YOKOGAWA av550g, User Manual

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< 12. Troubleshooting >
12-8
IM 11M12D01-01E
3) If the alarm is generated again during the recalibration, deterioration of or damage to the sensor
assembly is considered as the cause of the alarm. It is necessary to replace the cell with a new
one. Before replacement, carry out the following.
Check the cell voltages when the zero gas and span gas are introduced.
When the system is configured for automatic calibration, let the calibration gas flow from the
[Indication check] display and measure the voltage between terminals CELL+ and CELL- on the
channel card using a tester or relevant equipment. The measured voltage is the cell voltage. How to
perform the indication check, refer to Section 10.4, “Indication Check.”.
When the valves for the calibration gas can be manually operated, the cell voltage can be checked
on the display of the averaging converter. The procedure is as follows.
a. From the basic panel display, move to the [Detailed data] display of the channel where the alarm
is being generated.
b. The cell voltage should be indicated on the top line. (Figure 12.8)
c. Check whether or not the displayed cell voltage is very different from the theoretical value at
the oxygen concentration of the relevant gas. See Table 12.3 for the theoretical cell voltages.
Although the tolerance to the theoretical value cannot be generally specified, a reasonable one
may be approximately ±10 mV.
Table 12.3 Oxygen Concentration and Cell Voltage
Oxygen Conc. (%O
2
) Cell Voltage (mV)
1% 67.1
21% 0
4) Check whether the deterioration of or damage to the sensor assembly that caused the alarm,
has occurred suddenly during the current calibration by following the procedure below.
a. Call up the [Detailed data] display.
b. Use the ▼ key to check Calibration data (Figure 12.9). The span and zero correction ratios
of the last ten calibration can be checked here. By checking these data, whether the sensor
deterioration has occurred suddenly or gradually can be determined.
F12-8E.ai
Ch1
Cell voltage: 0 . 9 mV
Thermo voltage: 2 9 . 4 mV
C.J.resistance: 1 1 7 0 . 2 Ω
Cell temperature: 7 5 0 ° C
C.J.temperature: 4 3 ° C
F12-9E.ai
Ch1
Calibration data:
1. 2 4 Jun. 2 0 0 4 1 2 : 0 1
Span gas ratio: 0 . 1 %
Zero gas ratio: 1 0 1 . 3 %
2. 0 0 0 0 2 0 0 0 0 0 : 0 0
Span gas ratio: 0 . 0 %
Zero gas ratio: 0 . 0 %
Figure 12.8 Detailed Data Display Figure 12.9 Calibration History
5) If the sensor assembly has deteriorated suddenly, the check valve that prevents moisture in the
furnace from entering into the calibration pipes may have malfunctioned. If the furnace gas flows
into calibration lines, the gas is cooled and thus condensation develops and accumulates in
the pipe. During calibration the condensate is carried with the calibration gas and blow onto the
sensor assembly, whereby the cell is cooled quickly. This results in the failed sensor assembly.