The combination of sampling frequency and record length forms the time base of an oscilloscope. To setup the time base properly, the total measurement duration and the required time resolution have to be taken in account.
There are several ways to find the required time base setting. With the required measurement duration and sampling frequency, the required number of samples can be determined:
With a known record length in samples and the required measurement duration, the necessary sampling frequency can be calculated:
In the Multi Channel oscilloscope software, both record length and sampling frequency can be set independently, to give the best flexibility. They can be selected from menu's, using toolbar buttons but also keyboard short cuts are available. For more information, refer to:
The Multi Channel oscilloscope software also provides controls to change record length and sample frequency simultaneously to specific combinations to obtain certain time/div values:
- Clicking the decrease/increase Time/div buttons and on the instrument toolbar.
- Clicking the Time/div indicator on the instrument toolbar and selecting the required time/div value from the popup menu.
- Using hotkeys Ctrl + F11 (lower) and Ctrl + F12 (higher)
Because a certain time/div setting can be created from different combinations of record length and sampling frequency, the Multi Channel oscilloscope software must decide which combination is used. The software will try to use the highest sample frequency possible and will adjust the record length accordingly to obtain the required time/div setting.
To avoid the record length becoming this long that collecting the measured values takes longer resulting in the scope responding slower, the record length for time/div settings is limited to a value that can be set in the program settings. When the time/div setting is adjusted by one of the corresponding controls, the maximum record length is limited to this value.
This limit does not apply to manually adjusting the record length.