8.6
Corrective maintenance of measuring system
8.6.1
Oxygen transmitter
Simulation of oxygen measurement:
To perform a functional test of the instrument,
the COS 21 sensor can be simulated by
resistors. Since the display value greatly
depends on the sensor slope setting and on
temperature, the following values should be
considered as reference values:
Simulation value
value indicated
for COS 21
[mg O
2
/l]
∞
(open)
0
13 M
Ω
7 ... 13
With 13 M
Ω
and tem-
perature equivalent
resistance 27.0 k
Ω
Recalibration
9.0 ... 9.2
27.7 M
Ω
3.3 ... 6.1
Simulation of temperature sensor:
The COS 21 sensor uses an NTC sensor
(22.0 k
Ω
/25 °C) for temperature measurement.
Use the following equivalent resistances to
test the temperature measurement:
Simulation value
value indicated
for COS 21
[ °C ]
64.9 k
Ω
0.0
41.3 k
Ω
10.0
27.0 k
Ω
20.0
22.0 k
Ω
25.0
18.0 k
Ω
30.0
Test procedure:
• Connect the O
2
equivalent resistance (e.g.
decade resistor) to terminals 90 and 91.
• Connect the temperature equivalent
resistance (e.g. decade resistor) to
terminals 11 and 12.
• Air pressure measurement:
On instruments equipped with the Plus
packet, the air pressure measured can be
checked in field S11.
Caution!
•
The absolute pressure is
displayed (a normal barometer
indicates the relative pressure
referred to sea level and cannot
be used to evaluate the air
pressure measurement).
Cleaning the front panel
To clean the front panel, only use standard
cleaning agents.
The front panel is resistant to the following
cleaning agents (acc. to test for DIN 42 115):
• Isopropanol
• Thinned acids (3 %)
• Thinned alkalis (5 %)
• Ester
• Hydrocarbons
• Ketone
• Household cleaners
Caution!
•
Do not use any concentrated
mineral acids or alkalis, benzyl-
alcohol, methylene chloride or
high-pressure water vapour at
over 100 °C.
Diagnostics and corrective maintenance
Liquisys M COM 223 F / 253 F
66
Hauser
