Basic I/O list for pump control.

Hello Everyone,

This is my first post and this website has helped me a lot since i started work, the advice found here is just priceless.

Now I need help, Could any one kindly tell me the basic I/O list used to control a pump from your experience.

I'm a new recruit at this company and have been told to work on a project which is to write a PLC program to control 6 pumps for an underground water storage level control. The contracting company has not given us an I/O list. I'm a recent joinee and im still learning PLC , from my point of view ive come up with the following:

DI
1) Pump on 2) Pump off 3) Emergency Stop 4) Phase Loss 5) Voltage Trip
6) Level Switch 7)Auto 8) manual 9)open valve 10) close valve

But im lost..

I would greatly appreciate it if some one could guide me in the right way for selecting the basic I/O for a pump control. i.e Digital input/output and Analog input/output.

This information will help me a long way.
thank you.

keep it simple for the first time:
switch input pump output
do this for 6 pumps
pay attention to not start within 30 seconds the next pump
ask your tutor about it. or check a drawing

Thank you,

The Previous engineer working on this project (who quit) had set the following inputs :

DI DO AI AO
Actual I/O 173 42 12 3

that would make it roughly abt 28 DI, 7 DO, 2AI per pump.

out of the 6 submersible pumps 1 is used as backup.

pumps used are AMACAN P - 1000lts/hr X 4
Amarex KRT - 100 lts/hr X 2

its for a storm water drain project. Basic idea is where the storm water gets collected in a tank then reused for irrigation.

Proposed PLC- GE RX 3I.

its for a storm water drain project. Basic idea is where the storm water gets collected in a tank then reused for irrigation.

Click to expand...

Then it seems the stormwater will run into the underground storage tank by gravity-feed, then the 6 pumps will pump the water out as irrigation is needed.

That would make it roughly about 28 DI, 7 DO, 2AI per pump.

Click to expand...

I can't imagine needing 28 digital inputs to start/stop one pump. Most likely there are about 50% spares, and there are many other devices in the project, such as High and Low Level switches (or sensors if analog) for the tank level, and there may be control valves and pressure switches to switch the irrigation water into different outlet pipes.

You really need a PID drawing of the project, or at least a one-line diagram or schematic drawings. The pumps could be controlled by one or more variable speed drives and that would explain the analog I/O.

If you want it simple then your PLC needs one digital output per pump. As for inputs, well what have you got? What is the input for tank level, is it a series of float switches set at different heights or is it an analogue level transmitter maybe with a backup of a high level float switch?

You see how we have too many questions because this is not the right way to start the project?

You need a P&ID (Process & Instrumentation Drawing), this will show all the tanks, pipework, valves, sensors and pumps. You also need a specification from the customer, how do they want it to work, don't try to guess, however clever you are you can't read the customers mind. I know it may seem obvious but guarantee whatever you do the customer will say BUT I was expecting it to do something slightly differently. This specification is called a User Requirements Specification (URS)

Once you have a URS you (or someone else on the project) can generate a Functional Design Specification (FDS), this specification should go into full details about how the system will work eg if level gets to x then pump 1 starts, if it gets to y pump 2 starts, at z pump 3 starts. When levels falls to z pump 1 stops etc. The customer may want the pump duty to rotate (so all pumps get used equally), may want failure alarms etc. When the FDS is complete it is sent back to the customer to approve.

Only once you have the FDS approved can you start to design your control system and even then you should really generate a SRS which is a Software Requirements Specification.

It may sound long winded but if you skip any steps you will be heading for problems.

I like to remember these two quotes:

"Failing to plan is planning to fail" ie if you don't get it right at the FDS stage then the final project will never be right or at least it won't be right first time which means you will have to start altering wiring, PLC code etc.

and

"Planning is an unnatural process; it is much more fun to do something. The nicest thing about not planning is that failure comes as a complete surprise, rather than being preceded by a period of worry and depression", yep it is much more fun writing PLC code than writing a specification, but if you do that without a plan then almost guarantee you will get those surprises, some of them may not be nice, some of them may cause damage, some of them will be very expensive. They will all involve in you doing more work, they often result in PLC code ending up in a complete mess because it has been changed and tweaked too many times.

What is your goal, do you want to get it right first time, to impress your boss, to have a happy customer. If the answer is yes then start at the beginning and get it down on paper and get the customer to approve your plans and get that approval in writing.

It is possible too that Mistavince has some PID drawings handed down from the guy that quit, but does not know how to read them.

The amount of I/O for a pump varies with the size of the pump, the owner's budget, and the designer's preference. A simple fractional horsepower sump pump only needs one digital in - float switch - and one digital out - pump run. On the other hand, I've seen large horsepower pumps with vibration monitors on case and bearings and motors, bearing and pump case and motor RTDs, suction and discharge pressure transmitters, seal water monitoring switches ....

You get the idea. As others have suggested, go back to the original project documentation as others have suggested above and verify the instrumentation and design intent.

Thank you very much for all your input .