Control.com - Nerds in Control

I am kind of new to all this and don't have any in-plant experience. We are putting a transmitter in a cooling tower basin to measure the depth. The basin is going to be very dirty. Toilet bowl dirty. I talked with a vendor about using a capacitance level rod and he said that the only issue was how often it was cleaned and that if too much stuff was sticking to it, it would let you know. How often do these need to be cleaned if they are used in an application that is toilet bowl dirty. Would going to a bubbler be a better option?

There are dozens of ways to measure the level in a cooling tower basin. The continuum is from cheap to maintenance free.

The cheaper stuff is generally more maintenance intensive.

Maintenance free (within reason) would be direct pressure transducers and ultrasonic level gauges. You could use radar, but you don't have to. The price of ultrasonic transmitters has come down incredibly, in recent years, and they have no moving parts and don't contact the fluid. They can be damped, also, to deal with wave action in the basin, too. If you have foam, you'll have problems, though.

Of course, this begs the question of why you have "toilet bowl" dirty cooling water sumps. You shouldn't. You might also investigate what is causing this problem and fix it, while you're at it.

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

I had problems about 20 years ago with some of the same reliability and maintenance issues so I simply installed a float valve with a mechanical float. The results have been 20 years of problem free operation. By the way, it was cheaper than any electrical solution we had tried and we needed a valve any way.

I hope this helps,

William Hinton

Municipalities routinely use float switches in sewage lift stations. The float is some sort of elastomer (rubbery material) has an internal switch that connects to a controller through the cable. It works well.

But then there are floats that run move up and down vertically on a rod. Bad idea for crummy media - the rod will crud up and the float will stick.

Floats are fine for fixed switch points.

For continous level measurement, either ultraonics or radar do not contact the sump contects, but do cost more, as does any continuous measurement.

Dear Doug,
we have a bubbler level control working very well in our cooling tower basin, I had have a lot of bad experiencie with capacitance level measuring in closed tank, but I think that in open basin will work good, maybe the frecuent maintenance will be the little problem.

Regards
J.Pinzon
Instruments Techniccian

What's the height? And is there any obstruction cutting the ultrasonic cone?

If no, then seems like perfect place for Ultrasonic.

It's not that expensive either!

Drex

Yes, the bubbler type LT can work better. We are using in STP tank level and in some other corrosive liquid measurement. They are working very fine.