4-20ma Linear/Non-Linear Tank Level Scaling

Actually the second pressure sensor is for density measurement.

cardosocea said:

Do you have what people in the marine world call a sounding table?

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I've heard them called 'strapping tables' but apparently others call them Dip tables.

The tank vendor probably provided one, the task can be getting the customer to put his hands on it.

Dan

cardosocea said:

You could also determine level off of two pressure transmitters with a known distance between them. However, the measurement isn't great throughout the range.

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I've done several density measurements with differential pressure sensing points at two different elevations and it takes the accuracy of a high quality industrial DP transmitter to get a useable density.

Using two gauge pressure transmitters and subtracting to get the difference is fraught is potential measurement error with a resulting density error.

The distance between the sensing points is generally limited (because the upper sensor point always has to be 'covered' with fluid) so the overall measurement is a low head pressure measurement and then has to be referenced to the physical elevation difference.

A gauge pressure measurement for level is OK on open-to-the-atmosphere tanks provided the range is appropriate for the expected head pressure.

cardosocea said:

Actually the second pressure sensor is for density measurement.

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Yes, you can measure density that way, but only if both pressure sensors are covered. A much simpler way is to have a gauging level probe at a known volume. You are also not reliant on the accuracy and calibration of the two analog instruments.

danw said:

I've heard them called 'strapping tables' but apparently others call them Dip tables
Dan

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https://www.apgsensors.com/about-us/blog/what-is-a-strapping-chart said:

Other Terms For Strapping Chart

There are several other terms used that mean the same thing. These include:

• Strapping Table
• Calibration Table
• Tank Chart
• Tank Calibration Chart
• Tank Gauge Chart
• Gauge Table
• Dip Charts

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Lots of them....

On the subject of density measurement (a little OT, but it was raised), you have to be careful. Any attempt to measure density using pressure gauges requires that the "fluid" is homogenous, i.e. uniform in density throughout.


It is often a need to know the density of non-homogenous "fluids" such as Yeast Slurries etc., and in truth the only way to know the average density of the contents of the tank is to accurately know the volume (roll back a few posts), AND to know the overall weight (roll back a couple of posts)....


Faced with whatever it is you actually want to measure, and how accurate you want the results, you have a choice of several methods, and you choose whichever methods are applicable to your particular case, and of course how much money you have to spend on doing it.