Why does the DPO2000 or MSO2000 series oscilloscope sometimes present the record length selections as 100k and 1.00M but other times it presents 125k and 1.25M+ or 125k and 1.00M?
Here are the rules to understand when a record length is available:
For the "short" record lengths:
100k record lengths: Time/Div <= 40us (40 us/div and faster)
125k record lengths: Time/Div >= 100us (100 us/div and slower)
For the "long" record lengths:
1.00M record lengths: Time/Div <= 400us (400 us/div and faster)
1.25M record lengths: Time/Div >= 1ms (1 ms/div and slower)
The reason for the longer than advertised record lengths at slower timebases is so the instrument offers the advertised 1 M record length at all timebases. The formula to calculate the record length for an acquisition is: Time *Sample Rate = Record Length. The design of the MSO 2000 and DPO2000 series has fixed sample rate possibilities (e.g. 1GS/s, 500 MS/s, 250MS/s, 125MS/s) and keeps time/div numbers consistent (i.e. 1, 2, 4). So the record length has to change since the other two "variables" in the equation are kept constant (Time*Sample Rate = Record Length where Time is the time on screen or time/div * 10).
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