Grounding Oscilloscopes and Function Generators

[ViperDoc]

I just cracked the box on a function generator and oscilloscope, I'm looking forward to learning how to use them. I notice an earth connection on the back of the function generator. What's the best thing to connect that to? Do you try and connect it to mains earth? I don't imagine you would use a ground to an AC socket?

[xtian]

My scope and function generator are both grounded to earth by its 3-prong power cord (function generator is powered by 5v USB connection, but is also earthed via that USB connection).

So technically, there's no need to use the ground wire on either scope or function generator leads. You are scoping a signal or a voltage WRT (with respect to) ground/earth. However, for lowest noise (like when injecting 0.1vAC signal into your guitar input jack) it's best to clip the ground lead to the input jack's ground. Or when scoping loose capacitors for the foil connection (lowest noise), you'll use both signal and ground clips on the scope lead.

A big WARNING: because the scope and gen are grounded to earth, you do NOT want to connect the ground clips to anything other than the amp's earthed chassis. Like, what if you wanted to scope the AC ripple on a filter cap? Would you clip the ground lead to B+? NO! Or better yet (been bit by this one) try to scope the output of a non-grounded, differential power amp. BAM! SMOKE!

Going back to your question, yes, bond your signal generator's ground to earth or amp's chassis however is convenient. Amps' chassis should always be earthed when plugged into AC.

[ViperDoc]

Is the generator’s earth terminal only used for field work, then? Seems like it would create a ground loop anyway since it’s power is well-grounded with the 3-prong cord.

[xtian]

Don't know! But use your multimeter to check the earth conductivity, just to confirm what we're thinking. Check whether the generator's earth terminal is indeed connected to the earth prong on the power cable.

[sluckey]

I notice an earth connection on the back of the function generator.

Which function generator? Post a pic of the back of the unit.

[ViperDoc]

It’s a Siglent 1032X. Here’s the back panel:

[xtian]

Yeah, maybe if you’re using a laptop under battery power, that gives you an easy way to earth the equipment.

[xtian]

But what do I know? My signal genny cost $32!

[sluckey]

Just pretend you didn't see it. Try not to get lost in the menus.

[ViperDoc]

OK, got it. I admit, this thing is a bit more hot rod than I need/deserve, but hey, I got a good year-end deal on it. No LAN hookups likely in my future. Now to make a BNC-1/4 inch cable!..or perhaps just clip a 1/4 plug.

[sluckey]

Now to make a BNC-1/4 inch cable!..or perhaps just clip a 1/4 plug.

I prefer to just use bnc to bnc cables and keep a variety of adapters, tees, etc. Look through some Pomona stuff...

https://www.amazon.com/s?k=pomona+adapt ... _sb_noss_1

[ViperDoc]

Now to make a BNC-1/4 inch cable!..or perhaps just clip a 1/4 plug.

I prefer to just use bnc to bnc cables and keep a variety of adapters, tees, etc. Look through some Pomona stuff...

https://www.amazon.com/s?k=pomona+adapt ... _sb_noss_1

Thanks for the hot tip, Steve. I made a 1/4 inch cable end with clip rings, but I like your idea better.

Cheers.

—Brian