Simplistic PLC

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hardworkingstiff

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Wilmington, NC
I was at a facility today that had a 3 HP pump feeding (water) to a 1,000-gallon pressure rated tank. They had a small air pump keeping pressure in the tank, but it had a low CFM rating. Theory being when the water was high in the tank it would keep enough pressure in the tank during small demand periods that will keep the submerged pump from cycling on/off too much.

I questioned the design and they admitted they were having some "tweaking" problems.

Seems like they need a very simple PLC with a pressure transducer for water height and one for air pressure in the ullage space. Write the correct logic and you have a nice control system that is easy to modify after usage experience.

Does anyone know of a product like what I think I'm describing?

Thanks,
 
Local water district has a 'made just for that purpose" on a subdivision well. It is an Air Charger and uses a liquid level control to detect when the water gets to high in the tank. Once it reaches a certain level the compressor turns on and recharges the tank with air. The electrodes have to be cleaned on occasion to keep them working.

It is not that it needs the pressure but the air volume in the tank to keep the pump from cycling to fast.
 
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I'm not real experienced with the OEM stuff but a micrologix 1500 with analog expansion card would work wonderful for a low cost. At our facility we use Rosemount pressure transmitters on the bottom of our puree tanks to tell us the level. They provide a 4-20ma signal that once scaled in the PLC will provide accurate data.
 
Honeywell contollers work great for these apps. Lots of different ways to read level. Systems with "air pads" can be tough to dial in until you get the whole system filled with water and up to pressure.
 
The ones I have worked on have had two level switches and a pressure switch. The low level switch was the start for the pump and the high level switch was the stop, set up as a standard 3 wire start stop circuit for the motor starter. The pressure switch ran the compressor to keep the pressure up as the water level dropped toward the low level pump start switch.
 
don_resqcapt19 said:
The ones I have worked on have had two level switches and a pressure switch. The low level switch was the start for the pump and the high level switch was the stop, set up as a standard 3 wire start stop circuit for the motor starter. The pressure switch ran the compressor to keep the pressure up as the water level dropped toward the low level pump start switch.
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This seems to be the best route unless they are trending levels or pressure.
 
For mini-PLC's, I've tended to favor the IDEC "smart relay". It's sold under several rebranded names.

450970.jpg
 
Options are endless! So many need toys out there to accomplish what you want. One thing to keep in mind if you are going to be responsible for maintenance of equiptment keep it simple. The less complicated you make it the easier it will be to troubleshoot and maintain when it quits and eventually it will quit. Of course with the PLC you will need all the added software but troubleshooting or modifying will be a breeze. Don't know about you guys but it seems around here that everyone knows exactly what they want until they see what you can give them then plans change.:grin:
 
mdshunk said:
For mini-PLC's, I've tended to favor the IDEC "smart relay". It's sold under several rebranded names.

450970.jpg
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Never worked with these before from the picture I can't see any analog I/O is there any? And does this program from the display?
 
iaov said:
This looks similar to a GE Smart Bloc. Are they the same?
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I don't think so, but I'm just not sure. Most of the manufacturers have a micro-PLC of some sort. The only thing GE I've worked with much is their really cool Genius I/O modules.
 
Strahan said:
Never worked with these before from the picture I can't see any analog I/O is there any? And does this program from the display?
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Yes, and Yes. It also has separate software you can use if you don't want to program through the front panel. I've used this thing to lock doors and for lighting control, mostly, due to the fact that it has a really nice calendar and timer built-in. The thing only cost about 75 bucks.
 
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