
Measurement principle
Manual CWD 2005
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Manual CWD2005.doc
9.2.3. Functional diagram
Figure 19: Functional diagram of the Specific Gravity measuring cell
9.2.4. Output signals
The standard measuring range is 0.2
– 2,2 Specific Gravity (Air = 1.0)
The output signal for the measuring cell is expressed as: U
Specific.Gravity
0 - 5 Volt
U
Spec. Gravity
/ V = 2.5 x Specific Gravity
– 0.5
In certain cases, the measuring range is 0.0
– 2.0 Specific Gravity (Air = 1.0)
The output signal for the measuring cell is expressed as:
U
Specific.Gravity
0
– 5 Volt
U
Spec. Gravity
/ V = 2.5 x Specific Gravity
9.2.5. Commissioning
The specific gravity cell is supplied with a transport lock, after installation remove the
tie wraps. The cell is fitted with tension springs that mechanically de-couple the
system. Vibrations in the unit (air fan etc.) cannot be transferred to the specific
gravity cell if the cell can move freely.
The differential pressure across the specific gravity cell is shown on display [53]. It
should be approximately 4 mbar (+/- 0.5 mbar) controlled by regulator [23] adjust the
regulator if necessary as a low differential pressure will slow response speed. (If the
regulator [23] is out of range, see section 11.5.1 for more details). The measuring cell
is already connected and is provided with DC power from the ST2 plug. Part of the
process gas (approx. 4-5 l) flows through the measuring cell, this small sample is
returned to the main gas stream and no gas is vented to the atmosphere.