LPG Loading Automation System

1. TURN OFF YOUR CAPS LOCK. IT'S CONSIDERED SHOUTING!

2. What type of Mass Flowmeter? The most usual type is a Coriolis Mass Flowmeter. There are others that are NOT true Mass Flowmeters. They are volumetric, which means that they need a correction factor for the density/specific gravity difference.

3. You state that it is off by 60-150 Kg; but out of what for the total? If it is off by 100 Kg out of 1000 Kg, then the error is 10%. If it's out of 10,000 Kg, then the error is only 1% which is normally acceptable.

4. Endress & Hauser (in my opinion) make pretty good meters. They usually aren't fancy, but they are usually sturdy, long lasting pieces of equipment.

5. If the "Multiplying Factor" they put in was to compensate for the density/specific gravity difference, then it is probably good to go now. But I would find out for sure. A correction factor for a known physical principle is one thing, a "fudge factor" that someone just threw in to make it match is quite another. Fudge factors are like flames 3 feet high; they burn my butt!

6. Just because you "gave all the process parameters", doesn't mean that they were entered in correctly. Or even entered in at all. Sorry, it's an imperfect world.

7. How is the batch controller totalizing the weight? If the period it uses between adding readings is too large, it could be off by a significant amount. Not very likely though, as presumably this is a new piece of equipment.

8. Check the setup of the meter, both physically, and electrically. Most errors I have seen in flowmeters have been poor installation.

Dear Sir,

Thanks for the reply.

1. The mass flow meter is coriolis type.

2. An error of 60 to 80 is for 7000 kg's. The in % it seems to be low, but I account in terms of money it costs a lot. A kg cost is 60 Indian Rs.

3. It is not that they have compenstated for density. They have enetered the value just by taking the ratio of Wigh to mass flwo meter reading and entered the correction factor.

4. Batch controller just picks the reading from the massflowmeter. The reading of BC and massflow matches but it doesnot with the weighbridge.

5. The mounting is as per OEM's supplied sheet.

Hope now you may help further.

Regards

Dear Sir,

As an Inventor and designer I have worked on Automation of LPG systems for IOCL,BPCL,HP, specifically on LPG Cylinder Truck loading/unloading Robotic systems besides, cylinder valve leak detection and Cylinder "Check" weighing on-line systems on line @1200 cylinders per hour at Cuddappah, Cherlapally and Manali.The reason I am mentioning this is to say that I am familiar with the site conditions during all the seasons of the year and problems being cited by you for the Tank truck loading.

I have a few observations made by me and wish to share with you which might be helpful.

1. Please check Wind load on the truck.,

2.Please check EMI/RFI in the vicinity of the signal cables and electronic instruments and equipments.

3.Please check the Least Count of the Weigh bridge and corelate to varying discrepancy.

4.Please check for "Mischief" on the weigh bridge display, specifically "Zero" setting.

5.Please check for "Full range" calibration chart and matching with random check value.

6.Please check for temperature compensation on the weigh scale.

7. Please check for "Empty" radiators of the Truck engine, which help to "smuggle out" at least 60-80 Kg. of product (LPG) being loaded.

Of course, these are peripheral to the problem at hand but are contributory to error generation.

Dear Naidu ji,

Thanks for the valuable reply.

We all can really gain from your valuable experience.

Sir, in reference to your mentioned details, kindly clarify further:

1. 100% agreed regarding ur wind load observation. But how to calculate that, kindly narrate.

2. Emi/Rfi is to be checked. How to ensure this? However, we had properly grounded the system.

3. The WB LC is 10 kg and we donnot consider an error of +/- 10 kg.

4. The WB zero has been cross checked many times. Even the calibration is checked twice.

5. The WB is 0-50 T and we donot have such big load available at site. So only point calibration is checked at 7 and 16 T. The cal. is checked at these points, found ok.

6. No temp compenation is avialable. However the temp compensation must have been taken care in caluculation itself by the vendor as the measuerement is through load cell arranged in WS bridge. Also seen that the error doesnot varry much in morning/afternoon session.

7. What are you talking about radiators? Kindly narrate. The truck driver is not allowed to go near the truck, when the loading is on. Also the error is + w.r.t massflowmeter i.e. WB shows more, it is not showing less. We feel this point is ruled out.

Hope your reply may help me to sort out the problem.

You said "60 to 80 is for 7000 kg's". It means something about 1% so it's so hard for your case "to jump over your head". I am supposing it's complying to accuracy class of meter. Isn't it?

Unfortunatelly here's inborn shortcoming of this kind of instrumentation technique where the measurement of significant amount of mass is subsituted by flow rate metering which should be integrated afterwards with inevitable errors.

Nevertheless you can improve real perfomances of your facility on site having applied adjusting procedures as often as you only can. You should note such factors as wind direction and velocity, temperature during adjusting/calibrating procedure to find a corellation between accuracy and these influencing factors. I would suggest you to use intermidiate model tank (if it's possible).

Hi!

Since this is happening in India, you really should check what is happening at the site :-)

The coriolis meter does have a calibration factor which is determined at the plant during initial calibration. This value is based on the coil dampening and is specific to each meter. By varying this factor you can, in fact, finetune the meterreading almost by 1-2%. So if you want you can bring the meter reading in accordance with the weigh bridge, try and toy around with this value.

But you should also take into consideration the volatility of LPG - and the flow rate/ pressure values involved. Typically weigh bridge accuracy is around 0,6% whereas with mass flowmeters (we ae using Micromotion F and CMF series by Emerson Process Management we get an accuracy of at least 0.4% - so for all business purposes, the flowmeter reading is used

Dear Guest,

Noted your observations Sir.

Agrreed that there is a factor in massflowmeter. However if the factor is adjusted according to density, then we too would have agrreed. Actually this is not the case. So just be manipulating the factor, by effect the results at any time.

How to compenstate for volatility, pressure and flow rate for LPG?

Kindly inform.

Regards.

All meters must be calibrated on site. The coriolis meter is factory calibrated on water. The meter responds to sound waves and the speed of sound is a variable so you must calibrate in the fluid its metering.

The meter needs to be zero'd. You need to pull a vacuum on the meter and compare its base vacuum frequency with the factories base Vacuum frequency.

Hi Neeruvti,

I think it is not the question of the flowmeter calibration, flow meter is only one factor of the system. where is the mass calculation made? are you getting the raw volume from the mass flowmeter or direct mass flow output? What kind of control valve are you using? can you send some picture?

Dinoy,

Could you let me know What size is the mass flow meter,

and what size is the system pipe.

Let me know also the working flowrate.

Then I can tell you what happen with the flow meter.