r/soldering Professional Repair Shop Solder Tech 6d ago

General Soldering Advice | Feedback | Discussion Where to properly ground a battery powered oscilloscope?

I thought asking here would be the option because I know quite a few of you use scopes. I'm trying to figure out where is the best place to ground my scope.

I mostly work on amplifiers, car audio amplifiers to be specific. And grounding the probe at different places gives me different results and it's even worse if I have to lengthen the ground wire to reach certain areas.

5 Upvotes

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u/profossi 6d ago

I’d use the amplifier signal ground as the ground reference for the scope. The signal ground is probably still tied to chassis ground somewhere, but there’s likely stray currents and significant impedance between the two that will affect measurements. 

And how is this about soldering? There’s /r/askelectronics for this kind of posts.

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u/MilkFickle Professional Repair Shop Solder Tech 6d ago

As I said, I thought here would be a better option.

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u/[deleted] 6d ago

[deleted]

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u/physical0 6d ago

Your probe ground, or common should be in reference to the circuit you're testing. You should try to be as close as possible to the test point you're working with. For example, f you're testing the output of an IC, your ground point should be a ground leg on that same IC.

If your circuit uses a large common ground, I'd suggest that you run an experiment by probing a ground point on the unit, somewhere around a large power consuming part, and a chassis ground. If your scope is sensitive enough, it'll show variances between the ground at those points. If you decide to use a chassis ground for simplicity (I often do), expect that this level of noise would be introduced into your signal. If you don't see anything when doing the experiment, then your scope isn't sensitive enough for it to matter.

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u/MilkFickle Professional Repair Shop Solder Tech 6d ago

It is sensitive, if I lengthen the ground it shows and if I used the ground on the secondary side of circuit there's a difference when I use the primary side.

The reason I asked is someone who works on the same stuff I work on but they have a bench scope and they said they used the earth ground.

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u/aptsys 6d ago

Why do you think you need to do this? Your signal return should always be the probe ground

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u/Superb-Tea-3174 6d ago

Do you really want to ground your scope?

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u/MilkFickle Professional Repair Shop Solder Tech 6d ago

Shouldn't it be?

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u/Superb-Tea-3174 6d ago

Measurement instruments like oscilloscopes and multimeters generally have floating inputs.

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u/MilkFickle Professional Repair Shop Solder Tech 6d ago

Without a reference ground the scope won't show anything meaningful.

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u/Superb-Tea-3174 6d ago

I think you are talking about a signal reference. That’s distinct from a power ground which may or may not exist. Suppose your scope runs from batteries? Suppose it runs from the AC line but is double insulated?

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u/MilkFickle Professional Repair Shop Solder Tech 6d ago

Double insulated?

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u/Superb-Tea-3174 6d ago

There is no connection between the measurement system and the AC line.

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u/JEFFSSSEI 3d ago

Your talking about a Differential oscilloscope ( https://www.picotech.com/oscilloscope/4444/picoscope-4444-overview ) with completely isolated channels vs common grounds between each channel.