Yokogawa ISC450 4-Wire Analyzer for Inductive Conductivity - Manual (Page 61)

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IM 12D06D05-01E
A
APPENDICES
If it is more convenient, the user may make
solutions from Sodium Chloride (NaCl or com-
mon table salt) with the help of the following
relationship table. This table is derived from the
IEC norm 60746-3.
Table 11-3. NaCl values at 25 °C
Weight % mg/kg Conductivity
0.001 10 21.4 µS/cm
0.003 30 64.0 µS/cm
0.005 50 106 µS/cm
0.01 100 210 µS/cm
0.03 300 617 µS/cm
0.05 500 1.03 mS/cm
0.1 1000 1.99 mS/cm
0.3 3000 5.69 mS/cm
0.5 5000 9.48 mS/cm
1 10000 17.6 mS/cm
3 30000 48.6 mS/cm
5 50000 81.0 mS/cm
10 100000 140 mS/cm
APPENDIX 4
Measurement principle
Contrary to contact electrode conductivity,
the EXA ISC Series analyses the con duc tiv i ty
with out any contact between electrodes and
proc ess fluid. The measurement is based on in-
ductive coupling of 2 ring trans form ers (Toroids)
by the liquid.
V3 V1
N3 N1
Drive coil Receive coil
The converter supplies a reference volt age at
a high frequency to the “drive coil”. The core of
this coil is of a high permeability mag net ic ma-
terial, and a strong magnetic field is generated
in the toroid.
The liquid passes through the hole in the toroid
and can be considered as a “one turn” second-
ary winding.
The magnetic field will induce a voltage in this
secondary winding. The induced cur rent in the
liquid winding is proportional to this volt age and
the conductance of the liquid “one turn winding”
is according to Ohm’s law.
The conductance (1/R) is proportional to the
specific conductivity and a constant factor that
is determined by the geometry of the sensor
(length divided by surface area of the hole in
the toroid) and the installation of the sensor.
There are 2 toroids mounted in the “dough nut”
shaped sensor. The liquid also flows through
the second toroid and therefore the liquid turn
can be considered as a primary wind ing of the
second ring transformer.
The current in the liquid will create a mag net ic
field in the second toroid. The induced volt age
being the result of this magnetic field can be
measured as an output.
The output voltage of this “receive coil” is there-
fore proportional to the specific con duc tiv i ty of
the process liquid.