Level Control for Water Tank

S

Thread Starter

sensorless

We have an application in which there is a 5000 gallon capacity tank and water has to be filled in it (via pump). There has to be 3 level switches/sensors in the tank to indicate 3 definite levels in the tank. The system will be PLC controlled.

My question is that what kind of level switches/sensors should be bought for this application? I am aware about float switches. Please guide for other types of level sensors/switches which can be bought for this application. Please aware me for types of level switches/sensors recommended for water control & management applications.
 
B

Bob Peterson

A lot depends on the water. If it is sewer water, you probably want something a little different than for DI water.

There are a bunch of different designs of float switches that accommodate all kinds of different situations.

There are sensing methods that only work with certain kinds of vessels as well.

You questions is so open ended that it is hard to give you a serious answer.

--
Bob
http://ilbob.blogspot.com/
 
> My question is that what kind of level switches/sensors should be bought for this application?

We use Flowline LU20 for single level control (multiply by 3 for your application), they have the advantage of being non-contact and can be used in a intrinsically safe environment.

We've used stainless steel probes (four probes for your application I believe. Well, three and a common).

And we use float switches for non-DI water applications.

We also use differential pressure transmitters for one of our large DI water tanks on the roof (just be sure to protect it against the weather if you live in a cold part of the country).

And we use a "bubbler" in our sludge pit.

http://blog.lesman.com/2012/01/04/bubbler-systems-for-measuring-liquid-level/

We are now trying out a Moore Industries SPA2 for a solvent recovery application where it will give us four trip points off of one current/voltage/RTD input. This will forego the need for a PLC in this application. Looks like a nice unit! (Not something that I have come to expect from my contractor. :) )

Like Bob says, if you are using DI water in your application, then you have to use devices that are compatible with it (someone here at the plant replaced a stainless steel plug with a mild steel one on our Phosphate tanks. We found out about when 5000 gallons of DI water hit the floor. So take it seriously).
 
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PLC_Programmer

A pressure Transmitter can be used for the same.

Use it in the exhaust pipe before the isolation valve. this will give you continuous readings of the pressure in relation to the volume of water in the tank. Use trial and error for determining levels which can be easily mapped to in percentage or mm by the PLC through scaling. U can make alarms or process switches in the PLC program or HMI for multiple levels.

Highly reliable, accurate and easy for maintenance as well as assigning different level set points for the future without having to re-position the transmitter.

We currently use this in applications such as Water De-mineralisation plants for Power Plants.
 
Hi Sensorless

You could also look into using a GSM Communicator/PLC such as the GSM Commander (www.gsmcommander.com)

With this device you can connect any float switch / probe or ultra-sonic level sensor to the device.

I would suggest running either the probes (as previously suggested) or 3 simple float switches.

Each switch will get connected to a input on the device and when it hits your low level you can activate your pump (high level will de-activate the pump).

You can also request level from the device via SMS and if the pump has not switched on in a unusual amount of time the system can inform you vis SMS of the fault.

This application is very common for the GSM Commander and it can also work as a M2M so if your pump is a couple of kilometers away then you will have an independent system operating the pump (and the water tank system will SMS the Pump to turn on or off).

I hope this helps!
 
I would recommend looking at Pretech Solutions Inc. as a monitoring solution for inputs and outputs that can directly interface to a PLC. PLC's are great for processing but poor in monitoring actual field wiring and switch conditions. Pretech claims they will discern between an open and closed switch while monitoring field wiring conditions for "open", "short", and "ground" faults. This is a non-programmable monitoring solution.

> We have an application in which there is a 5000 gallon capacity tank and water has to be filled in it (via pump).
> There has to be 3 level switches/sensors in the tank to indicate 3 definite levels in the tank. The system will be PLC controlled.

> My question is that what kind of level switches/sensors should be bought for this application? I am aware about float switches.
 
There are sensors on the market that will give multiple inputs with one switch. The ranges/set points are programmable. You could also use a pressure switch with analog feedback given that the system will be PLC controlled.
 
Hello,

i work as a process technician/electrician at a dairy. If you don't want to use a pressure sensor in the bottom, i would recommend Endress + Hauser FTW33. Depending on water quality (dirty, foaming etc) there are some different models. I use them in many tanks for many different products. Food safe, stainless steel, easy to install and quite cheap.
 
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