The World's Most Stable Resistance Standard

IET continues to manufacturer the SR102 & SR104 to the same exacting specifications as esi/Tegam

The esi SR102, SR103 & SR104 are a highly stable (±0.5 ppm/year) and accurate (1 ppm), 100 Ω, 1 kΩ, 10kΩ resistance standards. The SR102, SR103 and SR104 Standards are equipped for five-terminal measurements used for Standard Resistor readings and for Temperature Sensor readings. Individual calibration data, which identifies the standard deviation, and the temperature coefficients, is supplied with each unit. In addition, each unit is equipped with a thermal well so that the exact temperature of the resistance standard is known. This allows the user to make highly precise, temperature compensated, measurements.

esi SR102 100 Ω Primary Resistance Standard
These resistance standards were designed to provide an important link between Quantum Hall resistance values and traditional decade resistance values. 100 Ω provides unique reference capability.

esi SR103 1000 Ω Primary Resistance Standard
New resistance standard recently developed to improve the range of primary standards available.

esi SR104 10 KΩ Primary Resistance Standard
This has been the long-standing industry standard for the 10 kΩ. This everlasting standard is the benchmark for high accuracy, stability and low temperature coefficients for calibrations requiring traceability to the SI.

The SR102, SR103, and SR104 Precision Transportable Resistance Standards are oil filled, hermetically sealed, five-terminal resistance standards designed for precision bench top or oil bath applications.

The long-term stability of these resistance standards is typically less than 0.2 ppm per year and temperature coefficients are less than 0.1 ppm per degree Celsius.

esi Primary Standard History

esi originally designed the SR104 in the late 1960s or early 1970s.The primary resistance standards consists of at least 10 equal resistors (R) that are connected in series, parallel, or series-parallel. This results in resistance values that are l0R (SR104), R/10 (SR102), or R (SR103).

Excellent long-term stability and low temperature coefficient was achieved by using matched groups of resistors, constructed using the alloy Evanohm-R on a mica card.

The New IET Labs SR104 Design
In January of 2007 IET Labs purchased the esi resistance product line from Tegam. TEGAM had acquired the esi (Electro-Scientific Industries) product line in 1993 from esi.

The new SR102, SR103 and SR104 are no longer designed using Evanohm-R wire but instead use 10 custom hermetically sealed oil-filled Bulk Metal® Foil resistors.

Each resistor is individually tested and then combined in sets that are matched for absolute tolerance and temperature coefficient.

These sets are then allowed to age typically for several years before use.

The resistors are still connected in series, parallel, or series-parallel to achieve the final resistance value.

Each SR102, SR103 and SR104 is tested using an MI6010 and transfer standards that are calibrated annually by primary standards labs such as NRC. Typical calibration uncertainty is < 0.4 ppm.

The resulting low temperature coefficient allows high performance applications of these standards inside or outside an accurately controlled temperature environment.

Maximum accuracy is calculated as a temperature corrected resistance value. This is accomplished by using the built-in RTD temperature sensor to measure the internal temperature and referencing a temperature correction chart provided with each unit. The measurement accuracy of the built-in RTD thermometer is better than 0.1 degree Celsius.

Very low power coefficients are achieved by using standard resistors constructed with large surface areas like our original Model SR104, 10 kΩ standard resistor. The resistors are surrounded by oil to conduct heat generated by the measuring currents out through the stainless steel case.

These characteristics facilitate precise laboratory comparisons without critical environmental controls and are used wherever a need for a very accurate, stable resistor of low temperature coefficient is required.

EEvblog post on calibration and SR104
Excellent post on calibration from eevblog in 2019 on SI redifinition and my "TiN" experience with NMI calibration this also references IET's SR104 standards.

Models
100 ohm Transportable Resistance Standard: SR-102
1,000 ohm Transportable Resistance Standard: SR-103
10,000 ohm Transportable Resistance Standard: SR-104
Optional:
For deleted case version add -DC at the end of the part number

Each unit includes:
5 Year Warranty
Built-in temperature sensor
Temperature correction chart
Instruction manual
ISO/IEC 17025 calibration certificate

Features: