5
The optical system of Hanna's C 99 & C 200 multiparameter
photometers is based on special subminiature tungsten lamps and
narrow-band interference filters to guarantee both high performance
and reliable results.
Four measuring channels (at four different wavelengths) allow a wide
range of tests.
C 200 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 iden-
tical to provide the same measurement conditions. Whenever possible
use the same cuvet for both.
It is also necessary that the surface of the cuvet is clean and not
scratched. This is 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.
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.
