1594A/1595A Super-Thermometer
Specications
6
Primary Specications: the core set of measurement accuracy specications of the Super-Thermometer. They
are guaranteed for performance verication at the 99% condence level.
Ancillary Specications: additional specications 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 verication but should be considered typical.
General specications: general specications such as measurement range, environmental operating range,
dimensions, etc.
2.2.2 Primary Specications
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 specications 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 specied using a factor as explained in the following specica-
tion table. Performance verication is guaranteed for 99% condence level specications within the specied
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% condence 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% condence 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
†Specications are in terms of absolute ratio
All specications listed in this table apply when using a 25 W or 100 W
reference resistor. Multiply stated specications 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
20mA. When using a 10 kohm reference resistor, internal or external, use the
Absolute Resistance Accuracy specication 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 specications apply using the
given reference resistor over a one-minute average. The specications 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.