Creating a function in ac450/800xA
I want to define a pump characteristic curve based on two available variables: rpms and power. By using the defined characteristic I could determine flow delivered from a pump.
Is it possible to create such a custom function in an ac450 controller, or is this preferably a scripting task for 800xa?
Alternatively, I have access to AC800 controllers if those are more suitable.
I have absolutely no idea on how to achieve such a feature in the ABB environment, but I'm familiar with C/C++, Matlab etc. for scripting in general.
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You can use UDPCE for user defined elements in AC450. But it's a licenced feature and for this application I suspect not worth the cost and effort.
You are better to use "type circuits" for Repeated use of the same code. See the Function Chart Builder guides for more info.
In any case, I think all you need here is a FUNG-1V lookup table.
Its always possible if the curve is of a linear Form or you could bring it into a Formula form. Using various logic components its possible to deduce.
But if your characteristic curve contains complex functions i am not sure it may work.
If you can provide more specific details, People can help you out here.
To be more specific:
From the motor drive unit I have both the speed and power delivered to the pump.
The pump characteristic I want to implement is attached below. The area below 50kW is not of interest, and thus the primary characteristic of interest is the 1800 rpm curve, and it is not linear. However, it could be piecewise linearised using eg. 4 pieces without significant loss of accuracy.
So the question is how to implement this feature: by taking the known variables speed and power into a function which returns a flow value taken from the x-line at the figure bottom.
Hope this is more explanatory!
I have done a lot of process simulations for AC450 written in AMPL over the last 15 or 20 years, and have simulated numerous pump and fan curves as the one you show here. I always use the FUNG-2V PC element, and enter data for the family of curves as pressure as a function of rpm and flow. You then need a good idea about the down stream piping and valve Cv losses, to be able to estimate the flow based on pressure generated. The estimated flow is fed back to the input of the FUNG-2V. If your data is reasonably accurate, the model will quickly hone in on a stable soultion and provide a good dynamic simulation.