The annual IEEE Symposium on Electromagnetic Compatibility (EMC) was held August 5 through 9 at the Denver Convention Center. EMC engineers and EMC-related vendors from all over the world met to present the latest technical information, as well as the latest products and services.
Please go here, for the whole article.
Many of you may know, as an EMC consultant, I’ve been partnering with one of the best EMC test labs in Colorado, EMC Integrity, in Longmont, north of Denver. EMC Integrity was founded by Vince Greb in 1993 and now owns two of only three 10m semi-anechoic chambers in the state (the other is owned by Hewlett-Packard in Ft. Collins). They specialize in both commercial and military EMC testing. Check them out at www.emcintegrity.com. They were recently featured in an article in the Boulder County Business Report (March 15-23, 2013). Check it out here…
I’ll be presenting a comprehensive two-day EMC design and troubleshooting short course there April 2-3 (sold out), with a possible follow-up course later this year.
Technician, Casey Lockhart running a radiated emission test at one of the 10m chambers. Photo courtesy BCBR (© Jonathan Castner).
The annual “Top Twelve Articles from 2012” was just published by Interference Technology Magazine. My article, “The HF Current Probe – Theory and Application” was the number one most read article last year! Thanks everyone!
Figure 1 – A pair of DIY current probes constructed using split-core ferrite chokes.
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.
Most simple DIY comb generators seem to run out of steam about 1 GHz. I recently ran into David Bowman’s 2.4 GHz circuit and measured an upper usable range of about 6 GHz. While greatly attenuated above 3 GHz, this circuit should still be valuable for measuring semi-anechoic chambers in the GHz ranges.
If there’s been one spectrum analyzer that’s created buzz lately, it’s the recently announced Rigol DSA815 budget ($1,295) spectrum analyzer, which tunes from 9 kHz to 1.5 GHz. A tracking generator option will run an extra $200 and the EMI option, which provides quasi-peak detection and the three EMI bandwidths (and especially excites us EMC engineers), is an extra $600. There are a number of other options available. I was able to get my hands on a review unit and have put it through its paces during some recent EMC seminars and client projects. More…
Figure 1 – The Rigol DSA815TG (with tracking generator).