Why Are the Results of Vpp, Vmax, and Vmin Measurements Incorrect at Low Frequency on 53230A?

Frequently Asked Questions (FAQs)

Summary

Vpp, Vmax, and Vmin measurements are not guaranteed for input frequencies less than 50 Hz

Question

Why are the results of Vpp, Vmax, and Vmin measurements incorrect at low frequency?

Answer

Vpp, Vmax, and Vmin measurements are not guaranteed for input frequencies less than 50 Hz. Vpp, Vmin, Vmax are determined using a binary search technique and the counter’s input comparators. Once a threshold is established by the comparators, the binary search begins from that level until a “peak” is determined. The window during which the amplitude is determined is very short for input signals of 50 Hz and less. Thus, the actual (accurate) peak is not consistently determined.

For the user's pulse width of 100 ms the counter is able to accurately determine the amplitude. For a 1 ms pulse width it is not. For any frequency below the auto-level cut-off frequency (50 Hz), however, the Vpp, Vmin, and Vmax values should not be considered valid. These measurements are “secondary” measurements. Their intent is to provide the user with information on the input signal level from which applicable trigger levels can be set. They are not intended to have the accuracy and stability of a digital multimeter.