User manual
36
A Reference information
A.3 pH electrode
The pH electrode is of the sealed
combination double junction type.
It contains a sealed Ag/AgCl
reference which cannot be refilled,
an internal electrolyte bridge of
4 M KCl saturated with Ag/AgCl,
an outer electrolyte bridge of 1 M
KNO
3
, an annular ceramic
reference junction and a low
profile pH membrane. The pH
electrode is delivered with a
transparent cover.
The flow cell should not be used
with any other pH electrode.
A.4 Conductivity cell
The flow cell has two cylindrical titanium electrodes positioned in
the flow path of the cell. An alternating voltage is applied between
the electrodes and the resulting current is measured and used to
calculate the conductivity of the eluent. The monitor controls the AC
frequency and increases it with increasing conductivity between 50
Hz and 50 kHz giving maximum linearity and true conductivity
values.
The conductivity is automatically calculated by multiplying the
measured conductance by the flow cell’s cell constant. The cell
constant is pre-calibrated on delivery but can be measured with a
separate calibration procedure. This procedure is described in
Reference information section B.2.
One of the electrodes
has a small
temperature sensor
for measuring the
temperature of the
eluent in the flow
cell. Temperature
variations influence
the conductivity and,
in some applications when highly precise conductivity values are
required, it is possible to program a temperature compensation
factor that recalculates the conductivity to a set reference
temperature.
Eluent
Temperature sensor
Sealing
Internal electrolyte
bridge containing
4M KCl saturated
with AgCl
Silicone sealing
Internal annular
coaxial ceramic
reference junction
External electrolyte
bridge containing
1M KNO3
O-ring
Glass electrode
containing diluted,
buffered KCl
External annular
coaxial ceramic
reference junction
O-ring
Ag/AgCl reference
electrode
Monitor UPC-900
User Manual 18-1125-55 Edition AE