Sunday, September 20, 2015


Pressure Measurement - Bourdon Gauge -Working Principle Advantages and Disadvantaged

  • Sunday, September 20, 2015
  • denizen robo

  • Working Principle Of Bourdon Gauge 

    If a tube having oval cross section is subjected to pressure its cross section tends to change from oval to circular.

    working principle of Bourdon Gauges

    Construction of a Bordon Gauge 

    Bourdon tube gauges consist of a circular tube.

    One end of the tube is fixed while the other end is free to undergo elastic deformation under the effect of pressure.

    Fixed end is open and pressure which is to be measured is applied at the fixed end.

    Free end is closed and undergoes deformation under the effect of pressure.

    Due to applied pressure the circular tube tends to uncoil and become straight along the dotted line.

    Bourdon Gauge Construction

    Working of Bourdon Gauge 

    As the pressure is applied at the fixed end free end undergoes deformation.

    The free end is attached with sector which further meshes with the pinion on which pointer is mounted.

    Deformation of the pointer is transferred to pointer via this mechanism.

    As a result point undergoes deflection and shows the pressure reading on calibrated dial.

    Advantages of Bourdon Gauges 

    2.Simple Design
    3.Good accuracy except at low pressure.
    4.High-pressure range.
    5.It can be easily used with electrical devices like LVDT.

    Disadvantages of Bourdon Gauges.

    1.Susceptible to shock and vibration
    2.Gauges are subjected to hysteresis

    Related Topics
    Basics of Pressure Measurement 
    Pressure Measurement - Manometer 
    Classify Pressure Measuring Instruments 


    Sunday, September 13, 2015


    Differential Pressure flow measurement - How it works ? Advantages and Disadvantages of DP flow measurement

  • Sunday, September 13, 2015
  • denizen robo

  • Working Principle of Differential Pressure Flow Measurement 

    Flow measurements are essential to  run a plant efficiently and safely.There are no real flow measurement technologies available including differential pressure flow also known as DP flow which utilizes a variety of measurement instruments.

    DP flow is measured with the combination a primary element and a secondary elements.

    The primary element is placed in the pipe to create a differential pressure and connecting
    the secondary element to the process.

    The secondary element or transmitter takes measurements from the primary element and converts them into useful quantitative values and transmits those values to a control system.

    There are many types of  primary elements including traditional orifice plate cone venturi nozzle wedge
    Primary elements differential pressure flow measurement

    How to select a differential pressure flow measurement Primary element?

    Primary element selection is dependent on process conditions.All these different primary 
    elements have one thing in common, they constrict the flow in a pipe causing a pressure 
    drop from one side to the other. the difference in pressures is the differential pressure. 
    The square root DP is proportional to the flow rate.

    Working Principle - Differential pressure Flow Measurement

    Traditionally transmitters were connected to the process with external impulse piping.
    Modern DP Flow Transmitters -The impulse piping is built into the primary element this allows the transmitter to be directly mounted to the process line.Advantages of this type of flow transmitters are Easy installation and reduce maintenance cost

    Advantages of Modern Differential Pressure Flow Transmitters.

    1.Simple technology with no moving part.
    2.Compact sensor
    3.Configurable for bi-directional flow
    4.Usable over a very wide range of sizes 
    5.Relatively inexpensive

    Disadvantages of DP flow measurement.

    1.Limited accuracy and turndown range
    2.Causes a pressure drop and reduces pipe's free passage
    3.Orifice often a wear-prone point
    4.Depends on good pressure sensor practice
    5.Changes in liquid characteristics can affect readings.

    Related Topics:


    Sunday, August 23, 2015


    Variable Area Flow Meter - Application - Working Principle - Advantages

  • Sunday, August 23, 2015
  • denizen robo
  • Variable Area Flow Meters 

    Variable area flow meters are used to measure the volume flows of liquid and gases.

    Application of Variable Area Flow Meter - Volume flow measurements of Liquids and Gases

    Components -  Vertical Conical Measuring Tube
                              Mobile Float

     It consist of vertical conical measuring tube which widens upwards and a specially formed float which can move up and down freely in the measuring tube.

    Working Principle - 

    Variable area flow meter working principle

    The reference of position of the float to the measuring tube creates a variable ring orifice.The higher the position of the float the larger the ring orifice and therefore the cross sectional area through which the medium come pass through the float.This is the origin of the English designation of the device.

    When there is no flow, gravity keeps the float at the bottom end of the measuring tube.
    As soon as the medium flows through the tube from bottom to top the float rises again until the acting forces are in balance.

    Three main forces act on the movable float.
    1. Graviatation force (W = Weight) - Operates downwards as a reset force.
    2. Buoyancy force (B)
    3. Flow force (D=Drag)

    Weight = Drag + Bouyancy

    W and B = Constant

    The position of the float is a flow indicator.
    The physical operating mode shows that the position of the float is a flow indicator.
    With glass cones flow rate can be read on a scale on the measuring chip itself.

    With the metal cones the float is not visible so they have a magnetic transfer onto the pointer.For this purpose a magnet is built into the float.Through a magnetic coupling installed on the point of axis the linear movement of the float float is converted into the rotary movement of the pointer which displays the flow on a scale.No auxiliary power supply is required.

    Advantages of Variable area flow meter

    Advantages of Variable area flow meter - Purely mechanical.No auxiliary power is requires.

    Related posts - 
    Flow transmitter calibration 
    Type of Valves


    Sunday, August 2, 2015


    hat are the different types of DC Motors and how to select DC motors for your application?

  • Sunday, August 2, 2015
  • denizen robo
  • The most common DC motors types are

    1.The basic brushed DC motors
    2.Brushless motor
    3.Permanent Magnet motor

    Brushed DC motor

    In a brushed DC motor, the magnet acts as the stator.The armature is integrated onto the rotor and a commutator switches the current flow.Commutator function is to transfer current from fixpoint to the rotating shaft.Brush DC motors generate torque straight from the DC power supply to the motor by using internal commutation.

    Advantages of Brushed DC motors - Low initial cost  
                                                                Simple control of motor speed

    Disadvantages of Brushed DC motors - At certain period during a DC motor rotation commutator must reverse the current causing reduced motor life due to arching in friction.


    Brushless DC motor

    A brushless DC motor is essentially a DC motor without mechanical commutation of the brushed DC motor.Brushless DC motors are powered by Direct current and have electronic commutation system. The Permanent magnet is housed in the rotor and the coils are placed in the stator.
    Advantages of Brushless DC Motor - Resistant to mechanical wear and tear 

    How to select DC motor for your application?

    For selecting motors for your application, you have to have a full understanding of the application parameters including power,speed,torque,physical size,efficiency,lifetime expectations.

    Key criteria for selecting a DC motor includes first finding out what voltage is readily available for the application and what physical size the motor needs to be.Torque and speed have an effect in motor frame size.High torque motors are often larger in size than their low torque counterparts.

    Related articles:


    Sunday, June 28, 2015


    Level Measurement - Ultrasonic Type Working Principle Application Advantages and Disadvantages

  • Sunday, June 28, 2015
  • denizen robo
  • Ultrasonic Level Detectors

    Ultrasonic sound waves with frequencies of 1 to 5 megahertz can be used to detect liquid or solid levels.

    Ultrasonic are sound waves but are at higher frequencies that cannot be detected by the human ear.

    ultrasonic level measurement working principle

    The most common kind of ultrasonic transducer consist of a piezoelectric crystal.When a voltage is applied to the plates the piezoelectric crystal expands or contracts.If the voltage is alternating at an ultrasonic frequency,the crystal expands and contracts at same the same ultrasonic frequency.The crystal vibrates and these vibrations can be transferred to a diaphragm to produce ultrasonic sound waves.

    Piezoelectric device can be mounted in the bottom or in the top of a vessel.The liquid surface acts as a reflector and the transducer receives the reflection of its transmitted pulses.The transducer is connected to a transmitter and to a receiver,into which the echo is fed.The transmitter and receiver are both connected to an echo timer which measures the amount of time between the emission of the sound wave and the reception of echo.The elapsed time can be converted into units of level of liquid.

    Application of Ultrasonic Level detector

    For situation where it is impractical or undesirable to install an instrument inside a tank ,non penetrating ultrasonic sensors are available.

    Advantages of ultrasonic level detectors

    1.Can be used in any tank size
    2.Can be used in a vacuum
    3.Can be used under high pressure
    4.Relatively easy to maintain because they don't have no moving parts.

    Disadvantages of Ultrasonic level detectors

    2.sensitive to wide range of temperature variations.

    Selection consideration - Ultrasonic sensor

    1.Choose a sensor range that at least as tall as the tank,doubling sensor margin to add margin against higher temperatures,condensation and turbulence.
    2.Tank height is defined as the distance from the installed face of the transducer down to the bottom of the tank.
    3.Riser height is the distance from the face of the transducer to top of the tank.
    4.Fill height is defined as the distance from the bottom of the tank,upto the maximum desired liquid height.
    5. Deadband is defined as the minimum distance from the face of the transducer from which the sensor can measure.

    how to select an ultrasonic level sensor

    Related Articles


    Pressure Measurement - Manometers Working Principle - Vaious types of Manometers

  • denizen robo
  • Manometers

    Manometers are one of the oldest type of pressure measurement.

    Manometers can be used to measure gauge pressure,differential pressure and absolute pressure.

    Various types of Manometers
    1.U tube Manometer
    2.Well type or reservoir manometer
    3.Inclined manometer
    4.Float type manometer

    various types of manometers

    U tube Manometer.

    U tube is made of glass.The tube is filled with a fluid known as Manometer fluid.

    Manometer fluid may be  mercury , water etc...

    If the manometer is connected to same pressure source (P1 = P2) the level of the manometer will be same.
    U tube manometer

    If the manometer is connected to two different pressure source there will be a difference in level of the manometer fluid in both the limps.

    U tube manometer working principle

    If P1>P2 the differential pressure P2-P1=@h
    @=density of the fluid

    h=height difference

    While choosing the manometer fluid for a particular application we need to remember following things.
    Manometer fluid should not wet the wall
    Manometer fluid should not absorb gas
    Manometer fluid should not react chemically
    Manometer fluid should have low vapor pressure
    Move freely

    Mercury is one of the most commonly used manometer fluid.

    Well type Manometer

    In a well type manometer,one leg is replaced by a large diameter well.Since the cross sectional area of the well is much larger than the other leg,when pressure is applied to the well,the manometer liquid in the well lowers only slightly compared to the liquid rise in the other leg.As a result of this,the pressure difference can be indicated only by the height of the liquid column in single leg.
    For static balance,
    P2-P1= @(1+A1/A2)h
    A1= area of smaller-diameter leg
    A2= area of well

    If A1/A2 << 1 then P2-P1 = @h

    If the area of well is 500 or more times larger than the area of vertical leg,the error involved in neglecting the area is negligible. 

    Well-Type manometer

    Inclined-Tube Manometers

    The inclined  leg expands the scale so that lower pressure differentials may be read easily.

    Sensitivity of the manometer increases.

    The scale of the manometer can be extended greatly by decreasing the angle of inclined leg to a small value.

    Float-Type Manometers

    This is a variation of well-type manometer

    Recording type manometer

    Span of the measurement can be changed by changing the diameter of the leg

    A large float can be placed to generate enough force 

    Float type manometers

    Related Articles:


    Sunday, June 21, 2015


    Level Measurement - Magnetic Gauges

  • Sunday, June 21, 2015
  • denizen robo
  • Magnetic Gauges

    Magnetic gauges can often be used in applications where a sight glass is not practical.
    A Magnetic gauge uses the attraction between two magnets to follow the level of a liquid.One magnet float on the surface of the liquid.The other magnet is inside a nonmagnetic tube passing through the liquid.

    The passing through the liquid is made of a nonmagnetic metal.The magnet inside the tube is balanced by a counterweight so that it can rise or fall easily.The ring-shaped floating magnet fits around the outside of the tube and follows any change in liquid level.The magnet inside the tube follows the floating magnet and moves the indicator along a calibrated scale.

    Magnetic Gauges should not be used to measure liquids that can cause the floating magnet to stick to the tube.
    The material for the tube itself must be able to withstand the temperature, pressure and chemical action of the liquid that is being measured.

    magnetic gauge level measurement working principle