konnect Issue-date: 30th September, 2019.

ISA membership number: 3306 9656


“SMART NETWORKED SENSORS OR BUILDING AUTOMATION”

Buildings are becoming more and more advanced and the demands on building services are increasing. Building Automation is changing from local BMS to remote management of multiple buildings. The different control systems are becoming smarter for building predictive maintenance. Smart Sensors become the basic part of this change. The current analog sensors must change in view of huge cabling required to connect and as well for remote health monitoring. These smart sensors shall have networking feature with wired or wireless media. The internet of things is becoming very relevant for the new buildings for a common remote building management solution integrated with Information Technology. The IT/OT integration with AI and Analytics.
The key areas for Building Management are all energy hungry and need to be managed very efficiently. For this we need to manage different types of sensors for the different applications.

The SMART Buildings, there is very essential to manage all areas with common system and as such need standard protocols for sensors and controller for integration. The Sensor Data and data from associated controllers are very essential for analytics and artificial intelligence for cost effective solution and user convenience. Smart buildings also need standard networking infrastructure with serial, Ethernet and wireless for handling automation. A smart building uses digital control systems to manage the comfort, operational and energy HVAC, Lighting, Safety and Security requirements.

The commonly used protocols for inter communication are Modbus, BACnet, Bluetooth, KnX, Zigbee, Industrial Ethernet, HART, Profibus.
The Physical media for Communication network is generally RS485 multi drop and Ethernet IP, Wi-Fi and as well in special cases power line Ethernet. Normally Ethernet adds cost and hence sensors are mostly on RS485.
For ease of installation for greenfield and as brown field systems wireless sensors are a big advantage. Wi-Fi, Bluetooth, ZigBee, Lora are being used for communication. Bluetooth is very low-cost network and is now being adopted multiple building automation solutions like Lighting control etc.

RS485 Network:
RS-485 network allows devices (up to 256) to communicate at halfduplex on a single pair of wires, plus a ground wire. Both the length of the network and the number of nodes can easily be extended using a variety of repeater products on the market.

Network topology is probably the reason why RS485 is the favorite of the serial interfaces in data acquisition and control applications. RS485 is the only of the interfaces capable of internetworking multiple transmitters and receivers in the same network. Currently available high-resistance RS485 inputs allow this number to be expanded to 256. RS485 repeaters are also available which make it possible to increase the number of nodes to several thousands, spanning multiple kilometers. It is the reason why RS485 is so popular with computers, DDC, PLCs, micro controllers and intelligent sensors in scientific and technical applications. In the picture below, the general network topology of RS485 is shown in picture-2.

N nodes are connected in a multipoint RS485 network. For higher speeds and longer lines, the termination resistances are necessary on both ends of the line to eliminate reflections. Use 100 Ω resistors on both ends. See Table 1.

Wireless Sensor Network, Today, smart grid, smart homes, smart water networks, intelligent transportation, are infrastructure systems that connect our world more than we ever thought possible. The common vision of such systems is usually associated with one single concept, the internet of things (IoT), where through the use of sensors, the entire physical infrastructure is closely coupled with information and communication technologies; where intelligent monitoring and management can be achieved via the usage of networked embedded devices.

In such a sophisticated dynamic system, devices are interconnected to transmit useful measurement information and control instructions via distributed sensor network. With advent of I O T the Control and monitoring architecture for building is undergoing a big change. A typical architecture is shown in Picture 3.

A wireless sensor network (WSN) is a network formed by a large number of sensor nodes where each node is equipped with a sensor to detect physical phenomena such as light, heat, pressure, etc. WSNs are regarded as a revolutionary information gathering method to build the information and communication system which will greatly improve the reliability and efficiency of infrastructure systems. Compared with the wired solution, WSNs feature easier deployment and better flexibility of devices. With the rapid technological development of sensors, WSNs will become the key technology for IoT.

A WSN can generally be described as a network of nodes that cooperatively sense and control the environment, enabling interaction between persons or computers and the surrounding environment. WSNs nowadays usually include sensor nodes, actuator nodes, gateways and clients.
A large number of sensor nodes deployed randomly inside of or near the monitoring area (sensor field), form networks through self-organization. Sensor nodes monitor the collected data to transmit along to other sensor nodes by hopping. During the process of transmission, monitored data may be handled by multiple nodes to get to gateway node after multi-hop routing and finally reach the management node through the internet.

Sensor nodes
The sensor node
is one of the main parts of a WSN. The hardware of a sensor node generally includes four parts: the power and power management module, a sensor, a microcontroller, and a wireless transceiver, see Figure below.
The power module offers the reliable power needed for the system. The sensor is the bond of a WSN node which can obtain the environmental and equipment status. A sensor is in charge of collecting and transforming the signals, such as light, vibration and chemical signals, into electrical signals and then transferring them to the microcontroller. The microcontroller receives the data from the sensor and processes the data accordingly.
The Wireless Transceiver (RF module) then transfers the data, so that the physical realization of communication can be achieved. It is important that the design of the all parts of a WSN node consider the WSN node features of tiny size and limited power.
With costs of microcontroller and new sensors coming down, the building automation technology is changing; apart from building control and monitoring the control systems also being ministered and diagnosed for their health. This making the buildings management more predictable.

Note: This article was published in International Society of Automation-Building Automation Systems Division(BASDIV) Newsletter, July 2019. Available at http://www.isa.org/basdiv