Hi all,

Does anyone have experience with weight control systems for fluid batching applications using scales?
I'm interested to understand what are tipical control systems implemented for this application (PID...). In particular the system involves a fluid to deliver to a bag positioned on a scale through a pump.
Thanks

 

On first read you are asking us how your process works .....

The nearest I have is cement being bagged for the domestic market: aerated cement is very fluid.
Control wise you are looking at a small sequence,
- bag recognition on scales
- run pump for preset time / or obtain real time weight from scales
- stop pump early to cater for 'in flight' material
- measure actual weight to that requested
- manual bag take off

However everything depends on how the pump and scales performs relative to what you are trying to achieve;
which suggests input from a Process Engineer.
Quality Control and labels spring to mind.
It is usually the case that the setup does something you don't want !

Food industry [for example] has mixer vessels sat on load cells.
Dry product is dispensed by screw feeders or similar based on the above sequence.
Typically four would be dispensed in turn, noting actual weight before proceeding with the next sequence.
There is a lot of maths involved there, but at the end the mixer starts without manual intervention - an automated process !

 

google gravimetric and volumetric hopper systems. Like oneye said there is some funky maths involved, it is surprisingly tricky to set up, but it is well within the reals of a PLC control. The PID part of the control will be one of the easier bits to set up....but as soon as you have some code down that has a PID part to it you will see all the other issues....
I've seen a few of these systems and like I said they are tricky to set up