Replacing a Level Transmitter

What issues are you having with unstable process density? It might have some bearing on what our answers will be.

However, just to give an immediate answer, I would use load cells (weight measurement). I've had problems with differential pressure transmitters (product sticking to the diaphragms) so I shifted to load cells.

regards,

Vulcan

Hi there,

You are going to have to provide a bit more data. You say it is an open system, but you have problems with changing density. Is the medium single or multi phase? Do you have agitation in the vessel? What is the process medium and what are it's chemical properties?

All these and more will determine your choice of measurement type selection.

Load cell is definately very good - but expensive if your vessel is huge.

Try to provide a bit more chemical and mechanical data and you will get a better answer. No instrument engineer will commit to a definate answer with the data you have provided as it is impossible to answer any single one of your questions.

Regards

Craig

If changing densities are the issue then obviously weight is variable so load cells won't help you determine the volume (liquid level) in your application. You need to provide alot more specifics for a rational answer....

- density variations (specific materials) and other material specifics

- foaming?

- vessel (tank) size

- location

- available or retrofitable nozzles

- remote indication?

- etc....can't supply "too much" info.

If changing densities are the issue then obviously weight is variable so load cells won't help you determine the volume (liquid level) in your application. You need to provide alot more specifics for a rational answer....

I agree. I just provided the load cell solution as a suggestion since that's what I used. We're not really concerned with having an accurate indication of level. We're more concerned with preventing product from overflowing. To address that, we calibrate the tank using the lowest density solution we will be putting in the tank (water actually). That way, when a product with higher density is put into the tank, the level at 100% indication is actually lower.

If we wanted to, we could put a density meter in the tank so that we can compensate for it. However, as I said, we're not concerned with that.

The added benefit of using load cells was reliable level indication. With differential pressure transmitters, we had problems with product sticking to the diaphragms and preventing them from indicating the level correctly.

regards,

Vulcan

a- Primary factors include the environmental conditions for the transmitter (temperature/pressure/chemical/other) and density extremes of the material (as the material separates, what is the maximum density? minimum density?). You should also consider how much churning or wave action there is at the point of measurement, which would determine if you need any type of measurement delay time or dead band. The precision and accuracy requirements for the measurement will also help determine the type of system you need.

b- I would seriously consider using a float system. You can get them for just about any type of liquid. I have used them in sumps, acid tanks, mixing vats, and many other situations. Select a sensor which will float on top of the lightest density extreme of the process material. For example, if you have a mixed liquid, take a sample and let it sit until it stratifies. Draw off the lightest fluid (the top layer) and measure the density/specific gravity. Select a float with a density about 5-10% less than the measured sample.

c- Talk to an application engineer at the float manufacturer. I sometimes talk to 2 or 3 different companies. It gives me a better understanding of all the options, as people tend to downplay the limitations of their own product, and emphasize any weaknesses in their competitor's system.

Implementation planning, including safety aspects, cannot be accomplished without detailed information on the process material, process system, and physical arrangement.