Scope Probe query please.

Discussion in 'General Electronics Chat' started by orbiter, Jul 7, 2010.

  1. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
    3
    Hi all,

    I've tried to gain an answer to this question from Owon and Mouser (UK) but neither company seem intrerested in emailing me back with assistance.

    The problem is.. I've managed to crack one of my scope probes so would like to replace the ones my scope came with, preferably with some new Pomona ones. I should be very grateful if somebody could please take a look at the following Mouser link, and tell me which pomona probes would be suitable for my scope please?

    Pomona probes...http://gb.mouser.com/_/N-scv7?Keyword=oscilloscope+probes&FS=True&Ns=Pricing|0

    Pomona probe specs... http://www.pomonaelectronics.com/pdf/d4550b-sp150b_6_01.pdf


    My original probes have what looks like a Tektronix number on them (P6060 & 60MHz)

    My scope specs are....

    Bandwidth 25MHz
    Input impedance: 1MΩ ±2%, in parallel with 20pF ± 3pF

    Original probes...

    1x/10x
    Compensation range...... 20pF - 40pF
    Input resistance.......... 1Mohm +/- 2% / 10Mohm +/- 2%
    Input electrical capacity... 1x = 85pF - 115pF / 10x = 14.5pF - 17.5pF


    I can supply more info and pics of my probes if required?

    Thanks for your help guys

    orb
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Last edited: Jul 7, 2010
    orbiter likes this.
  3. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
    3
    Yes those look the same as mine, however they are pretty cheap ones, and since I've broken one of mine.. I'd like to get myself some good ones. I know Pomona ones are pretty good as I use them with my meter.

    I'd just like someone who has experience of probe specs to check out the pomona probes AND my scope specs to see which are suitable, as it's important for both scope & probes are compatible.

    regards

    orb
     
    Last edited: Jul 7, 2010
  4. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
    3
    Still need help to original post guys please.

    Sorry for double post but couldn't edit previous one as the button went missing :(
     
  5. timrobbins

    Active Member

    Aug 29, 2009
    318
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    Any of the Pomona 1/10 will do a reasonable job - but not if you are doing above 300Vpk or want specified max B/W.

    Always cal the probes, and do a swap comparison if you get into high spec applications.

    Ciao, Tim
     
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  6. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
    3
    I don't understand my friend. Why so many Pomona probe variations then?

    I do understand the max bandwidth part. However I have read that it is very important to get a set of probes with the correct attenuation and compensation range too. And this is what is confusing me as the Pomona spec page I linked to doesn't show probes specs that are close to my scope specs as regards attenuation and input capacitance etc.

    Please advise further

    Kind Regards

    orb
     
    Last edited: Jul 7, 2010
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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  8. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
    3
    Please don't take this the wrong way beenthere, but did you read my first post?
    I know what I'm after, I just want to make sure the Pomona probes I order are correct ones for my scopes specs. I'm a noob when it comes to this sort of thing you see and I need some help from you guys so that I don't order something that won't work properly, or is the wrong spec.

    Regards

    orb
     
  9. tom66

    Senior Member

    May 9, 2009
    2,613
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    I have the exact same probes (100MHz) mentioned by bountyhunter. Been using them about 2 months, no problems so far, but I haven't been using them for precision applications, so can't confirm their accuracy (manual says 1% DC accuracy) or their -3dB bandwidth etc. I measured the FSB clock (approximately a sine wave) of a computer using them, at 133 MHz, with no problems, on my 100 MHz scope, which was pretty cool.

    As far as I understand, pretty much any scope probe will work with any other scope, provided they aren't 'special' like some kind of FET input type or differential or something like that, and that they have the right connector.

    Most probes have adjustable capacitance settings as a trimpot. The impedance is not usually a problem because most scopes in my experience are not more than 0.5% accurate (mine is 1.5%, a new scope will do about 1%) when it comes to measuring voltage. Just make sure that if you buy a 1 megohm probe you use it with a scope with 1 megohm input impedence. Usually the probe lets you select between a 9 megohm resistance and zero, in the 10X and 1X modes.
     
    Last edited: Jul 7, 2010
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  10. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
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    Ok Thanks tom for explaining, I think I understand.

    The confusing part for me is this input capacitance range. I was lead to believe this was a critical part in choosing a probe?

    Am I right in thinking then that... As long as my scopes input capacitance (20pF +/- 3pF) is between the the probes compensation range (10 - 60pF) which it is. I'll be fine choosing the cheapest (£70 :eek: ) 4550B probes?






    [​IMG]

    Kind Regards

    orb
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    4550B looks like the best choice to me.
    The input capacitance column refers to the capacitance at the probe tip for X1 and X10 attenuation. The 4550B has 64pF input C at X1, and 10.5pF input C at X10, for a scope with 20pF input C, which yours has.
     
    Last edited: Jul 7, 2010
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  12. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
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    OK so just to confirm please..

    I needn't worry about all the other figures in the Pomona chart. And the the '4550B' probes specs are fine for a 25MHz scope with a Input Impedance of... 1MΩ ± 2%, in parallel with 20pF±3pF?

    Regards

    orb
     
  13. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    The 100MHz X10 probe BW, in conjunction with the 25MHz scope, will reduce the system BW to about 24MHz.
    The 15MHz X1 probe BW, in conjunction with the 25MHz scope, will reduce the system BW to about 12MHz. Note that none of the probes in the table you posted have a readout actuator pin. On some scopes, this pin, if present, will illuminate the appropriate scale factor on the scope's attenuator. I don't know if any of the TEK scopes have this function for the X1/X10 probes.
     
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  14. beenthere

    Retired Moderator

    Apr 20, 2004
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    The 475 had that function. My 2221 does not.
     
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  15. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
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    Ah ok, This is what I was worried about you see in not getting probes that where 100% compatible. I had an idea all those numbers meant something ;)

    OK.. I guess to be on the safe side then I should just get a similar pair of probes to the ones I have now from ebay. I can get some tek clones (same as I have now) for around £6. At least this way I'll not loose any BW by getting the same type.

    Thanks guys

    Regards

    orb
     
  16. lightingman

    Senior Member

    Apr 19, 2007
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  17. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What's the part number of the probes you are replacing? I suspect they have similar bandwidth limitations.

    The X1 BW of the probes on Ebay is only 6MHz.
     
  18. orbiter

    Thread Starter Active Member

    Jun 17, 2010
    58
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    The probes that came with the scope are tektronix copies I think and are 60MHz probes. The part number is P6060.

    EDIT: My currenty probes specs are..

    DC: Up to 6 MHz (x1) and (up to scopes full BW which will be 25MHz (x10)
    Compensation range: 20pF - 40 pF
    Input capacity: 85pF - 115pF (1x) 14.5pF - 17.5pF (x10)
     
    Last edited: Jul 8, 2010
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