DIY Oscilloscope Probe Ground Spring  - Page 1
Forum section: electronics / beginners

author: Simon_RL
author_rank: Regular Contributor
timestamp: February 15, 2020, 01:19:20 pm
content: I recently bought a new Hantek Oscilloscope and it didn't come with any ground springs. So I figured I will make some as I need them for a current project. Other than the wire needing to be stiff are there any other requirements, like low resistance? Is there a specific wire that I need to get?

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2020, 03:15:23 pm
content: Random image from GoogleIf you mean the one like above example, yep, they get lost easily, I made my self, use piano/guitar wire, wind it on a stiff steel, such as a nail, but abit smaller in diameter compared to the probe's ground near tip, as it will un-wind a bit by itself, it will be nice fit & snug to the tip, suggesting to do trial and error 1st.Reheat with hot air if needed during the winding at certain wire.Actually copper wire works too, but not as robust as the steel wire, once the winding is done, wrapped it with heat shrink tubing to maintain the tight winding.

author: Simon_RL
author_rank: Regular Contributor
timestamp: February 15, 2020, 03:30:48 pm
content: Quote from: BravoV on February 15, 2020, 03:15:23 pmThanks Bravo much appreciated.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 15, 2020, 07:18:21 pm
content: If making them doesn't work there are some purchase sources:https://www.caltestelectronics.com/ctitem/37-5mm-probe-accessories/CT3668- this is for 5 mm, probably other parts for other diameters available toohttps://www.caltestelectronics.com/ctitem/34-probes-accessories/CT2714

author: tautech
author_rank: Super Contributor
timestamp: February 15, 2020, 07:39:44 pm
content: 0.6mm TIG wire wound around a suitable former works fine too.Anyone with a small TIG welder should be able to spare a few feet for you to experiment with.

author: tggzzz
author_rank: Super Contributor
timestamp: February 15, 2020, 07:49:38 pm
content: Quote from: Simon_RL on February 15, 2020, 01:19:20 pmThey carry negligible current (unless there's a fault), so resistance is unimportant.The key point is to minimiseinductance, since a standard 6" ground probe has an inductance of 150nH or so. Couple that with the "high" impedance *10 probe's 15pF tip capacitance, and you have an resonance at ~100MHz.You minimise inductance by keeping the length short, and there are many ways of achieving that, e.g.https://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/or

author: Simon_RL
author_rank: Regular Contributor
timestamp: February 16, 2020, 10:42:10 am
content: Quote from: tggzzz on February 15, 2020, 07:49:38 pmThanks tggzzz. I was wondering what issues could arise from a wrapped wire. I really like the look of the short wire version. Quick and easy to make

author: ebastler
author_rank: Super Contributor
timestamp: February 16, 2020, 10:46:05 am
content: Quote from: Simon_RL on February 16, 2020, 10:42:10 amJust to avoid any misunderstandings: The wrapped (spiral) part of a typical ground spring will not cause any inductance issues. The wire makes contact with the probe tip's ground shield right at the beginning of the spiral part. The additional spiral turns are there only for mechanical attachment to the probe, they are not electrically relevant.

author: Simon_RL
author_rank: Regular Contributor
timestamp: February 16, 2020, 11:41:20 pm
content: Quote from: ebastler on February 16, 2020, 10:46:05 amThanks for clearing that up ebastler, it make perfect sense when you think about it.