For low resistance transfer standards, consider the esi SR1010 or SR1030
IET Labs continues to manufacturer the SR1050 to the same exacting specs as esi/Tegam
Each of the esi SR1050 transfer standards consists of 11 equal steps. These steps are available in increments of 1M Ù, (SR1050-1M) and 10M Ù, (SR1050-10M). The esi SR1050 provides a three terminal connection for each step or for a series of resistance steps. Specially designed lever switches separate each resistor from the others. This allows the standard to be configured in series, parallel, series-parallel, or separately without the use of external shorting bars.
Precise transfer measurements up to 110 M Ù relative to a single 100 k Ùresistance standard can be obtained with the esi SR1050 High-Resistance Transfer Standards. The unit is available in two models: 1 M Ù and 10 M Ùresistance sections.
Based on a unique method for establishing known ratios, the esi SR1050 standard utilizes a transfer technique that consists of switching resistance sections in parallel, series or series-parallel sections. An outstanding design feature is a structure in which the only insulation leakage paths (other than those within each resistance section) are from the external terminals to ground. This eliminates insulation leakage errors in the transfer of calibration from one resistance level to another using three-terminal measurement techniques.
A specially designed lever switch provides a convenient means of switching into parallel and series parallel configuration without introducing insulation leakage errors. External shorting or paralleling bars are not necessary. Each resistance section consists of precision wire-wound resistors connected in series. The reduced heat concentration of the series connection improves the thermal characteristics of a resistance element with an already low temperature coefficient
Advantages of Transfer Standards
In order to perform calibrations with a high degree of accuracy, reference standards must be employed at every range or decade of the measuring or calibration instrumentation. Clearly, this can be difficult and costly since these standards must be highly stable and their precise values must be known with a high degree of certainty and sufficient resolution.
To minimize the cost and difficulty, more practical means of performing such calibrations is to use transfer standards.
esi SR1050 Transfer Standards Basic Specifications
Transfer Accuracy Limited only by short-term repeatability of resistance values. Typical repeatability 2 ppm
Initial Accuracy 25 ppm of nominal value, matched within 10 ppm, for 1 M Ù, 30 ppm of nominal value, matched within 10 ppm, for 10 M Ù
Long-Term Accuracy 50 ppm of nominal value
Calibration Accuracy 10 ppm for 1 M Ù; 15 ppm for 10 M Ù Calibration Conditions 23 ¨¬C, low power, three-terminal measurement
Temperature Coefficient 5 ppm/¨¬C, matched within 5 ppm/¨¬C
Power Coefficient 0.05 ppm/mW per resistor
Maximum Power Rating 1W/step or 5W distributed over 10 steps, or maximum voltage of 2.5 kV where this value does not result in power excess of 1W per resistor
Breakdown Voltage 5000 V peak between active terminals and case
Leakage Resistance Greater than 10 T Ù from terminals to case