Date of Award

5-2004

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

Committee Chair(s)

Charles Swenson

Committee

Charles Swenson

Committee

Jacob Gunther

Committee

Alan Shaw

Abstract

In-situ probing of the Earth's upper atmosphere has greatly contributed to the understanding of the ionosphere's variations and structures. The purpose of this research project has been to develop the digital component of a Swept Langmuir Probe that will be used on a sounding rocket to be launched through the equatorial ionosphere. The probe will make measurements of the plasma density and temperature in the ionosphere.

The digital component uses an FPGA to perform three main functions in parallel which are generating a sweeping voltage on the probe, sampling data channels, and communicating measured data to external devices. The FPGA controls a Digital to Analog converter to create a sweeping voltage. The current measured from the probe is split into two different channels with different gains to allow for a more dynamic range of current measurements. Sampling accomplished by controlling Analog to Digital converters and co-adding the results eight times to reduce noise. The FPGA provides two different interfaces for communication to the outside world. The interfaces are a serial communication interface, via RS422 transceivers with a NASA telemetry encoder, and an interface with a PC for calibration purposes. The purpose of calibration is to measure how the instrument works under varying conditions to help understand the effect the instrument has on the readings. To accomplish this task a special diagnostic mode was programmed into the FPGA that allows a PC to control the probe. The PC is able to control the voltage sweep and decide when to sample a desired channel.

A top down approach is taken to simplify the design by partitioning the design into smaller and easier pieces to work with. This report will give an overview of how the instrument functions, how it was designed, how it was programmed using VHDL, and then show results of how it worked.

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