In the dim and distant days of the last century, EMC emerged relatively late on the evolutionary scale. Although engineers “of a certain persuasion” were laying the foundations as far back as the early 1960s, it was not until the European Union decided on a common identification mark (CE) to be a legal requirement in December 1994 that EMC became mainstream among test engineers. Test equipment manufacturers look back misty eyed on those times, remembering the phenomenal rise in demand as the date of implementation approached. Because the CE marking requirements were quite specific, being embodied in so called “generic” standards, it was relatively easy to define the operating parameters for a compact tester. Less easy was to shoehorn four previously autonomous test generators, ESD, EFT, Surge and Dips into a single enclosure with one common Coupling / Decoupling Network (CDN).
WHAT MAKES A COMPACT IMMUNITY TESTER?
From a purely technical standpoint, the compact immunity tester was a quantum leap in design. Basic engineering combined with creative thinking was required. An obvious starting point was rationalizing voltage requirements into a single PSU to provide power to all the circuit elements. Using a commercially available unit would keep costs down and allow the design to move forward quicker. Something that requires more thought and a lot of experience in EMC test equipment design is the single EUT power outlet. This is a masterstroke taken very much for granted. The concept is brilliant, place a mains connector on the instrument front panel and switch automatically between test modes. An EUT can be connected to the test equipment using it’s own power lead (which incidentally should be a test requirement anyway). Simple! The hardware to achieve this is anything but simple. It requires a CDN with characteristics for both SURGE and EFT requirements combined with the ability to source 500A inrush current for the DIP test. Real estate is at a premium so to achieve all this common circuits need to be placed on a few PCBs. This all leads to a physical reduction in the instrument size. This creates a new problem, because there is now limited space on the instrument front panel for all the knobs, dials and switches. The obvious answer was to develop a controller and system software with intuitive user interface. This formula has worked well, in varying degrees, since the birth of compact designs until the present day.
WHY CHANGE A WINNING FORMULA?
Sixteen years is a long time on the electronic evolutionary scale. A lot has happened in the intervening years, some of it even good. Just like in the halcyon days of CE testing, standards are central to and continue driving the EMC business. Whether the design and production is in Europe, America or Asia, customers are international and they, mostly, demand compliance. Also people think in a different way. It is an interesting observation how much society has changed with regard to the environment. Laws have been enacted and suddenly we are separating our garbage! There is a logical extension of the environmentally friendly society into the design of electronics. We have become obsessed with how many Mega Watts we consume in the standby LEDs on our multi-media systems and do you know how much energy is required to send an e-mail or surf the web? Changes in public opinion can be a strong motivation to take a long hard look at how we do things. Another aspect is the education of users. The honeymoon period is long over and, increasingly, users are becoming aware of the shortcomings in current compact tester designs. What, in the beginning, was the main advantage is proving to be an Achilles heel of compact designs. Modern electronics are inherently reliable, but if one of the circuits does expire, that usually means the tester is out of operation until a repair can be affected. Clearly, having all the voltage supplies in a single unit is a tremendous space saving, but again, failure renders the whole tester unusable. The revolution in electronics over the last 16 years has provided solutions. It is now possible, without a corresponding expansion of volume to overcome these issues. In fact, it is possible to make a truly modular design which fulfils the promise of user expansion without the need for an excursion to the manufacturer.
LOOKING FORWARD, THE GREEN REVOLUTION
Everybody nowadays takes environmental issues very seriously. Implementation of the RoHS directive in 2006 has already given us lead free soldering and banned the use of certain materials such as Mercury and Cadmium. While the WEEE directive tells us how to dispose of unwanted materials in a safe and environmentally friendly way. The next hurdle is to reduce power consumption so the scarce resources we have will last, at least until alternative energy sources are sufficiently robust. The ever increasing use of intelligent power in test equipment is the best way to achieve this aim. Fully modular circuits help to meet this objective by allowing power management systems to only activate circuits when they are needed. This has the effect of dramatically reducing overall power consumption. Power management systems also include the effective use of ventilation, which can be controlled through temperature sensors embedded at strategic points. Not least this concept greatly reduces noise pollution levels.
LOOKING BACKWARDS, MODULAR ARCHITECTURE
Imagine a world where it is possible to choose where and when to expand your test equipment. As your business develops, so further elements can be added to increase capability. If one circuit needs to be calibrated, it can be taken out on site and with minimal fuss, forwarded to the cal lab as a light weight low cost package, saving money and valuable fuel resources. A modern compact generator with truly modular design is the realization of this dream. By placing intelligence in every module users are, for the first time, given the ability to configure a test system to include any combination of ESD, EFT, SURGE, DIPS, Voltage VARIATIONS or COMMON MODE tests. This unprecedented flexibility opens whole new horizons for test laboratories that can optimize equipment to meet current demand but add new capability as and when the need arises. A side effect of the distributed intelligence concept is that integration with other test equipment can further expand test capability.
WHICH WAY TO GO?
The relentless progress of time has finally sounded the death knell for tried and trusted communications interfaces. RS232 and GPIB are children of a different age. Remote control of a tester with RS232 interface is only possible using a USB convertor as modern PCs no longer support this protocol. GPIB was the fastest communication protocol of it’s time and is still widely used. However, it requires expensive additional hardware and software. Modern test equipment takes full advantage of the Ethernet LAN port and web browser which is fast and provided as standard with every new computer. Modern test systems utilizing this combination offer users a low cost remote control solution. On the surface, USB may appear to be the most suitable interface type. However it has one major drawback, a susceptibility to EMC interference. In a generator designed to produce these disturbance sources, this is a major problem. USB still has its place as a handy interface to transfer data between machines using the ubiquitous “stick.”
POWER THROUGH PROGRESS
New designs using latest technology allow a step further on the path of compact test equipment design. If approached intelligently, further expansion of test capability can add to the attractiveness of a combined tester. One such example is the IEC61000-4-16 common mode test requirement. This requirement comes from the same stable as the other more common test types. It is therefore logical to include it in any new compact design. It fits perfectly with the modular concept and greatly expands capability to include tests at DC, AC and in the frequency range up to 150kHz. Not everybody will need to perform this test type, so just like all the other modules, users could add it only if required. Another example of the modular concept working to the advantage of test engineers.
THE INFLUENCE OF TEST STANDARDS
Having mentioned that standards are driving our industry forward, what changes have taken place and what’s in the pipeline? In general, IEC standards are becoming tighter in relation to acceptability of impulse tolerances. The first move has been for the IEC61000-4-2 (ESD) to be released with a clearer definition and for the first time in an IEC publication, the implementation of measurement uncertainty. Test equipment with parameters on the extremes of the tolerance band, will fall outside when uncertainty is taken into account. A general “tightening-up” is taking place as this process will be implemented throughout the IEC, and eventually CENELEC, to cover all basic standards. It is important to understand that every measurement made includes an uncertainty due to random effects that are beyond our control and systematic components such as measurement probe cable and oscilloscope tolerances. These can be accounted for by calculating a standard uncertainty value (k). The figure illustrates how a perception of pass or fail enters a grey area once uncertainty has to be considered. Measurement A, is clearly within the amplitude tolerance even allowing for uncertainty. Measurement D is clearly outside the amplitude tolerance and is not acceptable. Examples B and C are the grey area where the probability of a measurement being within tolerance limits is reliant upon the uncertainty of the measurement equipment. To be sure parameters remain within tolerance limits, basic generator waveform parameters need to be fairly close to the nominal values.
SUMMARY
When introduced to the market in the early 1990s, the Compact tester was a revolution. Aimed at satisfying a particular market niche, for CE compliance testing to the new European EMC directive. The Compact tester represented a huge leap forward in EMC test equipment technology and offered significant price saving compared to the “stand-alone” equipment that was previously in use. However, the realities of squeezing so much circuitry into such a small volume lead to compromises in design and serviceability. From this initial experience, everybody has got older and wiser. The standards too have matured and place new requirements on both test equipment and processes. The customer expectation is not least a factor in the evolution of compact test equipment. Equipment availability and automation are essential to meet twenty first century demands.
Nicholas Wright is international sales manager at EMC Partner AG.
