Is 10x more accurate than 1x? - Page 1
Forum section: electronics / testgear

author: rg2113
author_rank: Newbie
timestamp: October 30, 2023, 02:19:55 am
content: I recently got an oscilloscope, I hardly used one before, and I'm trying to learn the ins and outs. I am just curious if the 10x mode on a probe is more accurate? This is a Siglent scope with the standard 1x/10x probes. Channels 1 and 2 hooked up to the same test points looking at this PMW signal, but the 2nd channel see things a little differently. Channel 1 is 1x, channel 2 is 10x. I can see jitter with the probe set to 10x versus the 1x probe.

author: ataradov
author_rank: Super Contributor
timestamp: October 30, 2023, 02:36:16 am
content: 1x will have lower bandwidth, and this is what you are observing,The exact bandwidth values would be specified in the documentation for the probes.

author: tautech
author_rank: Super Contributor
timestamp: October 30, 2023, 02:40:47 am
content: Welcome to the forum.Both channel tabs display a 1x probe but we know looking at the same signal so the one with the higher input magnification is the 10x probe.Press the channel button and set it correctly.A 10x probe offers far less circuit loading which matters much for high impedance signals.Good observation for a DSO newbie and keep the questions coming when you see something strange rather than scratch your head about it.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 30, 2023, 02:47:39 am
content: Also, it goes without saying, that probing a hi-Z circuit node with a 1X probe will load it much more (and therefore have a larger error) than probing it with a 10X probe.

author: djacobow
author_rank: Super Contributor
timestamp: October 30, 2023, 03:11:52 am
content: I feel like new folks come on here pretty often and get confusing messages about switchable probes.Here is the right answer: use 10x.Later, when you are probing very small signals and the probe loading is not important, the answer changes, but most new folks are not going to be doing this, and by that time you should understand the trade-offs.Maybe it's just the kind of work I do, but I can't even think of the last time I wanted to use a probe in 1x mode and in fact most of my probes are fixed 10x because Ihateit when the switch gets moved.

author: ataradov
author_rank: Super Contributor
timestamp: October 30, 2023, 03:17:22 am
content: Yes, the simple answer that works 99.999% of the time is to use 10x. I too don't remember needing to use 1x. All my switchable probes have a dab of epoxy in the switch to fix in 10x mode.

author: rg2113
author_rank: Newbie
timestamp: October 30, 2023, 03:33:32 am
content: Thank you all for the answer and helping me understand. I did check the specs for the probe (siglent PP510), it just lists bandwidth as 100mhz, only input resistance/capacitance and max voltage are listed as different for 1x/10x mode.I found this document while searching online. It seems like maybe this is an effect of input capacitance? Spec sheet lists 10x ~20pF, and 1x ~100pF.https://assets.testequity.com/te1/Documents/pdf/probes-affect-measurement-an.pdf

author: tautech
author_rank: Super Contributor
timestamp: October 30, 2023, 03:36:13 am
content: Quote from: rg2113 on October 30, 2023, 03:33:32 amYep exactly that.We set everything for 10x as part of our PD checks for this very reason.BTW, have you compensated the probes....only to be done at 10x settings.

author: ebastler
author_rank: Super Contributor
timestamp: October 30, 2023, 05:09:11 pm
content: Quote from: rg2113 on October 30, 2023, 02:19:55 amWelcome to this forum, and to the exciting world of oscilloscopes!As mentioned earlier, great observation on the different signals measured by the two probes. Just a little terminology nitpick: The oscillations you observed with the 10x probe would not be called "jitter", but "ringing" or "overshoot". The term "jitter" is reserved for fluctuations in the timing of a signal, and in of edges in the signal. E.g. when a signal that is nominally periodic, and has a 1 MHz frequency on average, shows short-term fluctuations where its period deviates up and down from the nominal 1 µs.Not a problem at all for the present thread, since you made things very clear from the start by sharing the screenshots. But it might come handy in future electronics discussions.

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2023, 05:26:29 pm
content: It depends on the application. In general, x10 is better because it has a higher impedance and will load the circuit less, thus giving a higher accuracy, but if the circuit has a low output impedance, then x1 will be more accurate and lower noise, since the oscilloscope doesn't have to amplify the signal as much.

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2023, 08:52:13 pm
content: Quote from: schmitt trigger on October 30, 2023, 02:47:39 amWhat's the tip impedance of a 10Mohm//15pF probe at 250MHz?What's the tip impedance of a 50ohm *1 Z0 probe at 250MHz?Hint: the high impedance probe isn't high impedance!

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2023, 08:57:29 pm
content: Quote from: rg2113 on October 30, 2023, 02:19:55 amRinging, not jitter.To understand what's happening, seehttps://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/To learn more about probes and how they interact with the UUT, see the references athttps://entertaininghacks.wordpress.com/scope-probe-reference-material/

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 31, 2023, 01:37:50 am
content: Quote from: tggzzz on October 30, 2023, 08:52:13 pmThe TS is obviously asking a newbie question, which MOST likely means a performance comparison between the ubiquitous 10X/1X probes. He wasn’t never asking for a performance comparison to a 50 ohm probe or any other types of probes.Since a 10X probe is typically (10M || 15p) and a 1X probe is (1M || 60p or more) my answer is still valid.

author: tggzzz
author_rank: Super Contributor
timestamp: October 31, 2023, 08:42:19 am
content: Quote from: schmitt trigger on October 31, 2023, 01:37:50 amThe newbie almost certainly doesn't realise that the tip impedance of one of his "high" impedance probes is ~40ohms at 250MHz.If he is interested in "accuracy" then he should start to think about how that probe will affect the UUT.Once he thinks about that, he would probably want to find ways of reducing the problem, and a Z0 probe is a quick and easy way of doing it. All you need are a couple of resistors and a piece of coax. Easy to make at home, unlike a "high" impedance probe.

author: magic
author_rank: Super Contributor
timestamp: October 31, 2023, 09:43:41 am
content: Most likely neither of the results you have shown is correct.1x mode is definitely too slow for this signal.10x mode has overshoot and ringing which were likely caused by improper grounding of the probe. The bundled alligator clip cable is too long for fast signals, you need to remove the hook tip hood, attach a short wire to the ground contact on the probe and ground it to the board very close to the signal you are probing.These probes are a pain to use properly to their full potential. IME 100x are much more forgiving of sloppy grounding.