Vessel Filling

Hi,

I have a vessel filling project to complete and i would like to know your experiences for possible problems i will face.

What i have :
Mass flowmeter which gives 1 pulse output (every pulse is 10kg)
One 4-20mA analog input from mass flowmeter that i can configure as flow rate, density etc...
An on/off valve which cuts or lets flow (20 sec close and opening time)

My plan is like this: I will start filling vessel and after a few minutes i will send close command to valve and copy pulse count into a different register. After the valve is fully closed and pulse count doesn't change i will sub two values and i will have the amount of lpg for closing time.

Consider this is 50kg, when operator starts a filling job for 5000kg i will send close command to valve at 4950kg so i will have 5000kg when the valve is closed.

But i have some concerns like pressure. If line pressure changes, this 50kg will change so i will no longer have the correct fill at the end. What i need to do is somehow add flow rate to this equation.

Thank you.

I use something like this:

Zero accumulator
Open fill valve
Wait until (accumulator + (flow rate * k)) >= desired quantity.
Close valve.


k is a constant, and is used to account for the response time of your filling system. You may have to use trial and error to get the correct k value. If you want the valve to close sooner, increase k, later decrease k.
Once the k value has been established, the flow rate term will go up and down to take out the variances in delivery rates from pressure changes. I've used this method for years and once you determine the correct value for k, it is correct every time.

Mass flowmeter which gives 1 pulse output (every pulse is 10kg)??

If every pulse is 10Kg then you can never be sure you reached 5000Kg.

The simple way to control filling, is to have 2 valves, a big valve and a small valve. When you start filling you open the 2 valves, and when you reach the desired value minus a certain value or % you close the big valve, and when you reach the desired value you close the small valve.

You could close the valve once at say 4900 kg and then see how much it fills while closing. Then open the valve again and close it at a time determined by the earlier test run.

Dear Ken Moore

Your method is working great.

Thanks everyone for help.

Thanks for following up.
Glad to help.
As I mentioned, I've been using this method with great success for several years now.