Hanna Instruments HI 8733 - Manual (Page 8)

15 14
Rinse the probe with tap wa-
ter after every series of
measurements. If a more thor-
ough cleaning is required,
remove the PVC sleeve and
clean the probe with a cloth or
a nonabrasive detergent.
When reinserting the sleeve
onto the probe, be sure that
the sleeve is in the right direc-
tion with the four holes towards
the cable end.
After cleaning the probe,
recalibrate the instrument.
The probe body is in PVC. For
this reason it must never come
into close contact with a heat
source. If the probe is exposed
to high temperatures (above
50°C/122°F), the rings might
become loose or detached, re-
sulting in a serious impairment
of the probe. In such cases,
the probe has to be replaced.
PROBE MAINTENANCE
Highly acidic, alkaline samples or solutions with high salt content
might have a different coefficient than the customary 2% per degree °C.
In order to calculate this coefficient follow the procedure below:
• Immerse the probe of HI 8733 in the sample and adjust the
TEMPERATURE COEFFICIENT knob to 0% (i.e. no compensation).
• Condition the sample and probe to 25°C and note the conductiv-
ity reading, C
25
.
• Condition the sample and probe to a different temperature t°C
(approximately 10°C different from 25°C) and note the conduc-
tivity reading C
t
.
• The temperature coefficient
β
of the solution is calculated as given
by the following formula:
(C
t
- C
25
)
β
= 100 x
(t - 25) x C
25
The above procedure is suitable for determining the temperature
coefficient in a laboratory or where the temperature of the solution
can be controlled.
If this is not possible (e.g. on-site measurements), the following
procedure can be used providing the sample temperature varies by at
least 5°C or preferably 10°C:
• Immerse the probe of HI 8733 in the test solution and turn the
TEMPERATURE COEFFICIENT knob to 0% (no compensation).
• Check the conductivity reading and record the value. Make sure
the reading is stable, i.e. no greater variations than ±0.2 mS/
cm within a minute.
• Repeat the procedure when the temperature of the test solution
has changed by at least 5°C. Wait for the conductivity reading to
stabilize.
• Adjust the TEMPERATURE COEFFICIENT knob until the display
shows the same value as recorded earlier.
• The value indicated by the knob is the temperature coefficient of
the solution.
2.5
2
1.5 1
0.5
0
TEMPERATURE COEFFICIENT
DETERMINING THE TEMPERATURE
COEFFICIENT OF A SOLUTION (HI 8733)