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
