Pump Start Request from PLC

[Sapho]

I have a project to do. I'm required to design a pump controller. I have two pumps, one pump is on duty(active) and the other is on standyby(inactive). When there is low pressure the pumps must switch therefore the standyby pump must start operating. The must be a switching time/ time delay when the pump switch.

Please help with a design.

 

[nonuke]

This is a start. Please show what have you done so far.

http://www.plctalk.net/qanda/showthread.php?t=55379

 

[Lancie1]

Sapho,

What brand and model of PLC must you use?

Are you doing ladder-type programming, or something else?

How long is the time delay before switching to the new pump?

 

[Sapho]

Pump Start Request with PLC

Hey Lancie

I'm using the voltage based relay logic to control the pumps but I also need a pump start request from the PLC.

The delay time is 5s

Thank you

 

[Lancie1]

This is a very common problem and I am surprised that you did not find one of the dozens of Pump Alternatior programs on this site. Here is a place to start with a simple 4 rung program.

Due to lack of information, I AssUMed that your PLC is an Allen Bradley SLC 5/02 with RSLogxix 500 programming software. This program causes both pumps to go off when Low Pressure Switch is OFF, then wait 5 seconds AFTER the low pressure switch goes ON. (I hope that is correct).

 

[Sapho]

Pump Request with PLC

Thank you. I think this is correct. I'm still making sense of it. Need to figure out the entire operation.

If you don't mind may you please explain the function of the diagram.

Thank you once again

 

[Lancie1]

The function of the LogixPro diagram is to show the symbolic ladder logic program, a method to program Programmable Logic Controllers that is easily understood by electricians that are already familiar with relay ladder logic. The numbers above each symbol are the memory address of that instruction in the PLC.

In order of symbol appearance in the program:
--|/|-- = Examine If Open, or the same as a NC instruction in many other brands
--| |-- = Examine If Closed, or the same as a NO instructions in many other brands
--( )-- = Output Energize, a relay coil, or N Out operation in many other brands
--[TON]-- = Timer On Delay, a timer function that that enables its contact when the time setting has expired. Each timer has a Time Base, in this case 0.1 second for each number, so "50" x 0.1 = 5 seconds.

 

[Sapho]

Pump Request with PLC

Thank you once again. It's starting to make sense.

Please indicate the Stop and Start contacts.

What is P1/P2 toggle? I can't make sense of this line. How is the relay energized in line 000?

Thank you for your assistance

 

[Lancie1]

Please indicate the Stop and Start contacts.

Do you mean that you are supposed to have Start and Stop pushbuttons in your program? If so, how would you add such things? Is a Start pushbutton supposed to start a pump (which in your first post you said is controlled by a pressure switch)? Or do the Start and Stop pushbuttons only turn a System Run relay On or Off?

I'm using the voltage based relay logic to control the pumps ...

If so, then your Start and Stop pushbuttons should control the relay-based logic, and the PLC should only control the Pump Request bits. Those Pump Request outputs from the PLC need to be wired into your relay start-stop circuits.

What is P1/P2 toggle? I can't make sense of this line. How is the relay energized in line 000?

The P1/P2 Toggle bit is a type of logic alternator. There are many other ways to create a common logic alternator. Do a Search (click on "Search" at the top of this page) on this site for "alternator" or "flip-flop" or "toggle" and you will find them. The toggle bit switches from Pump 1 to Pump 2 to Pump 1 to Pump 2 and so on each time it goes On or Off. As you can see by the logic in Rung 0, the P1/P2 Toggle goes ON when Pump 2 Start Request is OFF and Pump 1 Start Request is ON. The P1/P2 Toggle goes OFF when Pump 2 Start Request is ON.

In the picture in Post #5, the Pump 1 Request bit is ON, so Pump 1 should be running (if your relay logic is hard-wired correctly). As soon as the Low Pressure Switch goes OFF, the Pump 1 Request bit will go off. Then the next time that the Low Pressure Switch goes ON, the Pump 2 Request bit is ready to go ON (because the P1/P2 toggle bit is ON).

PS: I copied your instructions as rung comments, including the "standyby" pump, but here the more common spelling is "stand-by" pump.

 

[Lancie1]

When there is low pressure the pumps must switch therefore the standyby pump must start operating.

Are you sure that the pumps are supposed to switch on Low Pressure, or are they supposed to be switched on Low Level?

Water well pressure tank switches often are pressure switches with a wide on-to-off range (30 to 40 PSI, typically on at 30 PSI and off at 70 PSI) . Are these water-well pumps?