Category Archives: General

EMC Troubleshooting Parts Storage

For those of you who regularly troubleshoot EMC issues, wouldn’t it be convenient to have all your “fix-it” parts all in one place? That’s what I thought as I was wandering around JoAnns (a fabric and hobby store) with my wife. I spotted this “photo keeper” storage box and thought it would be perfect to store all the little parts, gasketing, filters, etc., for quickly implementing fixes during the troubleshooting process.

IMG_1431

 

I had a chance to use this kit in a real-life consulting application as I helped a client in Chicago recently. I transported the kit inside a large Pelican case and used a quantity of bubble-wrap to protect it from shifting around. It survived just fine and added a sense of professionalism in the client’s eyes.

Hobby stores sell many similar storage boxes and you may find several to your liking. Read on for more details…

 

Question on Current Probe Calibrations

I recently received the following question on how to calibrate current probes and thought you’d be interested.

Question: Good morning.  I read your article, “HF Current Probe:  Theory and Application”, but now I have a question I’m hoping you can help me answer.  I am attempting to measure the transfer impedance of a current monitor probe using a probe calibration fixture or jig.  To keep the setup simple, I am using a signal generator and a power meter.  As in your example, I am setting the generator to source 0dBm and I will verify it with the power meter and sensor through an adapter; I will then connect the generator’s output and current probe to the calibration fixture and measure the probe’s output using the same meter and sensor.  This all works fine until the input SWR of the calibration jig reaches about 1.3 at 100MHz.  From that point up to 400MHz, the SWR of the jig reaches 3.4.  It appears that one would be measuring both the current probe’s insertion loss and the calibration jig’s mismatch loss.  Would it then be best to establish the reference by measuring the output of the signal generator while it is connected to the calibration fixture (without the probe inserted), so as to include the jig’s mismatch loss in both the reference and measurement sweeps?

Answer: You’re on the right track. You need to normalize out the effect of any mismatch from the jig setup. There are several methods for calibrating current probes. If you have the jig, that’s great. Basically, what you’re trying to do is measure the current accurately versus frequency – a not so trivial task to keep the current fixed as frequency changes. The problem is that any parasitics (R, C, L) in the wire to be measured can greatly influence the current value. That was the problem I was running into when measuring the wire in the referenced article. I tried to keep the value of current fixed by inserting a small resistor in series and measuring the voltage drop, keeping the this voltage drop steady by adjusting the RF generator output. It’s much better to use the 50-Ohm jig, but there will still be mismatch errors, which may be somewhat alleviated through the use of 6 to 10 dB attenuators. The goal is to measure the current through the probe versus the voltage at the probe terminals. Dividing the terminal voltage by the current gives you the transfer impedance. I’ve attached a few references.

Here’s a recent article from Interference Technology.

Teseq also has a calibration procedure within the instructions for their test jig, and look under the “downloads” tab.

Dr. David Pommerenke, of Missouri University of Science and Technology (MST), authored a paper with Ram Chundru and Sunitha Chandra on “A New Test Setup and Method for the Calibration of Current Clamps“, which runs through the historical calibration methods and then suggests an improved method.

2012 in review

The WordPress.com stats helper monkeys prepared a 2012 annual report for this blog. Thanks to all those who follow this blog. Happy New Year!

Here’s an excerpt:

These are the posts that got the most views on design-4-emc.com in 2012.

1 First Impressions – Rigol DSA815TG Spectrum Analyzer, July 2012

2Using A Tracking Generator, September 2012

3 Time for Business Cards, June 2012

4 iPhone and iPad Engineering Apps, April 2012

5 Low-Cost Handheld Spectrum Analyzer, February 2012 

I was a bit surprised to see the business cards posting rate so highly. I figured the others would be of interest.

Click here to see the complete report.

Cheers, Ken,

Wyatt Technical Services, Woodland Park, CO

Apple and Their iPhone/iPad Connectors

Once I left my long-time employer, who insisted we use PCs with all their issues, I quickly converted to Apple products, including iPods, iPads, etc. The one thing that I felt was a little “tweaky” was their original flat 30-pin I/O and power connector. The problem we users all had was that it wasn’t very easy to figure out the correct way to plug it in – especially in a dark room. The icon on the plug was not very distinct and you basically have a 50-50 chance of getting it wrong on the first try.
I got the idea to add a stick-on object to identify the correct side, such as those collections of stickers found in scrapbooking stores. Try to find a set of small stickers that have some dimensionally in the “z”-direction, so that you can feel it in the dark. I used a small “period” sticker that has worked great (see photo). This has worked out quite well for me.

Apple’s older 30-pin connector with polarizing “dot” attached.

I have to applaud Apple for finally devising a non-polarized power and I/O plug (the Lightning connector) on the one hand, but on the other, for millions of users, the conversion will be problematic for a (long) while.

Apple’s new “Lightning” connector with reversible (non-polarized) dynamically-assigned pins.

Editor of The Connecting Edge, Martin Rowe, has pointed out an issue with hardware add-ons, such as Oscium’s Wi-Fi spectrum analyzer, which uses the 30-pin connector. Apple’s 30-pin to Lightning adapter works for this receiver, but now the hardware will kind of “dangle” there on the iPad. Not very handy.

Perhaps instrument or accessory manufacturers could use Bluetooth (or similar wireless) connectivity for future products and avoid the hardware connectivity issue altogether.

Anyway, change is hard, but I guess we’ll live through it!

A Visit with Doug Smith

I’ve known Doug Smith for over 20 years and finally had chance to visit his new office and lab in Boulder City, NV, and interview him as I traveled out to the west coast for some other business. More…

Figure 1 – Doug at work in his new digs.

ESD-Caused Fires

While cellphones have been disproven to cause gas pump fires, ESD-caused fires do occur at regular intervals – as many as several hundred times per year, according to the ESD Association. As we approach the winter season, where, typically, we get lower humidity levels, we need to be extra careful about ESD discharges when filling our gas tanks. As a pilot, we were always cautioned to connect the earth lead from the pump to metal structure on the plane prior to fueling for just this reason.

I’ll describe a couple real events. more…

EMC Archive at T&M World Now On-Line

Martin Rowe, Sr. Editor of Test & Measurement World, recently collected over 80 EMC-related blog posts and articles published in the last several years and has placed them all into a single location in the T&M World “Vault”. Look for “EMC EMI RFI ESD“.

Check them out!

Where do you turn for help?

While most larger companies may be able to afford just one EMC engineer (or a small handful) to cover all products under development, many smaller companies can’t afford one at all and must rely on their existing designers to deal with compliance issues (many times at the end of the product development process!). So where does the lone EMC engineer or inexperienced product designer turn to for help in answering EMC questions?

Here are a few answers.

The Artech RCL Meter Tweezer Clone

Having used Advance Devices Smart Tweezers for several years, I was surprised to find what appeared to be a clone in a local electronics store for about $30. They were designed by Chinese company, Artech, as their Model VC6015. I decided to purchase them and compare with the newest Smart Tweezer Model ST5.

The Artech VC6015 RC (doesn’t measure L) meter clone.

The first thing I noticed was the clever slide-on protective cover around the tweezers. My impression went downhill from there. The nickel-plated tweezer tips were not aligned well and I had to bend them straight. They had trouble grasping the smaller surface-mount parts, but worked OK on 0602 size and larger. The unit is powered by a CR2032 Lithium battery.

Whoa, I next noticed it doesn’t measure inductance; just resistance, capacitance and diodes – a major drawback. Also, the display can’t be oriented 180 degrees for us left-handed users.

Otherwise, the resistance and capacitance measurements were pretty accurate (see charts in the main article). The auto range worked well, but was slower than the Smart Tweezers. Also, the ranges were more limited, which reduced the accuracy of the smaller component values. The Hold button was useful to freeze the measurement.

Basic Specifications

Maximum Measurement Ranges

Parameter

Range

Resistance

0.1 Ohms to 3.0MOhms

Capacitance

0.1nF to 30mF

Basic Accuracy 

Parameter

Measurement Range

Basic Accuracy

Resistance

300 Ohms to 300kOhms

<1%

3MOhms to 30MOhms

<2%

Capacitance

3nF to 300uF

<3%

3mF to 30mF

<5%

Using the Artech VC6015

The meter fits OK in your hand, but I had to learn to read the display upside down. The Auto ranging worked well, but was slow. The Hold button would allow me to flip the unit around to read the measurement. Pressing the Func button would switch from the Auto measurement to only C or R, but with slightly wider measurement scales.

Conclusion

While the resistance and capacitance measurements seemed pretty accurate, the tweezer tips were a little fiddly when measuring very small surface-mount devices. The lack of an inductance measurement was a show-stopper for me.

The Artech Model VC6015 is available for about $30 and may be ordered through local dealers. Their Web site is: http://www.artech-instruments.com.

Not recommended.

Review: IEEE EMC Symposium 2012

The annual International Symposium on Electromagnetic Compatibility was held in Pittsburg this year. As ever, I captured the event photographically, with the help of team members Tom Fagan, Jerry Ramie and Richard Georgarian. Although, tough at times, I also tried sitting in on several technical sessions, as well as meeting with a number of vendors. Here’s a quick synopsis, but for more detail, please check out Part 1 and Part 2 of the full report in The EMC Blog at Test & Measurement World.

The convention center in Pittsburgh is huge – so much so, that I’m sure I ended up walking a couple miles a day during the week there. Fortunately, I was able to rest occasionally in the volunteers office, which was situated near the middle of activity.

There were several new products of note. Dutch Microwave Absorber Solutions (DMAS) has introduced a high performance and environmentally friendly polystyrene microwave absorber that will cover the frequency range 30 MHz to 40 GHz. EM Software and Systems, inc., was there demoing their electromagnetics simulation software called FEKO. It’s useful for modeling antennas, radar cross-section, RFID, SAR, EMC, etc. Gauss Instruments was demoing their new wide-bandwidth (up to 162.5 MHz at a time) time domain EMI analyzer, the TDEMI 40G, which measures from 10 Hz to 40 GHz. Dudley Kay, from SCITECH Publishing, Inc., was there with a number of technical books for sale. He was also actively looking for EMC-related authors.

The convention center offered a nice aerial view of the vendor area.

As far as the technical sessions, Henry Ott again moderated the popular EMC Basics workshop on Monday, which was very well attended. I was also a part of a half-day workshop, “EMC Consultant’s Toolkit”, which was the best-attended session on Friday. We covered lots of business aspects and pitfalls of working as an independent consultants, providing the attendees with a host of knowledge to consider. I also included a short presentation on low-cost tools and equipment when you’re just starting out. We wrapped up with a panel discussion shown below.

The EMC Consultant’s Toolkit workshop had the highest attendance during the Friday workshop sessions. Shown are presenters (L-R) Jerry Meyerhoff (moderator), Bill Kimmel, Lee Hill, Kenneth Wyatt and Patrick André. Photo by Richard Georgarian.

The hardware experiments are always a popular event and this year was no exception, as we had several excellent presenters. One of my favorites is Dr. Tom Van Doren, who gave a couple demos; one on cable shielding and one on magnetic (low-frequency) shielding materials. I presented a new one on the effect of a high-frequency trace over a split return plane and showed how the result generated high levels of common-mode harmonics in attached cables.

Here I am demonstrating common-mode emissions generated by a high frequency trace over a gap in the return plane. Photo by Richard Georgarian.

The youth program was run by Amy Pinchuk this year and sixteen kids got to build shortwave receiver kits, as well as hear about ham radio from ARRL RFI expert, Ed Hare, along with a presentation on mobile electronic devices and why EMC is important for proper operation, by ETS-Lindgren engineer, Garth D’Abreu. They also had a nice tour of the vendor area.

After-hours social events scheduled included a really cool welcome reception at the nearby John Heinz History Center. Heinz was an avid collector of early memorabilia from Western Pennsylvania and Pittsburgh, in particular. The Wednesday Gala was a dinner cruise along the rivers bordering Pittsburgh.

Pittsburgh, “city of bridges”. Photo by Tom Fagan.

I guess that’s a wrap until next year, where it will be held in Denver, August 5-9, 2013. For more info, click here. Hope to see you all next year.