# A Survey on the Application of WirelessHART for Industrial Process Monitoring and Control
## 3 Industrial Applications of WirelessHART
### WirelessHART  
The evolution of the HART protocol is shown diagrammatically in Figure 5. From the figure, it can be seen that since 1988, with only around 4 million wired devices, the standard has incorporated devices such as digital control valves and controllers with HART6 by 2002. By 2007, EDDL and wireless technology were integrated into the latest version of the HART protocol (HART7), released as WirelessHART (IEC 62591), which is the first wireless communication protocol to adopt an over 2.4 GHz radio frequency channel in the IEEE 802.15.4 for industrial process control applications [41]. WirelessHART, being based on the traditional HART protocol, has already gained wide patronage in the industry due to the necessity of demand in the open international standard that suits industrial requirements. The latest version (version 2) of the WirelessHART protocol was approved by the International Electrotechnical Commission in 2016. The standard possesses some new updated features, such as:  
* Wireless mesh networking;
* Time synchronization and stamping;
* Network and transport layer;
* Security encryption and decryption; \begin{table}
\begin{tabular}{l c c} \hline \hline
**Wireless Standard** & **2012 (\%)** & **2014 (\%)** \\ \hline WirelessHART & 27 & 25 \\ ISA 100.11a & 10 & 11 \\ Hybrid & 22 & 16 \\ Others (WIA-PA and ZigBee) & 23 & 28 \\ Factory Automation & 13 & 13 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Preferred IWSN standards [12]. Figure 5: Evolution of the HART protocol [14]. Enhanced burst mode messaging;
* Pipes for high-speed file transfer. The WirelessHART communication protocol utilizes only five layers of the OSI model out of the seven layers. Figure 6 shows the usage of different OSI layers between the conventional wired HART and the WirelessHART protocols. The five OSI layers used by WirelessHART are the physical layer, the data link layer, the network layer, the transport layer, and the application layer. Routing, communication scheduling, and corresponding signal generation are handled by the central network manager. Further detailed discussion of the various OSI layers of WirelessHART and other IWSN communication protocols can be found in [6; 42]. An added advantage of WirelessHART is that it can be extended to control the process rather than simply monitor it. Wireless local area network (WLAN), Bluetooth, ZigBee, and Internet Protocol Version 6 (IPV6) are not extensively adopted for industrial wireless applications because of their limitations in controlling capabilities. At present, two of the most widely used industrial international wireless standards are WirelessHART and ISA100 Wireless [44; 45]. Among these two, WirelessHART leads with more than 30 million installed field devices, and it is projected that this figure will reach over 46 million by 2021 [46]. Hence, there will be very little or no need for training the plant operators to start using the WirelessHART. Based on its flexibility, interoperability, simplicity, and acceptability, the WirelessHART has many advantageous over the ISA 100.11a standard. Simultaneously, the ISA 100.11a standard is yet to gain approval from the International Electrotechnical Commission (IEC). This has given WirelessHART supremacy in industry [47]. Both standards aim at non-critical wireless applications for control and monitoring purposes. Figure 6: OSI layer of the conventional wired HART and the WirelessHART protocols [43]. Nevertheless, WirelessHART is generally preferred by industries since its legacy wired HART communication protocol was once the dominant and most widely adopted protocol in industrial field devices. Additionally, converting existing wired HART field devices to wireless ones is less costly and there is no need for additional sensor components [48]. The WirelessHART network control system (WHNCS) structure is shown in Figure 7. There are five essential elements present in the WHNCS, namely:  
1. Field device: connected to the industrial process plant. 2.