Low Water Level Sensor Recommendation

Looking for a low water sensor for a critical application. This is a large water bath with dirty water that has some surface ripples and movement and needs to hold a deadband between low and high of about 4'.

We have tried ultrasonic with mixed results and an exterior water level column with laser sensor is a maintenance nightmare because the water is dirty and clogs the level flow line between the main tank and the water column and keeps the sight glass of the water column very dirty.

Any suggestions for a top perorming sensor would be helpful. Price is really not an issue we are willing to pay top dollar to resolve this on a more permanent basis

Are you needing this sensor for controlling the level with this deadband of 4'? Or do you purely need a low level sensor?

Standard in the water/wastewater industry are pressure transducers for reading level and floats for high/low limits.

Use a pair of floats for the deadband but use the ones that are hanging on a cable. If there is a sliding float it will get sticky. We use them in swimming pool balance tanks all the time.

I have used the Flowline Echsonic II sensors with excellent results on most any liquid as long as I mount it above the deadband.

http://www.davis.com/Category/Flowline_EchoSonic_II_Ultrasonic_Level_Transmitters/57278

I have also used an IFM 0-100" H2O sensor in a static line at the bottom of a small tank with surprisingly good results. Even when I had to put one in the suction line from a tank, it was quite steady in its output. The sensor has built in signal filtering which is also helpful.

http://www.ifm.com/products/us/ds/PN2698.htm

EDIT: I may have misunderstood the range as being up to 4'

I have used these on well water tanks:

http://www.dwyer-inst.com/Product/Level/LevelTransmitters/Submersible/

These will work: http://www.jerguson.com/company_products/magnetic-level-gauges-accessories/.
Other companies make them.
Expensive but indestructible.

Would a standard DP cell like the Rosemount 3051 do the trick?

These products or variations of, have given us good service over the years
on both clean and waste water systems

We used the Omron control switch mainly because it was what we carried in stock

http://www.multitrode.com/
http://www.multitrode.com/products/multismart-and-probes/liquid-level-sensing-probe/

https://www.ia.omron.com/products/family/245/

I'm with BobB. Floats are the best for things like that...

But just as another alternative, a good solution for these kind of aplication are conductive rod level switches, but with custom made separated rods. The bought ones are to close for dirty water, but the "sensor" is just an inox rod, so it can be made, and it is very easy to clean. They are more precise than floats, when it is needed..


In this case, I'd go with floats...



edit: Gil was faster with the rods....

I second the float switches. Nothing can be simpler or more reliable. They can be adjusted by changing the length of lead they hang by.