Page 25 - EngineerIT September 2021

MEASUREMENT

materials in welding or carbon steel piping, galvanic reactions can lead to the formation of
monatomic hydrogen molecules. When these ions are released, they can seep through the
diaphragm if its molecular structure is not of adequate density. This leads to an increased
volume within the internal fill-fluid circuit, compromising performance and possibly
requiring the whole transmitter to be replaced.
This problem has in the past been solved by coating the diaphragm in gold, which
slows down the penetration of the hydrogen molecules. A more efficient solution is ABB’s
H-Shield protective coating. Consisting of a titanium-based nano coating, H-Shield
creates a protective layer that offers the highest resistance against the permeation of
hydrogen ions. As well as providing high protection, it remains flexible enough to allow the
diaphragm to move as pressure changes.
There is also the risk of abrasion, particularly in the filtration stages. Sea water
can contain a high percentage of minerals and sand, which can scratch the pressure
diaphragm, reducing both its performance and operational life. To counter this, ABB has
developed its Diaflex coating, a titanium-based composite with the hardness of diamond.
Diaflex is applied at a thickness of three to four microns, providing the highest level of
protection against scratching.

Accuracy and range
The accuracy and range of the device is also a critical factor to consider. Desalination
processes, particularly pumping and boosting, often operate at pressures as high as ABB Pressure Transmitter
700 to 1000 bar, with starting pressures of around 400 bar, and any selected pressure
instrument must be able to accurately measure these high pressures. from a single location.
Because leakage is a common problem in water distribution networks, the pressure Digitalisation also helps when
instrument must be able to accurately measure even a small drop in pressure if leaks are replacing a device’s electronics in
to be successfully traced and fixed. With the ability to measure flow, differential pressure the field. The most modern pressure
transmitters can detect variations of just a few millibars. This can indicate if a leak is devices store calibration data, which can
happening, even at high starting pressures. This is why it is important to use pressure be uploaded into the new electronics
transmitters with the highest levels of accuracy. For example, ABB’s differential pressure while avoiding the need to change the
devices offer a choice of 0.04 or 0.025 percent, ensuring desalination plant operators can transmitter itself. This can save the often
detect a leak rapidly. considerable time and cost of fitting and
configuring a new device.
Opportunities for advanced measurements With wireless technologies and
Pressure transmitters can also be used to measure quantities other than just pressure. advanced, long-life batteries, pressure
For example, differential pressure transmitters can also measure level, either directly or devices can increasingly be located
indirectly; gauge pressure devices can also be used in this way. anywhere they are needed, giving fast
Using multi-variable pressure transmitter devices is another possibility. Ideal for deployment and cutting the need for
calculating changes in flow density, these instruments can measure flows of liquids, steam costly wiring.
or gas with absolute pressure and temperature compensation.
Combining multiple forms of measurement into one unit, as well as the ability to use Meeting long-term demand
the signal converter as a flow computer, allows fewer devices to be used and reduces the Along with water conservation,
need for cabling and I/O devices, significantly cutting installation costs. Although multi- desalination will play an important role
variable has yet to really make its mark in desalination plants, it could be a useful way to in helping secure sustainable water
optimise the number of instruments in the field or meet more demanding specs such as sources. Although desalination has its
flue gas or steam management. own challenges, the advantages of the
latest generation of instrumentation,
Take advantage of digital together with the benefits of digitalisation,
New possibilities for optimising pressure transmitter performance can be found in the major can help water companies run their plants
advances made in digital technology. As well as pressure, flow and level, these devices also more efficiently.
offer a wealth of additional data, from totaliser data through to diagnostic data. Selecting the correct pressure
An example is ABB’s plugged impulse line diagnostic (PILD) function, which compares devices, while using the latest
the current performance of a pressure device to a background ‘template’ that is set during technologies to enhance performance,
the commissioning stage. If deviations from this template are detected, this could indicate can help not only in desalination
that either one or both impulse lines are blocked. A particular use of this function could be processes but also any pressure
to flag up potential clogging of filtering systems, allowing action to be taken before they measurement application in potable and
become completely blocked and interrupt the complete desalination process. wastewater treatment. n
Plugged impulse line detection comes into its own by cutting the need for preventive
maintenance. Remote access to the PILD data should make it available in the maintenance For more information about ABB’s
workplace and in the control room. Using digital networks such as field bus and asset offering for water applications, including
monitoring, it should also be possible to access the PILD data, as well as other device data, desalination, visit https://bit.ly/ABB_water.

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