8.8
Corrective maintenance of measuring system
8.8.1
Conductivity measuring cells
Soiling detected on conductivity measur-
ing cells can be removed as follows:
•
Oily and greasy coatings
Clean with detergent (fat solvent, e.g.
alcohol, acetone, poss. detergent).
Warning:
Hands, eyes and clothes are to be
protected when using the cleaning
agents described below.
•
Limestone deposits or metal hydroxide
coatings
Loosen coatings with diluted hydrochloric
acid (3 %), then rinse thoroughly.
•
Coatings containing sulphide
(from flue gas desulphurizing plants
or sewage treatment plants)
Use mixture of hydrochloric acid (0.5 %)
and thiourea (8 %), then rinse thoroughly.
•
Coatings containing protein (food industry)
Use mixture of hydrochloric acid (0.5 %)
and pepsin (1 %), then rinse thoroughly.
8.8.2
Simulation of conductive measuring cells for instrument test
A measuring instrument for conductive
conductivity is checked by replacing the
process and temperature sensor with
resistors. The accuracy of the simulation
depends on the accuracy of the resistors.
Refer to the table on the right for conductivity
(cell constant
k set to nominal value
according to column 2). Otherwise: display of
CD
[mS/cm]
=
k
⋅
1/
R
[k
Ω
]
.
Refer to the table below for temperature (no
temperature offset set on Liquisys).
Connect temperature equivalent resistance
using three-wire arrangement!
• Use the “CD test adapter” service kit to
connect decade resistors to the connector
of a conductivity measuring cable in place
of a conductivity measuring cell.
Order number: 51500629.
Pt100 equivalent resistances:
Temperature
Resistance
–20 °C
92.13
Ω
–10 °C
96.07
Ω
0 °C
100.00
Ω
10 °C
103.90
Ω
20 °C
107.79
Ω
25 °C
109.73
Ω
50 °C
119.40
Ω
80 °C
130.89
Ω
100 °C
138.50
Ω
200 °C
175.84
Ω
All resistance values are to be multiplied by
10 for a Pt 1000 temperature sensor.
Conductivity equivalent resistances:
Resist.
R
Cell
const. k
Display for
CD
Display for
M
Ω
10
Ω
1 cm
–1
100 mS/cm
10 cm
–1
1000 mS/cm
100
Ω
0.1 cm
–1
1 mS/cm
1 k
Ω ⋅
cm
1 cm
–1
10 mS/cm
10 cm
–1
100 mS/cm
1000
Ω
0.1 cm
–1
0.1 mS/cm
10 k
Ω ⋅
cm
1 cm
–1
1 mS/cm
10 cm
–1
10 mS/cm
10 k
Ω
0.01 cm
–1
1 µS/cm
1 M
Ω ⋅
cm
0.1 cm
–1
10 µS/cm
100 k
Ω ⋅
cm
1 cm
–1
100 µS/cm
10 cm
–1
1 mS/cm
100 k
Ω
0.01 cm
–1
0.1 mS/cm 10 M
Ω ⋅
cm
0.1 cm
–1
1 µS/cm
1M
Ω ⋅
cm
1 cm
-1
10 µS/cm
1 M
Ω
0.01 cm
–1
0.01 µS/cm 100 M
Ω ⋅
cm
0.1 cm
–1
0.1 µS/cm
10 M
Ω ⋅
cm
1 cm
–1
1 µS/cm
10 M
Ω
0.01 cm
–1
0.001µS/cm
0.1 cm
–1
0.01 µS/cm 100 M
Ω ⋅
cm
Note: The M
Ω
measurement is normally used
for pure and ultrapure water and is therefore
only practical with cell constants
k = 0.01 or
possibly
k = 0.1.
LM253E08.CHP
Liquisys M CLM 223 / 253
Diagnosis and corrective maintenance
Hauser
65
