Why Are Uncertainty Budgets Necessary?

Fanning, EMC Lab Manger

Today, Elite's EMC Lab Manager Craig Fanning gives us a few reasons why uncertainty budgets are worth the work to ensure proper CISPR 16 compliance.  Find out the other benefits he lists in this week's blog.

Uncertainty budgets…why??? I hear a lot of people in the EMC industry complain that uncertainty budgets are painful and not necessarily worth the time expended. That is a little bit understandable since we go through all the work to generate uncertainty budgets but don’t generally use them during everyday measurements. However, uncertainty budgets are necessary and can be pretty good tools for the laboratory.

CISPR 16 Compliant Measurements - Uncertainty budgets must be done for CISPR 16 compliant measurements. If the uncertainty budget of the laboratory meets the U_cispr values shown in Table 1 of CISPR 16-4-2, then no correction of the data is needed to determine EUT compliance. If the uncertainty budget of the laboratory does not meet the U_CISPR values shown in Table 1 of CISPR 16-4-2, then the measurement must be adjusted by the difference (U_lab - U_cispr) to determine if an EUT complies with the standard.

EMC Lab Personnel Training - Uncertainty budgets make the laboratory realize how good (or not so good) their measurements really are. We all need to have a good understanding of how the various parts of the test system contribute to uncertainty. We also need to know how measurement uncertainty can be reduced by purchasing higher quality (lower uncertainty) equipment. If the lab management and personnel understand the contributing factors, then the lab can do a better job at reducing measurement uncertainty (providing a better service to their customers).

Customer Education and/or Lab Differentiation - Many years ago a customer told me that he wanted a 200V/m radiated immunity test “no more no less” says the customer. The young electrical engineer did not realize that a radiated immunity test is not accurate to within 0.1 V/m (although the measurement instrument tells us so). Customers also wonder why a radiated emissions measurement made in one chamber is slightly different (a couple of dB) from a measurement made in another chamber. The people who make EMC measurements everyday (and understand measurement uncertainty) know that this is pretty good chamber-to-chamber or lab-to-lab repeatability. When you can show a customer how the accuracy of all parts of the system contribute to measurement uncertainty and that your uncertainty is better than the “standard” (or another lab), then that helps to educate the customer and differentiate your laboratory from the competition.

So the next time you have to work on uncertainty budgets, don’t think about how painful they are. Think about how they can be beneficial to your lab, personnel, and business. This will make the time (and money) expended more palatable.

Do you have any questions about EMC Lab Management, EMC Standard Changes, or other related topics? Please share your comments or questions below and this week's expert, Craig Fanning, will get back to you as soon as possible. 

Why SAE EMC Standards Are Being Withdrawn

Craig Fanning, EMC Lab Manager

Today's Elite Expert is Craig Fanning. Our EMC Lab Manager since 1995, Craig has overseen scores of test projects over the past 27 years with the company. He is also an iNARTE Certified EMC Laboratory Engineer and author of several papers for the IEEE EMC Symposium.  Finally, as a member of SAE EMI and EMR Committees, as well as a US National Committee technical advisor for CISPR-D, he undoubtedly likes to stay active in the EMC community. Read below to see what he has for us this week.

Users of SAE EMC standards may have noticed that many of the SAE J551 and SAE J1113 standards have been withdrawn over the past few years. These withdrawn standards are no longer being revised and updated. As these standards are withdrawn, the base standard of the series (SAE J551-1 or SAE J1113-1) is updated to indicate that the particular SAE standard has been withdrawn. The base SAE standard also directs the user to reference the equivalent CISPR or ISO standard. Unfortunately this results in having to purchase the more expensive international standard which replaced the SAE standard.

So, why are the SAE EMC standards being withdrawn???  A few years ago, SAE noticed that some of the SAE EMC standards were, for the most part, technically identical to some equivalent CISPR and ISO (international) standards.  This became a concern of SAE as they do not want to get into copyright conflicts with the international standards bodies. Therefore, the SAE EMC committee was given the directive to start withdrawing any SAE standards which were technically identical to an international standard.
 

How did this similarity of SAE and International standards come to happen??? The SAE EMC committee has developed many vehicle and component EMC standards over the years. The SAE standards were referenced mainly by the North American vehicle manufacturers in their corporate EMC standards. As the NA vehicle manufacturers evolved to Worldwide vehicle manufacturers, the trend to reference SAE standards in their corporate standard changed to the desire to reference international standards (if they existed) in their corporate standards.

Many of the same experts involved in the SAE EMC committee in the United States are also involved with at the International Standards development level (CISPR and ISO standards). During meetings at the international level, the need to develop a standard to address a particular field issue may be discussed. If an SAE standard which addressed the issue already existed, then the international standards committee would use the SAE standard as the basis for development of a new CISPR or ISO standard. Although the process to publish the international standard would take several years, the two standards (SAE and International) would eventually become very similar.

What is the long term benefit of using international standards over the SAE standards??? Although it may seem like a burden to purchase a more expensive CISPR or ISO standard, the use of the international standards does have its benefits. The test methods used to evaluate the EMC performance of vehicles (and vehicle modules) should be similar around the world to assure consistent performance. Products initially developed for sale in the North American market may also be more easily marketed worldwide when tested against the international standards.  

Ultimately, standardization helps to assure consistent performance and reliability no matter where the product is being used. By using international standards to evaluate the EMC performance of products (when available), this will help the product manufacturers to better achieve the consistent performance and reliability desired by the consumer. 

Do you have any questions about EMC Standard Changes, EMC Testing, or other related topics? Please share your comments or questions below and this week's expert, Craig Fanning, will get back to you as soon as possible.  

CISPR 12 vs. CISPR 25 - Deciphering Standard Applications

Today's Elite Expert is Craig Fanning, our EMC Lab Manager and US National Committee Technical Advisor for CISPR-D. Read below to see what he has for us this week. 

Knowing which standard to use is very important when selecting a test method for evaluating a product. When selecting a specification, the user needs to take into consideration the purpose of the standard. A good example is CISPR 12 and CISPR 25. Both CISPR 12 and CISPR 25 include radiated emissions measurements for vehicles. However, there are a few fundamental differences that the user should take into consideration when determining which standard to use for vehicle emissions measurements.

The radiated emissions measurements of CISPR 12 are performed for the protection of off-board receivers. As an example, this test is done to assure that receivers are not affected when the vehicle drives them. This is very important when the vehicle drives past houses in a city (which are typically closer to the roadway). The radiated emissions measurements of CISPR 25 Clause 5 are performed for the protection of on-board receivers. This test measures the RF interference that is generated by the vehicle and then picked up by vehicle mounted antennas (such as the AM/FM radio or GPS antenna). This is a “RF Terminal” noise voltage measurement that is made at the point where the antenna would connect to the vehicle mounted receiver (such as the AM/FM Radio or Navigation System).

Another thing to consider is regulatory vs. engineering testing. CISPR 12 is used as a regulatory standard by many countries. CISPR 25 is an engineering standard that is used mainly by vehicle manufacturers and not for regulatory purposes. As a quick recap, the next time you are trying to figure out which test to perform when radiated emissions from a vehicle is the concern, ask yourself a couple of questions:

• Question #1 - What are we trying to protect (off-board or on-board receivers)? 
• Question #2 - Are we doing this for regulatory or engineering purposes?

Once those questions are answered, you will know if CISPR 12 or CISPR 25 (or both) are applicable.

Do you have any questions about CISPR Test Applications, EMC Standards, or other related topics? Please share your comments or questions below and our expert, Craig Fanning, will get back to you ASAP. 

Craig recently guest-presented a webinar, "EMC for Vehicles: Truly Mobile Electronics", with Washington Labs on Thursday, August 15, 2013.  Please follow the link if you would be interested in learning more about other learning opportunities. 

Evaluating & Designing Around Specification Requirements

This week's Elite Expert is Craig Fanning. Elite's EMC Lab Manager since 1995 and one of our Sr. EMC Engineers, Craig has overseen scores of test projects over the past 27 years with the company. He is also an iNARTE Certified EMC Laboratory Engineer and author of several papers for the IEEE EMC Symposium.  Finally, as a member of SAE EMI and EMR Committees, as well as a US National Committee technical advisor for CISPR-D, our EMC Lab Manager undoubtedly likes to stay active in the EMC community. Read below to see what he has for us today.

Nothing is worse than going to the EMC lab and failing an emission test. This is especially true when you figure out that an operating frequency of the Device Under Test (DUT), that you designed, is causing excessive emissions within a frequency band which has a low limit. We see this time and time again in the test laboratory.

The best way to prevent this from happening is to evaluate the specification requirements before you start picking out clock frequencies and communication rates. If you look at the specification limits before you design, or during the design phase, you can determine frequencies that you should stay away from. Don’t select operating frequencies that fall into frequency bands with low emissions limits. Also look at the harmonic frequencies (especially the odd harmonics of the operating frequency) to see if a harmonic will fall into a frequency band with low limits. If possible, pick operating frequencies that fall into frequency bands with higher emissions limits.

Many times communications rates can be adjusted through firmware. This is something that can be in your “bag of tricks” when designing the product and/or troubleshooting a failure. When it comes to designing for good EMC performance…review and design to the specification. If you do, this will save a lot of future headaches and re-design costs.

Do you have any questions about CISPR Emissions Testing, Design, or other related topics? Share your comments or questions below and our expert, Craig Fanning, will get back to you. 

Craig is also guest-presenting a webinar, "EMC for Vehicles: Truly Mobile Electronics", with Washington Labs on Thursday, August 15, 2013.  Please follow the link if you would be interested in learning more.