This example demonstrates how the No Change feature can be used to check whether an analog point has changed by a specific percentage of its overall point range during any one-hour period.
Example - No Change in Span:
An analog point has configuration that includes these Limits:
Full Scale: 80
Zero Scale: 0
and these No Change properties:
Type: Percentage of Span
Deadband: 10
Interval: 1H
Severity: Alarm, Medium priority.
The No ChangeDeadband is 10% of the full point range of 0 to 80. Therefore, ClearSCADA will only deem the point value to have changed if its value changes by more than 8, over a one-hour Interval.
Whenever the value does change by more than 8, ClearSCADA restarts its No Change checking process for the point.
If the point value does not change by more than 8 for over an hour, ClearSCADA will raise a medium priority alarm to indicate that the point has not changed sufficiently. ClearSCADA will also restart its No Change checking process for the point.
In this example, the analog’s value changes as follows:
| Time | Value | Comments |
|---|---|---|
|
09:00:00 |
54.0 |
ClearSCADA starts its No Change checking process. It uses this time for the start of the Interval, and compares future values against this value to see whether they change by more than the 10% Deadband of 8. |
|
09:12:04 |
53.2 |
|
|
09:27:13 |
55.1 |
|
|
09:46:23 |
57.3 |
|
|
10:02:00 |
58.0 |
As the value has only changed by 4 in the last 62 minutes (and as such, has remained within the Deadband for longer than the specified Interval), ClearSCADA raises a No Change alarm. It also re-starts its checking process, using the new time and value as the basis against which to perform those checks. |
|
10:21:48 |
56.1 |
|
|
10:37:12 |
52.9 |
|
|
10:45:00 |
49.0 |
As the value has changed by more than the Deadband value of 8 in the last 43 minutes, ClearSCADA clears the No Change alarm and re-starts its checking process. It uses this time and value as the basis against which to perform its checks. |
|
... |
Further Information
Configure the No Change Properties for an Analog or Counter Point.