Remote Seal Transmitters Ranging Calculation

OPEN TANK CAPILLARY REMOTE SEAL LEVEL TRANSMITTERS

1. Transmitter installed exactly at HP tapping point – Open Tank

Remote Seal Level Transmitter installed exactly at HP tapping point

Tank span = Lmax x SG

Tank Span: (108 in. x 0.75) = 81 inH2O

4 mA = Lmin x SG + Hd x Sg

=(0 x 0.75) + (0 in x 0.934)= 0 inH2O

4mA = 0 inH2O

20 mA = Lmax x SG + Hd x 0.934

=(108in x 0.75) + (0)= 81 inH2O

20mA = 81 inH2O

2.Transmitter installed below HP tapping point – Open Tank

Remote Seal Level Transmitter installed below HP tapping point

Tank span = (Lmax x SG)

Tank Span: 108in x 0.75 = 81inH2O

Lmin

4 mA = Lmin x SG + (Hd x Sg)

= (0 x 0.75) + (60in x 0.934)

= 56.04 inH2O

Lmax

20 mA = L max x SG + (Hd x Sg)

=(108in x 0.75) + (56.04)

= 137.04 inH2O

SPAN = 81inH2O (137.04 – 56.04)

3.Transmitter installed above the HP tapping Point – Open Tank

Remote Capillary Transmitter installed above the HP tapping Point - Open Tank

Tank span = (Lmax x SG)

Tank Span: 108in X 0.75 = 81inH2O

4mA = Lmin x SG + (Hd x Sg)

= (0 x 0.75) + (120 in. x 0.934) = -112.08 inH2O

NOTE Pressure pulling down on the high sensor side will register as a negative pressure value.

20mA = Lmax x SG + (Ld X 0.934)

= (108 in. x 0.75) + (-112.08) = -31.08 inH2O

SPAN = 81 inH2O (-112.08 to -31.08 inH2O)

CLOSED TANK CAPILLARY REMOTE SEAL LEVEL TRANSMITTERS

Example A :

Transmitter installed exactly at HP tapping point – Closed Tank

Closed Tank Remote Seal Transmitter installed exactly at HP tapping point

Tank span = (Lmax x SG)

Tank Span: 108in X 0.75 = 81inH2O

4mA = Lmin x SG + (Ld x Sg)

= (0 x 0.75) + (120 in. x 0.934) = -112.08 inH2O

20mA = Lmax x SG + (Ld X 0.934)

= (108 in. x 0.75) + (-112.08) = -31.08 inH2O

SPAN = 81 inH2O (-112.08 to -31.08 inH2O)

NOTE Pressure applied to Low sensor side sensor will register as a negative digital value.

Example B :

Transmitter installed above HP tapping point – Closed Tank

Closed Tank Remote Seal Transmitter installed above HP tapping point

Tank span = (Lmax x SG)

Tank Span: 108in X 0.75 = 81inH2O

4mA = Lmin x SG + (Ld x Sg) + (Hd x Sg)

= (0 x 0.75) + (60 in. x 0.934) + (60 in. x 0.934) = -112.08 inH2O

20mA = Lmax x SG + (Ld X 0.934) + (Hd X 0.934)

= (108 in. x 0.75) + (60 in. x 0.934) + (60 in. x 0.934) = -31.08 inH2O

SPAN = 81 inH2O (-112.08 to -31.08 inH2O)

NOTE: Pressure (Ld) is applied to Low sensor side and will register as a negative digital pressure. Pressure (Hd) is pulling down on the high sensor side therefore would also register as a negative digital pressure therefore these values are additive.

Example C :

Transmitter installed below HP tapping point – Closed Tank

Closed Tank Remote Seal Level Transmitter calculation

Tank span = (Lmax x SG)

Tank Span: 108in X 0.75 = 81inH2O

4mA = Lmin x SG + (Hd x Sg) + (Ld x Sg)

= (0 x 0.75) + (60 in. x 0.934) + (180 in. x 0.934) = -112.08 inH2O

20mA = Lmax x SG + (Hd X 0.934) + (Ld X 0.934)

= (108 in. x 0.75) + (-112.08) = -31.08 inH2O

SPAN = 81 inH2O (-112.08 to -31.08 inH2O)

Pressure (Ld) is applied to Low sensor side and will register as a negative digital pressure. Pressure (Hd) is pulling down on the high sensor side therefore would also register as a negative digital pressure therefore these values are additive.

NOTE: The transmitter location in a closed tank does not effect the 4mA and 20mA set points as shown in example A, B & C.

Abbreviations:

Lmin = the minimum level of process and typically the 4mA lower range value

Lmax = the maximum level of process and typically the 20mA upper range value

Atm = Atmospheric pressure (vented tank)

SG = Specific gravity of the process

Sg = Specific gravity of the remote fill fluid

Hd = Capillary vertical distance from process to high side sensor

Ld= Capillary vertical distance going to low side sensor

Source : Emerson

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18 thoughts on “Remote Seal Transmitters Ranging Calculation”

  1. In the example A transmitter installed exactly at the HP tapping point closed tank i didn’t get where do you find that Hd=60 and Ld = 180 ? Because you have Ld =120in Thank you.

    Reply
  2. In the first example for calculating 20ma(Tx installed exactly at hp tapping point)given equation is Lmin instead of Lmax

    Reply
  3. I am facing one problem, also I am new to this plant.
    This Level Transmitter was not functioning for 7/8 years since plant running as per operation.
    I took up the challenge and installed a new remote diaphragm seal type transmitter.
    I had put following values as LRV and URV.

    LRV: -1620
    URV: -216

    C to C distance is 1530mm. Specific gravity of The Liquid Vacuum Residue: 0.9.
    At zero conditions i.e. both upper and lower root isolation valves closed, Diaphragm spacer rings drain and Vent caps opened , then I found PV: -1620 which I had entered as LRV.
    For URV, -1620+ (1530x 0.9)= -216 .

    Level Transmitter service is vacuum column slop distillate, Column pressure is -676mmHg. i.e. -9190mmWC.

    As I have not considered the vacuum factor for above calculation so I have doubt on my LRV and URV values.

    Kindly enlighten me about how to calculate LRV and URV values and how and where to consider the vacuum pressure factor in my calculation.

    Regards
    Dhrubajyoti Borah
    Numaligarh Refinery Limited.
    Assam

    Reply
  4. I wonder if leveling with a remote seal How will the effect differ when measuring using zero press and using drop zero?

    Reply
  5. Calculation shown on eg. 3B is in-correct, HP side we shall not consider SG, i.e. no pressure on HP side if Tx. is above HP tap.

    Reply
  6. Transmitter installed below the HP tapping point
    From example 3 B:
    It is mentioned both Ld and Hd pressure register negative digital pressure . according this mentioned the value will be -224.16 inH2O
    But it is given as below

    4mA = Lmin x SG + (Hd x Sg) + (Ld x Sg)
    = (0 x 0.75) + (60 in. x 0.934) + (180 in. x 0.934) = -112.08 inH2O

    Please explain

    Reply

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Remote Seal Transmitters Ranging Calculation

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