Chemistry Reference
In-Depth Information
4.5
4
4.0
3
3.5
3.0
2
2.5
2.0
1
1.5
1
1.05
1.10
1.15
1.20
1.25
1.30
1.35
Log
d
(mm)
10.5
Logarithmic relationship between measured impedance at phase-
angle shift of zero and the distance between the electrodes for
constant length of the electrodes (60 mm) and diameter of the
electrodes (0.2 mm) and different electrolyte concentrations: (1) 1
¥
10
-
1
, (2) 1
¥
10
-
2
, (3) 1
¥
10
-
3
and (4) 1
¥
10
-
4
mol l
-
1
.
where
R
is the measured resistance (W),
d
is the distance between two
textile electrodes (mm),
L
is the length of the textile electrodes exposed to
the electrolyte solution (mm),
c
is the concentration of the electrolyte (mol
l
-1
), and k is a constant factor at constant temperature.
The standard deviations given in Equation 10.1 are valid in the follow-
ing ranges of the investigated parameters:
•
c
:1¥ 10
-1
-1 ¥ 10
-4
mol l
-1
•
L
: 20-80 mm
•
r
: 0.1-1 mm
•
d
: 5-40 mm on the condition that a maximum value of 0.03 for the ratio
r
/
d
is respected.
For all values beyond these limits, it is still possible to use the electrodes in
applications but standard deviations increase. This will inevitably have a
negative influence on the precision, sensitivity and reliability of the method.
This increase is explained as follows: the experimental signals become too
small (high
c
and
L
) or too large (low
c
and
L
) to have a reliable imped-
ance, and the maximum ratio for 2
r
/
d
of 0.02 should be respected in order
to have a planar-like electrode configuration. For 2
r
/
d
values larger than
0.02, this planar-like configuration is no longer attained, which will result in
