Whether with scope probe or DMM sticks, I have trouble getting a reliable connection to terminal strips. With a crimp terminal stuffed under a round-head screw, and shrink covering the terminal's shank, there's not much to clip onto, especially with an alligator clip.
I'm tired of re-clipping probes and alligators that pop off with the slightest touch. How do others do this?
I thought about inventing a small magnetic button probe that would locate itself firmly on the top of the screw. Unless I can come up with another solution...
Thanks,
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DaveC
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A large percentage of terminal strips use nickel plated brass screws. Sometimes a mini-grabber type hook can get around the terminal between the screw and the terminal shank.
I think Fluke makes some very good clips, though. My favorite is the plunger style alligator clips. Sometimes these will even hold onto the screw itself.
Some terminals are still a problem, where no clip seems to work. If I can shut the unit off, I sometimes put another terminal with pigtail under the screw to hook test clips to.
Good idea. But with some machines that have rows and rows of these things, that a lot of pigtails! Powering-down the equipment, unscrewing, screwsing, powering up, taking readings, adjust, repeat... ugh!
My magnetic idea... someone pointed out that many screws are made from brass!
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There are several companies that have specialty test probe accessories, Pamona is a quality manufacturer. Test equipment usually just includes basic accessories, and users need to seek more specialized items best suited to their most common tasks.
The easiest solution would be to get some alligators with insulation-piercing spikes inside the jaws. This isn't the ultimate solution, and piercing can cause secondary problems in some applications, but it's simple. I think I've seen piercing scope probe tips too, but don't remember where.
Securely grabbing the small area of the sides of screw heads isn't an easy task. A possible design would include sharp points that are held with tension, involves points that will stay sharp with a clip that won't lose it's tension. Add to this design a method of insulating the clip, and the design gets more complex fairly quickly. A feature of replaceable points would be a good one, but probably not economically feasible.
Sometimes the best you can do is find something that's almost suitable, and modify it yourself. A little filing or reforming of the existing products might be the best direction. A Dremel-type tool is handy to have for small projects like this.
Nearly every technician will eventually make custom test leads that suit their particular test requirements. The main feature will be user safety.
If someone was often working with equipment that had the same identical terminal strips, it might be worthwhile to fabricate an insulated transferrable clip-on device that would attach to the terminal strip body (or over it), which had accessible test pins incorporated into the test clip design. If the terminal strips were located within a steel cabinet, a magnetically-mounted holder could possibly be utilized to hold the test interface pin header-type device in place temporarily.
I've been pondering a 2-wire clip-on device that could be attached to 2 soldered pads on circuit boards (on the solder side, instead of attaching to component leads on the component side). I figure it will look more like an old spring-tensioned clothespin with sharp points to dig into the thru-hole soldered lead areas, and stay in place for a short time without falling off. Too much spring tension would cause the points to cut (or plow) thru the solder, and the clip would pop off.
SoanarPlus (formerly PolyKom) makes magnetic connectors that are essentially a 40mm long piece of 0.65mm diameter wire bonded to a 6mm diameter button magnet. They might be a bit big though.
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