Gravimetric control

[JRW]

Any reference material or "kick start" for gravimetric control on a belt feed system?

 

[rdrast]

Okay, give me a hint... what are you looking for really?
We just installed a K-Tron weighbelt feeder, but use it only as mass throughput setpoint to a downstream mixer. Gravimetric control would be different, actually varying the speed of the belt, to deliver a constant LBS/HR.

http://www.ktron.com/Products/weigh_belt_feeders.cfm

-- edit --
Sorry, my confusion comes from what you want to achieve. If you use a weigh belt as a gravimetric system, then you need to use a weigh-belt that is capable of dealing with a 'fully stacked' vs 'free-flowing' infeed system. The one I mentioned in the link above, can deal with a fully loaded infeed, and regulate the output. Our older ones cannot, they just weigh whatever is dropped on them. So I need a bit more clarification of your intended use.

 

[JRW]

rdrast,

Thanks for your response and I apoligize for being so vague.
I did check K-Tron site before posting this and dug around Al Gores internet .
My particular control is for a weightbelt feeder and regulating the speed of the conveyor. I'm curious how the experts (Ktron..etc..) do it.
I was trying to find a good block diagram of the control scheme.

THANKS

 

[rdrast]

The unit in the link uses two load cells, mounted to arms under the belt. One is prior to the infeed, the other is after the infeed. The incoming cell is used to tare the belt, and the outgoing one measures the actual load of material on the belt.

As the belt runs, the controller for the unit acts as an integrator, basically summing up the weight of the material passing over the second cell and coming up with a mass-flow rate in pounds per hour. The flow rate is determined by the belt speed, which is controlled by a small drive. In absolute mode, you run the belt at a constant speed and just read the total pounds/hour output. In gravimetric mode, you enter a pounds/hour setpoint, and the controller regulates the belt speed to achieve that.

 

[504bloke]

Other than K-Tron check out Colortronics

 

[MartB]

K-Tron's usually switch from volumetric to gravimetric. Volumeteric on startup and then over to gravimetric after good control has been established.
What kind of information are you looking for specifically? I am just trying to get a handle on where you are going with this thread.
If you are looking for control basics then the K-Tron manual is very helpful in this area.