Yokogawa Integral Oxygen Analyzer ZR202 User Manual
Page 141
<10. Other Functions>
10-3
IM 11M12A01-02E
8th Edition : Jan.13,2012-00
10.1.1.6 Cell Voltage
The cell (sensor) voltage will be an index to determine the amount of degradation of the
sensor. The cell voltage corresponds to the oxygen concentration currently being measured.
If the indicated voltage approximates the ideal value (corresponding to the measured oxygen
concentration), the sensor will be assumed to be normal.
The ideal value of the cell voltage (E), when the oxygen concentration measurement temperature
is controlled at 750 °C, may be expressed mathematically by:
E = -50.74 log (Px/Pa) [mV]
where, Px: Oxygen concentration in the sample gas
Pa: Oxygen concentration in the reference gas, (21 vol%O
2
)
Table 10.1 shows oxygen concentration versus cell voltage.
Table 10.1 Oxygen Concentration Vs. Cell Voltage, (cell temperature: 750 ºC)
%O
2
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
mv 117.83
102.56 93.62 87.28 82.36 78.35 74.95 72.01 69.41
%O
2
1
2
3
4
5
6
7
8
9
mv
67.09
51.82
42.88
36.54 31.62 27.61 24.21 21.27 18.67
%O
2
10
21.0
30
40
50
60
70
80
90
mv
16.35
0
-7.86
-14.2
-19.2
-23.1 -26.5 -29.5
-32.1
%O
2
100
mv -34.4
T10.1E.ai
10.1.1.7 Thermocouple Voltage
The cell temperature is measured with a Type K (chromel-alumel) thermocouple. The
thermocouple cold junction is located in the detector terminal box. The cell temperature and the
thermocouple voltage (including the voltage corresponding to the cold junction temperature) are
displayed.
10.1.1.8 Cold Junction Resistance (C.J. Voltage)
The ZR22 Detector measures the cold junction temperature using an RTD (Pt 1000). (The earlier
model of ZO21D uses transistors to measure the cold junction temperature.)
If detector is “ZR22” is selected in the Basic setup display, the RTD resistance values will be
displayed. If the ZO21D is selected, the transistor voltage will be displayed.
10.1.1.9 Cell’s Internal Resistance
A new cell (sensor) indicates its internal resistance of 200 Ω maximum. As the cell degrades, so
will the cell’s internal resistance increase. The degradation of the cell cannot be evaluated just by
changes in cell’s internal resistance, however. Those changes in the cell’s internal resistance are
just a guide to the extent the cell is degrading. The updated values obtained during the calibration
are displayed.
10.1.1.10 Software Revision
The revision (number) of the software installed is displayed.