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FAQ - Magnetic Level Gauge - MLG

1.For which applications/ services MLG is suitable?

It is used for level indication of free flowing, aggressive, corrosive and non- corrosive liquids.


2.Whether MLG is used for interface liquids?

Yes, It is suitable for liquid – liquid interface, provided difference between specific gravity of upper and lower liquid is ≥ 0.2.


3.What wetted part materials are offered in MLG?

SS304, SS316, SS316L, Hastalloy C, Inconel-400, Titanium (Ti), PP, PVDF and PTFE lined SS.


4.What is maximum range / CC distance available?

Side mounted gauge is available from 300 mm to 5000 mm CC distance. Top mounted gauge is available from 500 to 3000 mm range for underground tank.

 


5.What is the minimum specific gravity of liquid for which MLG is suitable?

MLG is suitable for specific gravity (SG) of 0.8 as standard.However, it is available for the minimum SG of 0.5.

 


6.How does Magnetic Level Gauge works?

It is also known as Bypass Level Gauge. It is available as side mounted type for ground level tanks and top mounted for underground tanks.

  • Side Mounted - It consists of non-magnetic chamber containing float fixed with magnetic system and indicator is clamped outside the chamber. When gauge is mounted on side of the tank, magnetic float follows liquid level and its movement is tracked magnetically by external indicator. 
  • Top Mounted - When gauge is mounted on tank top, float follows liquid level and magnetic system fitted on top of the float stem also moves inside the chamber which rotates the flapper indicator magnetically. Refer figure 1.


7.How many types of indicator are available?

 Indicators are available in 3 types –

  1. Follower Capsule Indication
  2. Bi color (Red & White) Flapper Indication
  3. Bicolor (Red & White) Roller

Figure 1


8.What is the material of various types of indicators?

Follower capsule is in PP MOC and is suitable for max. temperature upto 150 °C

Flappers are in PP (150 °C) and SS304/316 (250 °C)

Rollers are in ceramic material (400 °C)


9.Whether indicator housing can be rotated at required direction?

Yes, Loosen the indicator clamp and rotate it at required direction and retighten it.

 


10.How level is read on indicator?

Level is read on the scale against capsule position or red column of flapper /roller.


11.What is Float Failure Indication (FFI)?

FFI is indicated below zero marking on scale in side mounted magnetic level gauge. When float gets punctured or damaged due to high pressure or corrosion, liquid ingress takes place, float become heavier and sink in the liquid at the chamber bottom. While sinking it causes flappers to rotate from white to red below zero indication, refer fig 2.

Figure 2


12.What is protection of Indicator Assembly?

Indicator protection is optional feature

  • Flapper (PP & SS) and roller indicators are available in IP66 protection.
  • SS Flapper Indicator is available in hermetically sealed protection.


13.What Max. Temp & Pressure of MLG can withstand?

MOC

Max. Temperature °C

Max. Pressure (kg/cm2)

PP

70 °C

3 kg/cm2

PVDF

100 °C

3 kg/cm2

PTFE lined SS

120 °C

3 kg/cm2

SS304/316/316L, Hastalloy C, Inco alloy 400, Ti

400 °C

250 kg/cm2


14.Whether switching and transmitting options are available?

Yes. MLG is supplied with Bi-stable switches for control function and transmitter for remote monitoring. 


15.Is MLG safe to use in hazardous environment?

Yes. MLG is available with ATEX (non-electrical) certification. Its switches and transmitters are provided with ex-proof Exd IIC or ATEX IIC enclosure for hazardous area applications.


16.Whether Switches and transmitter can be retrofitted on existing MLG?

Yes, With Techtrol make Magnetic Level Gauge MLG. Both switch and transmitter can be clamped externally on the existing gauge chamber.


17.How does Bi-stable switch work with MLG?

It is available in two types as 1) Bi-stable Reed Switch, 2) Bi-stable Micro Switch.

Switch actuates due to magnetic field of float traveling in one direction and remain latched during further travel of float in same direction and it de-actuates during traveling of float in opposite direction, hence bi-stable switching action.


18.How does reed chain transmitter work with MLG?

Transmitter consists of PCB strip of closely spaced reed switches and a chain of series resistors fitted inside

the guide tube and a transmitter card is housed in an enclosure. The float moves inside the chamber according to rise or fall of liquid level and actuates the reed switches and change in voltage is fed to the

(v to I) transmitter card to convert it into the linear analog signal output of 420 mA.


19.What safety measures should be considered during the installation of a gauge?

       General

  • In case follower capsule indication, fill water in polycarbonate tube for smooth movement of capsule.
  • Ensure indicators (capsule/flappers/rollers) are properly coupled with magnetic float to get proper level indication. If required, align it with external magnet.
  • Adjust scale on the chamber at zero position corresponding to center of lower process connection.

 Side Mounting

  • Ensure that the mounting location of gauge on the tank where the vibrations are minimum.
  • Ensure tank connections and CC Distance are same as gauge connection
  • Tank nozzles and connections are in plumb line.
  • The clearance from lower nozzle connection to ground should be min 500 mm for easy float removal /replacement. Ref figure 1.
  • Provide separate isolating valve between the tank connection and gauge connection for safety and removal of gauge for repairs and maintenance.

Top Mounting

  • Ensure inner diameter of nozzle is greater than float diameter/Stillwell ID.
  • Stillwell is recommended to guide for float movement.


20.What type of tests are provided in gauge?

Each gauge is hydro tested for its max. test pressure by default

Following tests are provided in gauge as required

  • PMI (Positive Material Identification)
  • D. P. Test
  • Radiography
  • Ultrasonic 
  • Material Certification as per 3.1 (EN10204)
  • Material Certification as per 3.2 (EN10204)
  • Helium Leak Test
  • Ferrite Number Test
  • NACE MRO103, NACE MRO175

Other testing available on request


21.What approvals and certificates are available in MLG?

  • CE 1282 as per 2014/68/EU
  • ATEX as per Ex h IIC T6… T1 Ga as per 2014/68/EU (Non_ Electrical)
  • ATEX Ex d as per 2014/68/EU (Electrical)
  • PED as per 2014/68/EU
  • CCOE/ PESO (Enclosures)
  • IBR 1950
  • Marine


22.What type tests are available with Gauge?

  • Seismic Test
  • Shock Test
  • Vibration Test
  • Environmental Test
  • ASME ‘U’ stamp

 


23.What information is required to get quotation earliest?

  • CC distance for side mounted
  • Range or tank height with nozzle height and ID for top mounted
  • Liquid and its specific gravity
  • Operating temperature and pressure

 


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