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Level Measurements

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Title: Level Measurements


1
  • Level Measurements

2
Purpose of Level Measurement
  • Level Measurement is an integral part of process
    control, and may be used in a wide variety of
    industry.
  • The purpose of level measurement is to provide a
    measured variable representing the height or
    material presence within a vessel.

3
Purpose of Level Measurement (cont)
  • The measured variable is then used in one or more
    of the following ways, where the measured
    variable becomes
  • a local level indication,
  • a detection of material presence,
  • an input signal to a level control scheme,
  • or a measured quantity in hydrocarbon inventory
    management.

4
Types of Level Measurements
  • There are two ways of level measurement
  • Point level Measurement
  • Continuous level measurement

5
Types of Liquid Level Measurement Configuration

6
  • Point level sensors are used to mark a single
    discrete liquid height a preset level condition.
    Overfill alarm , low alarm


Point level Sensor
7
Continuous Level sensors are used when a
complete level monitoring of a system is
required.

Continuous level Sensor
8
Point Level Measurements
  • Point level process measurements are a type of
    level measurement used when the level measurement
    device or system provides a logical (true or
    false, on-off) representation of material
    presence at some predetermined point (s) within
    the vessel.

9
When To Use Point level Measurements
  • You can use point level measurement in one of the
    following or in both
  • 1.Point Level Process Indication
  • 2.Point Level Process Control

10
  • 1.Point Level Process Indication
  • It provides an indication of process material
    level at a point within a vessel. A single point
    level alarm, such as a vessel level high alarm
    limit, is an example of point level process
    indication

11
Point Level Indicator

Circuit
Indicator
12
  • 2.Point Level Process Control
  • It provides the control of a material level
    between two points in a vessel.
  • To accomplish point level process control, more
    than one level switch senses a liquid presence at
    two (or more) measured point levels in a tank.

13
Point level Process Control

High level
Digital Circuit
LT
LT
Low level
14
Continuous Level Process Measurement
  • In continuous level measurement, a level
    measurement system can provide a numeric
    representation of the current position (height)
    of process material surface.
  • The level is measured continuously between lower
    and upper reference level

15
When to use Continuous level Measurements
  • Continuous level measurement is used in the
    following
  • Continuous level process indication
  • Continuous level process control

16
Terminology and Symbology
  • The following are considered when dealing with
    level instrument
  • Units of measure
  • Drawing symbols

17
Units of measure
  • Units of measure can be classified according to
    the application as follows
  • Distance meters or feet
  • Weight Kilograms or Pounds
  • Volume Cubic feet, Gallon, Liter, Barrel

18
Level measurement can be used to determine
volume and weight of process material as follows
  • V volume A vessel area L height of material
  • W Weight A vessel area L height of material
    D density

19
Drawing Symbols
  • Drawing symbols used in instrumentation are

LT
LG
LT
Level Transmitter Diff. Pressure Type
Level Gauge Glass
Level Transmitter Ext. Float Type
20
Drawing Symbols

LS
LS
Level Switch Externally Mounted
Multi-position level Level Switch Internally
Mounted
21
Instrument Legend

22
Level Measurement Principles
  • There different ways used to measure a level of
    liquid or solid in a vessel.
  • Different sensors with different design
    principles are commercially available.
  • Some of theses sensors are contact type and some
    of them are non-contact type.

23
Types of level devices
  • Sight
  • Float type
  • Displacement type
  • Force type
  • Pressure type
  • Electrical type
  • Ultrasonic Type

24
1.Sight
  • Sight level measurements gives the operator a
    visual indication of the materials level
  • Examples are
  • Dipstick
  • Tubular Gauge Glass

25
a. Dipstick
  • Is the simplest level measurement device and its
    accuracy depends on its scale.
  • It can be used only for vented and underground
    tanks.
  • Source of errors
  • Fast insertion
  • Insertion with an angle

26
b. Tabular Gauge Glass
  • The tubular gauge consist of glass pipe which has
    the level of the liquid in the tank.
  • Used in low pressure services to ovoid breakage
    .
  • Fitted externally , protector are available to
    protect glasses.

27
  • In conclusion, sight glasses are used for local
    indication and are important for calibration.
  • It is important to consider the following
  • Operating pressure
  • Operating Temperature
  • Process material
  • Fitting the device externally

28
Float Level Switch
  • Float Level switches is the basic point level
    sensor which moves with the liquid surface.

29
  • Float device include the following
  • Float switch
  • Tape float gauge
  • Magnetic type

30
a. Float Switch
  • A float switch is attached to lever that
    activates a relay at a predetermine level

31
Float switch (Cont)
  • A float resting on the liquid surface can
  • activate a magnetic switch
  • as shown.

32

Float Switch (Cont)
  • Spherical float are available from 3 to 7 in
    diameter
  • The small diameter switch is used for high
    density liquid
  • The larger diameter switch is used for
    liquid-liquid interface detection

33
Float Switch (cont)
  • Application of float switch includes
  • Emergency shutdown
  • Alarming
  • ON-OFF control application

34
b. Tape Float Gauge
  • An externally scaled indicator is attached to
    float As shown. When the liquid level is moving
    up or down the float will follow and the
    indicator will point the level.
  • Application Used in water
  • Storage tank

35
c. Magnetic Type
  • The float is called magnetic if a magnet is
    inserted in the float.
  • The float is magnetically coupled to a tape and
    the tape has a connection to a level indicator as
    shown.
  • Application
  • In utility service

36
(No Transcript)
37
Non-Contact Ultrasonic Sensors
  • The ultrasonic sensor consists of the
  • following
  • Sensor element
  • Analog signal processor
  • Microprocessor
  • Binary coded decimal range switch
  • And an output drive circuitry

38
Ultrasonic Level sensors
39

When determining what type of level sensor
should be used for a given application, there are
a series of questions that must be answered
  • Can the level sensor be inserted into the tank or
    should it be completely external?
  • Should the sensor detect the level continuously
    or will a point sensor be adequate?

40
  • Can the sensor come in contact with the process
    fluid or must it be located in the vapor space?
  • Is direct measurement of the level needed or is
    indirect detection of hydrostatic head (which
    responds to changes in both level and density)
    acceptable?
  • Is tank depressurization or process shut-down
    acceptable when sensor removal or maintenance is
    required?
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