Level Measurement Technology
Two Groups of Level Measurement - 1.Point Measurement (Discrete) 2. Continuous Measurement (Analog)
Common Types of Level Measurement Technologies
1.Plumb Bob
This is one of the oldest level measurement technology.
A worker drops a length of pre-measured rope until a float contact the material surface.
Advantages - Simple
Disadvantages - Human Non- reputability Hazard exposure Process damage from broken cable Not instantaneous
2.Ultrasonic (Non-Contacting)
Measure time of flight from transmission to received echo.This determines distance and calculates level.
Advantages of Ultrasonic Level Measurement- Non-Contact Well Proven Solids,Liquids,or Slurries Control Capabilities (Pumping and alarm) Potted/robust transducer for vibration and shock (No electronics in vessel) Remote display
Disadvantages of Ultrasonic Level Measurement- Sensitive to vapor changes in medium Can be sensitive to foam Limited pressure and temperature range
3.Radar (Non-Contacting)
Measure time of flight from transmitted signal to return signal for distance measurement.
Advantages of Radar Level Measurement- Non-Contacting Insensitive to vapor and dust Unaffected by temperature and pressure Very long ranges (up to 100 m)
Disadvantages of Radar level measurement- Can be sensitive to foam Can be sensitive to very heavy condensate Display and antenna are integral
4.Guided Wave Radar (GWR) or Capacitance (Contacting)
Both technologies use a rod or cable which extends into the material being measured.
Advantages of Guided Wave Radar or Capacitance level Measurement Able to measure the liquid-liquid interface of two imiscible liquids Wide temperature / Pressure range up to 427 deg C or up to 431 bar
Disadvantages of Guided Wave Radar or Capacitance level Measurement Can be sensitive to material build up Wear in solids Pull forces on roof-solids applications Equipment damage from broken rods.
5. Hydrostatic Level (Contacting)
Measure head pressure of material in vessel
Advantages of Hydrostatic Level Measurement Easy to use Complex internal geometry possible Suitable for high temperature and pressure Most common level measurement in all industries
Disadvantages of Hydrostatic Level Measurement Contacting - chemical compatibility with seals Susceptibility to specific gravity changes may require recalibration Adds fitting/piping to system if not submersible
