Mitsubishi Electric MELSEC-L Series - Data Missing

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CHAPTER 6 DATA LOGGING FUNCTION
6
6.7 Data Missing
6.7 Data Missing
When some of the data to be sampled is not obtained and data are not successively collected, this state is called
missing.
(1) Cases of data missing
Data missing occurs in the following cases.
(2) Missing due to processing overflow
If data sampling is performed at short intervals and processing is not completed within the interval, data writing
from devices to the buffer is not possible, resulting in missing of sampled data. The following two factors cause
processing to overflow.
(a) "The data sampling interval is too short." or "Too many data are to be sampled."
If the speed of saving data in the buffer exceeds the speed of saving data to the SD memory card, the buffer
will be full of sampled but non-overwritten data (that are not yet saved to the SD memory card). Because data
cannot be written from the device area to the buffer, data missing will occur.
(b) File switching occurs frequently.
During file switching, data are not saved from the buffer to the SD memory card. If file switching occurs
frequently, the buffer will be full of sampled but non-overwritten data (that are not yet saved to the SD memory
card). Because data cannot be written from the device area to the buffer, data missing will occur.
Item Description
Processing overflow Processing overflow occurs at the specified sampling interval or timing.
CPU module operation
When "Auto Start" is set in the Operation at transition to RUN setting, the CPU module is set to RUN,
STOP, and RUN again.
When "Auto Start" is set in the Operation at transition to RUN setting, the CPU module is powered on, off,
and then on.
When "Auto Start" is set in the Operation at transition to RUN setting, the CPU module is reset.
Operation by the special relay The special relay (Data logging start) is turned on, off, and then on.
Operation by the configuration
tool
After sampling pauses by the operation from the configuration tool, a start operation is performed.
:
18:55:18 67,723,36,0
18:55:19 68,741,36,0
18:55:20 69,712,36,1
18:55:20 70,724,36,1
18:55:20 71,732,36,1
18:55:20 72,733,
18:55:16 65,725,36,1
18:55:17 66,756,36,0
:
18:55:18 67,723,36,0
18:55:19 68,741,36,0
18:55:20 69,712,36,1
18:55:20 70,724,36,1
18:55:20 71,732,36,1
18:55:20 72,733,
18:55:16 65,725,36,1
18:55:17 66,756,36,0
:
18:55:18 67,723,36,0
18:55:19 68,741,36,0
18:55:20 69,712,36,1
18:55:20 70,724,36,1
18:55:20 71,732,36,1
18:55:20 72,733,
18:55:16 65,725,36,1
18:55:17 66,756,36,0
Stack file
Saved file
Saved file
1st sampling data
2nd sampling data
Device
area
Buffer
SD memory card
Specified
device data
sampling
CPU module
Buffer capacity for setting 1
3rd sampling data
nth sampling data
(a) Missing caused by short
sampling interval or too
many data to be sampled
(b) Missing caused by
frequent file switching