6
PRINCIPLE OF OPERATION
Absorption of Light is a typical phenomenon of interaction between electromagnetic radiation and
matter. When a light beam crosses a substance, some of the radiation may be absorbed by atoms,
molecules or crystal lattices.
If pure absorption occurs, the fraction of light absorbed depends both on the optical path length through
the matter and on the physical-chemical characteristics of the substance according to the Lambert-
Beer Law:
-log
I
/
I
o
=
ε
λ
c d
or
A
=
ε
λ
c d
Where:
-log
I
/
I
o
= Absorbance (A)
I
o
= intensity of incident light beam
I
= intensity of light beam after absorption
ε
λ
= molar extinction coefficient at wavelength
λ
c
= molar concentration of the substance
d
= optical path through the substance
Therefore, the concentration "c" can be calculated from the absorbance of the substance as the other
factors are known.
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)
19
or
• Press READ/TIMER and “SIP” will blink during
measurement.
• The instrument will show for three seconds the
CAL CHECK™ standard value.
Then the date of last calibration (e.g.: “01.08”)
appears on the display, or “01.01” if the factory
calibration was selected. In both cases the
number of the month is blinking, ready for date
input.
Note
: if the display shows “ERR” the calibration
procedure failed. Verify that both CAL CHECK™
Standards HI 95734-11 Cuvets,
A
and
B
, are
free from fingerprints or dirt and that they are
inserted correctly.
DATE INPUT
• Keep READ/TIMER pressed to scroll to the desired
month number (01-12).
• When the correct month has been set, press
ZERO to confirm. Now the display will show the
day number blinking. Keep READ/TIMER pressed
to scroll to the desired day number (01-31).
Note
: it is possible to change from
day
to
month
and vice versa by pressing ZERO.
• When both the day and month have been
selected, hold CAL CHECK for three seconds to
store date and calibration values. The instrument
will show for one second “Stor”, to confirm that
the new calibration data has been accepted.
• The instrument will return automatically to the
measurement mode by displaying the parameter
code (“734f” or “734t”) on the LCD.
or