Yokogawa SC4A 19mm Conductivity Sensors User Manual
Page 9
IM 12D7J4-E-E
7
3. OPERATION AND MAINTENANCE
3-1. Checking the cell
If a fault occurs, first check the cell for
visible damage. If damage is not appar-
ent, check the cell resistances measuring
between the cable connections.
a. 11 and 12 (or connector pins 1 and 2)
b. 11 and 13 (or connector pins 1 and 3)
c. 12 and 13 (or connector pins 2 and 3)
d. 12 and 15 (or connector pins 4 and 5)
e. 15 and 16 (or connector pins 5 and 6)
f. 13 and 14 (or connector pins 3 and 4)
g. 13 and 15 (or connector pins 3 and 5)
Celltype
a,
b, c, d, g
e, f
SC4A
Pt1000 value > 100MΩ
< 2Ω
If the cell has become fouled resistance will
be developed across the electrodes. These
resistances can be measured by making
contact directly with the electrode and the
relevant pin of the connector.
3-2. Calibration of the cell
The cell constant is determined under
laboratory conditions. It is possible that
slight variations in the cell constant may
occur dependant on the installation.
This possible error can be corrected by
recalibrating with a solution of known
conductivity value. The procedure is
descibed in ASTM D1125 or OIML
recommendation 56. Sensors with
long cables may exhibit an offset in the
temperature readings. This can be
adjusted in the transmitter or converter.
A calibrated thermometer should be used
as reference measurement.
NOTES:
The specific conductivity value of the
solution of known value must be near the
value of the liquid to be measured. Specific
conductivity is highly temperature
dependent, therefore in the above
calibration procedure the temperature of
the cell and the liquid should be allowed
to equalise and should be accurately
measured with a calibrated thermometer.
3-3. Cleaning of the cell
If the cell becomes fouled an insulating
layer may be formed on the electrodes and
consequently, an apparent increase in cell
constant may accur, giving a measuring
error. This error is:
2 •
x 100 %
Where:
Rv = the resistance of the fouling layer
Rcel = the cell resistance.
Cleaning methods
h
ti
w
r
e
t
a
w
t
o
h
s
n
o
it
a
c
il
p
p
a
l
a
m
r
o
n
r
o
F
.
1
domestic washing-up liquid added will
be effective.
%
0
1
..
.
5
a
.
c
t
e
,
s
e
d
i
x
o
r
d
y
h
,
e
m
il
r
o
F
.
2
solution of hydrochloric acid is
recommended.
e
b
n
a
c
)
.
c
t
e
,
s
t
a
f
,
s
li
o
(
s
g
n
il
u
o
f
c
i
n
a
g
r
O
.
3
easily removed with acetone.
a
e
s
u
,
s
d
l
u
o
m
r
o
a
ir
e
t
c
a
b
e
a
g
l
a
r
o
F
.
4
chlorinated solution (domestic bleach*).
d
n
a
d
i
c
a
c
i
r
o
l
h
c
o
r
d
y
h
e
s
u
r
e
v
e
N
*
domestic bleach simultaneously.
The liberation of the very poisonous
gas Chlorine will result.
(Rv)
(Rcel)