8
A microprocessor controlled LED emits radiation which is first optically conditioned and beamed to
the sample contained in the cuvette. The optical path is fixed by the diameter of the cuvette. 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 cuvette 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) cuvettes, are
optically identical to provide the same measurement conditions. Whenever possible use the same
cuvette for both. It is necessary that the surface of the cuvette 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 cuvette walls with hands.
Furthermore, in order to maintain the same conditions during the zeroing and the measuring phases,
it is necessary to close the cuvette to prevent any contamination.
PRINCIPLE OF OPERA
TION
The optical system of Hanna Instruments’
HI96751
colorimeter is based on LED and narrow‑band
interference filters to guarantee both high performance and reliable results.
HI96751
block diagram (optical layout)