1594A/1595ASuper-Thermometer
Specifications
6
Primary specifications:
the core set of measurement accuracy specifications of the Super-Thermometer. They
are guaranteed for performance verification at the 99% confidence level.
Ancillary specifications:
additional specifications 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 verification but should be considered typical.
General specifications:
general specifications such as measurement range, environmental operating range,
dimensions, etc.
2.2.2 Primary specifications
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 specifications 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 specified using a factor as explained in the following specifica-
tion table. Performance verification is guaranteed for 99% confidence level specifications within the specified
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% confidence 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% confidence 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
†
Specifications are in terms of absolute ratio
All specifications listed in this table apply when using a 25
W
or 100
W
reference resistor. Multiply stated specifications 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 specification in Table 4.
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 specifications apply using the
given reference resistor and excitation current and for a one-minute average. The specifications assume typical
laboratory conditions, which do not include transportation and large ambient temperature fluctuations.
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.
