|Publications and Product Related Information|
|NBS Technical Note 430:
for Surveillance of the Volt Maintained by a Small Group of Saturated Standard Cells
Authors: W. G. Eicke and J. M. Cameron
Abstract: When a local standard such as that for electromotive force is maintained by a group of standards, procedures must be established to provide evidence that the group has maintained its original value. One also needs methods for the transfer of the value to test items that provide efficient use of measurement effort while monitoring the measurement process and-providing information for updating the values of process parameters. Solutions to the more general problem of transferring the value from laboratory to laboratory and of maintaining agreement among laboratories depend on the existence of control within the laboratories.
This note is one of a number of contemplated reports having the general aim of providing methods for the surveillance of measurement processes with emphasis on the amount and kind of information needed for the estimation and control of the uncertainty in measurement.
Publish Date: August 1967, by NBS (presently NIST)
Design and evaluation of a low thermal electromotive force
guarded scanner for resistance measurements
Authors: Dean G. Jarrett, James A. Marshall, Thomas A. Marshall and Ronald F. Dziuba
Abstract: The design and testing of a low thermal electromotive force guarded scanner, developed to provide completely guarded switching when used with actively guarded resistance bridge networks, is described. The design provides a continuous guard circuit trace on the scanner circuit boards that surrounds the relay contacts and protects the measurement circuit from leakages to ground. Modification to the circuit boards and relays of the guarded scanner are explained. Several tests were developed to evaluate the guarding effectiveness, including isolating sections of the guard circuit to create a potential drop between the main and guard circuits. Calibration of standard resistors using the guarded scanner has shown relative differences less than 1 X 10-6 ,30 X 10-6 , and 150 X 10-6 for measurements made with and without the guarded scanner at nominal resistances of 1, 10, and 100 GW, respectively. The substitution method was used to significantly reduce the relative differences between channels to less than 0.5 X 10-6 ,3 X 10-6 , and 30 X 10-6 for nominal resistances of 1, 10, and 100 GW, respectively. Applications for the guarded scanner in automated direct current measurement systems are presented.
Publish Date: June 1999, REVIEW OF SCIENTFIC INSTRUMENTS, Volume 70, Number 6
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