Siemens 7MB2335, Руководство по эксплуатации, Страница: 31 / 168

Technical Description
Operating instructions ULTRAMAT 23 gas analyzer
C79000-B5276-C216-03 3-9
3.3 Function
Two independent, selective measuring principles are used in the
ULTRAMAT 23.
Infrared measurement
An IR source (7) at 600 °C emits an infrared radiation which is
modulated with 8 1/3 Hz by a chopper (5). After passing the
sample cell (4), the intensity of the radiation is measured by the
detector (11, 12).
The represented detector is composed of layers filled with the
component to be analyzed. The energy of the middles of the IR
bands of the measured gases is mainly absorbed in the first
layer. The second layer absorbs the edge energy which is tuned
on high selectivity in the third layer via an aperture.
When passing through the layers the radiation absorption results
in different pressure increases and so to a flow via the capillary
hole. The microflow sensor there generates a signal which is
nearly independent of interferences from components at the
band edges.
Note
The sample gases have to enter the analyzer dustfree. Avoid
condensate in the sample cells. Therefore an appropriated gas
preparation is required depending of the application.
The ambient air of the analyzer should be, in a large extent, free
of high concentrations of the component to be measured.
Mode of operation of infrared channel (example with three-layer
detector)
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Oxygen measurement
The oxygen sensor operates according to the principle of a fuel
cell. The oxygen is converted at the boundary layer between
cathode and electrolyte; the resulting current is proportional to
the concentration of oxygen.
ULTRAMAT 23, mode of operation of oxygen measuring cell
Essential characteristics
• Practically maintenance-free as a result of AUTOCAL with am-
bient air (or with N
2
, devices without oxygen sensor); both the
zero and the span are calibrated in the process
• Calibration with calibration gas is only necessary every
12 months, depending on application
• Two measuring ranges can be set per component within de-
fined limits;
all measuring ranges linearized;
autoranging with range identification
• Automatic correction of variations in atmospheric pressure
• Gas flow monitoring;
Low-flow alarm at <1 l/min (with viton sample gas path only)
• Maintenance request alert
• Two limits can be freely configured for each component, for
upward or downward violation.
Sample gas
inlet
Sample gas
outlet
1
2
3
10
9
11
9
1 Capillary
2 Second detector layer
3 Microflow sensor
4 Sample cell
5 Chopper wheel
6 Chopper motor 7 IR source
8 Reflector
9 Window
10 Aperture
11 First detector layer
12 Third detector layer
12
9
8
7
4
5
6
e-
1 Gold cathode
2 Electrolyte (acetic acid)
3 Thermistor and load
resistor for temperature
compensation 4 Signal output
5 Lead anode
6 Oxygen diffusion
membrane made
of FEP
4
U
Sample gas
1
2
3
6
5