Chemical Engineering December 2016 - 72

Pabs
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Electronic ∆p40 mbar
3
Final remarks
The electronic DP measurement is
an interesting alternative to the traditional
DP measurements. Electronic
DP measurement is especially
advantageous when temperature
differences are large, as well as operation
under vacuum or abrasive
conditions. Electronic DP measurement
is an economical reduction of
measuring points.
On the other hand, large pressure
Forced draft fan
2
Electronic ∆p40 mbar
FIGURE 4. Electronic DP measurement can be applied on a forced draft fan in a power plant
need for laborious laying of impulse
lines. Moreover, the expenses for
the required additional heat of the
lines can be saved. The oil-free ceramic
measuring cell works reliably
and, in the long-term, without any
drift independently of the ambient
temperatures. Thanks to the ceramic
measuring cell, no cleaning
or maintenance work on the sensor
are required.
District heating network. In district
heating
grids,
several
compensation
tanks with a height of
approximately 70 ft (21 m) assist
with maintaining the pressure. They
compensate for any leakages, as
well as temperature-related volume
fluctuations within the grid.
The necessary level measurement,
until now, was realized via DP transmitters
with flanges and long capillary
lines. These were laid outdoors and
equipped with an additional heating
system. For the total pressure to be
measured in addition, another sensor
needed to be installed.
In contrast, the electronic DP measurement
(Figure 5) is significantly
less expensive and easier to handle.
All the desired measured values can
be transferred to the control system.
An additional sensor for the total
pressure is not required.
Criterion
differences and a high static pressure
will continue to be the domain for mechanical
DP measurement. The final
decision as to which technology to
adopt ultimately depends on the application
in question.
n
Edited by Gerald Ondrey
Author
Christian Langensiepen is a senior
engineer at VEGA Grieshaber
KG (Am Hohenstein 113, 77761
Schiltach, Germany; Telephone:
+49-7836-50-0; Email:
c.langensiepen@vega.com) As a
technical author with focus on
pressure measurement and level
radar, he belongs to the VEGA
Product Management. He has
published many articles focusing on applications with
level and pressure field instruments, especially in the
pulp and paper industry. Langensiepen holds degrees
(Diplom) in Electrical Engineering from the University
of Applied Sciences Hagen (Germany) and in Economics
Engineering from the University of Applied Sciences
Bochum (Germany).
High static pressure
TABLE 2. COMPARISON OF MECHANICAL AND ELECTRONIC DP MEASUREMENT
Mechanical DP
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Temperature fluctuations during the process
Vacuum
Abrasion (ceramic)
High process temperature
Low installation and maintenance effort
High measuring accuracy at turn down > 20:1
Compact structure
Variety of process fittings
Measured value at total pressure
Measured value at static pressure
Measured value level
Measurement of minimal pressure differences
High temperature difference between the measuring points
Density and interface measurement
FIGURE 5. Shown here is the use of electronic DP
measurement on a compensation tank in a district
heating supply
66
++ very suitable
+ suitable
- unsuitable
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
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Chemical Engineering December 2016

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