Flow meters are easy. Dispensing a powder is too, unless you're talking minute quantities. Then it becomes a bit more involved if you want precision.

Bulk powder, like four for example are blown into a scale hopper with a load cell. Once the weight is reached you close the valve and shut off the feeder from the bulk bin. You then let the system pressure drop before shutting of the blower. You need an air pressure sensor to control the feeder from the bulk bin. Pressure is low the feeder drops powder into the line until pressure rises and shuts down the feeder, cycle continues until you've moved enough of your powder into the scale bin.

You have to have a pressure switch running the bulk feeder into the piping because powders will compact and plug everything solid if you put too much into a line. So it's done a little at a time.  Powdered cement is moved the same. Moving powders like this creates a lot of static electricity, so grounding straps need to be used along any breaks in the piping, say where you would want a clear lexan pipe to see that product is actually moving through the system.

BTW, IDK what forum I could move this to so you could find someone that is an expert in such things. I've maintained them in a food processing plant, but that was a loooooooooong time ago.