< 10. Other Functions >
10-2
IM 11M12D01-01E
10.1.3 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.
10.1.4 Cell temperature
This displays the cell (sensor) temperature, which is determined from the thermocouple electromotive
force (e.m.f.) and cold junction temperature. Normally it is 750°C.
10.1.5 C. J. Temperature
This indicates the detector terminal box temperature, which compensates for the cold junction
temperature for a thermocouple measuring the cell temperature. When the ZR22 Detector is used,
the maximum C. J. temperature will be 150°C. If the terminal box temperature exceeds this, take
measures to shield the terminal box from heat radiation.
The maximum C. J. temperature varies depending on the type of detector.
10.1.6 Span gas and Zero gas Correction Ratios
These are used to check for degradation of the sensor (cell). If the correction ratio is beyond the limits
as shown in Figure 10.2, the sensor should no longer be used.
These ratios can be found by calculating the data as shown below.
21.0
p1
0.51
81.92
ez
e1
es
0
C
A
B
Zero gas correction ratio = (B/A) x 100 (%) Correctable range: 100 ± 30%
Span gas correction ratio = (C/A) x 100 (%) Correctable range: 0 ± 18%
Cell
electromotive
force, mV
Calibration curve
before correction
Previous
zero gas data
Corrected calibration curve
(theoretical calibration curve)
Zero origin
Span origin
Span gas concentration
Oxygen concentration (vol% O
2
)
F10-2E.ai
Figure 10.2
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