23-04-2011, 10:47 AM
Presented By:
Jitendra Soni
ieee seminar.pptx (Size: 352.66 KB / Downloads: 105)
Liquid Level Measurement Based on Ultrasonic Echo Characteristic
introduction
Ultrasound is high frequency mechanical vibrations or pressure waves
Uses sound waves(>20000Hz)
Sound waves are transmitted as a series of compressions and rarefactions
Wave propagation is longitudnal and mechanical displacement in same direction
About Ultra Sonic Technique
Ultrasonic level sensors are used for non-contact level sensing of highly viscous liquids, as well as bulk solids
The sensors emit high frequency (20 kHz to 200 kHz) acoustic waves that are reflected back to and detected by the emitting transducer.
The requirement for electronic signal processing circuitry can be used to make the ultrasonic sensor an intelligent device
Types of level measurement
Non-Contact direct level sensor
Level is a function of the time it takes an ultrasonic pulse to hit the surface and return
Principles of Ultrasonic Inspection
Ultrasonic waves travel in a straight line and at a constant speed until they encounter a surface.
some of the wave energy is reflected and some is transmitted.
The amount of reflected or transmitted energy can be detected and provides information about the size of the reflector.
The travel time of the sound can be measured and this provides information on the distance that the sound has traveled.
ultrasonic instrument
Attenuation mode
A transmitter sends ultrasound through one surface
Receiver detects the amount reaching it on another surface
Imperfections reduce the amount of sound received
Efficiency is increased by couplant usage
Test Techniques
Divided into three primary classifications:
Pulse-echo and Through Transmission
Normal Beam and Angle Beam
Contact and Immersion
Contact Transducers
Level measurement sensors
FLOAT SWITCHES
NON CONTACT/CONTACT ULTASONIC SENSORS
CAPACITANCE LEVEL SENSORS
NUCLEAR LEVEL SENSOR
ACOUSTIC IMPEDANCE
It is a frequency depended parameter
Mathematically
Z=p/v*s
where, p=sound pressure
s=surface area
v=surface velocity
results are recorded in the form of curves
Advantage of Ultrasonic Testing
Sensitive to small discontinuities
Depth of penetration for flaw detection
Single-sided access is needed
High accuracy
Electronic equipment provides instantaneous results.
Detailed images can be produced with automated systems.
Limitations of Ultrasonic Testing
Surface must be accessible.
Skill and training is required
Normally requires a coupling medium
Cast iron and other coarse grained materials are difficult to inspect due to low sound transmission and high signal noise.