What are the differences between the two frequency measurements that the TDS1000 and TDS2000 Series make?

What are the differences between the two frequency measurements that the TDS1000 and TDS2000 Series make?

The TDS1000 and TDS2000 series scopes both make two different types of frequency measurements. They are:

Automatic Measurement of Frequency

• Method used to make measurement: Reciprocal of the Period measurement. Made over the first complete cycle in the record. Period measured from the first mid-ref crossing to the third mid-ref crossing
• Accuracy (Typical): ± (1 sample interval + 50 ppm * reading + 0.6 ns)
• Resolution: 4 digits

Trigger Signal Frequency Readout

• Method used to make measurement: Provides the user with a means of identifying the frequency of trigger signals with higher accuracy than the Automatic Measurements. Since measurement is averaged over a longer time span, the number of stable digits is improved over the Automatic Frequency Measurement
• Accuracy (Typical): ±51 ppm including all frequency reference errors and ±1 count errors
• Resolution: 6 digits
• Counter Range: AC coupled, 10 Hz minimum to rated bandwidth
• Frequency Counter Signal Source: Pulse width or edge modes, all available trigger sources. Frequency counter measures selected trigger source at all times, including when oscilloscope acquisition is halted due to changes in run status, or acquisition of a single shot event has completed
  • Pulse Width Mode: Counts pulses of sufficient magnitude inside the 250ms measurement window that qualify as triggerable events (e.g. all narrow pulses in a PWM pulse train if set to < mode and the limit is set to a relatively small time)
  • Edge Trigger Mode: Counts all pulses of sufficient magnitude
  • Video Trigger Mode: Frequency Counter does not operate in this mode