Teledyne 3000ZA - Trace oxygen analyzer - Manual (Page 20)

Operational Theory 3000ZA
Teledyne Analytical Instruments 8
Operational Theory
2.1 Introduction
The analyzer is composed of three subsystems:
1. Zirconium Oxide (ZrO
2
) Sensor
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 an electrical current. 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
2.2.1 Principles of Operation
Teledyne’s zirconium oxide sensor is a miniature solid state sensor.
It 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. The zirconia is heated to a temperature of about 500°C via a
built-in heater. By applying a suitable reference voltage (approximately
0.75 volt) across the cathode and anode, the heated zirconia acts as an
electrolyte which is capable of moving oxygen ions within its crystalline
structure. This allows for the reduction of oxygen molecules reaching
the cathode and the generation of a current equivalent to the parts per
million oxygen in the sample gas.
This sensor has been modified to sense low levels of oxygen—less
than 1 ppm and generate a current proportional to the concentration. The
sensor is designed for long term stability and an operating life of 5 years.