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 SpecificIndex Wobbe valueCalorific
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
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