Publication: Design and Evaluation of a Low Thermal Electromotive Force Guarded Scanner

Fri 31.07.2026

This paper describes the design and performance evaluation of a low thermal electromotive force guarded scanner developed for use with actively guarded resistance bridge networks. The system minimizes leakage currents and thermal EMF effects through continuous guarding of relay contacts and measurement circuits. Experimental results demonstrate improved accuracy in the calibration of high-value standard resistors and confirm the scanner’s suitability for automated high-precision DC measurement applications.

Paper: Design and Evaluation of a Low Thermal Electromotive

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 SCIENTIFIC INSTRUMENTS, Volume 70, Number 6

Link for the download: Paper: Design and Evaluation of a Low Thermal Electromotive 

 

Related Products

160B OPT1 16 Channel Scanner with cable inputs 160B OPT1 16 Channel Scanner with cable inputs
160B OPT2 - 16 Channel Scanner with terminal inputs 160B OPT2 - 16 Channel Scanner with terminal inputs
160B OPT4 16-Channel Low Thermal Scanner with Shielded Cable Inputs 160B OPT4 16-Channel Low Thermal Scanner with Shielded Cable Inputs
320B OPT1 32-Channel Low Thermal Scanner with Cable Inputs 320B OPT1 32-Channel Low Thermal Scanner with Cable Inputs
320B OPT2 32-Channel Low Thermal Scanner with Terminal Inputs 320B OPT2 32-Channel Low Thermal Scanner with Terminal Inputs
320B OPT4 32-Channel Low Thermal Scanner with Shielded Cable Inputs 320B OPT4 32-Channel Low Thermal Scanner with Shielded Cable Inputs

Our partners in other countries

Amtest-TM Kft. (HU) - Attila Polgar Amtest PL (PL) - Dariusz Koziello Amtest-TM ELTH srl (RO) - Bogdan Valcea ADELANTEST Ltd (RUS) - Igor Kozlov GIGA Electronic Ltd. - Danail Georgiev OÜ Est-Doma (EST) Promix Ltd. (UA) - Oleksandr Labuzov Vildoma (LT, LV)

We cooperate with partners and resellers in other European countries

View partners