DP Liquid Level; Once More

After a discussion with a friend who tried to adjust volume in his wet-reference leg LT, I think I need to make underline for DP type LT case that may cause many understanding. Probably I am wrong or pre-assumed that some people have different opinion, but sometime I found little bit dispute one another on below DP case. However let’s discuss about it although everybody has the same opinion.

Case#1

Vessel DPT

Above is DP type LT direct mounted to measure water in the tank. Which one gives higher pressure on the Hi-side of LT? A or B?

Case#2

Vessel DPT-Wet Leg

Above is DP type wet reference leg level transmitter to measure a liquid in the vessel. Both wet reference legs A&B are filled with glycol at same level; 2 meters. On B-side they add addional leg by putting union tee,  so it will have totally 2 wet reference legs. The question is which one gives higher pressure on wet reference leg-side of transmitter? A or B?

Case#3

Vessel DPT-Wet Leg2

Above is still about reference legs with glycol liquid filled 2 meters for A & B. On A side they use 1/4″ tubing, on B side they use 1/2″ tubing. Which one give higher pressure on wet reference leg side of level transmitter? A or B?

My answer will be:

Case#1

The pressure on the Hi-side of LT A and B is the same.

Case#2

The pressure on Wet reference leg transmitter of A & B is the same.

Case#3

The pressure on Wet reference leg transmitter of A & B is the same.

We will have discussion if my blogger friends either do not believe it or may have different opinion. It is open for any opinion. I just want to make last statement that instrumentation is not only about electronic however sometime we need go back to physics theory as a basic where we stand on.

Nova Kurniawan

I am working at J Ray McDermott, I was graduated at Bachelor degree from ITB-Bandung

5 Responses

  1. The amount of water has no effect on the pressure.
    Water pressure depends on height.
    thanks

  2. Mas Nova,

    I agree with our discussion, beside height, pressure also influence by specific gravity of liquid. My question..

    Could we add some liquid or mixed with other liquid which has higher specific gravity than glycol in one line of tubing?

    As we know, SG also influence on formula of calibrated range the LT. I need your opinion about this case.

    I still confuse till right now cause there is no problem with the other LT. The installation is quite similar and the indication is also absolutely same with level glass. Can you help me what i should check first…?

    I observe that the impulse line low of LT just like less of pressure so that the DP is small..If we add little bit pressure at impulse line low,the indication with level glass will be the same…

  3. Menurut saya reference leg jangan dicampur dengan 2 fluida yang SG-nya berbeda. Kecuali jika mau menghitung resultan SG dari kedua fluida tersebut. Paling bagus menurut saya adalah reference leg diisi dengan fluida yang sama dengan fluida yang hendak diukur. (Mas andi jangan menanyakan lagi kalau fluidanya sama apakah ada DP ya?). Karena ketika terjadi kondensasi fluida dari vesel ke reference leg, maka yang tercampur adalah fluida yang sama dengan SG yang sama.

    Karena SG merupakan komponen penentu pressure, maka harus dihitung sebelum kalibrasi range DP. Penggantian fluida dengan SG berbeda atau karena pencampuran harus re-calibrate. Karena tekanan reference-nya akan berubah.

    Check first:
    Apakah fluida di reference leg-nya bener-benar glycol aja atau sudah tercampur dengan propane?
    Bandingkan head pressure di kedua reference leg? (yang salah sama yang bener). Kalau head pressure-nya sama; maka yang salah transmitternya, just re-calibrate.
    Kalo pressurenya berbeda, karena satu-nya menurut mas andy less-pressure, satunya cukup-pressure maka fluida di kedua reference leg sudah menjadi berbeda SG-nya. Yang salah adalah fluida di dalam impulse line-nya. Ganti fluidanya…..

  4. Pak Nova, saya ada pertanyaan berikut. Mengapa di dunia migas DP level transmitter tidak begitu populer? Saya lebih sering melihat displacer dan magnetic level transmitter. Bukankah DP level lebih ekonomis dari kedua alat tadi?

    Terima kasih.

  5. Ketika fluidanya di dalam vessel terdiri dari dua misalnya campuran antara air dan condensate, maka saya fikir agak susah kalau menggunakan DP transmitter. Tapi kalo fluidanya sudah pasti misal diesel yg storagenya di pedestal crane maka DP menjadi pilihan.

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