Convert RAW Data from Level sensor to depth

[bearsgone 1]

Hello I have probably basic question but I could not find a clear example. I have pressure level sensor Wika LS-10 and trying to figure out how to convert the output into depth. Manual does not contain conversion formula. Any feedback would be appreciated.

[Chris Elston 78]

May sound kind of "simple" but for depth measurements.... I would get a tap measure out. Keep setting my sensor until I read 20ma on the "depth". Then measure with a tape measure in inches or millimeters... So now you know 20ma = "x" distance. Then do the same for the minimum depth. 4ma = "x" distance. EXAMPLE: 20ma = 10 inches 4ma = 0 inches Now you have "scaling"... 20ma maybe equal to 32,767 so in your case.... 32,767 analog units = 10 inches = 20ma 0 analog units = 0 inches = 4ma Looks like you are using - and + readings, you can configure how your analog card reads 4ma, that's what you see 32,767 and -32,767. It how you have your analog setup.

[bearsgone 1]

Thank you for explanation, but I am still not clear how I represent depth in inches on PanelView Compact. It can only read 4-20ma range and show % but if I want to show actual inches as the value changes, how would I go about it? Thank you

[b_carlton 61]

A manual I found online shows different pressure ranges (in bars) for differnet models. In fact it appears that the numbers in the model represent that pressure range. That same table showed "1 bar = 10.2 mH2O" So presumeabley you should be able to use the exact model number to come up with a depth reading.

[bearsgone 1]

Thank you for the response. My range seems to be 0-100m which I presume corresponds to 4-20ma. The question I still have how do I convert say 14ma to xx meters on PanelView Compact? Thank you

[b_carlton 61]

In your SCP shown in your first post why don't you convert directly to meters instead of to ma? Do you do PLC calculations in ma? A conversion to meters may be earier to display.

[JStevens 1]

This would definitely be the easiest method. Instead of your scaled min and max being 4 and 20 respectively, make it X and Y respectively, where X is the depth at 4mA and Y is the depth at 20mA. This way you can do native calculations on the depth instead of using mA values. This number should be stored as an integer. Then your PV can read the integer's value and display that as your depth. You did not state which controller you are using, but not all AB PLCs have selectable analog ranges. For example, on a ML1100 with the raw/proportional data format, 4mA corresponds to 6240 and 20mA corresponds to 31200. ~Jeff

[bearsgone 1]

Hello Not to be difficult but how do you convert to meters directly or how to assign/create X or Y values. My PLC is Micrologix 1400 with 1762-IF4 card? HMI is PanelView Component and it can only read one value, there is no place I can set X and Y for a tank. There is only 0-100% measurement. For Analog input input range -10 to + 10 dc and 4-20ma For Data Format I have Raw/Preportional and Scaled for PID Edited 14 Jul 2010 by bearsgone

[JStevens 1]

With regard to X and Y, these are values that you need to either measure yourself or find from Wika. I did a little reading, and it seems as though Wika produces the LS-10 in multiple pressure ranges. The closest I can see to 100m is the 0-10 Bar unit, which should be 0-102mH2O. You will have to verify this as being accurate. The minimum depth, X, is 0 Bars. Meaning that at 0mH2O, the sensor will output 4mA. To find the maximum depth your sensor can handle, Y, multiply the maximum number of bars by 10.2 to find the depth in meters. At this depth, in meters, the sensor will be outputting 20mA. Source: Wika LS-10 Datasheet Now for the scaling. Make sure the analog configuration is set for "4 to 20 mA" and "Raw/Proportional". Having the data format set to raw, will give you a bigger input range, which will make all of your math more accurate. At 4mA, the ML1400 will read 6240. At 20mA, the PLC will read 31200. This applies to the IF4 card only; the ML1400 base cannot accept current inputs. Source: AB ML1400 Reference Manual (Page 20) To put it all together, your SCP parameters should be as follows: Input: the address of the analog input word Input Min: 6240 Input Max: 31200 Scaled Min: 0 Scaled Max: [Pressure Range Maximum]*10.2 (You must calculate this yourself based on your actual sensor.) Output: the address of your destination (I recommend a floating point file, because you are sure to have a decimal and this will allow you to easily perform math in the PLC) Bear in mind, that this is based on the documentation I can find on the web, which may be inaccurate for your particular models. If there is a problem with this, let me/us know and I/we will do my/our best to help. ~Jeff Edited 15 Jul 2010 by JStevens

[bearsgone 1]

Got it going Thank you for your help