Clarification on general scope specs - Page 1
Forum section: electronics / beginners

author: Weez
author_rank: Contributor
timestamp: February 17, 2014, 01:19:06 am
content: Hello all, first time posting here. I'm glad I found this site...the sheer amount of info available is incredible.I'd like some clarification on max input voltage for scopes. I own a Tek 475 and just purchased a 465b, which should arrive within the week. Both tout max inputs of 500v...is this max assuming a 1X probe? I can't seem to find any clarification in the manuals, or maybe I'm overlooking it. I have tried searching this site (and others), but can't seem to find anything...I'm sure the info is here somewhere, but I don't seem to be doing a good job in my searches.Also, again just to clarify, if I'm using a 10X probe, it attenuates the voltage by a factor of 10...so if I probe 500v, the scope will only see 50v, yes? Or does it actually see the full voltage, but displays an attenuated signal? I realize the probe will see the full voltage, and naturally, safety/caution measures are in order...I'm not going to be poking around extremely high voltages just willy-nilly. I'm using these scopes, currently, to build/repair tube guitar amps, so the max voltages will be, generally 500-600v, and only that high in certain parts of the circuit(s).Another general scope question. I've noticed that a lot of the new DSOs and probes have lower max voltages...around 300v. Why is this? Maybe because the modern SS circuitry doesn't typically require such high specs? Is it to save money and keep costs down? A little of both? Just curious...Anyway, I've rambled enough for my first post. I appreciate any and all input.Richard

author: EEVblog
author_rank: Unknown
timestamp: February 17, 2014, 01:45:12 am
content: Quote from: Weez on February 17, 2014, 01:19:06 amYes, the probe has a 9M resistor in it, it attenuates the signal by 10.You will now be limited by your probe maximum voltage instead of the scope maximum voltage.

author: Weez
author_rank: Contributor
timestamp: February 17, 2014, 02:17:32 am
content: Very good, thanks Dave.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2014, 02:21:23 am
content: Volts as in, volts on that terminal.Probes also are usually rated by peak. Check the manual to be sure.You'll probably want to get a 100x probe, as 500V supplies mean 900V+ peaks, kind of dangerous for most probes. Note also, when the scope is on AC input, full DC bias reaches the scope input, even on a 10x probe (and probably 100x too..?), which puts full DC on the scope's "AC" mode coupling cap.Tim

author: Weez
author_rank: Contributor
timestamp: February 17, 2014, 03:10:57 am
content: Thanks Tim, I do plan to get a 100X probe soon.Honestly, I was thinking that the cap in the 10X probe would block DC, obviously that's not the case, or at least entirely the case here.I'm currently working my way through an old textbook by Floyd on the basics, slowly, making sure I thoroughly understand everything before moving on to the next section. I'm only just starting with parallel circuits, and so far everything is just resistors...haven't gotten to caps yet.I have a lot to learn.