Trouble using runScript

Ignition
1

Hi I am trying to use runScript in an expression tag that is part of a UDT.

the UDT has 3 query tags that pull values from my DB. All values are int.

I want to work out rate of change between two of the values using a script so if the rate is negative I can handle the value.

my project script called rateOfChange is as follows.

def getChange(current, previous): if current == previous: return 100.0 change = current - previous try: percentage_change = (change / float(old_value)) if multiply: percentage_change = percentage_change * 100 return percentage_change except ZeroDivisionError: return None

then in my expression tag I have added the following

runScript("project.rateOfChange.get_change({[.]5min},{[.]10min})",150000)

so the inputs in to my function are the tag values for 5min and 10min tags. I have also tried this without the “” but I get the following error

Last Error Cause com.inductiveautomation.ignition.common.expressions.ExpressionException: Error parsing script for runScript() expression: SyntaxError: ("no viable alternative at input '.'", ('<expression:runScript>', 1, 44, '__RESULT = project.rateOfChange.getChange({[.]5min},{[.]10min})\n')) ERROR\n')) ERROR

can anyone help?

2

Three changes are needed:

  1. You must construct a string for runScript()'s first parameter that is valid python by itself.
  2. You cannot use project.* scripts in expression tags, other than client tags. You’ll have to put the function you need in the shared.* scripts.
  3. Expression tags run at their scan class. The “15000” would have been ignored.

Something like this:runScript("shared.rateOfChange.get_change("+{[.]5min}+","+{[.]10min}+")")

3

thank you, i didn’t realise I had to build the string like that.

and yes my script was jargon :blush: all works now, thank you for the help

4

for anyone interested i wrote the following for my rate of change script

def getChange(x1,y1,x2,y2):
    if y1 == y2:
        return 0
    else:
    	try:
    		rate = (float(y2-y1)/float(x2-x1))
    		return rate
    	except ZeroDivisionError:
    		return 0
5

I noticed you posted in the v7.7 forum, so I didn’t mention the new features of runScript available in v7.8. But you might consider using objectScript() instead, from the Simulation Aids module, if you need more flexibility.

6

Hi Phil,

I’ve tried to use runScript in an expression tag part of a UDT also contained in another UDT but haven’t been able to make it work. I’ve even simplified the script so that it just returned a UDT tag with the same result. Any ideas will be welcome.

I’m usind V9.3

7

I wouldn't expect runScript to be much help in tag expressions. objectScript() might be more helpful, but you'll have to share the details. I only use UDTs to automate tag construction, not in bindings or expressions, so I'm not sure what underlying java types would be needed to return a UDT from a script expression.

8

How do you setup alarming for rate of change?