15 Reference
406 InfiniiVision Oscilloscopes User’s Guide
Using the 10 MHz reference clock
The 10 MHz REF BNC connector on the rear panel is provided so you can:
• Supply a more accurate sample clock signal to the oscilloscope, or
• Synchronize the timebase of two or more instruments.
Sample clock and frequency counter accuracy
The oscilloscope’s timebase uses a built-in reference that has an accuracy of 15 ppm.
This is sufficient for most uses. However, if you are looking at a window that is very
narrow compared to the selected delay (for example, looking at a 15 ns pulse with the
delay set to 1 ms), significant error can be introduced.
Using the built-in sample clock, the oscilloscope’s hardware frequency counter is a 5-digit
counter.
Supplying an external timebase reference
When you supply an external timebase reference, the hardware frequency counter is
automatically changed to an 8-digit counter. In this case, the frequency counter ([Quick
Meas]
&Select&Counter) is as accurate as the external clock.
For more information on the hardware frequency counter, see “Counter” on page 199.
To supply a sample clock to the oscilloscope
1 Connect a 10 MHz square or sine wave to the BNC connector labeled 10 MHz REF. The
amplitude must be between 180 mV and 1 V, with an offset of between 0 V and 2 V.
2 Press [Utility]&Options&Rear Panel&Ref Signal.
3 Use the Entry Knob and the Ref Signal softkey to select 10 MHz input.
Maximum input voltage at 10 MHz REF connector: Do not apply more than ±15 V at
the 10 MHz REF BNC connector on the rear panel or damage to the instrument may
occur.
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