8.8.3
Simulation of inductive measuring cells for instrument test
An inductive measuring cell cannot be
simulated by resistors.
However, the overall system comprising the
CLM 2x3-ID and inductive measuring cell can
be checked using equivalent resistances.
Note cell constant
k (e.g. k
nominal
= 2 for
CLS 50,
k
nominal
= 5.9 for CLS 52).
For an accurate simulation, the actual cell
constant (can be read in field C124) is to be
used to calculate the display value:
display of CD
[mS/cm]
=
k
⋅
1/
R
[k
Ω
]
.
Reference values for simulation of CLS 50 at
25 °C:
Simulation
resistance R
Cell
constant k
Conductivity
display
2
Ω
2.00 cm
–1
1000 mS/cm
10
Ω
2.00 cm
–1
200 mS/cm
100
Ω
2.00 cm
–1
20 mS/cm
1k
Ω
2.00 cm
–1
2 mS/cm
• Performance of simulation:
Pull a cable through the sensor opening
and then connect, e.g. to a decade resistor.
8.8.4
Checking of conductive conductivity measuring cells
• Measuring surface connection:
The measuring surfaces are connected
directly to the connections of the
measuring cell connector.
Check with ohmmeter for < 1
Ω
• Measuring surface shunt:
A shunt between the measuring surfaces is
not allowed.
Check with ohmmeter for > 20 M
Ω
• Temperature sensor shunt:
A shunt between the measuring surfaces
and temperature sensor is not allowed.
Check with ohmmeter for > 20 M
Ω
.
• Temperature sensor:
Refer to the measuring cell nameplate for
the temperature sensor type.
The sensor can be checked at the
measuring cell connector with an
ohmmeter:
–
Pt 100 at 25 °C = 109.79
Ω
–
Pt 1000 at 25 °C = 1097.9
Ω
–
NTC 10 k at 25 °C = 10 k
Ω
• Connection:
Check terminal wiring (interchanged?) and
tightness of clamping screws in the case of
measuring cells with screw terminals (CLS
12/13).
8.8.5
Checking of inductive conductivity measuring cells
The following specifications apply to
measuring cells CLS 50 and CLS 52:
• Testing of transmitting and receiving coils
(white and red coaxial cables, measure-
ment between int. conductor and screen):
- ohmic resistance approx. 0.5 ... 2
Ω
- induct. approx. 260 ... 450 mH (at 2 kHz)
• Testing of coil shunt:
A shunt between the coils (from coax red
to coax white) is not allowed.
Check with ohmmeter for >20 M
Ω
• Testing of temperature sensor:
Use the table in chapter 8.8.3 to check the
Pt100.
The resistance values between the green
and white wires and between the green
and yellow wires should be identical.
• Testing of temperature sensor shunt:
Shunts between the temperature sensor
(green, white or yellow) and the coils (red
or white coaxial cable) are not allowed.
Check with ohmmeter for >20 M
Ω
8.8.6
Checking of line extension and junction box
• Use the methods described in chapter
8.8.2 or 8.8.3 to perform a quick functional
check from the sensor connector
(conductive measuring cells) or from the
sensor (inductive measuring cell) to the
measuring instrument.
Decade resistors are best connected with
the “CD test adapter” service kit (order
number: 51500629).
• Check junction boxes for:
–
Moisture (influence in low conductivity
range or M
Ω
measurement; dry junction
box, replace gaskets, use desiccant bag)
–
Correct line connections
–
Outer screen connections
–
Tightness of clamping screws
Diagnosis and corrective maintenance
Liquisys M CLM 223 / 253
66
Hauser
