Hi Ken and the group, The attached file was interesting, but we understand current probes much better today (at least the people at FischerCC do). Actually, building current probes in a production environment requires knowledge well beyond what is in the paper using techniques developed over years. I am aware of some of these production techniques but cannot discuss them as they were shared with me by FischerCC a while back and is their intellectual property.
As far as checking E-field shielding, this is done in about 10-20 seconds by one of three methods I have written about. The effective shielding effectiveness is a strong function of the environment the probe is used in (relative strength of the E and H fields). But, again, it only takes seconds to determine if a probe is adequate for the measurement one is trying to make. In general, a lot of current probes out there are not useful for ESD current measurements. I have personally seen errors of 20% up to 100% in amplitude for current measurements of ESD currents.. Doug [https://lh4.googleusercontent.com/_HuR3Ky2TF_XhFHyxnYRmiq7nHQldnMsPNYFaLG6kb5T4y8MeCe-BDC_BscJtSFgszSSjssihHS-pjM3-jwNP8S0CwE-gN8fsRsPkojiAlmpBwb20vIVizS-siCUywW_jqrefbVr] From: Ken Javor <[email protected]> Sent: Friday, October 25, 2024 14:06 To: [email protected] Subject: Re: [PSES] current probe notes In a previous exchange, it was noted how much early work has been forgotten. Case in point, the attachment and its references. By a couple of gentlemen most of us on this side of the Pond knew, now sadly departed. -- Ken Javor Ph: (256) 650-5261 From: "doug emcesd.com" <[email protected]<mailto:[email protected]>> Reply-To: "doug emcesd.com" <[email protected]<mailto:[email protected]>> Date: Friday, October 25, 2024 at 1:12 PM To: <[email protected]<mailto:[email protected]>> Subject: [PSES] current probe notes Hi All, I want to discuss current probes a bit. They are among the most useful tools available to engineers. Current probes are very useful in EMC, ESD, and other troubleshooting and are required in some standards like conducted immunity testing. But current probes cannot be adequately characterized by the well published equations. For one, E field response is an undesirable characteristic that makes many current probes useless when used to measure ESD currents and some other applications. I have used a Fischer Custom Communications F-65 current probe for many years. Not only does it have a negligible E-field response, and therefore useful for ESD measurements and troubleshooting, but also has a flat frequency response over three orders of magnitude from about 1 MHz to 1 GHz. Designing anything that is not a 50 Ohm matched structure and has a flat frequency response for three orders of magnitude in a range where parasitics are important to account for is very difficult and requires a lot of experience. Current probe equations alone will not lead to a satisfactory design. This material is generally not treated adequately in my opinion in the engineering community except by me. That brings me to low-cost current probes I have seen on the market. One I checked out a few years ago had an E-field response that was equal to 50% of the H-field response, making more or less useless for that application, but users of that probe would normally have no idea their data was more or less useless. If one buys an inexpensive current probe (less than $1000) it may very work fine, but you cannot assume that it works unless the manufacturer publishes its E-field response and how that response was measured, or you measure the response by one of several methods I have published and teach. The problem with verifying the probe oneself is that an engineering employee cost to a company is on the order of $2,000 per worked day these days, especially in areas of lots of technology like Silicon Valley, so buying inexpensive equipment may not be the savings one thinks! Doug (current probe) Smith [Image removed by sender.] ________________________________ This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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