Introduction to WirelessHART

WirelessHART is a subset of the HART industrial instrument communication standard as of version 7, communicating process data over 2.4 GHz radio waves. Individual instruments communicate with a common “gateway” device serving as an interface between the wireless network and a wired network or a host control system. In addition to this, though, individual WirelessHART devices also form links with one another, so that the network data routes look like a “mesh” with all nearby nodes interconnected in addition to connecting with the gateway:

In a mesh network, devices (nodes) perform double-duty as repeaters to relay data from other instruments to the gateway as needed. In other words, data transmitted from one WirelessHART instrument may not be directly received by the gateway device if that path is blocked or too far away. Instead, the data may “hop” from one device to another nearby, which then re-broadcasts that information to the gateway via a clearer path.

The purpose of a mesh network is to provide redundant data pathways in case of device failure or changes in the environment interrupting radio communication between devices. In this way, data packets may be re-routed to the gateway if the shortest route fails, in a manner similar to how Terminal Control Protocol (TCP) and Internet Protocol (IP) work together to route data segments from source to destination over the “mesh” of the Internet. This feature is often referred to in WirelessHART technical literature as the self-healing property of the mesh network.

According to the HART Foundation, reliability for a well-designed WirelessHART mesh network is 99.7300204% minimum, and typically greater than 99.9999998%.

With each WirelessHART field instrument capable of functioning as a radio repeater, the potential exists to form wireless networks larger in size than the maximum broadcast/reception range of any one device. This illustration shows what is possible:

An important consideration when planning a WirelessHART network is battery life. With the main purpose of wireless field instruments being the elimination of wired connections to the host system, the field instruments cannot rely on a host system for their electrical power needs. Lithium-based batteries currently fulfill this role as primary power source, with life expectancies of several years. Interestingly, the amount of energy required by a WirelessHART device to transmit radio-frequency data is small compared to the energy required to power its essential instrument functions (e.g. pressure measurement, temperature measurement). This means a WirelessHART device operating as a radio repeater (in addition to being a measurement device) adds little burden to its battery.

Perhaps the greatest challenge in sustaining any wireless field instrument network is ensuring network integrity despite unending changes in the physical environment around the instruments. Remember that this is an industrial, field-instrument wireless network designed to be installed in less-than-ideal physical environments. These wireless devices must somehow reliably communicate with each other despite interference from high-power electrical devices (e.g. variable-frequency motor drive units), while mounted on or near metal objects such as girders, pipes, pipe racks, large vessels, motors, enclosures, shelters, and electrical conduits. Even the ground of an industrial environment can be an impediment to robust radio communication: steel-reinforced concrete and electrical grounding grids form what is essentially a solid “ground plane” that will interfere with WirelessHART devices mounted too close to ground level. Added to all this spatial complexity is the continual presence of large vehicles and other moving machines (cranes, forklifts, manlifts, etc.). It is not uncommon for scaffolding to be temporarily erected for maintenance work in industrial areas, presenting yet one more obstacle for RF signals.

In answer to these challenges is an integral and essential component of a WirelessHART network called the Network Manager: an advanced digital algorithm usually executed by the network gateway’s microprocessor. The purpose of the Network Manager is to manage the details of the network automatically, “tuning” various parameters for optimum reliability and data throughput. Among other tasks, the Network Manager assigns “timeslots” for individual devices to transmit, determines the frequency-hopping schedule, detects and authenticates new devices added to the network, dynamically adjusts device transmission power, and selects alternative routes between devices.

In a sense, the Network Manager in a WirelessHART network continually audits and tunes the RF system in an attempt to maximize reliability. The Network Manager’s functionality does not substitute for good planning during the design phase of the WirelessHART network, but it does eliminate the need for a human technician or engineer to continuously monitor the network’s performance and make the small adjustments necessary to compensate for changing conditions. When changes occur in a WirelessHART network that cannot be compensated by the Network Manager, the real-time statistics provided by the Network Manager are invaluable to the technician or engineer assigned to update the network.


Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

What Are Industrial Control Systems?

Control systems are computer-based systems that are used by many infrastructures and industries to monitor and control sensitive processes and physical functions. Typically, control systems collect sensor measurements and operational data from the field, process and display this information, and relay control commands to local or remote equipment. In the electric power industry they can manage and control the transmission and delivery of electric power, for example, by opening and closing circuit breakers and setting thresholds for preventive shutdowns. Employing integrated control systems, the oil and gas industry can control the refining operations on a plant site as well as remotely monitor the pressure and flow of gas pipelines and control the flow and pathways of gas transmission. In water utilities, they can remotely monitor well levels and control the wells’ pumps; monitor flows, tank levels, or pressure in storage tanks; monitor water quality characteristics, such as pH, turbidity, and chlorine residual; and control the addition of chemicals. Control system functions vary from simple to complex; they can be used to simply monitor processes—for example, the environmental conditions in a small office building—or manage most activities in a municipal water system or even a nuclear power plant.

In certain industries such as chemical and power generation, safety systems are typically implemented to mitigate a disastrous event if control and other systems fail. In addition, to guard against both physical attack and system failure, organizations may establish back-up control centers that include uninterruptible power supplies and backup generators.

There are two primary types of control systems. Distributed Control Systems (DCS) typically are used within a single processing or generating plant or over a small geographic area. Supervisory Control and Data Acquisition (SCADA) systems typically are used for large, geographically dispersed distribution operations. A utility company may use a DCS to generate power and a SCADA system to distribute it.

A control system typically consists of a “master” or central supervisory control and monitoring station consisting of one or more human-machine interfaces where an operator can view status information about the remote sites and issue commands directly to the system. Typically, this station is located at a main site along with application servers and an engineering workstation that is used to configure and troubleshoot the other control system components. The supervisory control and monitoring station is typically connected to local controller stations through a hard-wired network or to remote controller stations through a communications network—which could be the Internet, a public switched telephone network, or a cable or wireless (e.g. radio, microwave, or Wi-Fi) network. Each controller station has a Remote Terminal Unit (RTU), a Programmable Logic Controller (PLC), DCS controller, or other controller that communicates with the supervisory control and monitoring station. The controller stations also include sensors and control equipment that connect directly with the working components of the infrastructure—for example, pipelines, water towers, and power lines. The sensor takes readings from the infrastructure equipment—such as water or pressure levels, electrical voltage or current—and sends a message to the controller. The controller may be programmed to determine a course of action and send a message to the control equipment instructing it what to do—for example, to turn off a valve or dispense a chemical. If the controller is not programmed to determine a course of action, the controller communicates with the supervisory control and monitoring station before sending a command back to the control equipment. The control system also can be programmed to issue alarms back to the operator when certain conditions are detected. Handheld devices, such as personal digital assistants, can be used to locally monitor controller stations. Experts report that technologies in controller stations are becoming more intelligent and automated and communicate with the supervisory central monitoring and control station less frequently, requiring less human intervention.

Checklists for Industrial Wireless Systems Deployments

The document "Guide to Industrial Wireless Checklists", developed by the National Institute for Standards and Technology, is intended to be a practical guide used by engineers and managers facilitating them to go through the process of defining the objectives of their wireless systems and examining the environments where the wireless systems are to be deployed, then helping them in selecting, designing, deploying, and monitoring the wireless systems using existing technology in a factory.

Checklists from the above referenced document have been culled and available here for download.

Network Backbone Basics: Hubs, Bridges, Switches, and Gateways

As the process industry steadily moves to wireless networking components, its important to understand the basics. This post and the video below describe four key backbone components for data networking.

Signal flow and data transfer are assisted within a network by various devices known as backbones. The four different backbone devices are hubs, bridges, switches, and gateways. Each device transports data in a specific way.

A hub is a centralized connecting device. Often located at a center of a star network that automatically rebroadcasts any signal or data that it receives from one device to all other devices on the network. Because all the devices connected to a hub are competing for media usage, it's possible for collisions to occur when two devices send transmissions simultaneously. For this reason, it's important to avoid using a hub for messaging that requires immediate response.

Another network backbone device is called a bridge. Network bridges are smart devices that process and record information about signal traffic between devices in the networks. The bridge then uses this information to determine the most efficient path for data transfer, between a transmitting and a receiving device, without having to send it to every device in the network.

A switch is a multi-port network bridge that uses packet switching to forward data to one or multiple specific devices. Because more than one transmission can occur at a time, switch operating speeds are very fast. Switches are also full duplex devices that allow data signals to flow simultaneously in both directions. This eliminates the risk of data collisions that may occur in other network backbone devices.

When two segments of the same network have different communication formats a gateway is needed to connect them. A gateway performs a conversion function so that a computer on an Ethernet network using a TCP/IP protocol may communicate with a PLC on a subnet using the ControlNet protocol. Even though these two protocols are incompatible, the gateway can connect them on the same network and allow them to function together. Hubs, bridges, switches, and gateways - the backbones of networking - perform individual and important functions in keeping networks performing at their highest level.

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Wireless Instrumentation for the Process Control Industry

Analynk wireless instruments have been successfully implemented in process control applications including temperature measurements, 4 to 20mA bridges, discrete inputs/outputs, pulse inputs, lighting and pump controls. Contact Analynk Wireless today to discuss your plant's wireless requirements.

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Wireless for Safety

Wireless systems may be useful to enhancing the safety profile within a factory operation. These systems can be used to prevent injury through improved communication and enhanced situational awareness within the factory. Wireless safety systems are used in many applications including those designed to prevent chemical handling mishaps, avoid heavy equipment accidents such as “struck-by, and back-over” incidents, prevent falls through active position monitoring and safety interconnects, provide situational awareness within confined spaces, and improve safety for non-employees.

Along with adaption of wireless sensor networks for industrial automation, there are more applications of wireless technology created by users after they are more familiar and comfortable with the wireless technology. Also because of the strong benefits of wireless applications that can save project execution time and cost, more and more wireless has been used for secondary or backup systems for time-critical application such as safety or control applications. Based on this movement, ISA-84 working group (WG) 8 developed a technical report on wireless for safety systems other than those of a safety integrated system (SIS), i.e., those systems with a system integrity level (SIL) rating below ten. The technical report describes the additional elements needed to be addressed when wireless technology is used in an Independent Protection Layer (IPL). Refer to the ISA technical report TR84.00.08-2017 Guidance for Application of Wireless Sensor Technology to Non-SIS Independent Protection Layers for more information.

Reprinted from "Guide to Industrial Wireless Systems Deployments" by the National Institute of Standards and Technology. Get your copy here.

Business Case for Industrial Wireless

One of the key enablers of factory automation is the availability of wireless radio frequency devices. Some applications of radio frequency devices include process control, oil and gas refineries, pharmaceuticals, food and beverage, autonomous guided vehicles (AGVs) control, slotted microwave guides, pendants to control cranes and machine tools, active and passive radio frequency identifier (RFID) for tracking parts, tools and consumables, wireless barcode readers, remote sensing of critical process parameters, mobile telephony, door openers, emergency communication, and general factory Wi-Fi for internet connectivity. In addition, devices not directly associated with the manufacturing process such as microwave ovens and mobile telephone hot spots must be included when designing a factory wireless system. As useful as wireless communications is, it must be recognized that spectrum is limited and there must be judicious choices about when it should be used, and when wired connections are preferable.

In general terms, wireless (as with any upgrade to a factory or enterprise system) should satisfy a requirement related to quality, reliability, efficiency, safety, regulation, or environment as shown in Table 4. The requirements pertain to the business enterprise which in the case of a manufacturing operation means the plant or factory. A wireless deployment should be designed to satisfy one of the key business concerns listed.

Table 4. Purposes for initiating a wireless systems deployment

• Functionality - Is wireless required to achieve an aspect of function within the factory operation? For example, does the factory require a mobility to achieve a goal?
• Reliability - Is reliability of the production line improved? The ability to manufacture products, parts or assemblies which conform to the engineering definition, and can demonstrate conformity.
• Safety - Are people or equipment made safer? The ability of employees to perform their jobs free from recognized hazards including falls, hazardous energy, confined space, ergonomics, and hazardous materials, and being able to demonstrate compliance with all safety regulations.
• Efficiency - The ability to meet target costs and continue forever to reduce unit production costs.
• Quality - The ability to manufacture parts and assemblies which conform to the engineering definition, and be able to demonstrate conformity.
• Environment - The ability to demonstrate compliance with applicable government regulations at the city, county, state, and federal level.

Reprinted from "Guide to Industrial Wireless Systems Deployments" by the National Institute of Standards and Technology. Get your copy here.