ZigBee testing – the Default Response issue

Posted on 02/13/2012 by

As a ZigBee recognised test house we do a lot of certification testing of ZigBee products. One problem that we see repeatedly within the devices we test is the incorrect processing of the Default Response bit within the ZCL frame control header of an incoming frame.

The behaviour of a device which receives such a frame is defined in the ZigBee Cluster Library (075123r03) in section 2.4.12.2. This states that,

The default response command is generated when a device receives a unicast command, there is no other relevant response specified for the command, and either an error results or the Disable default response bit of its Frame control field is set to 0

What this basically means, is that when this bit is set to 0, then the receiving device must send back a Default Response frame if no other relevant response frame exists.

By way of example, consider a Read Attribute/Read Attribute Response frame exchange…

If the Read Attribute frame has the Disable Default Response bit set to 0, then this is ignored by the receiving side, as a relevant response frame already exists (ie. the Read Attribute Response)

However if the Read Attribute Response frame has the Disable Default Response bit set to 0, then the receiving side must send back a Default Response frame (usually with its Status set to Success)

This whole functionality is considered key to successful frame exchange management and as such was incorporated in an official Mandatory Advisory Note which was circulated to the membership by the ZigBee Alliance in Jan 2010.

As any frame, for any cluster, of any profile could make use of this functionality, it is important to check a device’s design carefully to ensure compliance. The Tracer test harness (produced by TRaC) comprehensively tests this and can confirm compliance to this requirement prior to attending the recognised test house for a formal certification test run.

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How Radio impacts our lives

Posted on 10/26/2011 by

This post is by John Charters, Radio Product Manager, TRaC

It recently occurred to me how often we come across RF connected devices in our day to day life.  Consider a typical day:

  • You’re woken up by the baby monitor signalling it’s breakfast time!
  • You go downstairs to turn off the wireless burglar alarm.
  • You unlock the car using a wireless key fob.
  • You press a button to start the engine via a keyless RF system, only to be told the tyre pressure is low by the in-built monitoring system which uses RF to communicate this to the engine management system.
  • On the road, you come across temporary lights using dipolar radar to detect oncoming vehicles and RF control to change the lights.
  • You get into work with your access control fob and log onto the WiFi network.
  • Later, you leave the office and phone home from the car using Bluetooth handsfree.
  • Someone at home answers using DECT.
  • In the evening, you play games on your Wii using wireless remotes.
  • You also check your domestic energy consumption using your wireless energy monitor.

 

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Automotive v Electrotechnical – The Standards Battle Lines are being drawn up

Posted on 10/26/2011 by
This post is by Steve Hayes, EMC & Safety Managing Director, TRaC

You cannot have failed to notice that there is a lot of activity in the world of Electromobility. This is the term for all facets of electric vehicles and the associated chargers and infrastructure. The current work is moving forward at two levels – strategic policy and test standards.

For the standards communities (and hence manufacturers) the challenge will be to decide if an electric vehicle is actually more electrical than automotive. This is a major issue since the test methods, limits and hence product designs will be different dependant on the standards used.

Let’s face it though, the only real difference between a variable speed drive (VSD) system for an industrial plant and an electric vehicle is that the drive shaft doesn’t connect to a wheel but a lump of metal, in the case of the machine tool.
I accept that the car has a different power supply, but the majority of electrical noise will be generated by the VSD.
IEC write electrotechnical standards whilst ISO write automotive. The standards written by both of these groups are then used by other areas of industry and are used in contractual situations – supplying to any of the major car manufacturers will require testing to their own standard which is itself based on either IEC or ISO standards. Changing from one standard to another will see many objections since test chambers and equipment will need to change.
Equally having standards written around the protection of the FM receiver in a car from the spark noise is somewhat irrelevant when there are no spark plugs fitted!
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No more interference!

Posted on 09/20/2011 by
This post is by Steve Hayes, EMC & Safety Managing Director, TRaC

I stumbled upon a section of the OFCOM website the other day and noticed that OFCOM no longer accept interference complaints from individuals or consumers – this has now been passed exclusively to the BBC and is essentially a web-based process that is followed to identify and resolve interference issues.

It appears from the OFCOM web site that the only interference issues they deal with are from pirate radio stations. Surely domestic users and pirate radio stations aren’t the only sources of interference, otherwise we wouldn’t need legislation like the EMC Directive?

I wonder about the reasons for OFCOM’s decision? Is it because there are so few interference complaints that it doesn’t warrant further mention; that they have too few staff to deal with the issues; that it is hoped that interference issues are dealt with directly between the victims?  What do you think – should OFCOM accept interference complaints from individuals or consumers?
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Certifying the Certification Houses

Posted on 09/20/2011 by
This post is by Steve Hayes, EMC & Safety Managing Director, TRaC

Many of our customers are surprised when we tell them that TRaC is affected by certifications and standards, even though we don’t sell products. The EMC directive, however, addresses both apparatus and installations, and as our EMC testing chambers are installations, they need to meet EMC regulations!

We’re currently building a new test facility, and some of the measures we have taken include laying out the many cables running in the building to reduce emissions and ensuring that our wired and WiFi networks will operate in the presence of interference.

It’s not just electrical issues that we have to deal with. The new facility also includes a powerful shaker to test products for resistance to vibration and shock. Our analysis team has conducted finite element analysis (FEA) to ensure that the shaker will work reliably, and that the mountings are able to withstand the powerful forces generated.
Using TRaC’s services as a customer gives us a different perspective on what we do, although as a test and certification organisation, we can’t complain about the challenge of meeting the relevant statutory requirements!
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Meeting MET

Posted on 08/18/2011 by

This post is by Mark Heaven, CEO, TRaC

Recently I gave two presentations at our North American Partner, MET Laboratories, annual customer appreciation seminar in Baltimore.

The presentations, ‘Global Wireless Approval Regimes’ and ‘ATEX – v – Hazloc – v – IECEX for the potentially explosive atmosphere markets’, illustrated how to best address compliance for complex products in global markets.

Attendees at the seminar had access to speakers in the fields of EMC, Safety, Reliability and Energy Efficiency, reinforcing to me how much can be gained from attending a compliance seminar.  They are one of the best ways of connecting with experts who are up-to-date in the diverse fields associated with compliance.

In discussions with seminar delegates I was reminded just how well accepted the MET safety mark is in North America.  The MET status as a Nationally Recognised Testing Laboratory (NRTL) means the MET Mark is acceptable under Federal law for products used in workplaces throughout the United States.

Talking to a wide range of US manufacturers, many have been using the MET safety mark to access their internal market for years, and were quick to praise the expertise, responsiveness and cost benefits that MET brings to their business. A big advantage is that MET has adopted the latest OSHA policy change, which allows for some companies to qualify for two factory audits per year, instead of four.

The US imported over $900 billion worth of electrical and capital goods in 2010 and if you are an EU company targeting the North American market, it’s good to know that, if you choose the MET mark to comply with this mandatory safety requirement, you are in good company – US manufacturers use it too.  There are now a very large range of products in the U.S. and Canada labelled with the MET mark.

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How the CE mark affects product design

Posted on 08/18/2011 by

This post is by Steve Hayes, EMC & Safety Managing Director, TRaC

Looking at the sleek electronic product that you’ve just bought and wondering why design has improved so much?

Safety standards can impact many aspects of product design, and can even lead to improved aesthetics! Here are my top 5 examples of how the CE mark has affected product design:

  • Restrictions on touch temperature have driven toaster manufacturers to put attractive plastic cladding around the product
  • The requirement to stop fingers getting into electronic products drove the design of the ventilation grill on your Playstation3
  • Safety standards that prohibit sharp edges and corners mean that TV manufacturers need to adopt modern stylish case designs with rounded corners and edges.
  • Lawn mowers have been restricted to a minimum weight to stop consumers using them as hedge trimmers
  • The sound of mobile phones now gradually increases to avoid ‘acoustic shock’

Whilst these changes offer clear benefits, some changes have received a less enthusiastic welcome. For example video games addicts will have noticed the removal of handy drinks holders on the tops and sides of arcade machines: a sensible measure in case liquid is spilt and drips onto the internal mains voltage.

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