Top 10 Mistakes

How do I avoid mistakes in adjusting my scope settings?

(1) Avoid under-sampling the waveform as a wider time is attempted to be viewed with too short of memory oscilloscope. Remember - Sample rate * Memory depth = Recording Time.

(2) Avoid not getting and reading all of the scope application notes that address our project.

(3) List, know, and account for all error sources in our measurement system. Percentage of errors introduced by each are accumulative. A critical choice is whether the scope will be used for relative or absolute measurements. If absolute values are to be gathered and used, accounting for error sources and calibration to an absolute standard is mandatory.

• ADC Effective Bits
  
• ADC Non-linearities
  
• Aliasing (Extreme Undersampling)
  
• Amplifier - BW Rolloff, Noise, Non-Linearity
  
• Amplifier - DC Offset
  
• Aperture Jitter
  
• Calibration Error
  
• Interpolation (Using Linear Vs. SIN X/X Near Nyquist Frequencies)
  
• Misinterpreting Causes and Effects
  
• Misinterpreting Instrument Setup That Negates Or Changes Intended
  
• Misinterpreting/Misreading Values Displayed
  
• Noise In Scope
  
• Noise In Signal
  
• Probe Effects (Loading, Delay, Compensation, Grounding)
  
• Timebase Drift/Jitter
  
• Trigger Jitter
  
• Triggering Under The Wrong Conditions
  
• Under Utilized Dynamic Range (not Filling The Screen)
  
• Undersampling (too Few Samples/Sweep)
  
• Undersampling (too Few Sweeps To Know What Is Actually Happening)
  

(4) Remember to use the scope's true measurement power. An 8 bit amplitude measurement made automatically by the scope can be up to 5 times more accurate than a "by eye" approximation where cursors or grid squares are used.

(5) Remember to measurement statistics and taking only 1 measurement instead of using a millon or more measurements with persistence, histograms, statistics, etc. to let the scope show what is changing over time. Check FFT displays to see what is changing in the frequency spectrum.

(6) Remember to take the time to really learn the scope and keep its firmware upgraded to the latest version for access to new and useful features and bug kills.

(7) Don't use a passive probe and try to measure a high frequency and/or load sensitive circuit.

(8) Remember - looking at too small an area of time so the deeper wider view of causes and effects are missed.

(9) Don't use less than 80% of full scale range. An example is squeezing 4 traces on a single grid and using the volts/div. control to scale each waveform to a little less than 25% of full scale. This throws away 2 or more bits of resolution and accuracy.

(10) Make sure to network with others in your company or team that use your same or similiar model scopes and get their techniques, front panel set-ups, remote control software, and list of best practice methods, etc. An informal users group can be an incredible asset.