Flow Control

I am looking to control a pump with a flow meter to pump a preselected amount of water. So that I can select for example 50L of water using a HMI and the pump will flow 50L of water then stop. I am looking for worked examples of this (Program), or any help or advise on the best way to do this. I am fairly new to programming

The program will depend on the type of pump, the type of flow meter (if any) and the type of PLC.

The pump will be a horizontal mount centrifugal pump 400VAC the flow meter has not been determined yet or PLC. Really looking for help and advise on this. You wrote " flow meter (if any)" could explain?

That does not narrow it down much as there are different types of outputs for flow meters. Digital (Pulse) or Analog Value.

The PLC you pick could also be a point of mixed variables for how you would write the program and what instructions you would use.

I am not sure if you are a student or not so I will spell it out in words to get you started and let you try and make the ladder logic yourself.

Here is an examples of a way you might do this with say a Allen Bradley Micrologix PLC Using Ladder Logic using 3 rungs.
There are many other ways this can be done though.

In my example the input to turn on the pump is a momentary push button or something that is not maintained.

And lets say that your flowmeter gives 1 pulse per liter.

Rung 1
You will need your momentary (XIC)input to start the pump with a branch extension around this. On the branch extension you will need a XIC to seal in the pump running output. At the end of the rung you will need the actual pump running output. Between your input and yout output you will need a XIO labeled as done from the counter you will install on rung # 2.

(This will allow your input to start the pump, the pump output will seal itself in and keep the pump running even after your input is false. (OFF) and the Counter NOT DONE instruction will break this seal in once the counter IS DONE.)

Rung 2
You will need input from you flow meter. (in this case 1 liter per pulse.) And at the end of this rung place your count up counter.

(This will advance the counter by 1 each time a pulse is given)

Rung 3
You will need a XIC labled as counter done and at the end of this rung you will need a reset instruction for the counter.

(This will reset your counter accumulation after the counter is done so it will be ready to count again when the next batch is called)

You would use the HMI to insert the # of liters you want into the Counter Preset.

Try to digest this and draw it out on paper if you dont have the software. Post your work and we will help you along with it.

If you dont understand what XIC (Examine if Closed) or XIO (Examine if Open) mean you can google it or look on YOU TUBE for Ron Beauford's instructional videos.

You can also use the search feature in this forum to look up "seal in" and the "XIC" and "XIO" instructions.

I have this written in ladder already to show you but in case you are a student you should put some thought, and effort into it yourself.

There maybe more variable to you plan also and we can figure that out once you get past this first step.

BCS

Also since you say the PLC is not yet determined, I would bet you dont have the software either then.

You can go to Rockwells site and Download RSLogix500 Starter Light FREE addition, and also download the Emulator so you can test drive the logic you make.
This free software can also be used to program an acutal Micrologix 1000 or Micrologix 1100 controller.

http://www.rockwellautomation.com/rockwellautomation/support/plc/micrologix.page

Another source you may look at is the Learningpit.com, I have hear that they also have a simulator that you can use for a couple of weeks for free.

Both of these packages represent the same software I gave you my example from. (Allen Bradley RSLogix500)


BCS

PaddyPower,
BCS gave you a good leg up on the programming. My specialty is Flow Measurement in the Oil Industry so I think I can help you with the Metering.

First thing to know is the maximum flow rate of your pump. You will need to get a meter than can handle that flow rate or you will have to have a Flow Control Valve (FCV) to keep the flow rate down to the meters max. Flow Control can be VERY complicated to program especially for a new programmer. So I would avoid that if you can.

Then you will need to select a flow meter that will work with your fluid. You will need to know the accuracy you require from the meter. Also what is the budget for the meter. From those 3 items you can select a meter. If it is just water and you don't need accuracy better than 1% a Mag Meter would do just fine. But there are turbine meters that do well in water service too. What ever you get make sure that the meter gives you multiple pulses per unit volume Example 50 pulses/Liter. The more pulses per unit volume (K-Factor) the better your measurement will be.

Next you will need to decide how the flow will stop. Will you just have the pump shut off or will you use a block valve? We use FCV's in my industry but again we have dedicated batch controllers to handle the flow control. If you don't need a very accurate shut off then I would just stop the pump and not worry about a valve.

On the PLC side, like BCS I would recommend the Allen Bradley MicroLogix 1100. They have models that have high speed counters. They will work with the software that BCS gave you the link for and work just about any HMI out there.

For HMI's I like the Red Lion Graphite series. If you are on a budget the G3 Kadet series is a lower cost option.

Hope this gets you going,
Come back

Another concern would be how often does this occur. Starting and stopping an induction motor too often can result in damage to the motor because of overheating. If it approaches once every 5 minutes you may have to use valving to control the flow and leave the pump motor running.

Bullzi,

Good stuff to know, I will add that to memory for use another day.

Thanks.

BCS

Hello,
I'm working in the milk industry with a lot of pumps and flow meters.
My opinion is that, if you have the possibility, use frequency converters.
Also very important the position of the flowmeter, because if you measure 50 liters of milk after the pump and you will have 10 meters of DN25 pipe till the tank/buket, you wont have 50 liters of milk at the end of the pipe.
Take this in consideration.
BR,
Boros