Products Solutions Services Level Measurement Transmitters Applying Level Measurement Ultrasonic FDU95 FDU93 FDU92 FDU91 FDU90 Slide 1 Slide 2 The Principle Time of Flight (TOF) Emission of ultrasound pulses Reflection of the pulses from the product surface Receiving of the reflected pulses Environmental effects on velocity of sound Air moisture 0.3% with change in relative moisture from 0 to 100% insignificant Velocity of sound co = 331.6m/s (1088ft/s) Temperature 0.17% / C measured/ compensated Measurement of the Time of Flight calculation of the distance between the device and the product surface by d = c 00.40 2 emitting Slide 3 Slide 4 receiving Pressure change 30bar /435psi change in run time approx 0.3% pmin = 10psia irrelevant x Rm (273 + T) c = M c: velocity of sound [m/s] Rm: universal gas constant (8314,3 J/kmol k) T: temperature [ C] x: adiabatic index M: molecular weight cair at 20 C = Vapor pressure 1.4 8314.3 (273+20) < 50mbar (20 C)? = 28.8 no problem = 344m /s (1088ft/s) Speed of Propagation for Ultrasound Ultrasonic Mounting Speed Speed Gas [m/s] [ft/s] CI 206 676 CO2 258 846 Ar 308 1010 O2 32 F 315 1033 O2 300 F 178 584 NO 324 1063 Air 32 F 331 1086 Air +68 F 334 1096 Air +104 F 355 1165 C p = r = k = T = C 0 = S p C T 0 1 273K pressure density adiabetic exponent temperature speed of ultrasound at 0 C pressure: no influence temperature: approx. 0.17 % / K (air: 0.59 cm / K) CO 337 1106 N 2 377 1237 Coal gas 441 1447 Helium 32 F 971 3186 example: filling of chlorine tank Air: 334 m/s (1095 ft/s) Cl: 206 m/s (676 ft/s) failure: 38% Slide 5 Slide 6 1
Reflection of Acoustic Energy Self Cleaning Transducer Face FDU91 FDU92 ideal conditions light foam big bubbles low density something in between condensed foam, heavy, small bubbles > signal absorption high density??? Advantage Because of an optimized coupling between piezo crystal and membrane much more mechanical force is applied to the membrane strong self cleaning effect (e.g. for condensation conditions) Slide 7 Slide 8 Free Space Radar Installations Basics Reflection Radar in comparison to Ultrasonic r =1 Air =0.001 r =80 Water =1.00 r : dielectric constant : specific density Slide 9 Slide 10 Basics Reflection Radar in comparison to Ultrasonic Radar Mounting Recommended distance from outer wall is 1/3 diameter of vessel. FMR 230/231 minimum distance to wall = 12 inches FMR 240/244/245/250 Minimum distance to wall = 6 inches r =1 Air =0.001 r =2 Oil =0.85 Shift caused by slower speed of propagation in oil r : dielectric constant : specific density Note It may be desirable to mount the radar closer to a wall to help ignore internal tank obstructions (i.e. agitators). Always observe minimum distance to tank wall requirements. Slide 11 Slide 12 2
The picture can't be displayed. The picture can't be displayed. 10/20/2017 Radar Mounting Radar Mounting A position above the filling stream will be subject to interference echoes A position away from the filling stream will avoid interference echoes. Echoes from fittings are suppressed during calibration A central position strengthens double echoes Min. 12 off wall A non central position avoids double echoes Slide 13 Slide 14 Radar Installed in the Middle of a Dome Vessel Radar unit jumps between level signal first harmonic second harmonic Special settings have to be made to detect the fist echo (Fist Echo Factor) This scenario can be avoided by a different installation Radar Plastic Tanks When measuring in plastic tanks, Microwave energy can penetrate and reflect off external metal structure. Slide 15 Slide 16 Dealing with Condensation FMR 245/244 with Condensation with condensation [water, ~ 113 F (45 C) w/o condensation Slide 17 Slide 18 3
Guided Wave Radar (TDR) TDR Principle of Operation typical envelope curve: amplitude Reflection from process connection Level 80% of the energy is concentrated within a radius of 8! 8 Sand Powdered clay Fly ash Talcum Lime Slide 19 Slide 20 End of probe Guided Wave Radar Installation Guided Wave Radar Nozzle Mounting Minimum Dimension A Smooth Metallic Walls = 2 inches Plastic Walls = 12 inches from external metal obstructions Concrete Walls = 36 inches Minimum Dimension B 12 inches from obstruction Minimum Dimension C Rope Probe = 6 inches Rod Probe = 0.4 inches Coax Probe = 0.4 inches longitudinal resonances in long (Greater than 6 ), narrow nozzles no additional ringing Long Nozzle Lengths are possible. Dielectric? Span Range? lateral resonances in nozzles with large diameters (Greater than 6 ) significant additional ringing reduced signal / noise ratio nozzle diameter >6 require special installation considerations! Note For Coax Probes, Distance from wall or internal obstructions are irrelevant. Slide 21 Slide 22 What about Probe Build Up? Guided Wave Radar in Plastic Vessels or Silos use a reflector (flange, metal plate) in plastic silos Metal plate Ø approx 8 12 level reflection buildup reflection Silo roof Metal flange 4 inch minimum * without reflector * Note with high dielectric material a 2 inch flange is possible Slide 23 Slide 24 4
Results of Radar and Guided Wave Radar Foam Test Capacitance Comparison of guided radar, free space radar at 6 GHz and free space radar at 26 GHz in an application with low density foam Capacitance Technology Slide 25 Slide 26 Capacitance Probe as a Component of a Capacitor Brief over view of capacitance Electronic Build up Compensation Standard insulated probe with conductive buildup for a continuous level application Material The buildup adds extra capacitance and resistance to the circuit _ + Tank wall [metal] SS rod Rod Build up effect Now this circuit has a phase shift of approximately 45 between the current and the voltage instead of the 90 with no buildup. The electronics can sense this phase shift and compensate for this built up effect on the circuit Process Tank Wall Slide 27 Slide 28 Buildup, Continuous Systems (Liquicap M) C build up Fully insulated probe Tank wall I Level Conductive Liquid, conductive build up, standard mode C build up R build up Products Solutions Services Tuning Fork Technology R build up I Meas C iso I R_build up U Mess C iso F I I Meas U Meas - 45 Slide 29 Slide 30 5
Point Level Instruments: Typical Installation Overspill protection MAX point level MIN point level pump protection Characteristics of universal limit switches active measurement principle independent of installation position and direction no calibration independent of process influences (e.g. pressure, temperature,...) independent of substance characteristics (e.g. conductivity, dielectric constant, density, viscosity,...) independent of gas bubbles foam solids (dirt, soiling) in process liquid Slide 31 Slide 32 Self Diagnostics Liquiphant M/S (FEL 51 67) Continuous monitoring of vibration frequency Reliable alarm function with each electronic insert! Submersion depth of fork [mm] fa 15% switch point at ca. 850 Hz fa =vibration frequency in air 1 khz Operation Independent of Medium Properties built up changing media 25 viscosity change 0 A L A R M A L A R M air bubbles foam suspension electrical properties pressure and temperature change 0 400 fa 15% fa fa+ 6,5% 1500 f [Hz] Normal operation corrosion alarm 60 s delayed sensorslarm 0,4 s delayed sensoralarm 0,4 s delayed plant vibration turbulences Slide 33 Slide 34 So, What Technology Is The Right Choice? There are many technologies for measuring level. All have good and bad applications. Ultrasonic The default standard for Open Channel Flow Lower cost than Radar or GWR Non Contact Technology Great for water storage tanks Not dependent on Dielectric Constant Patchy foam on surface Dusty applications (solids) Ice on transducer face (Heated Sensors are available) Vapors Foam Blanket Slide 35 Slide 36 6
Radar Not affected by vapors Non contact Technology Not affected by dust Foam Low Dielectric Materials (below 1.8DK) Plastic Vessels Dielectric below 1.4DK Guided Wave Radar Focused energy better with low dielectric Performs well when foam is present Contact technology compatibility Long Nozzles Agitated Vessels Concrete Vessels Plastic Vessels Dielectric below 1.2DK Slide 37 Slide 38 Capacitance Real time measurement Excellent for short span applications Contact technology compatibility Agitated Vessels Semi conductive materials (greater then I microsiemens but less than 100) Non stable dielectric properties Tuning Fork No Calibration simple commissioning No moving parts Can be mounted in any orientation Not affected by suspended solids or entrained air Contact technology compatibility Agitated Vessels may require support Viscosity over 10,000 centipoise Slide 39 Slide 40 Chemical Storage Bulk Storage Day Tanks Portable Tanks Depending on the vessel type and the material being measured, Ultrasonic, Guided Wave, Free Space Radar, or Capacitance could be the best solution. For hazardous Chemicals, Point Level Overfill back up is recommended Pump Protection A point level switch mounted in the pipe feeding a pump will indicate when the pipe is empty. This will prevent running the pump empty causing stator and seal damage Slide 41 Slide 42 7
Level measurement in storm water basin Requirements Level measurement in a storm water basin Control and recognition of the overload amount to the sewage treatment plant Solution Prosonic S with FDU91 sensor and mounting angle Flood proof sensor according to IP68/NEMA6P Level measurement in a reservoir Requirement Level measurement in a process water reservoir Solution Prosonic T/M Easy and fast commissioning with an attractive price Slide 43 Slide 44 Level measurement above a filter Requirement Level measurement above a filter Solution Prosonic T/M with mounting angle Easy and fast commissioning with an attractive price Water Well Level Hydrostatic Pressure Transmitters are the standard for water well measurement Slide 45 Slide 46 Sludge Level in Clarifiers The CUS71D transmitter measures the interface between the water and settled sludge in primary and secondary clarifiers. Questions? Slide 47 Slide 48 8