Testing Performance 3
S-Series Oscilloscopes Service Guide 41
Time Scale Accuracy (TSA) Test
This procedure verifies the maximum TSA specification for the oscilloscope.
Description
TSA refers to the absolute accuracy of an oscilloscope’s time scale. Because TSA
depends directly on frequency of a crystal oscillator, it is comprised of two
components: an initial setting accuracy component and an aging component.
The initial setting accuracy component applies to the oscilloscope’s 10 MHz OCXO
frequency accuracy immediately after a calibration, whether performed at the
factory, by a customer, or by a Keysight service center. The aging component
scales linearly from the time since the last time scale calibration and adds to the
initial setting accuracy component.
Specifications
TSA is published as a warranted specification, expressed by the following formula.
The aging component is specified by the 10 MHz OCXO manufacturer while the
initial setting accuracy component is derived from absolute frequency
measurements of the 10 MHz OCXO in a large sample of production units after a
time scale calibration prior to shipment. These measurements require the 10 MHz
OCXO to be powered on for a minimum of 2 hours. Longer is better to further
reduce the uncertainty and allow the OCXO frequency to settle onto the aging
trajectory of the crystal inside the oscillator.
TSA = ±(12 ppb initial + 75 ppb/year aging)
To see the number of years since the last time scale calibration, open the
oscilloscope application and click Utilities > Calibration.... The TimeScale entry in the
Calibration dialog box shows the date of the last time scale calibration.
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