Teledyne 3000ZA2G - Zirconium oxide analyzer - Manual (Page 21)

Trace Oxygen Analyzer Operational Theory
Teledyne Analytical Instruments 9
The sensor offset voltage changes with sample flowrate as shown in
Figure 2-1. Assuming that the environment remains constant and within
the specifications of the sensor, the difference in offset voltage between
a flowing reference gas at 200 ml/min and at 0 ml/min is nearly constant
over the operating range of sample flowrates (100-300 ml/min). This
offset is removed during calibration assuming that the sample flowrate
used in calibration is the same as the process flow. Hence the analyzer
can be used without a flowing reference gas during operation with only a
marginal degradation in performance. For best performance, a flowing
reference should be used.
Figure 2-1: Sensor Offset Voltage
The sensor assembly also provides the means of maintaining the
sensor operating temperature by surrounding the sensor tube with a
heater element, and measuring the temperature of the zirconia disc with
a thermocouple inside the sensor. (See Figure 2.2).
The logarithmic output of the sensor depends therefore on the
partial pressure of the oxygen in the sample gas.
The non-linear output is linearized by the system software and a
linear output signal is generated and used by the DAC circuit to produce
the requisite output signals.