i.CanDoIt® Guided Tour (p.7)
Thresholds or Event Rules |
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What are Threshold Rules? What are Events?
Where are the Alarms?
These questions all point to essentially the same answer. You build an alarm by defining a threshold rule. When the threshold rule is triggered or activated, we call this an event. There are several things you can do with an event, and you may treat any of them as an alarm. An event may result in turning specific I/O on or off. An event may result in a notification message being sent (e.g., via email to your cell phone). An event may send a message to a central server which then decides what to do. An event may simply be logged in an event file to simply record the fact that it happened sometime.
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How do I set up an Alarm?
I/O point data is placed in "registers" by easily configured I/O. Threshold "rules" determine what constitutes an event. The image below is a screen shot of a threshold rule that will result in an event when the sensor on input #7 exceeds a level of 1000. Data values are scaled to any units you decide. You find the threshold rules in the System->Action Rules->Thresholds page.
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How do I prevent spurious events when the test value is hovering around the threshold?
Hysteresis will prevent spurious events near the threshold. In the following example, the event will occur when register 7 reaches a level of 1000. If register 7 drops below 1000 by a margin less than 50, then returns to above 1000, the event will not repeat. The value of register 7 must drop below 950 and return to over 1000 before the trap will repeat.
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How do I generate an event only after the condition has existed for a minimum time?
The on/off time qualifications are used to add time to the criteria. The following example shows a minimum on time of 30 seconds. This means the data in register 7, most likely placed there by sensor hardware, must exceed a level of 1000 for at least 30 seconds before an event will be generated. If the minimum off time was also set, the rule must test false for that amount of time before it can repeat the "true" event.
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How do I change event thresholds based on time of day?
Start by using a register for the test threshold rather than fixed value as shown below:
Then alter the contents of this threshold register based on schedule in the Advanced->Scheduler->Weekly Schedule page as shown below.
Using the example setup shown above, the event will be generated any time register 7 exceeds a level of 1000 between 8AM and 5PM, Monday through Friday. The rest of the time, register 7 needs to exceed a level of 1500 before an event will be generated.
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