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CHAPTER 11 – Data Logging
Item Properties
These options enable an items name and associated expression to be entered. Its data type can be
selected and if required a deadband value can be applied to the measured value.
The Item Name field allows the Item to be given a meaningful name. The entry should be kept short
but also be logical for clarification. A maximum of 26 characters is allowed.
The Expression field defines the point name or expression that will be logged. The Browse button
allows easy point selection. For details on how expressions or points are formulated Refer to chapter
3, Points.
The Data Type field determines the type of data to be logged. Select either Boolean, Integer or Real.
For points, this is automatically picked up from the points database. For expressions, the required
type must be selected.
The Deadband field enables a percentage limit or 'Deadband' to be applied to the logging expression.
This allows the value of the expression to change within the percentage limit without being logged.
This is particularly useful when logging analogue values which are subject to noise. Each sample is
checked (when the value changes for 'On Change' sampling, or every log period for 'On Interval')
against the last logged value. While the value varies within the deadband, the values are ignored.
Immediately the value exceeds the deadband limits the new value will be logged. This may
dramatically reduce file size, and ease analysis.
Entering a value of 0%, i.e. no deadband, will cause every sample to be logged.
Page 178
OMRON
Release 2.0
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