Chemical Dosing

Hello all,
I am working on Water treatement project i need to prepare logic for Dosing Pump
the system has two Dosing pump they having Storke & Speed chartestics
Now i need to add Chemical as per Flow rate does nay one have AExp on it.
Pls Explain How it will be achived in ladder (Math calculation)

The PLC has AO 4 -20 mA

Best regards
sandymax

What kind of feed back do you have? Flow? Number of strokes? Timed?

The PLC is having AI for Speed as well as Lengh

also AO for Speed and Length

Pls let me how to achive it?

Thanks
sandymax

This is not easy to achieve with a math calculation. You need to make a "look up" data table using the output graph that should have been supplied with the dosing pump. Then monitor the flow rate analog input and set the stroke length and stroke rate from the entry table that is nearest to the dosing output you need.
If the PLC supports indirect or indexed addressing then use this to point to the correct entry in the look up table.

For instance assign the flow rate a value x from 1-100, then the address for the dosing level will be e.g N10[x] so if the flow rate is 43, the dosing amount will be held in address N10[43].

Does any one have Example how it is achived ?
Specially in Modicon Quantum

In the modicon use the LOOKUP_TABLE1 function block, input the points from your dosing pump graph and the table will convert your stroke into volume. From this you can work out how much to use for a certain process flow rate. I am only just starting with modicon PLCs so this is just from reading the help files.

The systems we've done leave the stroke set by the chemist, and we just use 4-20ma to control the speed of the pump over the range that the flow can go.

What kind of dosing pumps?

We typically will use LMI pumps for this type of application, and run them for a specific amount of time to achieve the proper dose.

With a little research, it looks like they have products to do just what you're asking for. http://www.lmipumps.com/corp/details/0,4387,CLI1_DIV12_ETI3700,00.html