Is it worth buying better oscilloscope probes? - Page 1
Forum section: electronics / beginners

author: RogerRowland
author_rank: Regular Contributor
timestamp: June 16, 2015, 04:53:58 am
content: I've had a 100MHz Siglent SDS1102CML for a few months now and although it serves me well for the sort of stuff I'm messing around with (mainly 8-bit PICs), I can't help noticing that the probes it was supplied with are exactly the same as a pair I picked up on eBay for £10 when I used an old analogue scope.Is it worth buying some "better" probes? What difference would I see? Do I have to use 100MHz probes or could I use 150MHz or 200MHz? Can I use HP or Tek probes withanyscope? I'm struggling to see how the prices vary so much, not just for 500MHz and up (which I sort of understand) but 100MHz - 200MHz probes can range from £5 to £70.Should I just use what I've got?

author: coppice
author_rank: Super Contributor
timestamp: June 16, 2015, 05:41:43 am
content: You haven't described a problem with what you are using now. Do you actually have one? Cheap probes are generally pretty reasonable these days. Probes are fragile, however much you pay. If cheap ones are working OK for you, stick with them. You won't cry when you turn quickly and rip the end off a $10 probe.

author: tautech
author_rank: Super Contributor
timestamp: June 16, 2015, 06:04:56 am
content: They're better quality than many that are shipped with this class of scope.Things to consider:They will match the scopes spec for a max of -3db waveform at rated bandwidth.The range of compensation adjustment WILL suit the scope better than some other probes.For replacements to be of any advantage, they should be selected to impose a lower loading on the DUT.All connections to a DUT will affect the resultant waveform to some degree, this is widely accepted.Solutions to this problem include Active probes, the cost of which will exceed the cost of your scope.One should be in the habit of using probes at 10:1 to affect the DUT waveform to a lesser degree.I've always thought the Siglent probes to be better than the P6*** probes that are widely available.

author: RogerRowland
author_rank: Regular Contributor
timestamp: June 16, 2015, 06:28:18 am
content: Ok, thanks guys, I'll stick with what I've got until I suspect I need otherwise.Quote from: coppice on June 16, 2015, 05:41:43 amNo ideaHow would I know? Is there any "obvious" symptom that would point at a poor probe?EDITActually, I just foundhttps://www.eevblog.com/forum/reviews/cheapest-100mhz-oscilloscope-probes-hands-on-review/, which is useful ....

author: tggzzz
author_rank: Super Contributor
timestamp: June 16, 2015, 06:41:40 am
content: Quote from: RogerRowland on June 16, 2015, 04:53:58 amIt is good to see someonethinkingabout the imperfections of their test equipment, rather than just accepting whatever they see. One way of seeing the strengths and weaknesses of your probe and probing technique is to look at theedgeof a fast digital signal (fast is <2ns risetime for a 100MHz scope)There are significant problems withanypassive 10Mohm high impedance probe:it isn't high impedance (not even kohm, let alone Mohm). The same problem is, to a lesser extent, true for lower frequency probes.it can show ringing at ~100MHz. This is often visible in pictures of digital waveforms postedthe risetime of a scope plus probe increases in a sum-of-squares fashion, so a 100MHz probe plus 100MHz scope has a combined bandwidth of 70MHzHave a look at the theory and practice probes athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/Have a look at the causes and cure for the "100MHz oscillation" athttps://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/Consider using a "low impedance Z0 probe" - which has ahigherimpedance than a 10Mohm probe.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 16, 2015, 06:48:59 am
content: You can bide your time and wait for some nice probes to happen to come your way too. Spot a nice set on ebay or here in the buy-and-sell maybe.I couldn't find the tip capacitance of the Sigilent probes, but a nice high frequency passive probe (300-500MHz) will be on the order of 9pF. It doesn't sound like much but at 100MHz that's effectively 176 ohms your loading down the circuit with when you probe. Note this shows how passive probes kind of hit the end of the road at these frequencies; the tip capacitance just kills them.

author: RogerRowland
author_rank: Regular Contributor
timestamp: June 16, 2015, 06:50:58 am
content: Quote from: tggzzz on June 16, 2015, 06:41:40 amExcellent! That's a really helpful reply, many thanksI've always grown up with the "trust nothing, question everything" approach that my father taught me (he's 87 and still preaching ... even though I'm now 56!) but as EE is a diversion from my normal profession, I've found it hard to find expert advice until I stumbled upon EEVBLOG - good stuff.