Volume of Chemical Chamber

Join Date
Oct 2014
Location
kochi
Posts
66
Hi all,
I have a horizontal chemical chamber(cylindrical) of length L and diameter D and radius R(D/2). I need to monitor volume of chemical in scada ie chemical is continuously filling inn to chamber through inlet.I have a level transmitter. But i dont have any device to calculate any angle... how can i find the volume of chemical filled(continuous reading)? can anyone help me? attaching a reference drawing of chemical chamber with this

HORZ CYLINDER1.png
 
Depending on the capabilities of your PLC and the accuracy you require, it might be a lot easier to create a look-up table.

I hope you can understand this. It's easy for me to understand it, but not so easy to explain!

Let's say you have two data tables, each with 250 registers. Calibrate the level sensor by putting a known volume of chemical into the tank. Record the analog reading from the transmitter in position 0 of one data table and the volume you added in position 0 of the other table. Continue doing this until the tank is full (it would be wise to divide the total volume of the tank by 250 and add that much chemical for every step).

You can use a if-then-else loop, indirect addressing or some other type of logic to "scan" the data table containing the analog readings. Let's say the current analog reading is 12,416 and you have 12,300 in position 19 of your data table and 12,450 in position 20. You know the actual volume is somewhere between between the volume readings you recorded in positions 19 (let's say 16,000 gallons) and 20 (16,275 gallons) of the second data table. You can even use simple math to extrapolate a value between the two "known" values.

In this example, the difference between the analog values is 150 (12,450-12,300), which is equal to 275 (16,275-16,000) gallons, meaning each analog "point" = 1.833 gallons. Since the analog reading is 116 "points" more than 12,300, a close approximation of the volume = 16,000 + (116 * 1.833) = 16,212.63 gallons. Close enough for most applications.
 
An equation can only improve accuracy if the PLC can "run" the equation. Also, the resolution of the level transmitter may be an issue. Vibration, vapours and electrical noise are only three potential causes of error, although vapour will not be an issue with a float or pressure transmitter.
 
but here i dont have any angular measurement to plc.. you can see an "arccos" is used in that equation..
I see a formula with an arccos indeed, but the numbers used in the formula are no angles at all, only the radius and length of the tank and the height between the fluid and the top of the tank.

Don't forget that informatics, so also industrial informatics thus PLC, is nothing more than applied mathematics. If you have problems to interprete this kind of formulae you maybe better stick to simple relay logic. At least this is my advice to my students: if you don't understand it, don't touch it. At least not until you tried your very best to understand.
 
Another thing to consider is the actual "roundness" of the cylinder. Cylinders formed by rolling are typically out-of-round by a bit (due to welding and the effect of gravity, which flattens the cylinder). Using a formula to calculate volume for sucha cylinder is, in many cases, less accurate than a look-up table.
 
From past experience with calculating the volume of a horizontal cylindrical diesel tank, you also have to consider the type of level sensor. In my case, it was a pressure sensor calibrated in inches of water, and mounted 4.5 inches above the bottom of the tank. I had to use offset factors in the Arccosine equation for the height and the density being 0.89 for diesel fuel, instead of 1 for water.
 
Last edited:
Thanks Tom Jenkins,
according to your formula, is the condition is linear? i have time independent level measurement.. can you please explain how did you generate this formula... if you dont mind)))
 
Thanks Tom Jenkins,
according to your formula, is the condition is linear? i have time independent level measurement.. can you please explain how did you generate this formula... if you dont mind)))

I had a set of tabulated values from an old reference book You could generate your own table from the formulas given by others.

I then entered the formulas into an Excel spreadsheet. I created a chart. Then I created a trend on the chart by right clicking the line and selecting create trend. I checked the boxes for polynomial, display equation on chart, and display R squared (1.00 is a perfect fit), and selecting order (I used 3). You can get the equation to display more digits by clicking on it, hitting Control 1, and playing with the number of decimal places.

I use this all the time to crate functions from data. It is one of the best feature of Excel.
 

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