Author Topic: 10x probe compensation looks different depending on view  (Read 1609 times)

0 Members and 1 Guest are viewing this topic.

Offline optimizer

  • Newbie
  • Posts: 2
  • Country: us
10x probe compensation looks different depending on view
« on: January 17, 2017, 05:46:59 am »
i just got a dso nano v3 and a 10x  probe. when i use the probes that came with the nano the wave out looks like a proper square wave, and when i use the 10x probe set to 1x. as soon as i flip the switch to 10x the square isn't properly compensated so i adjust it to look as good as it can. when i "zoom in" on the wave it looks like it isn't compensated anymore. i redid the compensation in this zoomed in setting, but then a different view looks like it isn't compensated anymore. attached pics are with the 10x  compensated to the zoomed in view.

« Last Edit: January 17, 2017, 05:49:04 am by optimizer »
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 17050
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: 10x probe compensation looks different depending on view
« Reply #1 on: January 17, 2017, 06:33:46 am »
Welcome to the forum.

Hmmm.
The first two shots are spot on and as one would expect.  :-+
Does it have an Autoset ? Does that change the result ?
There's a few things I want to point out but it does indeed seem something's not right.  :-//

Scopes all have a spec of capacitance in their inputs, usually 10-20 pF and the compensation adjustment range of any probe need fall within it.

Probes only need be adjusted for their 10x range.
Input attenuation need match the probe to ensure on-screen measurements are correct, yours aren't.
Zooming of the vertical axis in the manner you have can give unexpected results if the offset limits are breached.
Avid Rabid Hobbyist
 

Offline T3sl4co1l

  • Super Contributor
  • ***
  • Posts: 14551
  • Country: us
  • Expert, Analog Electronics, PCB Layout, EMC
    • Seven Transistor Labs
Re: 10x probe compensation looks different depending on view
« Reply #2 on: January 17, 2017, 09:02:59 am »
What you're doing is setting a capacitor on the probe, so that it complements the capacitance of the scope.  (The probe is a resistor divider at low frequencies, and a capacitor divider at high frequencies.)

As you switch ranges on the scope, switches or relays connect different dividers between the probe and the input amp / ADC.  These dividers are themselves like probes: resistor and capacitor dividers.

When you probe a probe (so to speak), you only get the right response when all the resistor and capacitor dividers match up.  If the dividers aren't perfectly matched, then the capacitance of the scope can vary with setting, which means the probe compensation needs to vary as well.

At a glance, I don't see any specifications on that thing even mentioning capacitance, so, I'm betting on poor design.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline danadak

  • Super Contributor
  • ***
  • Posts: 1875
  • Country: us
  • Reactor Operator SSN-583, Retired EE
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 10486
  • Country: us
  • DavidH
Re: 10x probe compensation looks different depending on view
« Reply #4 on: January 17, 2017, 01:01:15 pm »
The schematic for the DSO Nano V3 is available online and shows a toy input stage with adjusted compensation on only 2 ranges out of 5.
 

Offline macboy

  • Super Contributor
  • ***
  • Posts: 2003
  • Country: ca
Re: 10x probe compensation looks different depending on view
« Reply #5 on: January 17, 2017, 02:35:06 pm »
I once put together a DSO138 kit to give to a family member going into EE. It had the same issue: input capacitance was not consistent across voltage ranges. This meant that the probe compensation needs to be adjusted every single time that you switch ranges. (FWIW the DSO138 doesn't come with a 10x probe, and this isn't an issue with its alligator clips).
 

Offline optimizer

  • Newbie
  • Posts: 2
  • Country: us
Re: 10x probe compensation looks different depending on view
« Reply #6 on: January 17, 2017, 05:54:12 pm »
thanks for all the replies. i knew the nano was a low level scope when i bought it, but i'm really only using it for setting gain levels in my car. i guess i was wanting to know if there was a standard view setting in which to compensate a 10x probe or if it needed to be done for whatever view setting you were going to be using for your source. if i need to compensate it for every different view, how can i get my square wave source up to the level that i'm going to be testing? one of my amps was putting out about 50 volts before it clipped.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf