Non-Linear Scaling CLX5000

I have a cylindrical tank lying on it's side, ellipse on end.Length of cylindrical section is 145",radius of cylinder is 42",minor radius of ellipse is 14.5" and volume height is 84" full.Scaling it to height is no problem but scaling to volume is a different story.I'm using a pressure transducer 4-20ma.Can anyone show me an example of the logix needed to produce the result.

Regards

Below are a couple of links and a recent thread on the topic.

http://www.arachnoid.com/tank_volume/

http://mathforum.org/library/drmath/sets/select/dm_tank_volume.html

http://www.plctalk.net/qanda/showthread.php?t=42400&highlight=volume

Had this same thing years ago. It can be done but it's not
nearly as practical as a hash table.

Take measurements at different levels and us those values as
pointers into a table. If a reading is not specifically in the table then take the average of the two values it falls between.
The more reading you record the more accurate.

Good Luck,

(8{)} .)

(Yosi)

Yes, Yosi, but...

jpeek still needs to know the volume and all he knows is height. So unless he directly measures volume for a specific height or he integrates measured flow and saves these values at specific heights he still needs to calculate volume given height.

Keith

I'm with Yosi.

If you want it to be accurate, build a table of empirical measurements. The simplest way is to add fixed amounts to the tank and record the reading after each addition.

The problem with the calculated approach:
For all it's complexity, it depends on perfect geometric shapes, real tanks aren't.
Real tanks of this type are not always level, one end is low for drainage.
The location of the pressure transmitter is CRITICAL. Where on the perfect cylinder is the transmitter connected? Moving it up and down by a fraction of an inch can have dramatic effects on volume at near full and near empty conditions (which is the whole point of this exercise).

Think about how you would validate this measurement. Probably with a test very much like what it would take to build the table.

How accurate of a measurement are you after? What stored in this tank?

I would be willing to guess that a rough estimate on a general formula would be more than accurate enough for this tank.

Real tanks also tend to have internals - ie piping, ladders etc. which will affect the height - volume relationship.

I always use the table method.

This should be easy when using a Control Logix

Can't the data points be entered as position as a function of another position like one does using a cam table. Then one can use the level to index into the cam table to get the volume. This should be fairly accurate because the cam table uses third order or cubic interpolation.

We do that with our motion controller for all sorts of things. If you have cam tables then use them for lookup/interpolation.

JPeek
Out of interest what type of pressure transmitter are you using. Transmitters designed specifically for level applications often have built in functionality to perform these calculations. They also generally have ways to account for internal structures etc. These functions are often ignored because they are seen to be difficult to set up but a laptop and a free software package such as Pactware can solve that problem.
Andybr