Trace Oxygen Analyzer
Operational Theory
Teledyne Analytical Instruments
7
Operational Theory
2.1 Introduction
The analyzer is composed of three subsystems:
1.
The zirconium oxide (ZrO
2
) sensor with a 0-25%
analysis range
2.
Sample System
3.
Electronic Signal Processing, Display and Control
The sample system is designed to accept the sample gas and
transport it through the analyzer without contaminating or altering the
sample prior to analysis. The ZrO
2
sensor is a device that translates the
amount of oxygen present in the sample into a voltage output. The
electronic signal processing, display and control subsystem simplifies
operation of the analyzer and accurately processes the sampled data. The
microprocessor controls all signal processing, input/output and display
functions for the analyzer.
2.2 ZrO
2
Sensor
The zirconium oxide (ZrO
2
) sensor is a solid state sensor. It is a
voltage device with a logarithmic response. The sensor uses a stabilized
zirconia disc as an electrolyte with a sensing electrode (the cathode) and
a counter electrode (the anode) on each side of the disc and contains a
thermocouple. The sensor is designed to have a small sample of the
unknown gas passed inside the sensor tube. Air (20.95% oxygen)
surrounds the outside of the tube. A heater is mounted around the sensor
to keep the sensor hot. The sensor construction is shown in Figure 2.1.
CAUTION:
THE SENSOR IS HOT. DO NOT TOUCH THE SENSOR
OR ALLOW FLAMMABLE MATERIAL TO COME IN
CONTACT WITH THE ASSEMBLY.
THE SENSOR ASSEMBLY REMAINS HOT EVEN IN
STANDBY MODE. REMOVE POWER FROM THE
INSTRUMENT AND ALLOW SENSOR TO COOL FOR
