Advanced Event Detection

This is a more advanced example of Event Detection. It continues on from the Basic Event Detection Tutorial.

By the end of the first example, we've got the following graph.

Note - for clarity, we'll remove the 'Spike' metadata in the following examples.

One problem comes from inrush currents and high loads. These are moments of very high current use when the drive is starting up or when a particularly heavy product is being processed.

What makes this complicated is that the time-limits we're willing to accept change depending on just how far over the limits it actually is

For example, the motor can run at 102% for an hour without any danger, but should only run at 120% for 60 seconds - otherwise it might overheat or fail.

So rather than a traditional timer node, we might need to make our own.

You can use variables to store information. In this case, we're going to make a variable called Total Time to act as a counter.

• Right-click in the empty space, choose Add Node, Variables and Increment.
• Click on the name option and enter 'Total Time'.
• Connect the true output of the comparison node to the enable output of the new Increment node.

Although your analytic usually runs with 1 second resolution (if enough data is available), there are situations where it won't.

Because of that, we can't simply add 1 to our timer. To be safe, we should add an Elapsed node that gives us the correct number of seconds since the last sample.

• Right click in empty space, choose Add Node, Timing and Elapsed.
• Connect the output of the Elapsed node to the enabled input of the Increment node.

Right now, we've made a counter that constantly counts up - it never falls back down.

To let us reset the timer, we can add a Set node.

What we need to do here is set the value of the variable back to 0 whenever the power drops down under 100%.

• Right-click in empty space, choose Add Nodes, Variable and Set.
• Left-click the name option on the new node and type 'Total Time'.
• Create a new Basic/Const Number node.
• Click the value in the Const Number node and change it to '0'.
• Connect the output of the Const Number node to the value input of the Set node.
• Connect the false from the comparison node to the enabled on the Set node.

So our new nodes will…

• Increment the Total Time as long as the measured power is > 100%, and
• Reset the Total Time whenever the power is ⇐ 100%.

We can now adjust our logic by adding a new condition - we want to create an event only if the value of Total Time is greater than 5 (meaning 5 seconds have elapsed).

Right now, we've got a fixed time for our timer. If we're running at 101%, we're allowing 5 seconds before we consider it a problem. If we're running at 120%, we're also allowing 5 seconds.

What we need is to modify our timing based on how big a difference there is between our target (ie. 100%) and our actual value.

To figure out how severely we're over the limit, we'll make a change in our logic.

Instead of checking if the measured current is greater than 100%, we're going to subtract the maximum current from the actual current. If this number is positive, it means we're over the threshold.

• Right-click the background and choose Add Node, Math and Subtract.
• Connect the ARDI Point to the 'A' input of the subtraction node.
• Connect the '100' constant number to the 'B' input of the subtraction node.
• Connect the output of the subtraction node to the 'A' input of the comparison node.
• Connect the '0' constant number to the 'B' input of the comparison node.

We can now divide the time threshold by the difference in value.

Assuming we set a delay time of 120 seconds (2 minutes), this would mean that we'd see the following timings…

This gives us a response curve close to what we're looking for.

In this case, we're actually going to do this slightly differently - rather than divide the time threshold, we're going to multiply the time we're counting, by adding a Multiply node between the Elapsed and Increment nodes we made earlier.

Although you'd initially think this is the same, it actually gives us a subtle difference in behaviour.

If our value spiked up to 120% for 5 seconds and then dropped down to 101% and stayed there, the timings would look like this…