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The Wrong Way

A common, but very inaccurate method for measuring small signal voltages is the 10X oscilloscope probe with flying ground lead. The largest portion of the error is created by the large measurement loop consisting of the flying ground lead and the scope probe tip assembly. Another inaccuracy resides in the maximum sensitivity of the probe, which is usually 10 mV/div or 20 mV/div. Any small ripple measurement below the maximum sensitivity of the probe will be at the same order of magnitude of the channel noise and will be very hard to measure accurately. Note the measured output ripple in this example is approximately 70 mV peak-to-peak. This is the fastest way to make a measurement, but the results are not accurate.

PTM Published on: 2020-10-01