Angélica M. Muñiz-Mercado
University:
Gradation Date: May 2009
Hometown: Sabana Grande, PR
My Project (1): AUTOMATION OF 1 TΩ TO 100 TΩ ULTRA-HIGH RESISTANCE MEASUREMENTS
High resistance measurements in the range of 10 MΩ to 100 GΩ have been automated by the implementation of a guarded dual source bridge in combination with a low thermal electromotive guarded scanner. Because of the internal capacitance of the guarded scanner, standard resistors 1 TΩ and above require a manual connection to the bridge. This is because the RC time constant increases with the resistors’ magnitude, making the settling time longer. Manual connection to standard resistors in the range of 1 TΩ to 100 TΩ are time consuming, and restricted the operator from performing other research activities. To overcome this problem and to reduce uncertainties, a compact XY positioning system was developed. In the summer of 2007, I implemented the positioning system and fully automated the resistance measurements in the range of 1 TΩ to 100 TΩ using the Visual Basic computer language. My project this year was to test and improve the system in those resistance ranges. Results of those measurements will be reported at my seminar talk.
Applications of high resistance measurements include calibrating instruments such as electrometers and mass spectrometers, determining the purity of elements such as water and fuels, and characterizing high resistance materials such as ceramics which are ideal for surge-protection. The main purpose of this project is to provide the customers with the most accurate measurements of high resistance standards so they can certify their equipment with NIST traceable calibrations.
XY positioning system shown mounted on side of environmental test chamber at NIST. The close proximity of the standard resistors inside the test chamber to the dual source bridge keeps test lead lengths to a minimum. The XY positioning system can make guarded two-terminal connections for up to eight standard resistors to a high resistance bridge.
My Project (1): HIGH RESISTIVITY MEASUREMENT AT HIGH TEMPERATURES FOR SOLAR PROBES
I also worked with surface and volume resistivity measurements using a test fixture. The purpose of the test fixture is to ensure a fixed measurement configuration to obtain consistent results. Volume resistivity is the electrical resistance through a one-centimeter cube of insulating material and is expressed in ohm-centimeters. Surface resistivity is the electrical resistance between two electrodes on the surface of an insulating material and is expressed in ohms. Figure 2 shows the commercial resistivity test fixture with which we worked. Because of NIST expertise in high resistance measurements and characterization of materials, we started testing with high resistive materials with known parameters to then determine the feasibility of the measurement process as well as the confidence of the test fixture. After we determine the viability of the project, NIST will build a system similar to the one shown in Figure 3 to measure the high resistance materials at high temperatures (1000 °C).
This project is related to a Solar Probe mission to one of the last unexplored regions of the solar system, the Sun’s corona. The thermal protection system (TPS) resembles the orange cone shown in Figure 4 and will be constructed of the electrical insulator alumina (Al2O3) or other advanced materials. Also, at high temperatures alumina can be a thermally conductive material. Surface and volume resisitivity measurements will be used to determine the temperature dependent change in resistivity insulating materials which effects the charging of the TPS. This project will be considered as a future collaboration between NIST, NASA, and The Johns Hopkins University Applied Physics Laboratory (JHU-
Volume resistivity is measured by applying a voltage potential across the opposite sides of the insulator sample. Surface resistivity is measured by applying a voltage potential across the surface of the insulator sample.
High temperature (1000 °C) test fixture and guarded connections to resistance bridge. Temperature and resistance measured as temperature elevated to study the transition temperature where the insulating material becomes conductive.
Major processes that impact spacecraft charging. TPS (orange cone) protects instrumentation payload from heat of the Sun.
