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1594A/1595A Super-Thermometer
Specications
6
Primary Specications: the core set of measurement accuracy specications of the Super-Thermometer. They
are guaranteed for performance verication at the 99% condence level.
Ancillary Specications: additional specications that help the user understand more of the uncertainties
involved in measurement. Since they may be subject to the application and setting in which the Super-Ther-
mometer is used, they are not guaranteed for performance verication but should be considered typical.
General specications: general specications such as measurement range, environmental operating range,
dimensions, etc.
2.2.2 Primary Specications
2.2.2.1 Resistance Ratio Accuracy
Resistance ratio accuracy is the ability of the Super-Thermometer to measure the ratio of two resistances, Rx/
Rs. It is determined primarily by the linearity of the measurement circuit. The following specications apply
for resistance ratios measured with a reference resistor of 25 Ω or 100 Ω using a measurement current of 0.5
mA to 2.0 mA. Other reference resistors are specied using a factor as explained in the following specica-
tion table. Performance verication is guaranteed for 99% condence level specications within the specied
operating temperature range of 15°C to 30°C. The listed uncertainties are in terms of parts-per-million (ppm)
of reading unless stated otherwise.
Table 2 Resistance Ratio Accuracy Specifications
Ratio Range
1594A Accuracy
(ppm of reading)
1595A Accuracy
(ppm of reading)
95% condence level, 1-year
0.95 to 1.05 0.24 ppm 0.06 ppm
0.5 to 0.95, 1.05 to 2.0 0.64 ppm 0.16 ppm
0.25 to 0.5, 2.0 to 4.0 0.8 ppm 0.2 ppm
0.0 to 0.25 2.0 x 10
–07 †
5.0 x 10
–8 †
4.0 to 10.0 2.0 ppm 0.5 ppm
99% condence level, 1-year
0.95 to 1.05 0.3 ppm 0.075 ppm
0.5 to 0.95, 1.05 to 2.0 0.8 ppm 0.2 ppm
0.25 to 0.5, 2.0 to 4.0 1.0 ppm 0.25 ppm
0.0 to 0.25 2.5 x 10
–7 †
6.3 x 10
–8 †
4.0 to 10.0 2.5 ppm 0.63 ppm
†
Specications are in terms of absolute ratio
All specications listed in this table apply when using a 25 W or 100 W
reference resistor. Multiply stated specications by a factor of 2 when using a
10 W reference resistor with sensing current between 1 and 5 mA, and a factor
of 10 when using a 1 W reference resistor with sensing current between 5 and
20mA. When using a 10 kohm reference resistor, internal or external, use the
Absolute Resistance Accuracy specication in Table 4.
2.2.2.2 Resistor Stability
Resistor stability characterizes the ability of the instrument to accurately compare two similar resistances
within some time period using the internal resistors as references. The following specications apply using the
given reference resistor over a one-minute average. The specications assume typical laboratory conditions,
which do not include transportation and large ambient temperature uctuations.
Resistance stability is determined by the short-term stability of the internal reference resistors and control
stability of the temperature stabilizing block. It does not include measurement noise.