# A Survey on the Application of WirelessHART for Industrial Process Monitoring and Control
## 1 Introduction  
The network control system has been widely adopted in process industries and manufacturing plants producing goods such as food and beverages, chemicals, pulp and paper, crude oil refineries, and power generation plants to control and monitor field instruments. These industrial control systems consist of a single instrument or a group of instruments that form a single- or multiple-loop network based on their design and deployment. To maintain a steady output response in a system, the industrial control system must continuously monitor and maintain the parameters at desired levels. Hence, industries need to control and monitor numerous field devices that humans often handle. In the initial industrial era, communication between field devices and control systems took place via 4-20 mA analog signals, causing more errors that resulted in process instability and additional external noise [1, 2]. Thus, the concept of applying automated networking control systems to industrial processes has grown in many applications, yielding autonomous controllers without the need for any human intervention. This has led to the hybridization of combining analog and digital signals to create new wired communication protocols. These include, to list a few, FOUNDATION(tm) Fieldbus, Modbus, PROFIBUS, ISA 100.11a, and highway addressable remote transducer (HART), as well as their upgraded wireless versions, such as ZigBee, WirelessHART, ISA 100.11a wireless, and WIA-PA [3, 4]. For an industrial wireless sensor network (IWSNs) to be used in industry, it must provide thesame quality of controlling and monitoring service as--or better than--conventional wired communication systems [5; 6]. Some of the advantages of IWSNs over wired networks are:  
* They can eliminate the costly and bulky cabling used to connect the various field devices [7];
* They will dramatically reduce the deployment, redeployment, installation, and commissioning times, thus avoiding the problem of frequent cable maintenance [8];
* They will be self-organized and support a large number of battery-powered wireless nodes [9];
* They can be installed at any location irrespective of the surrounding environmental conditions [10]. The advancement in communication technologies changed control strategies from being based on electronic single control loops in the 1960s to single digital loop controllers in the 1970s. Multi-loop digital controllers were designed for single process plants in the 1980s. The present wireless digital controller is shown in Figure 1[11]. Self-diagnostic functionalities in wireless field instruments have encouraged process industries to shift from wired to wireless technologies, supporting both analog and digital instrument installation in any environment. Figure 2 shows a classical IWSN architecture, where multiple wireless nodes are placed in plants remotely and controlled through wireless networks. The closed-loop control system consists of both continuous-time and discrete-time data of the sensors, actuators, and controllers integrated with the process plant. In the closed-loop system, both the host application and the gateway will run on the same system to avoid the possible delay and clock drift. This closed-loop structure is the same in all existing wireless networks. The overall classification of the IWSN communication protocols is shown in Figure 3. From the figure, it can be seen that all the IWSN standards are based on the physical layer IEEE802.14.5 standard. However, modifications were carried out in the physical layer to suit the specific application needs of each standard. A significant characteristic of the WirelessHART is its time-synchronized MAC layer specification [4].