Standard Resistors
Model 5685 AC/DC Standard Resistors
 The design of these AC/DC Standard Resistors is based on work carried out over several years with co-operation of the National Physical laboratory. The design originated with F. J. Wilkins of the N.P.L. and has evolved as the result of many tests on stability and temperature coefficient using both a.c. and d.c. Some of the original design features have been discarded in the interests of simplicity, notably the horns which are no longer considered necessary.
The aim has been to produce four-terminal Standard Resistors to the highest specification, suitable for a.c. and d.c. work up to a frequency of 1592 Hz. 1 Ohm to 10,000 Ohm. The Resistors are made from a specially selected alloy having a low temperature coefficient mounted in a strain free manner on formers made from material of low dielectric loss but of high mechanical stability. All the connections are welded. Prolonged heat treatment of the elements ensures long term stability and low temperature coefficient of resistance.
The elements are hermetically sealed in stainless steel containers which are filled with dry oil (Castro! Whitemor WOM14). Provision is made for inserting a thermometer but the resistors are intended to be used in an oil bath which is temperature controlled.
Maximum dissipation for the Resistance Standards is 1 Watt but the highest performance will be obtained with a dissipation of 10 milli-Watts which is the ideal working condition. No harm will occur if the dissipation is increased to 1 Watt but self heating will take effect after a few minutes. Since the introduction of these Standard Resistors they have been adopted by National and Major Industrial Standards Laboratories as their primary standards. Information obtained from these laboratories over the past twenty five years indicate their exceptional high stability. For example, tests have shown that resistors of this type are stable to within 1 ppm over a period of ten years.
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Specifications
See the table below for a run-down of this product's specifications.
Type 5685A |
Values : 1, 10, 25, and 100 Ohm |
Type 5685B |
Values : 1,000 and 10,000 Ohm |
Calibrated accuracy |
3ppm for standard values as given above |
Accuracy of adjustment |
+/- 20ppm |
Stability |
2ppm / year |
Temperature Coefficient of Resistance |
typically 2ppm / °C |
Recommended Dissipation |
10milli-Watts |
Maximum Dissipation |
1 Watt |
Approximate Load Coefficient |
6ppm / Watt |
AC/DC Transfer Error up to 1592 Hz |
5ppm for 1 Ohm
1ppm for values 10 to 10,000 Ohm |
Construction |
Element: - Strain free, immersed in dry oil
Top Panel: - High Quality Bakelite with PTFE inserts |
Terminals |
Current |
0BA copper |
Potential |
4BA copper |
Earth |
6BA brass screw |
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Dimensions |
Container: - 114 x 76 mm diameter
Overall: - 140 x 83 mm diameter |
Net Weight |
0.7kg approximately |
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For more information about this product contact Tinsley
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