I have an open tank (water) that currently only drains down to about 10" from the bottom (where a drain exists) and must be manually sumped out about 400 times per year (about 500 gallons of sump). I'm thinking about using a level transmitter connected to a PLC that would trigger a diaphragm pump to empty the tank. I need the pump to start pumping when the water reaches a set level and stop when the tank is as empty as possible. I also need to make sure the pump does not kick back on when filling the tank (reaching the setpoint from the opposite direction). I have never done anything like this before. Any suggestions?

 

Hi- Not sure if you found a solution yet but I have a few ideas.

A float. It's cheap but you can't see a continuous level.
http://drlevel.com/float_gravity.htm

A conductivity unit that uses stop and start via cable probes in the water.
http://drlevel.com/conductivity.htm

An ultrasonic transmitter mounted overhead. A 4 wire unit with a relay built in or a 2 wire to a PLC that has relay control.
http://drlevel.com/EchoTREK.htm

 

i think you'd be mad to put a plc for such a simple task. your better of using float switchs. simple, effective, cheap and reliable .....

 

You can do this logic using a simple relay logic. don't need to have PLC unless you have one already. Check the ultrasonic level transmitter which can be calibrated for different level settings. If you detail your control philosophy. we can work out something.

 

You don't need a PLC for this application. A simple conductivity level probe with switching unit will do the job. Pl. contact E&H, Vega or level instrument manufacturers in your area. They will advise you in detail what has to be done. But if you already have a PLC you can use it.

 

I have a solution for your application...

1. On/Off Control
Ultrasonic level transmitter with 2 contact o/p is best solution for your simple application, and an automatic on/off control application.

Estimated cost: Rs.40,000

2. Continuous Control

To maintain the desired tank level you can use ultrasonic level transmitter with single loop PID controller.

Estimated cost: Rs.45,000

Ultrasonic is best solution for clear liquids and its non contact measurement.

Forbes Marshall (Krohne) and E&H, you can contact for level transmitter.

Call me at 98416070045.

 

Fact is, while I do like ultrasonic level, it is generally a little expensive for this type of application. Most people use a submersible pressure transducer, or a bubbler, or even a float. R45000 is about US1500 and you can do it for about half that. You don't need continuous level. Two float switches wired to a simple solid state relay will work fine. You can use a cheap PLC if you feel better about it.

Walt

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff
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Hi friend,

In my opinion, if you want to finish this project in a cheaper cost, you can use two float switches as some friends said. But you can't get continuous monitoring of level in the tank. Only you can control the pump action according the digital input signals given by those float switches.

But if you don't care about the cost, you can use Ultrasonic type of level transmitter. You can control the pump by level transmitter's feedback input signal. And also, since this is an analog type you can have continuous monitoring of levels of the tank as well.

Regards,
senthil kumar.M

 

My ideas are:

1. For sensor you can use float switch which has 3 foot (I have reference branch: Kasuga) 2 leg/foot for detecting 2 desired positions and 1 leg for reference.

2. Contactor relay & timer (for off delay) for motor/pump control according to contact from float switch.

I think the above ideas are cheaper if it's just control level on and off. I have used this control in my company.