Applying The Specifications - Fluke 8508A Extended Specifications

Operating and calibration
temperature ranges
As a metrology tool, the 8508A will commonly
be used in a calibration laboratory where the
temperature would be controlled to ±1 °C, and
the 8508A ±1 °C specifications are applicable to
those situations. The majority of electrical
calibration laboratories operate at a nominal
temperature of 23 °C, the temperature at which
the 8508A is calibrated by Fluke during manu-
facture and service. The 8508A is also capable
of being calibrated at any temperature between
20 °C and 25 °C and the ±1 °C specifications will
apply to operation within ±1 °C of that calibra-
tion temperature. In the 8508A specification
tables, the temperature of calibration is referred
to as TCal. Specifications for ±5 °C are provided
for situations where the 8508A is operated in
environments with wider temperature variations
up to ±5 °C. For applications where the knowledge
of the effect of temperature on 8508A perform-
ance is important, temperature coefficients are
listed in the 8508A specifications. If the operating
temperature is within the range 15 °C to 30 °C,
the 15 °C to 30 °C temperature coefficient
specifications are applicable; otherwise use the
5 °C to 15 °C/30 °C to 40 °C figures, provided
the temperature lies within that range. The
8508A may be operated at temperatures
between 0 °C and 50 °C, but performance is not
specified outside the range 5 °C to 40 °C.
The Fluke 8508A and 8508A-SPRT Standard
Platinum Resistance Thermometer

Applying the specifications

Applying temperature coefficient
specifications
The 8508A specification tables include
information for the typical operating conditions
of ±1 °C for calibration laboratories with tight
temperature control, and ±5 °C for calibration
laboratories with looser temperature control or
uncontrolled environments within that tempera-
ture range. For the majority of applications,
choosing the Absolute specifications for the most
appropriate operating temperature range will be
adequate. However performance at other
temperatures may be determined by including
an allowance for temperature coefficient over
the additional temperature range. Care should
be taken when making this calculation, as an
amount of temperature coefficient is already
included in the 8508A specifications, and those
specifications are themselves based on combining
contributions using techniques similar to those
employed in uncertainty analysis. For example,
consider operating at 33 °C, 10 °C from the 23 °C
calibration temperature. The ±5 °C specifications
already include a contribution for 5 °C of tem-
perature difference, so this amount of temperature
effect must be removed before the effect of the
10 °C difference is added. Consider 10 V on the
20 VDC range: 365 day absolute specification
(95 %) at 33 °C expressed in parts-per-million of
10 V is:
Fluke Corporation
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8508A Extended Specifications