Need help with some measurements.

Hi Jan,

Thanks for the video. It is an excellent idea and I am sure it will be of utility. I will do some experimenting with it tonight.

John

Hi Jan,

I had all day to think about the ideas that were in the video so by this evening I was ready to try some things to see if I could come up with an Oscilloscope Probe adapter based on the coiled wire technology. I began by rolling some wire around different size drill bits. It took me 4 tries to get the size that I needed. I am using 16 Ga Brass wire for the outer ground.

As you can see I have continued the coil quite a ways past the ground ring on the probe. While the added length will add some shielding the main purpose it to provide support for the central connection to the probes tip. The small coil is the one that will go onto the probe tip. Both outer and inner coils are wound with a right handed twist so that when one goes to put the adapter on the probe a right hand twist will cause the coils of the brass to open up. Likewise a right handed twist will be needed to remove the adapter. A left handed twist of the adapter will tighten the coils and lock the adapter more securely in place.

The next challenge was to attach the small coil to the brass non-slip point holder without filling the coil with solder. Brass has a pretty good affinity for solder and it would easily wick into the coil. Here is a picture of the process of soldering the coil to the brass tip holder. The second pictures shows the completed central assembly of the adapter.

The next step was to heat shrink enough layers on this central shaft that it sizes out to fit into the outer ground coil.

The outer coil of wire is fitted over the now heat shrink covered inner shaft.

By removing the center shaft and lightly coating it with epoxy and reinserting it into the coil we can get the two pieces epoxied together and not allow the glue to get back to the contact area of the probe. A thin layer of epoxy is also spread on the front section of the outer coil but not back as far as the part that slips onto the oscilloscopes ground ring. Finally a piece of heat shrink is installed over the entire assemble and then we wait for the epoxy to cure.

Here is the finished adapter with the non-slip point attached. Once the glue sets I will apply a right handed twist and if I have been lucky and no glue has seeped where it wasn't wanted I should be able to remove and reinstall the adapter as needed. If on the other hand the glue got away from me then I may have a permanent non-slip tip on this probe.

Thank you again for finding that video and inspiring my fun this evening.

John

Hi Jan,

The glue has set and the adapter came off as hoped.

Here is a picture looking into the back of the adapter.

While this has been a successful build for me it still will not make the production of a standard adapter possible as the dimensions of the different probes are not compatible. I do like the sturdiness of the adapter compared to the ones I did yesterday that were only supported by the 1 mm oscilloscope probe tip. I will just have to keep thinking.

John

I wonder if the coiled spring has enough "give" in it that another 0.1-0.2mm of probe tip diameter wouldn't matter too much? Furthermore, as some tips are somewhat angled, for those maybe making contact isn't as difficult.

Perhaps you could slip the adapter on another probe of yours and let us know how it works/doesn't work.

- Gough

Hi Gough,

The brass wire that I used doesn't have much elasticity and the center coil itself is even worse due to its small diameter. I had hoped to have something like the spring inside a wire nut but in the end it is sized very close to the 1 mm tip on this particular probe. I will check things out tomorrow and if possible I will see if it will work with my other probe set. Thanks for checking it out.

John

Interesting to see the insides.

I'm wondering now that you've provided the support with the ground that you could utilise something else for the probe inner contact.

They are usually high impedance so the contact resistance isn't as important as a high current connector.

It would be interesting to see how the clip end attaches ... if someone has a dead/broken version.

I have a couple of different versions of probes but haven't had time to get the calipers out ...sorry

Mark

Hi John,

Great series of posts. If I'm not too late I've measured my scope probe (Tektronix P6109B) for you; although it is quite old like me.

The tapered section of this probe measures 1.24mm diameter at the base to 0.89mm diameter just before the 45 degree chamfer starts. The collar before the insulating black section is 2.39mm diameter. The chamfer section is 0.49mm long (as being measured in photo).

Rod

OK, here are my two probes:

First a Keysight N2140A (from a DSOX1000 series): the tip is (apart from the sharp end) slightly conical - from 1.00 to 1.20mm. Total length of the tip is 4.65mm

Second, a Tektronix TPP0201 (from a TBS1000B-EDU series): its also conical, from 0.6mm to 0.85mm, total length is 4.5mm.

Looking into the hook fixture of the probes, their internals look like a double-spring contact (kinda like a IC socket, but two-sided). But the actual mechanism to attach the hook part to the probe is different between the two probes.

Hi Rod,

Never too late and thanks for the great closeup picture. As far as I can see so far there is a consensus among manufacturers about a range of acceptable dimensions but no standard dimension.

John

Thanks Hendrik,

I have added your measurements into my data base. Thanks for looking inside the attachments. I have been curious about them as well but they are likely unique to a given manufacturer.

John