tank capacity

siggibald

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Join Date
Oct 2012
Location
iceland
Posts
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i have a 2 -20 ma 0 - 0.6bar pressure metter in a tank on a big boat, Always when i working with this i use SCP [Scale with Parameters]instructions, but now i can't use that because it is so many points i have to pud in, like i show you here belowe. what instruction can i use for this :unsure:

0m - 0 m3
0.5m - 5.8 m3
1.5m - 21.7 m3
2.5m - 38.6 m3
3.5m - 56.1 m3
4.5m - 72.3 m3
5.5m - 83.0 m3
6.5m - 93.0 m3
7.5m - 102.9 m3
 
1st, this is first time i hear of 2 -20 mA sensor, usuallly it's 0-20 or 4-20mA

as for second it's non linear. if you don't need 100 % accuracy, maybe you find approx curve equation in excel and work with that. other solution would be multiple SCP then call them based on input value range

PS: excel gives: y = 0,523x4 + 0,9221x3 + 4,5827x2 + 9,0937x + 0,1318 or less accurate but linear y = 14,286x + 1,8047
where y is volume, and x is height
 
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pressure in a tank is directly related to the height of the column of fluid, so I would think either your sensor is bad or your measurements are incorrect. what is the make and model of your pressure sensor? Since you are trying to relate pressure to tank volume you will have to also include an accurate drawing of the physical dimensions of your tank to get an accurate answer.
 
balash said:
excel gives: y = 0,523x4 + 0,9221x3 + 4,5827x2 + 9,0937x + 0,1318 or less accurate but linear y = 14,286x + 1,8047 where y is volume, and x is height
Click to expand...

Balash, which function do you use in Excel to get the polynomial from the data points?
 
balash said:
add trend line... Trendline options... Show polynomial equation. Then you can choose from all sorts of approximation.

EDIT: ups, seems lare already answered...
Click to expand...


Don't worry, furthermore danw asked it from you (y) This is good to know feature from excel.
 
You shouldn't blindly apply a fourth order equation to a set of data unless you really don't know much about the data. In this case we know it is for tank volume vs height. We can chose the right equation if we know the shape of the tank. Then we can use the data to find the coefficients.

If the tanks cone shape of cylindrical or round it is possible to do a much better job of estimating the volume as function of level.
 
Peter Nachtwey said:
You shouldn't blindly apply a fourth order equation to a set of data unless you really don't know much about the data. In this case we know it is for tank volume vs height. We can chose the right equation if we know the shape of the tank. Then we can use the data to find the coefficients.

If the tanks cone shape of cylindrical or round it is possible to do a much better job of estimating the volume as function of level.
Click to expand...


exactly
 
Peter Nachtwey said:
You shouldn't blindly apply a fourth order equation to a set of data unless you really don't know much about the data. In this case we know it is for tank volume vs height. We can chose the right equation if we know the shape of the tank. Then we can use the data to find the coefficients.

If the tanks cone shape of cylindrical or round it is possible to do a much better job of estimating the volume as function of level.
Click to expand...

That is true. And as have said earlier, pressure sensor should give linear data.
Also starting from 2mA is something odd and 0,6bar pressure is pretty much 6m (water). But if you measure something else (like fuel or oil) then it can be 7,5m. I would check the readings first.
 
of course, knowing the shape would give exact formula for volume based on height, but as lare said 2mA is odd I would add that is odd also to measure the tank level through pressure when you have level sensors.
 
siggibald said:
i have a 2 -20 ma 0 - 0.6bar pressure metter in a tank on a big boat, Always when i working with this i use SCP [Scale with Parameters]instructions, but now i can't use that because it is so many points i have to pud in, like i show you here belowe. what instruction can i use for this :unsure:

0m - 0 m3
0.5m - 5.8 m3
1.5m - 21.7 m3
2.5m - 38.6 m3
3.5m - 56.1 m3
4.5m - 72.3 m3
5.5m - 83.0 m3
6.5m - 93.0 m3
7.5m - 102.9 m3
Click to expand...
If your sensor is 0 - 0.6bar then the height must be in the range 0 - 6m or the fluid must be lighter than water (which you didn't mention). If not your sensor is unsuitable. I find it strange everybody is discussing the calcs but nobody noticed this flaw.

BTW using a lookup table would be nearly the same as sounding a tank and using the tank table to determine the volume, as is standard procedure on board ships. But personally I would use some more points than you show here.

Kind regards,
 
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jvdcande said:
If your sensor is 0 - 0.6bar then the height must be in the range 0 - 6m or the fluid must be lighter than water (which you didn't mention). If not your sensor is unsuitable. I find it strange everybody is discussing the calcs but nobody noticed this flaw.
Click to expand...

it's not that nobody noticed this flaw, but to assume that water is in tank is as good as to use pressure to measure level (or that we assumed OP's using it for that). i mean of all the sensors (ultrasonic, hydro-static, conductive, capacitive....) for level to use pressure sensor for that is like dropping a stopwatch from top of the building to measure its height.

:confused:
 
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for a tank this size there will be a tank table book.
it has tables for the different angles the tank can be in like 10 degrees side or with different angles ahead/astern but they are related to the readings of the depth(draft)of the ship.
another one is density of the contents of the tank.
normally the level is measured with a tape and then looked up in the table, when they have pressure gauges an extra step is needed. and a different table as the position of the pipe and the sensor are not same.

on old ships it is a dirty book, on newer ones it is a three dimensional table in the computer.
 
balash it is the most used system on ships as the tanks are very difficult positioned and HFO does not like to have a capacity or ultrasound in it.
 

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