Scope Maximum Input Voltage (DC and AC) - Page 1
Forum section: electronics / beginners

author: bravoelf
author_rank: Contributor
timestamp: July 09, 2014, 08:11:29 pm
content: Hello Everyone,Recently I purchased a scope (Rigol DS-1052E), and I got a bit confused about, how much voltage it actually can tolerate.It is clear to me, that there are two things I need to take into account:1. Probe's max input voltage.2. Scope's max input voltage.As for the probes, I have a RP2200 probes.It has a max input of CAT II 300Vrmsin 10X ( Rigol's User Guide)orCAT II 300V AC (probe's specs pages).Note, that there is a "sqrt(2)" factor, so I can get sqrt(2)*300=424Vpk AC.Furthermore, no max DC voltage provided(why?).And the scope itself:According to the Rigol's User Guide, my device can tolerate a maximum of 400V (DC?AC Peak, 1M? input impedance).So here comes my second question: what does this line is actually mean?Does it says that I can input a 400V DC? Or maybe 400Vpk AC? Or 400Vpk AC with some DC offset?Hope, my questions are clear enough.Thanks in advance for help.Sincerely,

author: tautech
author_rank: Super Contributor
timestamp: July 09, 2014, 08:46:56 pm
content: Scope max input is rated as DC+AC < max.That is any AC(signal) plus DC offset must be less than max input.This is the first consideration.Secondly and more important for your safety.Probe Voltage de-rating with frequency.All probes are different in this respect and de-rating graphs must always be kept handy for quick referral.Real Example:60 MHz 10:1'1:1 probe600 V @10 KHZ de-rates to ~30 V @ 60 MHz250 MHz 100:1 probe1200 V @ 2 MHz de-rates to ~200 V @ 250 MHzThe graph traces for de-rating can be curved, linear and combinations, but must never be assumed.For most work, the voltages present pose little problem.But as you hold the probe,you must know it's limitations.

author: David Hess
author_rank: Super Contributor
timestamp: July 09, 2014, 09:25:44 pm
content: High impedance oscilloscope inputs are also derated by frequency like probes.The vertical inputs of a Tektronix 2235 for instance are rated at 400 volts DC + peak AC and are derated starting at 10 kHz to 12.5 volts at 500 kHz.

author: bravoelf
author_rank: Contributor
timestamp: July 09, 2014, 09:32:49 pm
content: QuoteThanks for that info.QuoteWhat about DC limitations? 400V DC (no AC with it) is the maximum?And what about 300Vrms vs 300V AC... which of them is my supremum?QuoteThat's what I'm actually trying to discover, for my earlier provided device specs (probes and scope).

author: bravoelf
author_rank: Contributor
timestamp: July 09, 2014, 09:37:04 pm
content: QuoteSo if I get you right, I need to find these "de-ratin" graphs in order to estimate which max voltage I can measure for each particular frequency?But still I can measure 400V DC?

author: bravoelf
author_rank: Contributor
timestamp: July 09, 2014, 09:58:33 pm
content: Ok I found, what you were talking about, this is the Probe's voltage de-rating curve.But still I have a few questions:1. DC Voltage Maximum...2. Does this graph applies to probes only? I mean, if there are some additional/separate voltage graphs that describe scope's behavior? Cause I didn't see any in User Guide...

author: Psi
author_rank: Super Contributor
timestamp: July 09, 2014, 10:16:13 pm
content: From memory some spec sheets list 400V peak and others say 300V RMS for 1052 inputsHowever you only get max 10V per div in 1x mode so the input is useless for more than +/- 40V or 80V DC.I have accidentally feed 230VAC into my 1052 on 1x, It just clamps the signal. Didn't seem to cause any damage.So the 400/300 rating is just the maximum the signal clamp can handle, rather than useful range.Probably intended just for that purpose (mains input on x1).

author: tautech
author_rank: Super Contributor
timestamp: July 09, 2014, 10:27:57 pm
content: Your quote answers max BNC input:QuoteRemember that max input ratings will be as a worst case scenario: 1:1With 10:1 probe attenuation the derating curves become your guide.When voltage is reduced by a 10:1 divider in the probe, then the probe characteristics become your guiding factor.For your safety, scope safety and for the least probe influence on the DUT use 10:1.All measurements affect the DUT in some manner.

author: David Hess
author_rank: Super Contributor
timestamp: July 10, 2014, 12:01:34 am
content: Quote from: bravoelf on July 09, 2014, 09:37:04 pmThat is right although the derating graphs are only approximate. One of my complaints about Rigol (and other cheap oscilloscope manufacturers) is the lack of detailed specifications.QuoteThis specification only means that inputs below this will not cause damage. A sensitivity of 5V/div which is typical now would limit direct measurements to 40 volts plus any offset capability in this particular case.

author: BillWojo
author_rank: Regular Contributor
timestamp: July 10, 2014, 03:29:17 am
content: Bravoelf, that was a timely question. I just picked up a scope myself off of ebay, should be here by the end of the week. It's a Tektronix 465M and I ordered a set of probes to. They are the cheap ones, 1x and 10x switchable. Not doing anything high frequency but will be looking at DCV of up to 170. Can't wait to get it and start learning how to use it.BillWojo

author: bravoelf
author_rank: Contributor
timestamp: July 10, 2014, 09:16:46 am
content: QuoteGlad that it helped you too )))To:David Hess, tautechThanks a lot, very appreciated your help.P.S.QuoteTotally agree, but for B.Sc. student like me, having such cheap scope is more than enough (IMO)