Wireless Industrial Controls
Increasingly, industry is adopting wireless protocols for monitoring and control of complex systems. These systems provide high reliability, low installation costs and rapid return on investment. Network protocols such as Zigbee and 802.15.4 provide ready-made solutions that can be quickly and effectively deployed to meet many applications.
FCE product developments include:
Asset tracking with wireless sensor networks
Meter reading for utilities
Electrical power usage tracking
>What is Zigbee?
The Zigbee Alliance and the research 802.15.4 Working Group have defined an international standard for a simple but powerful packet data protocol providing high reliability through message acknowledgement, error checking, prioritized communications, direct sequence spread
spectrum, the ability to change frequencies to avoid interference and user-selectable security levels.
Zigbee is optimized for applications that require low throughput, long battery life, low cost and thousands of nodes in a network.
Low data rate telemetry applications
Key features include:
Data rates of 10 kbps to 115 kbps
CSMA-CA channel access
Fully handshaked protocol for transfer reliability
Dual PHY (2.4GHz and 868/915 MHz)
Extremely low duty-cycle (<0.1%)
Range: 10m nominal (1-100m based on settings)
Low current requirements – 30 ma. transmit, .02 microamps in
sleep mode. By operating at a low duty cycle, battery life can
be extended to months or even years.
In all of its uses, ZigBee offers four inherent, beneficial characteristics:
The typical ZigBee radio is cost-effective. Chipset prices can be as low as $12 each in quantities as few as 100 pieces. While the 802.15.4 and ZigBee stacks are typically included in this cost, crystals and other discrete components are not; design-in modules fall in the neighborhood of $25 in similar quantities. This pricing provides an economic justification for extending wireless networking to even the simplest of devices.
Range and obstruction issues avoidance
ZigBee routers double as input devices and repeaters to create a form of mesh network. If two network points are unable to communicate as intended, transmission is dynamically routed from the blocked node to a router with a clear path to the data’s destination. This happens automatically, so that communications continue even when a link fails unexpectedly. The use of low-cost routers can also extend the network’s effective reach. When the distance between the base station and a remote node exceeds the devices’ range, an intermediate node or nodes can relay transmission, eliminating the need for separate repeaters (Figure 2).
As an open standard, ZigBee provides customers with the ability to choose vendors as needed. ZigBee Alliance working groups define interoperability profiles to which ZigBee-certified devices must adhere. A ZigBee-certified radio will interoperate with any other ZigBee-certified radio adhering to the same profile. This promotes compatibility and competition, which allows the end users to choose the best device for each particular network node, regardless of manufacturer.
Low power consumption
Basic ZigBee radios operate at 1 mW RF power and can sleep when not involved in transmission (higher RF-power ZigBee radios for applications needing greater range also provide the sleep function). Because this makes battery-powered radios more practical than ever, wireless devices are free to be placed without power cable runs in addition to eliminating data cable runs.
For purposes of this discussion, three areas of architectural responsibility are in a ZigBee engineering effort (Figure 3).
The physical and MAC layers take full advantage of the physical radio specified by research 802.15.4. The 802.15.4 specification describes a peer-to-peer radio using direct-sequence, spread spectrum (DSSS). The specification also calls out the data rates, channelization and modulation techniques to be employed.
The ZigBee Alliance specifies the logical network, security and application software, which are implemented in a firmware stack. It is the ZigBee networking stack that creates the mesh networking capability. Each microcontroller/RF chip combination requires its own ZigBee stack due to the differences in microcontrollers and RF chips. Typically, the ZigBee stack is included with either the microcontroller or RF chip. The stack may belong to the chip vendor, be provided by the chip vendor from a third-party source, or be provided by a third-party source for a specific microcontroller/RF chip combination.
The application layer is defined by profiles, of which there are two types: public profiles are those certified by the ZigBee Alliance for interoperability purposes, and private profiles are for use in closed systems.
A word about the ZigBee Alliance: The following discussion includes options that require access to intellectual property available only to members of the ZigBee Alliance. There are three types of membership; all companies that plan to release products incorporating ZigBee technology must become at least adopting members, an entry-level membership that provides such benefits as access to specifications and developer conferences/workshops. For information, visit www.zigbee.org.
Application note from Crossbow Technology
A CommsDesign Design Corner article
Article from EETimes
ZigBeenets – article
EiED Online ZigBee Kit by William Wong.
Home networking with ZigBee – article by Mikhail Galeev.
ZigBee Alliance Shows off Latest Devices – article by Marc Perton.
ZigBee news and information from ExtremeTech.
SmartMesh wireless solution from Dust Networks.
overview of designing a ZigBee Wireless Net DesignLine,
By Craig DiLouie, Lighting Controls Association
ZigBee and research 802.15.4 Resource Center.
Offers standard RF modules for operation in the license-free ISM bands at 315 / 433 / 429 / 868 / 915 / 2450 MHz, including ZigBee, provides compact modules that are easy to integrate and easy to use, for shortest possible time-to-market, for applications such as building and industrial automation, telemetry, automated meter reading, home automation, wireless sensor networks, asset tracking.
An overview of of the ZigBee standard for remote sensor, data collecting applications and its relationship to research 802.15.4.
Abstract from Ember Corp.
Designing a ZigBee-ready research 802.15.4-compliant radio transceiver, article by Khanh Tuan Le.
ZigBee starts its rise to power – article by Peter Judge.
Finding Uses For ZigBee – by Michael Sciannamea.
Connectivity in Telemetry”
White paper from Arcom Solutions.
ZigBee homes in on short range wireless by Tom Sanders.
ZigBee (Almost) Arrives – article by Eric Griffith.
Project involving the creation of a remote building monitoring solution.
ZigBee clears ratification hurdle – article by Graeme Wearden.
The ZigBee Alliance is an association of companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard.
A course which discusses the ZigBee Alliance and its goals, target markets and applications, from Freescale Semiconductor.
Project involving porting the ZigBee stack from Luxoft Labs into the Jennic MCU.
ZigBee is one implementation of the logical layer needed to implement the standard research 802.15.4 ractified in May 2003. The standard intends to be a simple packet data protocol, with a low power requirement and narrow bandwidth requirements. Its maximum speed is 250kbps, compared to Bluetooth at 720kbps and wi-fi from 11mbps (although we all know real life applications will have different performance).
The new standard provides Quality of Service through packet acknowledgement, and it is focused in data collection (sensors) and control. This includes assembly lines and remote data collectors. The RFID (Radio Frequency Identification) is the most direct competition for ZigBee.
Because of its limited bandwidth it’s not intended to be a wire replacement like Bluetooth, or a wireless network adapter like wi-fi.
The ZigBee technology is well suited to a wide range of applications in every industry. Essentially, any application that could benefit from interoperability, or that matches the fundamental RF characteristics of the research 802.15.4 standard would benefit from a ZigBee solution. Examples include:
Wireless home security
Remote thermostats for air conditioner
Remote lighting, drape controller
Call button for elderly and disabled
Universal remote controller to TV and radio
Wireless keyboard, mouse and game pads
Wireless smoke, CO detectors
Industrial and building automation and control (lighting, etc.)
According to the official ZigBee website the logical size of a ZigBee network depends on which frequency is selected, how often each device on the network needs to communicate, and how much data loss or retransmissions can be tolerated by the application. ZigBee’s addressing scheme supports 255 active nodes per ‘network coordinator’, and multiple network coordinators can be linked together to support extremely large networks. With support for 16 channels in the 2.4GHz band, and 255 nodes per network coordinator, ZigBee networks can contain over 4,000 unique nodes in a single network with high system reliability.
The site also lists a comparisson between ZigBee and Bluetooth. The main differences are:
The ZigBee stack is small (28Kbytes) compared to the Bluetooth stack (250K). This relates to lower cost and lower power consumption.
Ultra-low power consumption is a key system design aspect of the ZigBee technology to allow long lifetime non-rechargeable battery powered devices versus rechargeable devices for Bluetooth. As an example the transition from sleep mode to data transition is much faster in ZigBee than for Bluetooth.
ZigBee networking capabilities include 255 devices per network, compared to 8 for Bluetooth networks.
The data rate for ZigBee technology is 250kbps (peak information rate 128kbps) compared to 720kbps for Bluetooth wireless technology.
Range for ZigBee products is expected to be ~30 meters in a typical home, compared to ~10 meters for Bluetooth products (without power amplifier).
The ZigBee standard
While numerous wireless standards exist for
high-speed data applications, none of these address the unique needs
of remote monitoring and control for sensory network applications
in the way that ZigBee does. The ZigBee standard is built on the
research 802.15.4 global standard. The ZigBee stack, which sits on top
of research 802.15.4, adds an application services layer, security layer
and the mesh network layer to create the ZigBee standard. The combination
delivers low complexity, inherent reliability, long battery life
and the ability for networks to form autonomously and maintain themselves
without operator intervention.
How ZigBee works
While ZigBee supports a variety of network
topologies, including star, mesh and cluster networks, its mesh
network design is a fundamental and differentiating attribute. Enhancing
the overall network reliability, mesh networking topology increases
the number of pathways information can travel. If a device encounters
a closed path, it automatically seeks out another path to execute
the action. ZigBee devices will always know who they need to speak
to, what they need to tell one another, no matter how many devices
you have in your home.
ZigBee’s addressing scheme is capable of
supporting over 64,000 nodes per ‘network coordinator’, and multiple
network coordinators can be linked together to support extremely
large networks. The logical size of a ZigBee network ultimately
depends on which frequency band is selected, how often each device
on the network needs to communicate and how much data loss or retransmissions
can be tolerated by the application. Additionally, ZigBee’s capabilities
allow for very low average power consumption because the duty cycle
of battery-powered nodes within a ZigBee network are designed to
be very low.
The ZigBee Alliance
The technology is being driven by the ZigBee
Alliance, an association of companies working together to enable
wirelessly networked monitoring and control products based on an
open global standard. It includes a rapidly growing list of over
175 industry leaders from around the world including semiconductor
manufacturers, wireless IP providers, OEMs and end users. The collaborative
nature of the ZigBee Alliance has helped to foster its success.
Recently, the Alliance made the specification publicly available
to universities, research institutions and software developers to
review the technical details of the specification in its entirety.
This has helped individuals and organisations gain a greater understanding
of the value of ZigBee to their wireless networking efforts. The
opportunity to access and view the ZigBee specification directly
from the Web transcends geographic hurdles in educating people on
the benefits of ZigBee-based wireless networks.
By creating a standards-based wireless networking
solution, the ZigBee Alliance ensures that product solutions are
vendor independent. Companies will be able to easily and cost-effectively
include ZigBee-compliant wireless networking capabilities into their
products through the introduction of small, low-power, wireless
RF modules. The availability of standards-based hardware and software
solutions dramatically reduces the cost and complexity of integrating
embedded RF into the typical product design. Vendors will provide
software toolkits, including profile templates, to enable OEMs and
end users to efficiently create application layer solutions at low
cost, and reduce time to market.