Can we derive history from historical tag - duration above a certain value

Ignition
1

I have a tag monitoring an analog process value. It has been logged in the historian for many months. I’m displaying the value on a PowerChart.
I would like to add a label below the chart showing the amount of time the value was above a certain threshold.

Can anyone suggest a way of doing that with a history query? It would be like setting the aggregation mode to DurationOn but with a threshold of my choosing.

Many thanks.

2

A very very crude way if its saved periodically is COUNT rows where value >= * poll rate.

3

There is a little used/known, hidden in plain sight, capability of the historian scripting functions to accept custom aggregates. Custom Tag History Aggregates - Ignition User Manual 8.1 - Ignition Documentation

There are some restraints to their use for them to be the most performant:

  • The return size provided must be greater than 0
  • They should be used with a project script
  • The script must be located in the Gateway Scripting Project
  • The script library must have a name that starts with “shared” all lower case.

All of this is in the documentation.

Then you can provide a function similar to this to get what you are looking for.

def durationAbove(qval, interpolated, finished, blockContext, queryContext):
	duration = blockContext.getOrDefault('duration',0)
	lastTime = blockContext.getOrDefault('lastTime',None)
	if qval.quality.isGood() and qval.value >= 200:
		if not lastTime:
			blockContext['lastTime'] = qval.timestamp
		else:
			blockContext['duration'] += system.date.millisBetween(lastTime,qval.timestamp)
			blockContext['lastTime'] = qval.timestamp
	
	if finished:
		return blockContext.getOrDefault('duration',0)

Note: This is just an example and is completely untested. You’ll probably need to play around with it to get the results you want.