Yokogawa Single Channel Oxygen Analyzer System ZR22/ZR402 - Manual (Page 151)

IM 11M12A01-03E 10-3
10. Other Functions
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
ЊC., may be expressed mathematically by:
E = -50.74 log (Px/Pa) [mV]
where, Px: Oxygen concentration in the measured gas
Pa: Oxygen concentration in the reference gas, (21% O 2 )
Table 10.1 shows oxygen concentration versus cell voltage.
Table 10.1 Oxygen Concentration Vs. Cell Voltage, (cell temperature: 750
ЊC)
%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.EPS
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 Z021D 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 Z021D 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
⍀ maximum. As the cell
degrades, so will the cell’s internal resistance increase. The degradation of the cell
cannot be found only by changes in cell’s internal resistance, however. Those changes
in the cell’s internal resistance will be a hint to knowing the sensor is degrading. The
updated values obtained during the calibration are displayed.