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SITRANS LU Probe on Fuel Storage tank - Low Tank level readings off

Created by: ekersey at: 10/24/2013 8:10 PM (6 Replies)

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10/24/2013 8:10 PM	Rate (0)
ekersey Posts: 5 Rating: (0)	Hello All. My company uses these probes throughout our plant. I am having trouble with one center mountedon an 18' nominal height x 54" dia, unleaded fuel tank.All the setup parameters, including P006 and P007 are set up correctly, but the probeouputs zero (4ma) when the fuel level is actually about 4'. The readings below that are negative (ma). Reading above appear to converge to 18' (so the probe readings are linear). We have an old mechanical "tape" level reading system still in the tank and I'm wondering if this is causing interference. The "tape" is about 14" off thetank wall, suspended from the tank head. The only other culprit I can think of is the probe is out of calibration. Thank you for any assistance. Ed 10.28.13: The "float" for the tape gauge is either stainless or aluminum, and if it is "standard" float, it is 14" diameter. I am going to pull the float up to the top of the tank (out of sonic cone/wave) and see if this resolves. the issue. Attachment Unleaded Gasoline Tank Probe in Center of Tank.jpg (243 Downloads)
ekersey Posts: 5 Rating: (0)	Last edited by: ekersey at: 10/28/2013 6:40 PM Last edited by: ekersey at: 10/24/2013 8:11 PM
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10/24/2013 8:13 PM	Rate (0)
ekersey Posts: 5 Rating: (0)	Attached is tank readings graph. Attachment Unleaded Tank levels Graph 10_15 through 10_23 Actual vs Probe.pdf (244 Downloads)
ekersey Posts: 5 Rating: (0)
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10/25/2013 7:22 AM	Rate (0)
DavinderSingh Posts: 93 Rating: (2)	Dear Ekersey, Can you write what parameters are entered under P001, P003 ..... P007? Regards, Davinder Singh
DavinderSingh Posts: 93 Rating: (2)
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10/25/2013 6:24 PM	Rate (0)
ekersey Posts: 5 Rating: (0)	Plan to get these settings tomorrow morning. Thanks. Ed
ekersey Posts: 5 Rating: (0)
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10/26/2013 6:36 PM	Rate (0)
ekersey Posts: 5 Rating: (0)	P001 = 1 (Level) P003 = 1 (Slow response) P004 = 4 (units = feet) P006 =18.75 ft P007 = 18.0 ft
ekersey Posts: 5 Rating: (0)
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10/29/2013 3:09 PM	Rate (0)
danw Gold Expert Joined: 3/28/2010 Last visit: 9/5/2025 Posts: 1171 Rating: (220)	The ProbeLU could be reflecting off the float, but I suspect reflection from a sphere would tend to give you low signal strength, possibly Loss of Echo, not the linear but skewed response that your graph shows. More to the point, I wonder if the velocity/speed of sound value for air is significantly different than that for gasoline vapor, which evaporates so easily. A different sound velocity factor could result in the skew that you're encountering, which is handled by the Probe LU's 'range calibration' settings. I'd probably do the measurement as described below and then enter the value for the velocity calibration parameter. It can't hurt, you can always go back to factory or other custom parameter settings. The Probe LU manual on range calibration: Range Calibration (P650 to P654) There are two possible types of calibration: • Offset Adjusts the measurement by a fixed amount • Sound Velocity Adjusts speed of sound, and changes the measurement calculations Do Offset calibration at any steady level, unless a Sound Velocity calibration is also done. If both calibrations are done, then do Offset at a known high level, and Sound Velocity at a known low level. Using Sound Velocity Calibration Ensure a steady level at some low value (P653 and P654 adjusted accordingly). 1. Allow sufficient time for the vapor concentration to stabilize. 2. Press the measurement key (image of key is in manual, not shown here) to display the calculated reading. 3. Repeat step 2 at least five times to verify repeatability. 4. Measure the actual reading (use tape measure). 5. Enter the actual value. 6. Repeat this procedure if the atmosphere type, concentration, or temperature conditions are different from when the last sound velocity calibration was performed. P652 Offset Correction Stores the fixed offset value determined when an Offset Calibration is performed. Alternatively, if the amount of Offset Correction required is known, enter the amount to be added to the Reading before display. P653 Velocity Displays the value adjusted based on the Sound Velocity at 20°C (P654) versus Temperature (P664) characteristics of air. The units used depend on the setting for P005: • m/s if P005 = 1, 2, or 3 • ft/s if P005 = 4 or 5. Note: In gases other than air, the temperature variation may not correspond with the speed of sound variation. Use P660 and P661 to select a temperature source, and use a fixed temperature.

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10/29/2013 3:31 PM	Rate (0)
ekersey Posts: 5 Rating: (0)	Wow and thanks. Attached is drawing of the "float/tape" set up. It appears the float is more of a pancake shape than a sphere. Regardless, your evaluation seems much more plausible. Will try what you suggest and post results. We are only able to change parameters with the Siemens hand held remote and have to use manlift. Unable to change with HART communicator on ground. So it may take me a week or so to schedule manlift/get done. Again, thank you for your evaluation and time. Ed No change in reading when pulled float up on Unleaded tank on 10/29/13. Next step = schedule sonic probe (velocity) calibration per recommendation above. Ed Attachment MOORMANN STORAGE TANK GAUGE.pdf (251 Downloads)
ekersey Posts: 5 Rating: (0)	Last edited by: ekersey at: 12/17/2013 5:42 PM
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