based on special subminiature tungsten
lamps and narrow-band interference filters to guarantee both high performance and reliable results.
Block diagram (optical layout)
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.
18
• Wait for a few seconds and the display will show the validation standard value.
The reading should be within specifications as reported on the CAL CHECK™ Standard Certificate.
If the value is found out of specifications, please check that the cuvets are free of fingerprints, oil or
dirt and repeat validation. If results are still found out of specifications then recalibrate the
instrument.
• Place the CAL CHECK™ Standard Cuvet A
into the holder and ensure that the
notch on the cap is positioned securely
into the groove.
• Press ZERO/SET and “SIP” will blink on
the display.
• After a few seconds the display will
show “-0.0-”. The meter is now zeroed
and ready for validation.
• Remove the cuvet and place the
CAL CHECK™ Standard HI 95771-11
Cuvet B into the holder. Ensure that the
notch on the cap is positioned securely
into the groove.
• Press CAL CHECK and “SIP” will blink
during measurement.
• Select the parameter code “771” for chlorine
ULTRA HIGH RANGE or “701” for chlorine
LOW RANGE by holding ZERO/SET (see page 13).