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Flow rate of ejector air below 5 L/min causes reverse flow in a probe with perpendicular cut. In a probe with 45-degree cut, there is no reverse flow generally, because negative pressure is not produced at the tip of the probe.
Figures 6.4.3.1 replacing probe (oblique cut)
Figures 6.4.3.2 replacing probe (sensor holder side)
From this experiment, flow rate of ejector is determined as 5 L/min, which is equivalent to that of two other ships, and the probe has been replaced on June 24, 2002, when ANTARES pulled over to the Kobe Harbor.
6.4.3 Drift of NOx and O2 of ZrO2 Sensor at the Test Ships
Tables 6.4.3.1 to 6.4.3.3 and graphs in fig. 6.4.3.1 to 6.4.3.3 show the drift value of NOx and O2 from the data collected at the ship inspections.
Table 6.4.3.1 IKOMASAN
| |
NO |
O2 |
Zero drift
%FS/WEEK |
Span drift
%FS/WEEK |
Zero drift
%FS/WEEK |
Span drift
%FS/WEEK |
| 01/07/18 |
installation |
0.00 |
0.00 |
0.00 |
0.00 |
| 01/08/29 |
|
-0.06 |
-0.22 |
0.00 |
0.12 |
| 01/11/21 |
|
0.01 |
-0.25 |
0.02 |
0.07 |
| 02/01/02 |
|
0.02 |
-0.60 |
0.00 |
0.02 |
| 02/02/17 |
replacing
sensor |
0.00 |
0.00 |
0.00 |
0.00 |
| 02/06/27 |
|
-0.04 |
-0.22 |
0.00 |
0.10 |
| 02/08/11 |
removal |
0.08 |
-0.04 |
0.00 |
-0.38 |
|
Table 6.4.3.2 ANTARES
| |
NO |
O2 |
Zero drift
%FS/WEEK |
Span drift
%FS/WEEK |
Zero drift
%FS/WEEK |
Span drift
%FS/WEEK |
| 01/07/24 |
installation |
0.00 |
0.00 |
0.00 |
0.00 |
| 01/09/17 |
|
0.00 |
-0.37 |
0.01 |
0.11 |
| 01/11/12 |
|
0.02 |
-0.32 |
0.00 |
0.01 |
| 02/01/11 |
|
-0.01 |
-0.46 |
0.00 |
0.03 |
| 02/03/05 |
|
0.02 |
-0.86 |
0.03 |
0.05 |
| 02/04/29 |
|
0.02 |
-0.19 |
0.01 |
-0.04 |
| 02/06/24 |
replacing
probe |
-0.02 |
-0.27 |
0.00 |
-0.02 |
| 02/08/19 |
|
-0.03 |
0.08 |
0.00 |
0.01 |
| 02/10/16 |
|
0.00 |
-0.04 |
0.00 |
0.05 |
|
Table 6.4.3.3 Ship B
| |
NO |
O2 |
Zero drift
%FS/WEEK |
Span drift
%FS/WEEK |
Zero drift
%FS/WEEK |
Span drift
%FS/WEEK |
| 02/07/24 |
installation |
0.01 |
-0.26 |
0.00 |
0.03 |
| 02/07/27 |
|
0.01 |
0.07 |
0.01 |
0.02 |
| 02/09/17 |
|
0.01 |
0.07 |
0.01 |
0.02 |
|
The raw data of the sensor stored in a memory are collected at every inspection and compared with the data collected from the previous inspection, and converted to drift per week.
For both IKOMASAN and ANTARES, the drift is within 0.2% of full scale per week excluding the period of abnormal operation due to the sensor's exposure to water or temperature drop of ejector. It can be concluded that one calibration per month is sufficient because the drift is within 1% of full scale per month in rough estimation.
Interruption of power, even as short as 5 to 10 minutes, on ships cannot be ignored in continuous measurement. It has been examined several times in our test, though not visible on the graphs. In such case, interval of calibration is reset when power returns, causing extended calibration interval, for example, 2 or 3 weeks extended to 4 or 6 weeks. It is not desirable for the reliable measurements, however, it can be solved by the operation way of the instrument, such as performing calibration within a day after power is cut.
It's been found that there were several occasions where some parts of recorded data throughout the on-board test (for the first and second ship) were missing. The cause has not been clarified, but it seems that it was due to the carelessness of the crew. Data, collected every time when ship pulled over to a Japanese harbor at 40 to 80-day interval, was recorded and stored automatically in a flash card of a commercially-sold, light-weight and small recorder with on/off button and flip cover to start/stop recording. It's been confirmed several times that this cover had been opened while ship was on service. It seems that "Do not touch!" sign on the recorder cover had not been thoroughly acknowledged and followed by crews who frequently were replaced by shifts. On the third ship, the recorder was installed in the instrument panel hidden from crew s view. This has effectively prevented the same problem. Design of recorder to prevent this kind of problem is under consideration.
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