ABSTRACT
Differential Pressure (Liquid Head Detection) Method 654
Capacitance 655 Displacer 656 Magnetic Float 656 Nuclear (Radiometric) 656 Radar (Guided Wave) 657 Ultrasonic 657 Glass-Level Gauge 657 Coriolis Flow Meter 657 Other Considerations 658
Interface-Level Measurement from the Tank/Vessel Bottom 658
Standpipes 659 Emulsion Layer 659 Abbreviations 659 Organization 659 Bibliography 659
3.4 APPLICATIONS: NON-CONTACTING, NON-PENETRATING 660
Introduction 660 Radar 661 Nuclear (Radiation) 662 Ultrasonic 663 Laser 663 Load Cells 663 Microwave Switches 663 Bibliography 664
3.5 APPLICATIONS: TANK GAUGES FOR OIL AND GAS 665
Fuel Farm Tank Gauges 665 Operations and Stock Movements 665
Category 1 666 Category 2 667 Category 3 667
Automatic Overll Prevention Systems 667 Stock or Inventory Control 669 Custody Transfer 674 Leak Detection and Reconciliation 674 Density Stratication in LNG Storage 674 Inventory Measurements for LPG and LNG
Storage Tanks 676 Radar Gauges for LPG and LNG 676 Underground Fuel Storage Tanks 677 Denitions 677 Abbreviations 678 ASTM Standards 678 API Standards 678 British Standards 678 OIML Standards and Certicates 678
NMI (Australian) Standards 678 US EPA Standards 679 Special Tank Inventory Gauge Instruments 679 Emission Monitoring (Standards and
Techniques) 679 Bibliography 679
3.6 APPLICATIONS: WATER LEVEL MEASUREMENT IN NUCLEAR REACTORS 680
Introduction 680 The Fukushima Accident 680
Learning from the Fukushima Accident 680 Ex-Core Level Measurement 681
Conventional d/p Level Measurement 681 The Fukushima Design 682 Measuring the Level of Boiling Water 682 Thermal Ex-Core Level Measurement 682
In-Core Level Measurement 684 Thermal In-Core Measurement 684 New Developments 685
Conclusions 685 Abbreviations 685 Reading Materials 685
3.7 BUBBLERS 686
Introduction 686 General 688 Myths of the Bubbler 689 Purge Gas 690 Package Units 690 Sizing Calculations 690 Mass and Level 690 The Hydrostatic Tank Gauge (HTG) 691 Density 692 Calibration 692 Flow Rate and Plugging Considerations 692
Minimum Purge Flow Rate 692 Maximum Purge Flow Rate 692 Dip Tube Diameter Selection 692 Upsets and Plugging 693 Installation Details 694 Pressure and/or Flow Regulators 694 Diaphragm-Type Dip Tube 695 Sample Calculations 695
Level Detector Calibration Examples 695 Density Detector Calibration Example 695 Conclusions 695 Denitions 696 Abbreviations 696 Organization 696 Bibliography 696 References 696
3.8 CAPACITANCE AND RADIO FREQUENCY (RF) ADMITTANCE 697
What is Capacitance? 698 Introduction 698
Electric Characteristics of Process Material 699
Types of Probes 700 Mounting and Tank Entry 702 Electronic Units 703 Point Level Measurement, Switches 704
Switches for Conductive Liquid Applications 704
Switches for Insulating Liquid Applications 705
Switches on Plastic, Concrete, Fiberglass or Lined Metal Tanks 705
Switches for Liquid Interface Measurements 705
Switches for Granular Solids Applications 706
Continuous Level Measurement, Transmitters 706
Transmitters for Conducting Liquids Applications 706
Transmitters for Insulating Liquids Applications 708
Transmitters for Liquid Interface Applications 709
Transmitters for Granular Solids Applications 710
Conclusion 710 Specication Forms 711 Denitions 713 Abbreviations 714 Bibliography 714
3.9 CONDUCTIVITY AND FIELD-EFFECT LEVEL SWITCHES 715
Introduction 715 Conductivity-Type Level Switch 716 Pump Alternator Circuits 717 Advantages and Limitations 718 Field-Effect Level Switches 718 Denitions 719 Abbreviation 719 Organization 719 Bibliography 719
3.10 DIAPHRAGM LEVEL DETECTORS 720
Diaphragm Type Switches for Solids Service 721 Diaphragm Switches for Liquids 723
Continuous Level Sensors and Repeaters 724
Sump Control Service 725 Abbreviations 726 Bibliography 726
3.11 DIFFERENTIAL PRESSURE LEVEL DETECTORS 727
Sensing d/p 728 Wet and Dry Leg 729 Extended Seal Diaphragms 729 Chemical Seals (Extended Liquid-Filled
Capillary Tube) 730 Pressure Repeaters 730 Dry, Motion Balance Devices 731 Liquid Manometers 731 Level Applications of d/p Cells 732
Clean Liquids in Atmospheric Tanks 732
Clean Liquids in Pressurized Tanks or Vessels 733
Hard-to-Handle Fluids in Atmospheric Tanks 733
Hard-to-Handle Fluids in Pressurized Tanks/Vessels 734
Special Installations 735 Boiling Applications 735 Cryogenic Applications 736 Normal Ambient Temperature Bi-Phase
Applications 736 Zero, Span Elevation or Suppression 737 Interface Detection 739 Intelligent (Expert) Tank Systems 740 Intelligent d/p Cells 741
Multiple Sensing Transmitters 741 New Developments 742 Future Trends 744 Accuracy 744
Specication Form 744 Denitions 746 Abbreviations 746 Organizations 746 Bibliography 746
3.12 DISPLACER TYPE LEVEL DETECTORS 748
Introduction 749 Displacer Switches 749 Torque Tube Displacers 751
Sizing of Displacers 751 Interface Measurement 752 Rag Layer Detection 753 Installation 753
Spring-Balance Displacer 754 Force-Balance Displacer 755 Flexible Disc Displacer 756 Flexible Shaft Controllers 757 Intelligent State-of-the-Art Designs 757 Conclusion 758 Specication Forms 758 Denitions 761 Bibliography 761
3.13 FLOAT LEVEL DEVICES 762
Introduction 763 Float Level Switches 763
Reed Switch Designs 765 Float and Guide Tube Designs 766 Tilt Switches 766 Float-Operated Continuous Indicators 767 Pressurized Tank Applications 767 Magnetically Coupled Indicators 768
Density Measurement 770 Interface Detection 770 Conclusion 770 Specication Form 770 Denitions 772 Abbreviations 772 Organizations 772 Bibliography 772
3.14 LASER LEVEL SENSORS 773
Pulsed Laser Sensors (Time of Flight) 774 Triangular Measurement Sensor 775 Vapor Space Effects 775 Types of Targets and Angle of Repose 776 Material Surface Reection Effect 776
Laser Scanners 776 Two-Dimensional Laser Scanners 777 Three-Dimensional Laser Scanners 777 Inventory Management System 778 Limitations 778 Laser Eye Safety 779 Laser Power and Ignition Safety 779 Installation 779 Denitions 780 Abbreviations 780 Organizations 780 Bibliography 781
3.15 LEVEL GAUGES, INCLUDING MAGNETIC 782
Introduction 783 Tubular Glass Gauge 784
Circular Transparent Gauge 784 Transparent Gauge (Long Form) 784 Reex Gauge 786 Armored Gauges 787 Gauge Glass Materials 787 Design Features 787 Gauging Inaccuracies 788 Accessories 789 Application-Specic Requirements 790 Installation 790 Magnetic Level Gauges 791 Magnetic Followers and Indicators 792 Remote Reading Gauges 792 Differential Pressure 792 Conductivity 793 Bull’s-Eye Gauges 793 Circular Gauges 793 Conclusion 793 Specication Forms 794 Abbreviations 797 Organizations 797 Bibliography 797
3.16 MAGNETOSTRICTIVE LEVEL TRANSMITTERS 798
Introduction 799 Safety 799
Nonhazardous Areas 799 Hazardous Areas 799
Design and Operation 799 Installation 801 Applicable Documents 803 Comments 803 Conclusion 803 Bibliography 803
3.17 MICROWAVE LEVEL SWITCHES 804
Introduction 805 Reection Switches 806 Beam-Breaker Switch 807 Conclusion 808 Specication Form 808 Denitions 810 Abbreviations 810 Bibliography 810
3.18 OPTICAL AND IR LEVEL SWITCHES 811
Light Reection 812 Light Transmission 813 Light Refraction 813 Conclusion 815
Denitions 815 Abbreviations 815 Bibliography 815
3.19 RADAR: CONTACT LEVEL SENSORS (TDR, GWR, AND PDS) 816
Introduction 817 Theory of Operation-Guided Wave Radar 817
Guided Wave Radar in Saturated Steam Applications 819
Theory of Operation: Phase Difference Sensor 819
Guided Wave Radar System: Electronics and Probe 819
Interface Measurement 821 Recent Advancements in GWR 822
Advanced Algorithms 822 Advanced Probe Designs 822 Advanced Diagnostics 823
Conclusion 823 Denitions 823 Bibliography 824 Internet Articles/Sources 824
3.20 RADAR: NON-CONTACTING LEVEL SENSORS 825
Principles of Operation 827 Frequency-Modulated Carrier Wave 827 Pulse 828 Accuracy and Resolution Factors 828 Installation 829
Obtaining the Correct Readings 830 Installation and Selection Guidelines 830 Conguration Guidelines 832
Radar Echo Plots 832 Conclusions 834 Abbreviations 834 Bibliography 834
3.21 RADIATION LEVEL SENSORS 835
Radiation Phenomenon 836 Source Materials 836 Units and Attenuation of Radiation 837
Source Sizing 837 Safety Considerations 838
Allowable Radiation Exposures 839 Nuclear Regulatory Commission 839
Detectors 840 Geiger-Mueller Tube 840 Gas Ionization Chamber 841 Scintillation 841
Level Switch Applications 841 Continuous Level Measurement 842
Long Measurement Ranges and Narrow Vessels 843
Interface, Turbulence, and Foam 844 Continuous Level Measurement
Enhancements 845 Vapor Compensation 846 Auto-Zero Gauge 846 X-Ray Alarm 846
Installation Notes 846 Point Source and Strip Detector 847 Source and Detector Air Gaps 848 Calibration Considerations 848
Backscatter Designs 848 Traversing Designs and Density
Measurement 849 Electronics 849 New Developments 850 Conclusions and Trends 850 Specication Forms 852 Abbreviations 854 Bibliography 854
3.22 RESISTANCE TAPES 855
Application 856 Limitations 857 Installation 857 Actuation Depth 858 Pressure Effect 858 Temperature and Other Effects 859 Signal Transmission 860 Specication Forms 860 Abbreviations 862 Bibliography 862
3.23 ROTARY PADDLE SWITCHES (SOLIDS LEVEL DETECTOR) 863
Introduction 864 Rotating Paddle Switches 864
Installations 865 Conclusions 865 Specication Form 866 Bibliography 867
3.24 TANK FARM GAUGES FOR LIQUIDS AND SOLIDS 868
Introduction 869 History of Custody Transfer 869 Accuracy 870
Non-Mechanical Tank Gauges 870 Magnetostrictive, Capacitance, Displacer
and Hybrid Tank Gauges 870 Mechanical Tank Farm Gauges 871
Float-Operated Design Variations 872 Inductively Coupled Tape Detectors 873
Wire-Guided Float Detectors 874 Encoding 875
Temperature Compensation 876 Wire-Guided Thermal Sensor 876
Solids Level Detectors 876 Multiple Tank Systems 877 Conclusions 878 Abbreviations 879 Bibliography 879
3.25 THERMAL DISPERSION LEVEL SENSORS 880
Introduction 880 Thermal Conductivity Based Design 880 Thermal Dispersion Based Design 881 Heat Transfer Difference for Continuous
Detection 882 Thermometers as Level Sensors 882 Conclusion 883 Bibliography 883
3.26 ULTRASONIC LEVEL DETECTORS 884
Introduction 885 The Nature of Ultrasound 885
Level Switches 886 Damped Vibration Type 886 Absorption Type 887 Interface Detector 887
Level Transmitters 888 Interface Measurement 890
Newer Developments 891 Automatic Calibration 891 Multiple Tank Monitoring 891 Portable Monitors 891 Wireless Detectors 892 Displays and Communication 892
Conclusion 893 Specication Forms 893 Denition 896 Abbreviations 896 Bibliography 896
3.27 VIBRATING LEVEL SWITCHES 897
Vibrating Level Switches 898 Tuning Fork 899 Vibrating Probes 899 Smart Switches 899 Safety Instrument Level Rating 900 Conclusion 900 Abbreviations 900 Bibliography 900
INTRODUCTION
There more are than a dozen ways to measure liquid and solids levels (Figure 3.1a) and selecting the one detector that is best suited for a particular application is not an easy task. One must consider reliability, safety, accuracy, cost, maintenance, and many other factors. In the “real world,” this systematic selection process is often not carries out, and often there is a tendency to base the selection on nonengineering factors, such as past practices (or business lunches with manufacturers’ representative, etc.), because obtaining unbiased information and going through a systematic selection process for each level sensor in the whole plant would require too much time and effort. It is for this reason that in the past, if direct contact with the process uid was acceptable, most level sensors ended up to be d/p cells or displacer type units, or if noncontact detectors were needed radar and ultrasonic ones were selected.
