oscilloscope probes - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: September 09, 2012, 03:20:07 pm
content: Hi,I need some oscilloscope probes(voltage probes) for an old goldstar os-7020, 20Mhz 2 channel... There is something i should know before i buy something?

author: Unknown
author_rank: Unknown
timestamp: September 09, 2012, 08:14:24 pm
content: http://www.reprise.com/host/tektronix/reference/choosing_a_probe.aspShort version: you most likely want 10x (or optionally 10x/1x switchable) passive probes. Main thing to pay attention to is shipped accessories (should be OK for new probes, used probes are often missing accessories like ground leads or grabber hooks) and compensation range. You'd be hard pressed to find a 10x probe with less than 20 MHz. Compensation range might be an issue, since the input capacitance of your scope is likely to be fairly high.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 09, 2012, 09:05:28 pm
content: Given the limited bandwidth, and probably high capacitance of the scope input, I'd stick with a x1 probe.I bought these for my last scope:http://uk.farnell.com/testec/tt-lf312-2-6-10020-2-6/probe-oscilloscope-double-low-freq/dp/43080982x 150MHz switchable x1/x10 probes for just over £20, and there was nothing much wrong with them at all. There are lower bandwidth versions available for even less.

author: Unknown
author_rank: Unknown
timestamp: September 09, 2012, 09:48:29 pm
content: 1x probes suck, even at well below 20 MHz. Assuming probe + scope capacitance is 70 pF (this is quite optimistic, since a 20 MHz scope might have 47 pF of input capacitance even without the probe), impedance at 20 MHz will be about 100 ohm. This is quite a heavy load on most circuits. Many 1x probes don't have 20 MHz bandwidth, even driven from a 25 ohm signal gen source. For example, the probe you linked to is only 15 MHz at 1x.The critical spec for this application, which Farnell fails to list, is the compensation range from 10 to 60 pF. This should include your scope's input capacitance. This spec only applies to attenuating (eg. 10x) probes, not to 1x probes.

author: David_AVD
author_rank: Super Contributor
timestamp: September 10, 2012, 12:27:16 am
content: I bought some of the Uni-T 100MHz ones on eBay for general purpose use and they seem just fine. They came with colour coding rings, little ground spring, etc.

author: Unknown
author_rank: Unknown
timestamp: September 10, 2012, 08:50:39 am
content: I didn't know all of this... So i should buy a passive probe 1x/10x with at least 100Mhz for having an accurate measure at 1x isn't?

author: nctnico
author_rank: Super Contributor
timestamp: September 10, 2012, 12:01:24 pm
content: 100MHz probes are fine. No matter what the probe says it is useless to try and measure a signal over 100MHz with a standard 1:10 probe. What you should look for is a probe with a slim design so it is easy to probe in small spaces or connect multiple probes to a circuit.I use these:http://uk.farnell.com/testec/tt-lf312-2-6-10020-2-6/probe-oscilloscope-double-low-freq/dp/4308098And before I forget: the biggest mistake is to think probes last forever. Probes are expandables so be prepared to throw them in the bin when they get flaky.

author: robrenz
author_rank: Super Contributor
timestamp: September 10, 2012, 12:21:59 pm
content: Don't buy probes without making sure the the adjustable pF capacitance range spans the input pF capacitance of your scope. Otherwise you won't be able to to get a flat top on your square wave when compensating your probes. IMO most 100Mhz probes will not have enough pF range to work on your scope.

author: robrenz
author_rank: Super Contributor
timestamp: September 10, 2012, 12:36:57 pm
content: If your scope input is <40pF these will work and are incredibly cheap. this is the US circuit specialists site but they have a European site also.http://www.circuitspecialists.com/pp-80.html

author: David_AVD
author_rank: Super Contributor
timestamp: September 10, 2012, 08:58:45 pm
content: I had no trouble adjusting the Uni-T 100MHz probes to work with my scopes.

author: Unknown
author_rank: Unknown
timestamp: September 11, 2012, 08:08:10 am
content: where i see my scope input capacitance? Have I to mesure it or is just write somewere?

author: David_AVD
author_rank: Super Contributor
timestamp: September 11, 2012, 09:34:22 am
content: Quote from: Oracle on September 11, 2012, 08:08:10 amIt should be in the spec sheet for the scope I'd say. May even be marked on the front panel next to the BNC sockets.

author: Unknown
author_rank: Unknown
timestamp: September 11, 2012, 09:44:19 am
content: i just checked nothing, and the spec manual is gone... Anyway, i have an RLC meter could i measure it?

author: David_AVD
author_rank: Super Contributor
timestamp: September 11, 2012, 10:29:45 am
content: A 10 second Google search reveals this:http://bama.edebris.com/manuals/goldstar/os7020aYou'll need to download the djvu viewer application though. Link is on the same page.

author: Unknown
author_rank: Unknown
timestamp: September 11, 2012, 10:53:45 am
content: Quote from: David_AVD on September 11, 2012, 10:29:45 amThanks a lot man! I searched everywhere in Italian... English make miracles!the capacitance is 30pF parallel 1Mohm. I guess the probes posted before won't be so good for compensating signals.

author: David_AVD
author_rank: Super Contributor
timestamp: September 11, 2012, 11:27:18 am
content: The Uni-T 100MHz ones (example eBay link here) specify 15pF - 35pF compensation range, so should suit your scope.

author: Unknown
author_rank: Unknown
timestamp: September 11, 2012, 11:40:29 am
content: you are right: cheap and whit a good compensating range.... I'll take it.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 11, 2012, 06:47:13 pm
content: The Testec ones I linked to earlier will compensate up to 60pF, so they should be fine too.

author: Unknown
author_rank: Unknown
timestamp: September 11, 2012, 09:19:32 pm
content: Sorry, I didn't see the datsheetAnyway, it's good to know....From testec, i can order at my store: 150MHz,250Mhz.... should be ok? because i think it's a bit larger bandwidth

author: T4P
author_rank: Super Contributor
timestamp: September 12, 2012, 06:32:55 pm
content: Take the UNI-T anyway.

author: Nirios
author_rank: Regular Contributor
timestamp: September 12, 2012, 09:04:39 pm
content: Quote from: robrenz on September 10, 2012, 12:36:57 pmThose look *exactly* like the probes that came with my GWInstek scope. Thanks, now I know where I can find cheap replacements.