Ruby is an undergraduate student at UH Manoa pursuing a
bachelor’s in Electrical Engineering. She graduated from
Kaiser High School on Oahu, where she developed an interest
in robotics. At UHM, she joined team RoSE (Robotic Space
Exploration), which competes in the University Rover
Challenge. This year, she became the electrical lead and
designed the battery and power system. In her free time she
likes to play video games, build scale models, and practice
photography.
Home Island: Oahu
High School: Kaiser High School
Institution when accepted: UH Manoa
Site: University of California Observatories (UCO). Santa Cruz, CA
Mentors: Aaron Hunter & Phil Hinz
Project title: Characterizing an Eddy Current Sensor for use in the Keck Adaptive Secondary Mirror
Project Abstract:
The Keck Adaptive Secondary Mirror (KASM) is a project to install a deformable mirror to
compensate for atmospheric turbulence. The secondary mirror is 1.45m in diameter and will use
3106 actuators to deform the mirror’s surface. Typically, capacitive sensors are used to measure the
mirror’s deformation. Capacitive sensors are expensive and highly prone to error due to debris
getting between the sensor and the mirror. Another option is an eddy current sensor, which is much
cheaper. It uses a magnetic field to determine the distance from the mirror to the sensor by
measuring the natural frequency of a resistor-inductor-capacitor (RLC) circuit, which changes with
distance from the target. The project is to test the newly developed Time-to-Digital Converter (TDC)
eddy current sensing board. It times how long it takes for the sensor to detect a set number of
oscillations in the RLC. This board is a development over a previous design, an inductance-to-digital
converter, which measured the frequency of the oscillation. Both of these results change
proportionally with the distance of the inductor from the target. The TDC will be tested in various
conditions to determine the smallest resolution it can perceive, how the frequency of measurement
affects this resolution, how temperature affects measurements, and an idea of how distance from
the actuator affects resolution. To find the resolution of the sensor, the sensor is measured across
various distances, and the standard deviation is calculated. Then a conversion equation is used to
convert the result from the TDC to a distance, and the slope of this is multiplied by the standard
deviation to find the noise-limited resolution.