Ultrasonic level Sensor working Principle

Ultrasonic level transmitter is continuous level measurement in liquids and solids with ultrasonic level sensorsUltrasonic waves detect an object in the same way as Radar does it. Ultrasonic uses the sound waves, and Radar uses radio waves. When ultrasonic pulse signal is targeted towards an object, it is reflected by the object and echo returns to the sender. The time travelled by the ultrasonic pulse is calculated, and the distance of the object is found. Bats use well known method to measure the distance while travelling. Ultrasonic level measurement principle is also used to find out fish positions in ocean, locate submarines below water level, also the position of a scuba diver in sea.




We will refer to picture and make an effort to understand the technicalities of ultrasonic level transmitter. An ultrasonic level transmitter is fixed at the top of a tank half filled with liquid. The reference level for all measurements is the bottom of the tank. Level to be detected is marked as “C”, and “B” is the distance of the ultrasonic sensor from the liquid level. Ultrasonic pulse signals are transmitted from the transmitter, and it is reflected back to the sensor. Travel time of the ultrasonic pulse from sensor to target and back is calculated. Level “C” can be found by multiplying half of this time with the speed of sound in air. The measuring unit final result can be centimeters, feet, inches etc.

Level = Speed of sound in air x Time delay / 2

Applications ultrasonic level Transmitter : 

Storage tank levelReservoir level , Open channel flow of weirs and flumes , Effluent pit level , Buffer tank level , Underground sumps , Cooling tower sumps and Waste water and slurry processing/ handling.

Range :-  For tanks and silos (pulse usually travels in vapor space), up to 230 ft (70 m) for some special designs and up to 50 ft (15.3 m) for most standard systems. For wells (usually submerged), up to 2000 ft (600 m).

Design Pressure :- Probe switches are used up to 3000 PSIG (207 bars  =  20.7 MPa); transmitters are usually used for atmospheric-type service up to 60 PSIG (4.1 bar), but some special units are available for use up to 250 PSIG (17.2 bars).

Design Temperature:-  Switches from  − 100 to 300 ° F ( − 72 to 149 ° C) with special units to 750 ° F (399 ° C);transmitters from  − 40 to 302 ° F ( − 40 to 150 ° C)

Price :-  Level switches cost from $150 basic to $950 (smart, multipoint); transmitters costfrom $650 to $2500, with an average cost around $1200

Installation position of Ultrasonic level transmitter :

  • Avoid contact of the sensor with the wall of the tank. In case of an installation in a stilling pipe diameter less than 100mm, an in-situ calibration will be required to respect accuracy specification. For a coaxial version, there is no problem you can install it without precautions.
  • Avoid an installation too close to an agitator. The cables/ rods may become entangled.

Ultrasonic level transmitter advantage and disadvantage

Ultrasonic lever sensor Advantage :-

  • Ultrasonic transmitters are easy to install on empty tanks or on tanks containing liquid.
  • Set-up is simple and those devices with on-board programming capability can be configured in minutes.
  • As there is no contact with the media and no moving parts, the devices are virtually maintenance free. Wetted materials are usually an inert fluoropolymer, and resistant to corrosion from condensing vapors.
  • Because the device is non-contacting, the level measurement is unaffected by changes in the liquid density, dielectric, or viscosity, and performs well on aqueous liquids and many chemicals.
  • Changes in process temperature will change the speed of the ultrasonic pulse through the space above the liquid, but temperature compensation automatically corrects this.
  • Changes in process pressure do not affect the measurement.




Ultrasonic lever sensor disadvantage 

  • Ultrasonic transmitters rely on the pulse being unaffected during its flight time. Liquids which form heavy vapors, steam or vapor layers should be avoided (use a Radar transmitter in these instances). As the pulse needs air to travel through, vacuum applications are not possible.
  • Obstructions in the tank, such as pipes, strengthening bars and agitators, will cause false echoes, but most transmitters have sophisticated software algorithms to allow masking or ignoring of these echoes.
  • The condition of the liquid surface is also important. Some turbulence can be tolerated but foaming will often damp out the return echo.
  • Materials of construction generally limit the process temperature to around 158 °F (70 °C) and pressure to 43 psig (3 bar).
  • Ultrasonic transmitters can be used on silos containing dry products such as pellets, grains or powders, but these are more difficult to commission. Factors such as surface angle of repose, dusting and long ranges must be taken into account. A Guided Wave Radar transmitter is better suited to dry product applications.

Read Next :-

Guided wave radar gauge

Capacitance Level Measurement

Laser Level Measurement

Magnetic level gauges

 




Ultrasonic level Transmitter Technical specification :

1.TAG NO./ QTY.LT-501
2.SERVICE Oil
3.P&I NO./ VESSEL NO. 320/33
4.AREA CLASSIFICATIONNon-Hazardous
5.MEASURING PRINCIPLEUltrasonic
6.TANK / VESSEL DRAWING NO.12345
7.TANK / VESSEL TYPEClose
8.TANK / VESSEL HEIGHT3000 mm
9.TANK / VESSEL DIA1500 mm
10.NOZZLE SIZE6″
11.NOZZLE ORIENTATION30 Degree
12.NOZZLE RATING300 #
13.C-C DISTANCE1200 mm
14.UPPER FLUID/ LOWER FLUIDXXX
15.SP. GR. UPPER/ LOWER1
16.DENSITY UPPER/ LOWER0.98
17.VISCOSITYXXX
18.PRESSURE          MIN./ NORM./ MAX.XXX
19.TEMPERATURE   MIN/NORM/MAXXXX
20.TYPESmart with HARTprotocol
21.OUTPUT SIGNALXXX
22.ELECTRICAL POWER SUPPLY4-20mA HART
23.ACCURACY,+/- 1%
24.ENCLOSURE MATERIALSS 316
25.ENVIRONMENTAL PROTECTIONWeatherproof/Dustproof
26.ENCLOSURE CLASSIP 65/ NEMA 4X Minimum
27.INDICATORIntegral,DigitalLCD,0-100%
28.MOUNTING 
29.CABLE GLAND CONNECTION1/2″NPT(M)SS316/NOTE2




Ultrasonic Level Transmitter Inspection and Test Plan :

This is a sample ultrasonic level transmitter inspection and test plan. You might need to change it to meet your purchase order specifications.

Ultrasonic Level Transmitter Inspection and Test Plan TaskVendorTPI InspectionClient
Ultrasonic level transmitter mill test reportHRR
Ultrasonic level transmitter Calibration testHWR
Ultrasonic level transmitter Performance test including hystersisHWR
Ultrasonic level transmitter Insulation resistance testHWR
Ultrasonic level transmitter Final visual / Dimension InspectionHHR
Ultrasonic level transmitter Documentation review prior to release(Final activity of Technical Inspection)HHR
Ultrasonic level transmitter Pre-shipment InspectionHHR




H: Hold Point implies that relevant production activities shall not proceed until the continuation of work is permitted by Purchaser. (Notification req’d)

W: Witness point implies that Purchaser intends to witness the designated inspection feature. If Purchaser decides not to witness the relevant feature, production can proceed without permission of Purchaser. (Notification req’d)

S: Witness, but spot check basis. Initial operation will be witness point and subsequent operation will be witnessed at discretion of Purchaser considering the results of previous inspection. (Notification not req’d : Randam Inspection)

R: Review inspection & test records (Notification not req’d)

General Note for Ultrasonic Level Transmeter :

1) Ultrasonic Level Transmitter witness/hold point by Code Inspector, when applied by Code /Local Regulation, is to comply with its requirements and to specify in Vendor’s ITP.

2) Type of Inspection by Ultrasonic Level Transmitter Purchaser may be changed according to equipment criticality and vendor QC evaluation at job stage.

3) When requested in the requisition, detailed Ultrasonic Level Transmitter ITP shall be submitted by Vendor.

4) Monitoring/Observation of Ultrasonic Level Transmitter Vendor shop daily routine works (i.e. Storage of materials, Adherence to approved procedures, Testing tool calibration check,workmanship,cleanliness and etc.) shall be done by Purchaser during inspection visit.

5)100% Ultrasonic Level Transmitter inspection which is covered by the combination of witness / spot check / record review inspection & tests listed above and vendor’s original QC activity shall be confirmed by Purchaser’s inspector prior to shipment.



6)  Unless otherwise specified in Ultrasonic Level Transmitter REQ., the sampling Q’ty of ” S (Spot Witness Check) ” shall be as follows:

3 to 20→3Pcs(all if total 2 and less) , 21 to 50→5Pcs, 51 to 100→10Pcs,101 to 200→20Pcs, 201 to 300→30Pcs, 301 to 500→50Pcs

Minimum 25 pcs or more of the commodity shall be arranged for H/W/S inspection and test at one time inspector’s visit as much as practical.

 

7) Final Ultrasonic Level Transmitter Visual Inspection/Documentation Review/Pre-Shipment Inspection may be combined within one time visit.

Ultrasonic  Level sensor  Manufacturer 

Ultrasonic Type Level Transmitter Manufacturers / Vendors Country Website Phone No.
AMETEK PANALARM(AMETEK PRECISION INSTRUMENTS LTD) UK www.ametek.co.uk +44 1383825630
EMERSON UK www.frco.com +44 1162822822
ENDRESS & HAUSER GERMANY www.endress.com +49 71562090
KROHNE MESSTECHNIK GMBH & Co. KG GERMANY www.krohne.de +49 2033010
SOLARTRON MOBREY UK www.solartronmobrey.com +44 1243833333
VEGA GERMANY www.vega.com +49 7836500

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