Case Study:
We have a backup generator that is scheduled to automatically exercise once a week by starting and running for half an hour. We want to be notified if it fails to start during this prescribed run time.
Step 1: We define an input that will sense the closure of a contact which closes any time the generator is running. We select a universal input, set it to be dry contact, inverted. We assume our contact from the generator provides a closure to ground (B-) when the generator is running. This means the value in our register #1 will be 0 when not running, and 1 when running.
Step 2: We need to tie the schedule into our notification somehow. The easiest way to do this is simply have the scheduler put a reference value into an arbitrary register. In the example below, we are telling the scheduler to place a value of 1 in register 99 from
8:00
to
8:30
(AM) on Monday. The rest of the time, the value in register 99 will be 0.
Step 3: Tie this all together into an event. The threshold rule shown below is watching register #1, which is our generator running status. If this status value is less than the value in register 99, we have a “true” event.
Most of the time, register 99 will contain zero. Our generator running status register can only have values of 0 or 1, and neither of these is less than zero. Therefore, most of the time, the threshold rule will test false regardless of whether the generator is running.
For half an hour on Monday morning, register 99 will contain a value of 1. During this half hour, the event will test true if the generator is not running. However, we want to give it some time to start and some leeway in scheduling. Therefore, we set the minimum on time to 25 minutes. Now the generator has to fail to run for an entire 25 minutes of the 30 minute window we have allowed for running before the event will become true. If the generator starts at all, this event will be cancelled. You could implement additional rules to see if the generator ran long enough.
Step 4: Now that our scheduled event is ready to go to work, the only thing left is reporting this event when it happens. Select the appropriate notification method. Selecting Notify on True via email is illustrated below. Setting up email requires additional configuration of the SMTP server, etc. You can also select notification based on this event to generate an SNMP trap.
