Fractional-order PID (FOPID) controllers have been used extensively in many control applications to achieve robust control performance. To implement these controllers, curve fitting approximation techniques are widely employed to obtain integer-order approximation of FOPID. The most popular and widely used approximation techniques include the Oustaloup, Matsuda and Cheraff approaches. However, these methods are unable to achieve the best approximation due to the limitation in the desired frequency range. Thus, this paper proposes a simple curve fitting based integer-order approximation method for a fractional-order integrator/differentiator using frequency response. The advantage of this technique is that it is simple and can fit the entire desired frequency range. Simulation results in the frequency domain show that the proposed approach produces better parameter approximation for the desired frequency range compared with the Oustaloup, refined Oustaloup and Matsuda techniques. Furthermore, time domain and stability analyses also validate the frequency domain results.

Advancement in recent wireless technology has triggered the need for devices to run on independent power sources. This is evident especially with the wireless sensor network (WSN). This can be accomplished via harvesting energy from the surrounding environment such as solar, wind etc. These enery harvesting devices can power the wireless sensor nodes either directly of in conjunction with a battery. This paper presents the development of a solar energy harvesting mechanism for WirelessHART sensor node using photovoltaic (PV) cell array. Experimental results on the WirelessHART nodes proved that the developed harvester is capable of powering the nodes.

Process monitoring and automation in the industrial sector are hitherto done over wired connection between devices. It is evident that the amount of wires required increased proportionally to the complexity of the industry and their installation is time consuming. The wires used in the industry must withstand the harsh environmental conditions, hence expensive to install and maintain. In the event of loss of connection due to accident or any other reason, the cost incurred as a result of the downtime is high. The highlighted problems necessitated the need for an open, interoperable wireless standard like WirelessHART that can overcome these problems. Three categories of applications running in any process plant with increment of criticality are for monitoring, control and safety. The current application of wireless technology including WirelessHART in the industry so far is limited to monitoring and some attempts are being made to apply it for control. This paper examines the extent to which WirelessHART technology is applied especially for the purpose of control.

The performance of a wireless industrial process plant is affected by wired and wireless link's reliability. While recent related works focus mainly on wireless link's reliability, this paper focuses on wired link's reliability between the controller and the wireless highway addressable remote transducer (WirelessHART) node. In control application for a process plant with fast sampling, when the wired link delay is too short, message transmissions to the node could occur concurrently resulting in packet collision and packet dropout, thus leading to local contention. This can cause process plant with critical control application to be unstable. Therefore, this paper proposes an effective design of exponentially weighted moving average filter to mitigate the contention's effect and improve the process plant's performance. In order to make evident and validate the existence of local contention, an experiment is carried out using a WirelessHART device. From the experiment, the controller delay is 0.1475 s and the estimated packet dropout is 12.29%. Simulation results with the designed filter show a significant improvement in process performance in terms of percentage of overshoot compared with performance of the process plant using traditionally optimized PID controller.