Test & measurement


Digital data capture via Ethernet is improving safety and efficiency for process operators. The introduction of Power over Ethernet promises to further increase simplicity and reduce installation costs, as ABB explains...


D


igital technology has made inroads in all aspects of our lives and has had a particularly profound effect on


industry. One of the biggest has been in measurement and analytics technology - the flowmeters, pressure sensors and temperature measurement devices that form the eyes and ears of process plants. Although many instruments still use analogue


4-20mA instruments, they are gradually being replaced by digital instrumentation. The drawback with analogue instruments is


that errors can be introduced at each of the stages of measurement, amplification, conversion and transmission. Digital technology wins by rapidly converting the measurement into a digital signal, cutting the risk of errors by using a stream of discrete ones and zeros, to provide an accurate representation of process values. Another advantage of digital over analogue


is the ability to add measurements such as density, temperature or pressure to the instrument’s main measurement. For example, chemical analysers and level


detectors can also provide temperature sensing, while flowmeters can also detect air bubbles that can be caused by damaging pump cavitation. This data can be used by the control system to assess process conditions and recommend actions. But how do we get these signals to where they can be used?


EnTEr EThErnET Historically, many data transfer applications have used Profibus. Essentially a protocol for fieldbus communication in automation technology, Profibus has been particularly popular in food and beverage plants, possibly because they have a lot of instruments, all of which must be linked to the DCS for recording and traceability Yet, the drawbacks of Profibus are


becoming more apparent. A major disadvantage is that the end user must be an expert on the particular protocol and how to set it up, and specially trained people must be employed to maintain it. Specific cables, connections and line


terminations must be used, and it also needs specialist equipment for maintenance and troubleshooting.


Although Profibus is quite an open


protocol, fieldbus users can be locked into a single vendor at the control system level, while fieldbus devices often need to be reconfigured when returned to the network following servicing. Fieldbus systems are increasingly being


supplanted by Ethernet, which was designed as a way to connect computers in a Local Area Network or LAN. The basic idea is that multiple computers have access to it and can send data at any time. As a ‘plug and play’ technology, Ethernet is


very easy to set up, using more common commercially available electrical components that keep costs down. Other benefits include high bandwidth, low


signal loss, high reliability and high speed, with some varieties able to handle the needs of real time motion control. One similarity that can limit the use of


both Fieldbus and Ethernet is that both networks are limited in the cable lengths they can use, typically around 200 metres. ABB has taken Ethernet one stage further


with its 4-wire Ethernet, which combines the technology with the classic world of mA and digital outputs. Offering a modular design allows the combination of both worlds and makes flowmeters future proof. Flowmeters equipped with ABB 4-wire


Ethernet now include the CoriolisMaster, ProcessMaster and HygenicMaster, with more to follow. With Ethernet, CoriolisMaster and ProcessMaster are the world’s first flowmeters to offer Power over Ethernet, allowing power and data to use the same cable.


OvErcOming ThE hurDlEs Using Ethernet for measurement applications has been held back by the lack of relevant standards and the limited processing power within the signal converter from a device. Today, with much smarter transmission technology, this is no longer a limiting factor. One of the key advantages of


Ethernet is that, combined with Edge computing, it allows individual instruments to be linked to the Internet, opening the way for Cloud solutions.


Cybersecurity has been a great concern for customers but this has largely been overcome using Edge PCs that are designed from the ground up for maximum security. ABB’s Ethernet solution offers a number


of features to enhance the cybersecurity of measurement instruments using it. These include password protection procedures such as encrypted storage of passwords. The password can be changed by the user and there is also a dedicated password reset procedure.


BEyOnD PrOcEss DATA Using Ethernet to connect digital instruments opens up a whole new world of information and control. Some measurement devices include a web server within the transmitter. This means the instrumentation user has no need for specific tools or protocols and also gets storage for information such as manuals and supporting documents. A web server also allows parameterisation


values within the device to be sent to a PC to build up a log of trend data, removing the need for expensive add-ons.


POwEr AnD DATA frOm OnE cABlE Ethernet also offers the capability of Power over Ethernet or PoE, which uses a network cable to carry electric power, removing the need for both a data and a power cable. This comes into its own where devices could be far from a mains connection or where connections to the device are difficult to make. A centralised power supply unit covers all demands in the field, with no need for additional electrical outlets or running different cables. This can increase the reliability of an installation,


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September 2021 Instrumentation Monthly


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