Presentation on theme: "Level Measuring Sensors"— Presentation transcript:
1Level Measuring Sensors A Presentationof“Industrial Instrumentation”
2Presented to:Dr. Ing. Naveed RamzanPresented By:Yasir Javed2007-Chem-30
3Level Measuring Sensors Level measuring sensors detect the level of substances that flow, including liquids, slurries, granular materials, and powders.The substance whose level to be measured can beInside a container or in its natural form (e.g. a river or a lake).In open tank or closed tank
4Classification of Level Measuring Systems Liquid or Solid Level MeasurementPoint or Continuous Level Measurement *Electromechanical or Electromagnetic Level MeasurementContacting or Non-Contacting Level Measurement
5General Considerations in Level Measuring Sensor Selection Density and viscosityChemical compositionAmbient temperatureProcess temperatureProcess pressureRegulated environmentProcess agitation
6Point/Switch Level Measurement And Detection Systems Point level measurement sensors are used to mark a single discrete liquid height–a preset level condition.They are:FloatsDisplacersConductivity ProbesVibrating fork Resonance
7Floats A float operated liquid level control operates on the basic buoyancyprinciple, which states, "a body (float)immersed in a liquid is buoyed upwardby a force equal to the weight of thedisplaced liquid". As a result, floatsride on the liquid surface partiallysubmerged and move the same distance the liquid level moves.
8Advantages and Disadvantages The Advantages of this method are that it is relatively simple, suitable for various products, and very accurate.The Disadvantages are that it requires a certain amount of mechanical equipment, especially in pressure vessels.
9DisplacersDisplacer level sensors are force balance devices in accordance with Archimedes' principle which states that “the buoyant force acting on an object equals the weight of the fluid displaced”.
10Advantages and Disadvantages The obvious Advantage of this method is that the absolute level does not change. The Disadvantages are that it is dependent on relative density and requires a signiﬁcant amount of mechanical equipment. Cost of installation for displacers is high and many refineries are now replacing them due to the inaccuracies experienced under process density changes especially on interface duties.
11ConductivityThe principle for this form of level measurement is that the presence of a product will cause a change in the resistance between two conductors.
12Advantages and Disadvantages The Advantages of this method are simple, inexpensive and suitable for dual or multiple point control.The Disadvantages are probe cannot become contaminated with grease or other deposits and has limited suitability for products of varying conductivity.
13Vibrating Forks Resonance Frequency changes which shift tuning fork Piezo crystal which oscillates forks and Solution causes a reduction in resonant frequency Second crystal detects.
14Advantages and Disadvantages No moving parts, thus no maintenance.Can be mounted in any position.Small and can be mounted in a 1-in or smaller mounting boss.Disadvantages:They are prone to material buildup between the tines.Build up material can cause inaccurate reading.
15Continuous Level Measurement and Detection Systems Continuous level sensors are more sophisticated and can provide level monitoring of an entire system.They include;Radar SystemsUltrasonic SystemsRTDMagnetostrictive
16RadarExtremely short microwave impulses with low emitted power in the 6.3 GHz frequency range are emitted by the antenna system to the measured product, reflected by the product surface and received again by the antenna system.
17Advantage and Disadvantage The Advantage of radar is its broad applicability on most liquids and measurement independent of pressure, temperature, vapor, and (to a degree) product dielectric constant.The Disadvantage is that the measurement may be lost because of heavy agitation of the liquid or the formation of foam.
18UltrasonicUltrasonic transmitters work on the principle of sending a sound wave from a peizo electric transducer to the contents of the vessel.The device measures thelength of time it takes for the reflected sound wave to return to thetransducer.
19Advantages and Disadvantage The main Advantages of ultrasonic level instrumentation are that the transducer does not come into contact with the process material, they have no moving parts and a single top of vessel entry makes leaks less probable than fully wetted techniques.The main Disadvantage is that there are various influences that affect the return signal. Things such as powders, heavy vapors, surface turbulence, foam and even ambient noise can affect the returning signal. Temperature can also be a limiting factor in many process applications.
20Time-Domain Reﬂectometry TDR The principle of this technology is to launch an extremely short microwave impulse on a waveguide, which can be a cable or rod.This waveguide, or probe,contains the signal in aclose area around thecable or rod.
21Advantages and Disadvantages The Advantages of TDR level measurements are disregard of the presence of vapors, steam, dust, gas layers, buildup, temperature changes, pressure changes, acoustic noise, changing density of the material to be measured, changing dielectric constant of the material to be measured, and changing conductivity of the material to be measured.Some Disadvantages of this measuring system are that it does come in contact with the process and is an intrusive form of measurement. The system is not suitable for highly agitated liquids.
22MagnetostrictiveA magnetostrictive system consists of a magnetostrictive wire in a probe and a donut- shaped ﬂoat containing a permanent magnet. The ﬂoat is the only moving part and travels up and down the probe.
23Advantages and Disadvantages Advantages are high accuracy and independence from material characteristics such as conductivity and dielectric constants.Disadvantages are limitations to relatively clean liquids and anything that would cause the ﬂoat to hang up on the probe.