Dosing Pump control

kedardahivale · Mar 10, 2014

Hello,i am a final year student of instrumentation, I have this project in which i have to do optimum chemical dosing in water for that i am using a digital dosing pump(Grundfos DDC pump)But i am not getting how should i do this automatically by using PLC in short, how should i control that pump by using PLC.please help me

Tom Jenkins · Mar 10, 2014

It depends!

Can you measure the concentration of the chemical in your process? Is it sufficient to have the dose be a constant proportion of the water flow? What instrumentation do you have in place?

We won't do your project for you.We will ask you questions to put your thoughts in the right direction. As a final year student you should already know the fundamentals of feed forward and feed back control!

kedardahivale · Mar 10, 2014

thanks for the reply sir, we have turbidity sensor and a magnetic flow meter, based on the value of turbidity we need to do dosing

shooter · Mar 10, 2014

so you have two inputs, one if the flow of the water and one is the turbidity.
suppose you only use the flow sensor to drive the pump, it will only work when turbidity of the influent stays the same, so you will need a cascade control, when turbidity is low enough slowdown the pump.

kedardahivale · Mar 11, 2014

Thank you sir for your reply,I will use the cascade control technique but the problem i am facing is, the pump i am using is digital dosing pump of GRANDFOS company and i am not getting how should i control that pump by using PLC

meghnesh · Mar 20, 2014

Hi kedardahivale !!

1.You need to consider the flow rate for proper Dosing.Depending on the flow rate you are suppose to control the speed of the dosing pump.Tune a PID in PLC which works in a way like "If the flow is more,proportionally the dosing should be more, hence increase the speed of the dosing pump".And then in this case provide a Correction signal to your PID from the turbidity Analyzer in the form of a Closed Loop.

If you don't have a Variable Frequency Drive to control the speed of the pumps you can:-
2.Using Turbidity as an analog input to the PLC
You can set Limits of Turbidity.
Example: When the Turbidity is MORE than X Value, Trigger START command to the pump.
And when turbidity is LESS than X Value, STOP the pumps.

Else if you still can't arrange a Variable Frequency Drive to control the speed, let me know, I have a solution for it.

Regards.

kedardahivale · Mar 20, 2014

Thankyu for reply meghnesh sir and sorry for delay in reply , we don't have VFD to control that pump. what we did is we formed a equation a linear equation from past turbidity and dosing values like if i am having X turbidity then if i put the value of X in that equation then it will gives a required amount of dosing value and the PUMP we are having is a digital dosing pump of GRUNDFOS company and we are trying to implement that equation in PLC but not geting how should we control the speed of that pump, but i am thinking of PID control

Velociraptor · Mar 20, 2014

Hi Kedardahive,

The more clearly you can define the problem, the better the help will be. Some questions -
1. How large is the tank that you are trying to maintain chemical levels in?
2. What are the inflow and outflow rates, or ranges of rates?
3. This dosing pump; how does it work? Does it pump at a constant volume per minute, when on?
4. What does "optimum" mean? Are you trying to maintain within a range?

Lemming · Mar 20, 2014

I think U should read the manual for the DDC, it will do everything you need for variable dose rates..

Velociraptor · Mar 20, 2014

I looked at the Grundfos DDC on their web site. I could find a brochure, but not the manual. It appears that this pump is driven by a built in stepper motor and has a range of adjustment on the order of 1000:1. It also says it has a controller that is programmable (no detail). If it also has a measurement input, you may not even need a PLC. The key is understanding the pump operation.

jag131990 · Mar 20, 2014

You could just wire in the 4-20 from your mag flow meter straight to the pump and have it operating via flow-pacing. But if you would like to correct for turbidity, you should scale flow-rate into the PLC. Come up with an algorithm to determine how much extra dosing is required based on X turbidity (as someone else here has said). Then increase the dosing rate proportionally (analogue out signal 4-20).

meghnesh · Mar 21, 2014

Hi Kedardahive,

Unfortunately you cannot control the amount of dosing until & unless you have a control over SPEED of the PUMPS or a control over the a VALVE which may increase/decrease the dosing amount.
No matter what equations you write in PLC, you wont be able to control the dosing as the only ELEMENTS for DOSING CONTROL is SPEED and DOSING AMOUNT CONTROL(valve)

Still if you don't have a VFD I can give you a suggestion.
Go for AUto-Transformer.
Arrange 2-3 Nos of Auto transformers set at different TAP positions to give different values of volatges and hence speed.
Use Contactors of Motor Rated to make a switch over from one transformer to another transformer.

and build a logic in PLC by use of turbidity value and flow value to making switching between transformers.

jag131990 · Mar 21, 2014

Cannot be sure of what model he has.. but if he has this Grundfos Alldos DDC pump:

http://www.wesdp.com/media/downloads/80/Grundfos_Alldos_DDC_SMART_O_M_Manual.pdf

then he can control speed via an external 4-20mA signal.

Lemming · Mar 21, 2014

Auto transformers ?? did I wake up in 1963????

meghnesh · Mar 21, 2014

Hi Lemming !!

You can suggest some other methods

Dosing Pump control

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