Hanna Instruments HI 93703 - Manual (Page 7)

13 12
CALIBRATION
A monthly calibration is recommended. To
check the date of last calibration, simply hold
the DATE/
⇒
key down for few seconds.
A more frequent check of the instrument is
suggested by using the supplied standard solu-
tion.
CALIBRATION PROCEDURE
• Turn the meter on and
wait for the display to
show "----".
• Press the CAL key
once, the "CAL" mes-
sage will blink on the
display for about 6
seconds, then the
c a l i b r a t i o n m o d e
stops.
• While the "CAL" mes-
sage is still blinking,
press CAL again. The
instrument is now in
the calibration mode
and a "CL" will ap-
pear on the lower part
of the display. The
date of calibration can
be edited now by sim-
ply pressing the
DATE/
⇒
k e y . T o
scroll to the correct
number press the
READ/
⇑
key
.
The de-
fault blinking param-
eter is the month, on
the left hand of the
display (MM.DD).
SOURCES OF INTERFERENCE
• Presence of floating debris and coarse sedi-
ments which settle out rapidly will give false
readings.
• The infrared light source used for HI 93703
turbidity meter, according to ISO 7027 Inter-
national Standard, can effectively minimize
errors due to colored dissolved substances.
This effect, named "true color", is a common
interference for most commercially available
instruments operating in the range of visible
light.
• Air bubbles and the effect of vibrations that
disturb the surface of the sample will give
false results.
• Dirty glassware could also affect readings
along with scratched or edged vials.