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How to calculate flow using level with a PLC (ladder programming)

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Last Modified: 2015-07-15
Hi guys. This is kind of an odd question for EE I know but I thought it was worth giving it a shot.

I'm making a project for my company where we use a PLC/HMI to get real-time data from several transmitters both digital and analog (pressure, on/off switches and level). The level is measured with a HART radar using a 4-20mA loop from Siemens in a tank.

What I need is to calculate the flow of the liquid going into the tank using only the level. If I were using a PC programming language like C++, Basic, Java or even PHP, it would be easy but since the calculation has to be done by the PLC which uses LADDER programming, I don't know what is the best way to calculate it.

The flow calculation doesn't even has to be in real-time. I mean, I can refresh it every 10 to 30 seconds.

We've tried using a BLINK for X seconds (tried 10 and 20 seconds) that grabs the level when the blink began and then the level when the blink ends but I don't like that. Is it possible to use a ramp calculation or something like that? What would be the best (with the less error) way?

Thanks in advance!
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