HP 53132A Assembly And Service Manual page 243

Measurement Definitions
Definitions of Systematic Uncertainty Terms
• Trigger Error
External source and input amplifier noise may advance or delay the trigger points that define the beginning and end of a measurement.
The resulting timing uncertainty is a function of the slew rate of the signal and the amplitude of spurious noise spikes (relative to the input
hysteresis band).
The (rms) trigger error associated with a single trigger point is:
Trigger Error ------------------------------------------------------------------------------------------------------ - (in seconds)
=
Input Signal Slew Rate at Trigger Point
where
= RMS noise of the input amplifier: 1 mVrms (350 µVrms typical). Note that the internal measurement algorithms significantly
E
input
reduce the contribution of this term.
E = RMS noise of the input signal over a 225 MHz bandwidth (100 kHz bandwidth when the low-pass filter is enabled). Note that
signal
the filter may substantially degrade the signal's slew rate at the input of the trigger comparator.
• Fractional Time Base Error
Time base error is the maximum fractional frequency variation of the time base due to aging or fluctuations in ambient temperature or line
voltage:
f ∆

Time Base Error ---- -
=

f aging rate
Multiply this quantity by the measurement result to yield the absolute error for that measurement. Averaging measurements will not reduce
(fractional) time base error. The HP 53181A counters exhibits negligible sensitivity to line voltage; consequently this term may be ignored.
Typical Versus Worst Case Specifications
Specifications identified as "Typical" represent performance of the instrument that the majority of users will perceive under a wide variety of
conditions and signals. The specifications identified as "Worst Case" should be used when the instrument is under extreme environmental
conditions or when the accuracy of the measurement results are critically important.
Chapter 8 HP 53181A Specifications
Measurement Definitions
2 2
( ) ( )
E + E
in put signa l
f ∆ f ∆

---- - ---- -
+ +

f temperature f line voltage
Assembly-Level Service Guide 8-9