Process plants and related facilities such as tank farms are filled with vessels, tanks and similar storage units, and most of these units could benefit from a system to measure, monitor and view inventory on a near real-time basis. "Logistical benefits of tank level monitoring include reduced emergency deliveries, better inventory management and labor productivity improvements," says Michael Robinson, director of solutions, Endress+Hauser.
Wireless is a particularly good fit for this application, as most tank level instruments are installed at the top of a tank, a tough spot to access with wiring. Many tanks are located far from control rooms, requiring long home-run wiring. Wiring installed in the corrosive environments where tanks often reside has a tendency to fail at connection points, and conduit systems can rust and deteriorate. Finally, many tanks are installed in areas classified as hazardous, making it expensive to run and maintain wiring.
Available wireless level measurement technologies include differential pressure and radar, each of which can be made truly wireless with a battery-powered option. Relying on battery power could be a serious limitation in wireless instrument applications with rapidly changing process variables, but in the case of tank level monitoring, it's feasible to have a very low update rate and correspondingly long battery life, up to 10 years in some cases.
But many tanks have existing conventional wired instruments, and others need to use level measurement technologies not available in wireless versions. For these instruments, a wireless adapter can be used to convert the wired instrument output to wireless. Although this isn't a completely wireless solution, such as a wireless radar or DP level instrument, it does solve the problem of wiring back to an inventory management system.
In either case, transforming level measurements into wireless signals is only one part of the equation, with the second being transmitting this information to a tank inventory monitoring and management system. The two main options for creating this data link are via the cloud or a local Wi-Fi network.
"Our wireless tank inventory monitoring solution can include an AC-, battery- or solar-powered cellular communication modem which transmits tank level information to our cloud-based service SupplyCare, which is hosted on secure Endress+Hauser servers. SupplyCare receives and stores the tank data and is configured to trigger visual notifications, email alerts and transaction information," explains Robinson.
One could configure a system similar to SupplyCare by buying a modem, contracting with a cell provider, contracting with a cloud storage firm and installing appropriate tank inventory management software, such as an HMI with database storage capability, in the cloud. Once tank level data is sent to the cloud, it can be accessed for inventory management by any device with an Internet connection and proper login credentials. Typical devices used for accessing cloud data include PCs, laptops, tablets and smartphones.
Emerson Process Systems installed its Rosemount tank gauging equipment for inventory measurement of liquid storage tanks for St1, a Swedish petroleum refinery located in the Gothenburg harbor area. The plant has a mixture of wired and wireless equipment for level and temperature measurement, all connected to a wireless gateway.
Emerson's local Smart Wireless Gateway collects tank data from the instruments and makes it available through a WirelessHART Wi-Fi network. Initially, instrument technicians could only perform monitoring and configuration by entering the tank farm area with a laptop PC. To improve access to the wireless network, St1 added a wireless connection from the control room to the local gateway via the Wi-Fi based Pervasive Field Network (PFN) solution from Emerson.
The PFN link at St1 includes three industrial hotspot units. One hotspot is connected to the local gateway and to a remotely installed directional panel antenna. A second serves as a repeater to achieve line of sight. It is connected to two remotely installed panel antennas, one receiving and one transmitting, to relay data.
The third hotspot unit is installed in the control room area, and it's connected to a remotely installed panel antenna. In addition, it is equipped with an integrated antenna to create a Wi-Fi zone, enabling operators to access the wireless network from any place in the control room via a laptop equipped with the appropriate software. This data is also now available to any tank level management and inventory system with the Wi-Fi coverage area.