8508A
Users Manual
Equipment Requirements
The equipment required for performance verification of the 8508A is identical to the
equipment required for routine adjustment listed in Table 6-1. Alternate equipment may
be used, but users should ensure it provides adequate uncertainties, and consider the
impact of those uncertainties on allowable tolerance limits.
Interconnections
The Fluke 8508A-7000K Calibration kit contains a specially designed lead set which
connects directly to the terminals of the 8508A, the 5720A, and the 5725A for the
purpose of 8508A adjustment and performance verification. It is recommended that this
lead kit be used to avoid introducing measurement errors due to interconnections and to
duplicate the configuration used by Fluke for 8508A Calibration. A diagram showing the
interconnections used in detail appears in the Routine Adjustment section. If alternate
leads are substituted users must ensure they are metrology grade leads, and of adequate
voltage and current rating. Leads should be kept as short as possible, constructed from
low capacitance low leakage dielectric material (PTFE) with low thermal emf
terminations, and exactly duplicate the configuration and interconnections shown.
When checking the 2 GΩ and 20 GΩ resistance ranges the 1 GΩ standard resistor
supplied in the Fluke 8508A-7000K Calibration kit plugs directly into the 8508A front
input terminals without any interconnecting leads. If alternate resistance standards are
used for verifying performance of the resistance function, refer to the resistance
measurements section of Chapter 3 ‘Making Measurements’ for connection details.
Applicable Verification Tolerance and Conditions
The tolerances* listed in this verification procedure are derived from the 8508A 365 day
Tcal ±1°C 99 % Confidence Level Absolute specifications, which include contributions
for the performance of the 8508A itself and the uncertainty of the calibration standards
used to perform adjustment of the 8508A at the Fluke factory. They are applicable to a
verification performed within a period of 365 days from adjustment and at a temperature
within ±1°C of the temperature at which adjustment was performed (23°C for
calibrations performed by Fluke). It is recommended that these tolerances only be used
for verification of the 8508A following adjustment by Fluke, and if the above time period
and temperature conditions are met. No allowance has been made for the uncertainty of
the equipment used for verification. If the required conditions are met but the temperature
lies within ±5°C of factory adjustment, it is recommended that the user applies the 365
day Tcal ±5°C Absolute specifications instead.
For other circumstances, such as following adjustment by another laboratory, it is
recommended that the user derive verification tolerances* from the applicable 8508A
99 % Confidence Level Relative to Standards specifications (90 day or 365 day)
combined with the calibration uncertainties applicable to the previous adjustment. (RSS
summation is recommended, with calibration uncertainties also expressed at 99 %
confidence level).
The 8508A temperature coefficient specifications should also be applied if the
temperature at verification is outside the range applicable to the 8508A specifications to
be used.
Refer to Chapter 5 for further information on applying specifications and combining
uncertainties.
Note that the tolerance testing is done with 7-digit resolution for speed and efficiency
reasons. However, the tolerance limits are based on the tighter specifications of 8-digit
measurement resolution. (The minor tolerance adders for the reduced resolution are
disregarded as practically insignificant in most cases. These adders apply to DC volts,
6-36
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