Optimizing VOM leads

[mklotz]

I have a bookmark file for electronics, VOM's, meggers, thermometers, pyrometers, certain unique hardware; guess what joined recently?

I'm flattered to make it into the Toolmaker library. If you do a lot of battery checking, especially coin batteries, you might want to add one of these...

Battery testing aid

to the reference.

Maybe one of these...

Resistors for current measurement

as well.

[Toolmaker51]

It pleases me as well, Marv. In case it's not clear, there are hundreds here, who hang on every word in your posts........ I for one, very glad you 'worked for our side'.

Experience at the mechanical services company (pumps and motors) wound it's way into machinery service. Built a tidy bank of metering as we've both described above. Been going through multitude (spindles, feeds, pumps) of motors far beyond anything I could before. Most are 3ph/ 440v, a few single 240v, two are 50 cycle; but all should run proper rotation first time. Insulation checks, motor windings, grounding, continuity of myriad connectors...the most fun to be had carrying a meter, notepad, and penlight. And a block of foam.

Low volt DC, I guess capability was better, but need didn't go past a nice old Realistic VOM. It's probably 50 years old now. Latest addition is a Power Probe, those are the bomb, as I'm often working alone. Like tracing a defunct back up alarm, 30 something feet away, from inside cab, in the box truck.
Ain't no way I'll start it, trust PARK or NEUTRAL, air brake, even chocks; scooting around a creeper in diesel exhaust. Probed? Maybe 3 minutes. There, it turns out, is no hydraulic transmission switch, but a micro in the shift selector hanging under the dash. That and 12v run a tiny motorcycle-type device, way back over the axle, of minimal annoyance. They are available with increasing decibels beyond finch fart.

Proper electronic components aren't quite in the mix yet. Maybe when itch for plasma cutter kicks in. The Electro Arc Tap Disintegrator comes first, no one around has one.

[object]

I don't think the effect is anything to worry about and probably would require the sensitivity of a Wheatstone bridge to detect. Nevertheless, I did an experiment to check.

I have three 50w 1% precision resistors - 10, 1, and 0.1 ohms. I measured all three of them first with no aluminum in the circuit and then with it in. These were the results...

10: 10.2, 10.3
1: 1.2, 1.2
0.1: 0.2, 0.2

I like your execution, very cool. The reason probe ends, terminals, and test point connections are nickel, gold, or rhodium plated is that they don't oxidize. Because aluminum does it will directly affect readings accuracy. Over time oxidation will change them, they could vary month to month. If you are just going for simple go/no-go it's probably fine but if you are doing current measurement or board level troubleshooting to a schematic your test point readings will vary from indicated values. Aluminum forms and oxide layer immediately after it's machined. It's basically an insulator. You can mitigate this (somewhat) by chasing the tapped holes again, quickly adding battery terminal dielectric gel then immediately reinstall the screws. for the banana ends you can fill the voids with the gel. The gel will prevent more air from reaching the machined surfaces. However, some air will reach them as oxidation is immediate after machining.

More here:

https://physics.stackexchange.com/qu...ce-oxide-layer

[Toolmaker51]

I like your execution, very cool. The reason probe ends, terminals, and test point connections are nickel, gold, or rhodium plated is that they don't oxidize. Because aluminum does it will directly affect readings accuracy. <<<<<<<snipped>>>>> Aluminum forms and oxide layer immediately after it's machined. It's basically an insulator. You can mitigate this (somewhat) by chasing the tapped holes again, quickly adding battery terminal dielectric gel then immediately reinstall the screws. for the banana ends you can fill the voids with the gel. The gel will prevent more air from reaching the machined surfaces. However, some air will reach them as oxidation is immediate after machining.

More here:

https://physics.stackexchange.com/qu...ce-oxide-layer

Recall from decades back, no one has ever seen clean aluminum. Even the marine grades, resistant as they are. The lowest grades, suited for extrusion "look" clean the longest, hence use as trim material indoors and out.

[object]

I don't think the effect is anything to worry about and probably would require the sensitivity of a Wheatstone bridge to detect. Nevertheless, I did an experiment to check.

I have three 50w 1% precision resistors - 10, 1, and 0.1 ohms. I measured all three of them first with no aluminum in the circuit and then with it in. These were the results...

10: 10.2, 10.3
1: 1.2, 1.2
0.1: 0.2, 0.2

I wish you the best.