Wireless is well suited to applications in those hard-to-reach or widely dispersed locations where the cost of connectivity appears to make the measurement impractical. Tank farms and level measurements are just this sort of environment because they tend to cover large areas with few field devices.
For the more demanding applications on these large vessels, the level sensors tend to require more power than can be expected from a battery-powered system and therefore, either a 24 VDC or AC supply are installed. If you are installing a power supply for a millimeter-accurate level gauge on a 500,000 barrel or larger tank (at these diameters every millimeter equates to a large volume), putting in signalling cable at the same time is a given, at least for the primary measurement, in part because the number of signals include not just level but also correction factor calculations and those inputs.
What about all the other sensors on a typical tank that may not be located in the same area as the primary level transmitter; or the associated pumps or agitators, including the venting system (open or closed, flowing in or out, pressure); or a back-up, less accurate sensor on the other side of the tank; or the fire and gas detectors within the containment area; or the positioner for (and maybe the solenoid to activate) the isolation valve going through the dike wall; or one of the many other applications that are either across the road or too far away to make economic sense? These are a good fit for one of the IEEE 802.15.4 WSN’s that are well covered by the different proponents of those technologies.
I’m not sure, but I’m confident that there are far more standalone tanks out there than there are tanks inside plant boundaries. These level measurement applications are also well suited to wireless connectivity, as are widely dispersed single vessels, such as chemical injection tanks, where it’s important to know when the chemical level is low so that whatever the chemical is protecting stays that way; water distribution system still wells, to be sure they are operating within their normal range; mobile tanks such as for frac fluids that may have a long lead time for the associated special materials they store; fuel storage for a remote generator; or even a farm during harvest that can be monitored by the fuel supplier dispatcher, thus only making the fuel run when necessary; and other remote locations with one or just a few signals.
These applications, because of their distribution with each point miles from any other, are unlikely to use typical IEEE 802 solutions, but instead will use cellular communications, where the host /central server either dials out to poll for data, or the remote site calls out and transmits at a predetermined interval. Deciding which to use depends on the application and therefore, the associated control engineer or integrator.
Because we don’t want to be continuously connected on a wireless data plan for the low amount of data being generated, the cellular end point needs to incorporate remote terminal unit (RTU) functionality, where it stores data and then either sends or replies to a remote query with a concentrated burst of the data, stored at a predetermined polling frequency archived in memory, or in the event an alarm level is reached, dialing out with both the alert and the associated historical data. Unfortunately, because there is no standard associated with this data transfer, it’s likely to be presented as HTML table, comma-separated values (CSV), or some other generic format that you will have to import to a more permanent storage method for reporting and archiving.
With the coming of 5G networks that include support for multiple different automation use cases, we can fully expect that wireless communications using cellular networks will continue to grow. Cellular manufacturer Ericcson expects the number of cellular IoT connections to reach 3.5 billion in 2023, increasing at a CAGR of 30%. Making this possible will certainly ensure that cellular-based data collection should increase from where it is today, so expect more announcements along those lines from major device suppliers soon. Regardless of where you are now in your comfort space for wireless measurements, it appears that to realize the vision of operations technology, that level will have to continue to go up.