Abstract
Recent advances in wireless networking technology and the proliferation of industrial wireless sensors have led to an increasing interest in using wireless networks for closed loop control. The main advantages of Wireless Networked Control Systems (WNCSs) are the reconfigurability, easy commissioning and the possibility of installation in places where cabling is impossible. Despite these advantages, there are two main problems which must be considered for practical implementations of WNCSs. One problem is the sampling period constraint of industrial wireless sensors. This problem is related to the energy cost of the wireless transmission, since the power supply is limited, which precludes the use of these sensors in several closed-loop controls. The other technological concern in WNCS is the energy efficiency of the devices. As the sensors are powered by batteries, the lowest possible consumption is required to extend battery lifetime. As a result, there is a compromise between the sensor sampling period, the sensor battery lifetime and the required control performance for the WNCS. This paper develops a model-based soft sensor to overcome these problems and enable practical implementations of WNCSs. The goal of the soft sensor is generating virtual data allowing an actuation on the process faster than the maximum sampling period available for the wireless sensor. Experimental results have shown the soft sensor is a solution to the sampling period constraint problem of wireless sensors in control applications, enabling the application of industrial wireless sensors in WNCSs. Additionally, our results demonstrated the soft sensor potential for implementing energy efficient WNCS through the battery saving of industrial wireless sensors.
Highlights
Networked Control Systems (NCSs) are an approach for current applications of distributed control systems using networked architectures for communication and control, in which the controller, plant, sensors and actuators are physically separated and connected through an industrial network [1]
Due to this focus in monitoring applications and the need to provide a long battery lifetime, these wireless sensors allow a maximum sampling of information, depending on the product model, every 4 s, 2 s or 1 s [40], which limit their application in many closed-loop control applications
The results demonstrate that the soft sensor based on the process model (DC motor identified) developed in this paper enabled the use of industrial wireless sensors in Wireless Networked Control Systems (WNCSs)
Summary
Networked Control Systems (NCSs) are an approach for current applications of distributed control systems using networked architectures for communication and control, in which the controller, plant, sensors and actuators are physically separated and connected through an industrial network [1]. The radio is the main energy-consuming subsystem, and the energy consumption of the wireless sensor is directly related to the data transmission on the wireless network [16] In this sense, a problem raised in WNCS is the restriction or limitation of the sampling period of industrial wireless sensors, which occurs due to the impracticality of transmitting the sensor data at very fast rates [17]. This paper develops a model-based soft sensor and a multi-rate control strategy for WNCSs, focusing on minimizing energy consumption while guaranteeing stability and control performance. The contributions of the paper for practical implementation of WNCS are as follows: overcoming the sampling restriction and increasing battery lifetime of industrial wireless sensors for closed-loop control applications.
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