
Manual CWD 2005
Measurement principle
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Manual CWD2005.doc
85
The measuring principle is described below. Two independent physical
measurements are carried out. These are Wobbe Index value and Specific Gravity
and the computer calculates the Calorific Value using following formula:
Gravity
Specific
Index
Wobbe
value
Calorific
9.2.
Thermopile measuring system
Figure 18: The main components of the calorimeter
1
Range orifice
2
Burner
3
Cooling air flow
4
Thermopile (hot junctions)
5
Thermopile (cold junctions)
6
Output signal
7
Gas flow
8
Pressure regulator
9
Pressure sensor
10
Temperature sensor
11
Temperature sensor
12
Temperature sensor
13
Specific Gravity cell
14
Cooling air fan
15
Heat exchanger
16
Pressure sensor
17
Temperature sensor
16
Ignition transformer
Sample gas is passed to the burner (2) via a wobbe range orifice (1) at very precisely
regulated pressure, and burned at atmospheric pressure. The gas flow is therefore
dependent on the specific gravity of the gas.
The flue gases are mixed with the cooling airflow (3) the temperature of the overall
mix is measured by the thermopile hot junctions (4). At the cold junctions (5), the
thermopile measures the temperature of the incoming flow of cooling air. The result is