Technical Conductivity and Resistivity
Conductivity measures the ability of a solution to conduct an electric current between two electrodes. In solution, the current flows by ion transport. Therefore, with an increasing amount of ions present in the liquid, the liquid will have a higher conductivity. If the number of ions in the liquid is very small, the solution will be "resistive" to current flow. AC current is used to prevent complete ion migration to the two electrodes.
Conductance = 1/Resistance
Conductivity:
mho = Siemen
Normal unit of measurement is:
1 micromho (µmho) = 1 microSiemen (µS),
1 millimho (mmho) = 1 milliSiemens (mS) = 1,000 µS
Resistivity:
ohm
Normal unit of measurement is:
megohm = 1,000,000 ohm
Example - Conductivity to Resistivity Conversion:
Conductivity:
= 20 µS
= 20 x 10-6 S
= 2 x 10-5 S
= 2 x 10-5 mho
Resistivity:
1 ohm/2 x 10-5
= 1/conductivity
= 1/2 x 10-5 ohm
= 0.5 x 10-5 ohm
= 5 x 10 4 ohm
Conductivity and Resistivity (NaCl and CaCO3 Solutions at 25°C)
|
ppm
as CaCO3
|
ppm
NaCl
|
Conductivity
micromhos/cm
|
Resistivity
megohm-cm
|
|
1700
|
2000
|
3860
|
0.00026
|
|
1275
|
1500
|
2930
|
0.00034
|
|
850
|
1000
|
1990
|
0.0050
|
|
425
|
500
|
1020
|
0.00099
|
|
170
|
200
|
415
|
0.0024
|
|
127.5
|
150
|
315
|
0.0032
|
|
85.0
|
100
|
210
|
0.0048
|
|
42.5
|
50
|
105
|
0.0095
|
|
17.0
|
20
|
42.7
|
0.023
|
|
12.7
|
15
|
32.1
|
0.031
|
|
8.5
|
10
|
21.4
|
0.047
|
|
4.25
|
5.0
|
10.8
|
0.093
|
|
1.70
|
2.0
|
4.35
|
0.23
|
|
1.27
|
1.5
|
3.28
|
0.30
|
|
0.85
|
1.00
|
2.21
|
0.45
|
|
0.42
|
0.50
|
1.18
|
0.88
|
|
0.17
|
0.20
|
0.49
|
2.05
|
|
0.13
|
0.15
|
0.38
|
2.65
|
|
.085
|
0.10
|
0.27
|
3.70
|
|
0.042
|
0.05
|
0.16
|
6.15
|
|
0.017
|
0.02
|
0.098
|
10.2
|
|
0.012
|
0.015
|
0.087
|
11.5
|
|
0.008
|
0.010
|
0.076
|
13.1
|
|
0.004
|
0.005
|
0.066
|
15.2
|
|
0.002
|
0.002
|
0.059
|
16.9
|
|
0.001
|
0.001
|
0.057
|
17.6
|
|
none
|
none
|
0.055
|
18.3
|
Probe
Constants
Probe constant defines the volume between the electrodes. Solutions
with an extremely high conductivity require a sensor with a probe
constant greater than 1.0. Solutions with extremely low conductivity
require a sensor with a probe constant less than 1.0. The greater
the distance between the electrodes, the smaller the current signal.
|
Conductivity
(Micromhos/cm) |
Resistivity
(Ohms-cm) |
Dissolved
Solids
(ppm) |
|
.056
|
18,000,000
|
.0277
|
|
.084
|
12,000,000
|
0.417
|
|
.167
|
6,000,000
|
0.833
|
|
1.00
|
1,000,000
|
.500
|
|
2.50
|
400,000
|
1.25
|
|
20.0
|
50,000
|
10.0
|
|
200
|
5000
|
100
|
|
2000
|
500
|
1,000
|
|
20,000
|
50
|
10,000
|
|
|
  |
|
 |
||