Effectiveness of cable ferrite clamp at some distance? - Page 1
Forum section: electronics / projects

author: lpc32
author_rank: Frequent Contributor
timestamp: May 05, 2015, 07:56:12 pm
content: How much of a difference would it make if a clamp ferrite core's internal diameter is 2-3mm more than the diameter of the cable inside?I'm looking for a clamp that will do both for 4 and 7mm cables, if possible. TDK'sZCAT1518-0730 or ZCAT1730-0730Ahave an internal diameter of 7±1. In the specs table for the 1730 it says the "applicable cable outer diameter" is 4 to 7mm. Yet, am I better off going with something smaller for a 4mm cable?ZCAT1518-0730:ZCAT1730-0730A:

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2015, 08:29:02 pm
content: It'll do the impedance it claims. The main difference is, a larger inner diameter needs an even larger outer diameter, and/or longer length, for the same impedance, so you spend a lot more space and money on an ill-fitting part.Nice part about an overly large one is, you can potentially put multiple turns through it, at least just for testing. Whether you'd want to do it that way for production, I don't know.Tim

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 05, 2015, 11:31:20 pm
content: It looks like ZCAT1325-0530A has about the same impedance curve but with a 5 mm core. It actually seems to get up to 100 ohms at a lower frequency.The larger one might be on the edge of slipping on the cable.

author: lpc32
author_rank: Frequent Contributor
timestamp: May 06, 2015, 12:33:41 am
content: I missed something on the first look. Below the minimum impedance tables there's a note: "Test conditions: When passing through an impedance meter (unloaded) ø1mm copper cable".Though it doesn't say what cable diameter was measured for the graphs, they show higher values than the table. And unlike the table, the graph does show higher impedance for the 1730-0730A compared to the 1325-0530A. So presumably the dropoff for 2-3mm would be something between the data in the table and the graphs.I guess the "applicable cable outer diameter" refers to the gripping teeth in the ZCAT-A. There are none in the ZCAT non-A (despite what's shown under "internal construction"), so it's probably considered only for the nominal cable diameter. I don't get the "fixing band" there. Supposed to go through the loop in the clamp and tighten to the cable? Strange.

author: macboy
author_rank: Super Contributor
timestamp: May 06, 2015, 04:21:17 pm
content: A bigger diameter ferrite may be a blessing in disguise. Wrap the cord multiple times around one side of the ferrite, enough to fill the space, then snap it shut. Impedance is proportional N2, where N is the of number of loops. This explains it well:www.leadertechinc.com/assets/files/catalogs/ferrites.pdf

author: lpc32
author_rank: Frequent Contributor
timestamp: May 06, 2015, 05:00:01 pm
content: Yeah, T3sl4co1l suggested it. But 4mm won't fit twice in 7mm, and the bend radius is a concern.Interesting PDF.Thanks, everyone.

author: coppice
author_rank: Super Contributor
timestamp: May 07, 2015, 02:57:51 am
content: Quote from: lpc32 on May 06, 2015, 05:00:01 pmWhy wouldn't two 4mm round, but somewhat squashy, objects fit in a 7mm round hole?

author: Dago
author_rank: Frequent Contributor
timestamp: May 07, 2015, 04:51:42 am
content: Remember that depending on what frequencies you are hoping to attenuate more turns does not necessarily always mean better. Due to the capacitive coupling between turns the attenuation for higher frequencies can get worse than with just one turn:http://www.autoemc.net/Newsletter/Issue10/KeenanFRtech.PDF(slide number 9, impedance vs. frequency with 1, 2, 3 turns).More info:http://emcesd.com/tt2005/tt090105.htm

author: lpc32
author_rank: Frequent Contributor
timestamp: May 07, 2015, 01:21:04 pm
content: Quote from: coppice on May 07, 2015, 02:57:51 amI suppose it might. Or if that 7±1 happens to be 6.5mm and the cable 4.5mm, it might not. Either way, it's ugly.Dago: Thanks.