On 7/11/2016 5:49 PM, Schaefer, David wrote:
These were all calibrated probes, and three were identical models. The
one that was way off wasn’t the odd model. Our cal house measures a DC
voltage for accuracy, and bandwidth.
What’s causing the inaccuracy? How can I prevent this problem in the
future? Moving to all active probes isn’t an option right now.
In addition to what's been written in other replies, there is a
difference in calibration if you even hold the oscilloscope probe
differently when measuring faster, high-frequency signals. It's always
better to use the short steel wire (or coaxial tip adapter) ground
connection provided with a high-frequency probe when making high-speed,
high frequency measurements – and changing the ground lead requires
*readjusting the probe's user calibration*. That's what the CAL
terminal on a 'scope front panel is for.
Metrology departments might think probe calibration is sacred and
forever, but it's not.
Cortland Richmond
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