How to calculate cumulative change in value only if certain condition is true

[gourav saini]

Hi all,
I have a process where different solvents are added to a single vessel via actuator valves. The total weight inside the vessel is captured from a load cell.
I want to create application where total amount of each solvent added to vessel is captured.
For that I want to log the total amount of weight increment in the vessel when the valve is open.
But I am not able to create a meta script point where total increment in weight when valve is in open condition is captured.

[phildunlap]

Hi gourav,

It sounds like you want a numeric Meta point something like this...

//valve is the boolean point controlling the valve, updating ontext, logging on change
//total is the numeric point measuring the weight in the vessel
if(valve.value || my.time > valve.lastValue().time) return "no value"; //we'll not be logging here... set data type exception to ignore!
//Okay, valve just closed
var values = valve.last(2);
var difference = total.value - total.pointValueBefore(values[1].time).value;
return my.vaiue + difference;