Delta OHM HD 8706-R1, Инструкция по эксплуатации

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ENGLISH
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t
keys, set the conductivity value determined at point c. If the conduc-
tivity of the calibration solution is very different from the one used in
automatic calibration, “E1” (slope >150% of the rated value) or “E2”
(slope <30% of the rated value) is displayed. In both cases it is suffi-
cient to press the
s
or
t
key to cancel the error signal. Using the same
keys, set the conductivity value determined at point c.
e) Press the CAL key again to confirm the value displayed. The µS (or
mS) symbol stops flashing. Rinse the probe with water. If measure-
ments are later made at low conductivity, we advise rinsing it in
distilled or, better, bidistilled water.
At this point the instrument is calibrated and ready for use.
4 TEMPERATURE COMPENSATION
The temperature coefficient α
T
is the percentage measurement of the vari-
ation of conductivity with temperature and is expressed in %/°C (or %/°F).
The electric conductivity of a metal decreases as the temperature increas-
es, while it increases in a liquid.
There therefore arises the problem that the conductivity of two liquids can-
not be directly compared if the measurement has not been made at the
same standard reference temperature, which in chemical measurements is
20°C (25°C).
If the measurement is taken at a temperature different from 20°C (25°C),
an approximate assessment of the conductivity of the liquid at 20°C (25°C)
may be obtained by means of temperature compensation, defined by the
following formula:
where: = temperature expressed in °C
= conductivity at temperature (°C)
20 (25) = conductivity at 20°C (25°C)
α
T
20 = temperature coefficient expressed in
%/°C
Unfortunately the formula does not give good results if the temperature is
appreciably different from 20°C (25°C) because
α
T
is not costant, but a
non-linear function of the temperature and the conductivity.
Also, it is not generally know before taking the measurement, unless it can
be found on tables referring to the liquid to be examined.
α
T
may be exper-
imentally determined by taking two measurements, one at 20°C (25°C) and
another at the temperature
, having previously excluded temperature
= 20
α
T
100
1 + ( - 20)