Feature: Sensors
Wired or wireless – which is best for sensor deployment?
An ever-growing number of sensors are installed at remote locations By Paul O’Shaughnessy, Channel Sales Manager, Advantech IIOT T
aking measurements from real-world processes has always been fundamental to data-acquisition systems. Aſter the application specification
has been determined, the system is defined around it, adopting the most suitable technologies for best results. Tis is somewhat different in IoT applications, where there’s a growing demand for increased measurement data, bringing its own challenges. Te inherent flexibility of IoT
systems means that the required data measurements evolve over time, requiring strategies to integrate pre- existing measurement points with new ones, which may not necessarily be part of existing wiring or communication links. In these cases, the cost of adding new measurement points – or the cost of recovering the data – is oſten a deciding factor for system enhancements. It is therefore understandable that
engineers are interested in using wireless measurement systems, which can be installed much more quickly and cost-effectively than wired systems which require laying out and installing complicated infrastructure. However, adding wireless sensing
technology involves compromises, which determine the ultimate choice of wired or wireless architecture and technology type.
The case for wired infrastructure Traditionally, sensors have been connected to data-acquisition systems via wired interfaces, typically 4-20mA current loops or higher-speed voltage- based systems for more specialised measurements. Tese connections carry power to the sensors, are reliable and accurate, offer faster measurement transmission and update times than wireless systems and, if correctly installed, are both highly secure and insensitive to noise and other interference. Tese characteristics come at a cost, however:
48 December/January 2021
www.electronicsworld.co.uk
installation can be very costly, oſten involving alterations to buildings or digging trenches in which to lay the cables. In some cases, cabling to a remote sensor may not be practical at all. It is also usually not possible to use wired interfaces to mobile equipment, unless the range of movement is limited and accurately determined.
Remote I/O Telemetry has been used for many years to alleviate some of these limitations. By moving the physical sensor interface closer to the sensor, digitising its data at that point and then sending it on via a serial or data connection, the costs of installation can be significantly lower whilst also reducing noise susceptibility – particularly where multiple sensors are involved. It also becomes possible to use radio to transmit the data, extending the reach of data-acquisition systems to remote sites.
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