PRODUCT INFORMATION
Level Measurement at Vessels
with Gaseous Phase
GPC (Gas Property Compensation)
Special applications require special solutions.
So it is not rare, that vessels where the level is
measured are pressurized, which results in an
increased gas density above the actual bulk or
liquid level. Hence, the radiation coming from
the source will be partly absorbed in the gas, before it reaches the detector. If the gas density
changes, the absorption changes too and hence
the level reading. In other words, the indicated
level reading is falsified by variations in the gas
density.
Measurement at Vessels with
Fluctuating Gas Phase
gas phase
leveldetector
source
The trend illustrates how the level reading is falsified, if the gas density in the vessel rises.
falsified level reading
ga s
ity
d ens
actu
al level
gas density
(g/cm3)
level (%)
How strong the reading drifts, not only depends
on the gas pressure, but also on the following
gas properties:
- temperature
- gas density abnormality1
- hydrogen content in the gas2
t
If these properties are not constant throughout
operation a compensation by gas pressure can
only partially improve the level accuracy. A reliable compensation will only be possible if the actual absorption in the gas is measured.
The Answer
point source
for compensation
measurement
compensation
detector
Therefore a second radiometric measurement is
installed to be used as compensation measurement. Its signal will be transferred to the level
detector and processed automatically to provide
a highly accurate level reading.
Measuring systems from Berthold Technologies
with GPC-funcitonality offers this option. The
gas absorption value from the compensation detector is transferred via RS485 connection to the
level detector. Hence an accurate and reliable
level measurement is realized indicating the actual reading even if the gas density fluctuates.
1
RS485
Van-der-Waals-Equation for real gases, especially at high
pressure
2
stronger absorption of gamma radiation in hydrogen
1
PRODUCT INFORMATION
Level Measurement at Vessels
with Gaseous Phase
GPC (Gas Property Compensation)
GPC Design
When designing a GPC-measurement the following
points should be considered:
1) The compensation measurement must be positioned above the maximum level.
compensation
detector
2) Any interference between the compensation measurement and the level gauge must be ruled out.
3) You can use the GPC-function for following detector source designs:
- Point source with UniSENS (picture 1)
- Rod source with CrystalSENS or SuperSENS
(picture 2)
compensation
detector
(Picture 1)
- Rod source with UniSENS
4) For a compensation detector a CrystalSENS is
used. For vessels with large diameter and thick
walls the SuperSENS is recommended.
(Picture 2)
Detector Versions with GPC
CrystalSENS (Point Detector)
UniSENS (Rod Detector)
SuperSENS (Point Detector with highest sensitivity)
2
PRODUCT INFORMATION
Level Measurement at Vessels
with Separation Layer
GPC at Separation Layer
Also for level gauges at separation layers the GPC
measurement is suitable, provided that the density
of the light phase fluctuates. The light phase is comparable with the gas phase described in the previous pages.
During the design following is to be considered:
compensation
detector
- The light phase must always cover the radiation
beam of the compensation detector.
level detector
- The density of the light phase must be homogeneous in order to get a representative reading
from the compensation detector.
light phase
heavy phase
Berthold is a renowned supplier of very reliable
radiometric instruments for more than 60 years.
Your Partner
BERTHOLD TECHNOLOGIES
Our speciality is developing the optimum solution for your measuring problem.
We offer an exceptional spectrum of measuring
systems, sources, source shieldings, detectors
and technical know-how.
Please contact us, we will find the solution also
for your measurement problem!
3