annaknapp / zirconia-oxygen-analyzer

Software and hardware files for an oxygen analyzer

This repository contains the hardware design files and software for a high precision oxygen analyzer.

Analyzer hardware description: The analyzer uses a fast-response dual-cell zirconia oxygen sensor manufactured by Process Sensing Technologies. A thermocouple probe is fitted into the sensor to enable a PID controller to hold the sensing element at a constant temperature. An analog feedback loop based on the one described by Benammar and Maskell (Benamar, 1993) holds the average O2 partial pressure inside the sealed central chamber of the sensor at a fixed ratio with that of the external sample gas. A 16-bit digital-to-analog-converter (DAC) is used to generate a 1 Hz sinusoidal waveform to pump oxygen into and out of the central chamber using the pumping cell. The digital pumping signal is controlled by a custom-built digital lock-in amplifier. The Nernst potential generated across the sensing cell is digitized with a 32-bit analog-to-digital converter. The amplitude and phase of the sense signal is calculated by the lock-in amplifier and a 10-second moving average filter is applied.