L.4 - Level Flashcards
What are point measurement devices referred to?
Switches
What are continuous level measurement devices called?
Indicators or Detectors
Define Direct Level Measurement:
Level is determined by direct measurement
Define Inferential Level Measurement:
Level is determined by measurement of another variable (eg. hydrostatic tank level is determined by measuring hydrostatic pressure in tank)
List some Direct Level Measurement Methods:
1) Dipstick
2) Sightglass
3) Constant Displacement Float and Tape System
What is a Dipstick measurement?
Wetted length on a calibrated rod or stick
What is a Sightglass measurement?
External glass tube indicates level of liquid in a vessel
What is a Constant Displacement Float and Tape System measurement?
A buoyant object or float lies on the liquid surface. The float is mechanically connected to an indicator or transmitter mechanism
List some Inferential Level Measurement Methods:
1) Ultrasonic Level Measurement
2) Microwave/Radar Level Measurement
3) Capacitance Level Measurement
4) Nuclear Level Measurement
5) Variable Displacement Float System
6) Hydrostatic Level Measurement
7) Open Tank Measurements
Talk about Ultrasonic Level Measurement
> a pulse of ultrasonic sound energy is emitted by a transmitter. The sound travels outward until it is reflected back by striking a surface or interface.
> it needs medium to operate
> no contact with liquid
> can be affected by changes in temperature and pressure
Talk about Microwave/Radar Level Measurement
> a pulse of high frequency electromagnetic energy is emitted by a transmitter. The energy travels outward and a portion is reflected back by striking a surface.
> no contact with liquid
> not affected by temperature and pressure
> more expensive
Talk about Capacitance Level Measurement
Capacitance is the measure of the amount of charged stored per volt of electrical potential between two conductors C=Q/V
Talk about Nuclear Level Measurement
> Used to measure the level of solids in vessels.
> a nuclear source emits a beam of gamma radiation that is focused on a radiation detector
> vessel filled with solid, absorbs gamma radiation preventing it from reaching detector
Variable Displacement Float System
Float placed in a fixed position relative to the bottom of the vessel. as liquid changes, portion of submerged float changes, resulting in change in buoyant force
Hydrostatic Level Measurement
Hydrostatic pressure (head) exerted by a column of liquid is measured (need to know density)
