9500B
Calibration Manual
68
Calculation of Acceptance Limits
1.
Introduction:
The first part of the verification procedure in section Verification Measurement
Procedure deals with measurement of rise/fall times, into an input impedance of
50
Ω
. Each rise/fall time is measured on a wide-bandwidth oscilloscope, whose
pulse response time is taken into account.
To calculate the Acceptance limits at each verification point, we must take into
account the User's Total Measurement Uncertainty and the specified 9500B
Speed Limit. These are combined using an RSS calculation.
2.
Example: Calculation of Acceptance Limits (500 ps at 25 mV)
•
From the Oscilloscope Specification, let us say that its Total Measurement
Uncertainty (500 ps at 25mV), is: ±20 ps.
•
With this we must combine (by RSS Method) the 9500B Speed specification.
At 500 ps, the 9500B specification speed is +50 ps to -150 ps.
•
Considering the upper limit:
Acceptance Limit =
(
) (
)
[
]
2
2
50
20
ps
ps
+
= 53.85 ps
•
We must now add this Acceptance Limit to the Nominal value of 500 ps,
giving the Upper Acceptance Limit of 553.85 ps.
•
Considering the lower limit:
Limit =
(
) (
)
[
]
2
2
150
20
ps
ps
+
= 151.32 ps
•
We must now subtract this Acceptance Limit from the Nominal value of 500
ps, giving the Lower Acceptance Limit of 348.68 ps.
Calculation of Acceptance Limit and Edge Speed Check
1.
Calculate the User's Total Measurement Uncertainty and Acceptance Limits, and
enter in the appropriate columns of the copy of the Table. For further assistance,
refer to Calculation of Acceptance Limits.
2.
Check that the Measured Value is at or between the Upper and Lower Validity
Acceptance Limits.
3.
Check that the difference between the '9500B Displayed Value' [recorded in
Verification Measurement Procedure operation 7(d)] and the 'Measured Value'
[recorded in Verification Measurement Procedure operation 7(c)] is within the
9500B displayed value accuracy specification of the Measured Value (see note †
below the table).
