mixing station help

To start, I have a hopper that i will be weighing (via a load cells) to find out the rate of flow. I will be sending a 4-20ma signal into a micro 1100.

I need to calculate how much additive to add to the product based on this rate.

my question would be. what would be some good ways of writing the code to get the most accurate amount of additive included.

thanks

What type of material, liquid or solid?

The most accurate would be to measure the flow before it hits the vessel, either with a flowmeter (liquid) or weigh conveyor (solid).

The method you are doing will always have a lag, therefore will be somewhat inaccurate.

If you cannot add the above, then I would run a few tests to see what the typical start flow is, to enable a sensible pre-start feed for the additive.

Also, I'm assuming you have a method of distinguishing between the main and the additive (not expecting to feed both at once and read from the load cells, this would be impossible of course as you would not know what the weight of each is).

It is a solid, the product gets dumped into the hopper at once, then is dispensed through an auger. The additive will be in a separate hopper and monitored seperatly.

I would install a "Loss in Weight" controller, with a 4-20 mA output signal that is proportional to the calculated flow rate. These special-purpose controllers are common, and self-contain everything needed to do accurate flow-rate control of material from a hopper (using the loss in weight as determined by your load cells). Use this flow-rate signal as input to a PLC PID block to control the speed of the auger (I hope you have a VFD on that auger!), thus keeping the flow constant at a setpoint (which can be sent from your PLC to the LIW controller as a LIW input).

Merrick is one company that makes a LIW controller.

Somone here might have a Micrologix PLC program that would do the LIW function. As for the additive, once you have an accurate material flow rate, I think it would simply be a ratio control- Additive = X% multiplied by Material Flow Rate. Then you will need another VFD auger on the additive hopper so you can control the additive rate.