Test and Measurement Forum

Calibrating of USB Oscilloscope 4424

Post any questions you may have about our current range of oscilloscopes

Calibrating of USB Oscilloscope 4424

Postby Erne » Fri Jan 06, 2012 3:06 pm

Hello together,
is it necessary (and possible) to calibrate the input channels of the scope?
If i measure on both channels the same dc-voltage (8V), i get a difference of A-B=17mV (measured with dc average on math channel A-B). Afterwards i interchange the probes and do the same measurement with the same result. With that the reason for the difference is not a voltage drop of one of the probes. What can be the reason, and what to do to avoid this?

best regards
erne
best regards
Erne
Erne
Newbie
 
Posts: 0
Joined: Fri Jan 06, 2012 2:53 pm

Re: Calibrating of USB Oscilloscope 4424

Postby Hitesh » Tue Jan 10, 2012 1:31 pm

Hi Erne,

We normally recommend calibration on a yearly basis:

http://www.picotech.com/calibration.html

You are free to choose where to calibrate the device - if you would like us to calibrate the device, please e-mail support@picotech.com

With regards to the offset, it should be 1% of the full scale range e.g. +/-5uV for a +/- 50mV range.

Regards,
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2004
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: Calibrating of USB Oscilloscope 4424

Postby Erne » Fri Feb 10, 2012 7:25 am

Thank you for the hints...

best regards
Erne
best regards
Erne
Erne
Newbie
 
Posts: 0
Joined: Fri Jan 06, 2012 2:53 pm

Re: Calibrating of USB Oscilloscope 4424

Postby Hitesh » Fri Feb 10, 2012 2:39 pm

Hi Erne,

I appreciate I may not have answered the question fully as I thought it was just a calibration issue. We've taken a further look into this and the suggestion is to setup a Custom Probe for each of the channels as required in order to scale the values.

The steps to take are as follows:

  • Use a 50 Ohm terminator or a short on each channel to measure the offset from 0V in PicoScope.
  • Apply the 8V DC input on each channel and measure the voltage.
  • Reverse the input to achieve a -8V signal and measure the voltage on each channel - this will help to see if the difference is the same at the positive and negative end.
  • Subtract the offset from your readings for each channel if it is 1mV or above.
  • If you have obtained negative readings, you can average the magnitude with the positive readings to obtain an average reading.
  • If your reading is outside 1% of the range, then you will need to scale the value.
  • Divide the average reading by 8V to obtain your scale value.
  • Next within PicoScope, click on the Channel options icon for the channel you need to scale, in our case it was Channel B.
  • Next click the '...' icon next to the Probe drop-down menu.

    Channel_Options_Probe.png
    Channel options - Probe selection

  • In the Custom Probes window, click 'New Probe...'
  • Click 'Next >' when the Custom Probe Wizard appears.
  • Leave the 'Probe Output Units' as volts.
  • In the Scaling Method dialog, enter your scaling value (m) and offset as required.

    Scaling_method.png
    Scaling method - set for 99% scaling.

  • Click 'Next >' and 'Next >' again on the Range Management dialog.
  • Enable the Filter as required and click 'Enter', then click 'Next >'.
  • In the Custom Probe Identification dialog, enter a name for the Custom Probe and a short description.
  • Click Finish.
  • A new probe will appear in the Library.

    Custom_Probes.png
    Custom probes dialog.

  • Select the probe and click 'OK' to begin using it.
  • Repeat for the other channel as necessary.

I have attached an example Custom probe that I created which scales the value to 99%. You can use the Import function in the Custom Probes dialog to load this into PicoScope.

ChB_Probe_99_pc.psprobe
99% scale probe
(988 Bytes) Downloaded 130 times


Hope this provides suitable clarification.
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2004
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire


Return to USB PC Oscilloscopes

Who is online

Users browsing this forum: No registered users and 0 guests