Rate of Change Tag Type Properties: Settings Tab
The Settings tab is used to select which tag is to be watched and how frequently it is to be checked.
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Use this option to select the tag to be monitored for changes in value.
If you would like to monitor the rate of change of some combination of tags or a calculated value, you should create a calculation tag with the expression you need and use it as the source.
If the data source is a rate (e.g. flow rate) rather than an amount (e.g. tank level) then you should use this field to match the data source’s measurement rate. Available options include: per Second, per Minute and per Hour.
When checked, the absolute value of the rate of change will be shown. Otherwise, a decreasing value in the source tag will be displayed as a negative rate of change.
• The Refresh Interval sets how frequently the rate of change is calculated. This value is always measured in seconds.
• The Period defines the length of time over which the change is to be measured. It is also measured in seconds.
The rate of change is roughly defined as the amount by which the value has changed during a given period, divided by the length of time in the period. To state it more accurately, the rate of change is the calculated derivative (dy/dx) of the plotted value.
Note: The rate of change calculation is affected by data noise and transient spikes. The period should always be set to a value larger than the frequency of data noise. To avoid alarms due to transient noise, set a delay on the alarm. (see: Rate of Change Tag Type Properties: Alarms Tab.)
Used by various drawing methods. Set this field to display the units of the rate of change.
Use this field to flag the tag’s data in the event that you suspect the values it is reporting might not be accurate, or when this tag has initially been created and you wish to ensure that its data is marked for extra monitoring.
This optional field allows you to provide a constant value that will be used instead of input read by the communication driver. It is commonly used when testing a new Analog Input tag when application is not attached to a live data source. Tags that are using manual data are marked on screen by a flashing exclamation mark.