• Prepared by:
- Kbrom Lbsu(Msc)
- Course: Measurment
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Level measurement
• Level measurement is used to establish the quantity of a substance within a vessel.
• This could be a solid or liquid substance like oil, chemicals, coal dust, etc.
• involves determining the filling level of media in industrial containers, such as process and storage tanks, silos or open
channels
• The level measurement devices are usually place on top of the vessel.
• The purpose of level measurement is to:- Provide a measured variable representing the height or
material presence with in a vessel.
- Detect the presence of the material.
- Measure the quantity in hydrocarbon inventory management
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Cont..
❖Two main types of level measurement technics are used on industries, depending on the process requirements:
those are
1.
Point level measurement: in case of this technic, level detection is determined by level
switch, that only detect the level presence on a particular point or position.
2.
Continuous level measurement: whereas, a level transmitter constantly measures the
level on an extension from 0 to 100% range and then delivering an analogue output
proportional to the measured level.
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Types of level sensors
❖ Based on the above classification of level measurement technics we have 7 main level sensors .
1.
Capacitive level sensor:
-
Work with range of solids, liquids, and mixed material.
-
Works based on change of capacitance and
-
the capacitance depends on the Fluid level
-
Capacitor consists of two electrode plate separated by a small thickness of an insulator.
-
The value of C depends on C = 𝜀(𝐾. 𝐴/𝑑)
-
Are operated by using electrodes for checking the level change.
-
These level changes are converted to analog signal.
• Features
- they are clean and easy to use
- don’t have moving components
- they are small and inexpensive than other sensors.
- they are very accurate..
Yet – they may require calibration
- and can only be used in a certain liquids.
• Application
- tank level monitoring in chemical processing.
- food, water treatment
- power and brewery industries.
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2. Optical Level Sensors
- Works based on the change of transmission in infrared light emitted
From an IR LED.
- by using high energy IR diode and pulse modulation method
- simply, they work by converting light rays into electrical signals
- by measuring the physical quantity of light and then translate into
a measurement.
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• Features
- compact, no moving parts
- high pressure and temperature capability.
- can detect tiny amount of liquids.
Nevertheless;
- invasive as the sensor requires contact with liquid
- requires power
- certain thick substance can cause coating on the prism
- so, cleaning is must if the lens gets dirty or coated.
• Application
• Tank level measurement and leak detection system.
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3. Conductive level sensor.
• Are also known as resistive probe sensors.
• Are used for point – level sensing conductive liquids such as
water and highly corrosive liquids.
• It uses probe to read conductivity
• The probes consists of pair of electrodes, with different length
• Simply, put the two metallic probes in to a tank
• The long probe transmits a low voltage, the second shorter
probe is cut , so the tip is at the switching point.
• When a liquid covers the probe its electrodes form a part on an
electric circuit, causing the current flows across both probes to
activate the switch.
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Cont..
• Features
- easy to use and install
- inexpensive and have no moving part
- they are safe due to low voltage and current.
But;
- they are invasive and can only sense conductive liquids
- probe erosion over time.
• Applications
- tank level measurement for boiler water and reagent monitoring
- highly corrosive liquids
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4. Vibrating (Tuning fork) level sensor.
• Are perfect for liquid level measurement control, including sticky
materials and foam as well as powder and fine grained solids.
• A fork shaped sensing element with two tines is used in this types
of sensors
• The tuning fork vibrates at its mechanical resonance frequency of
~ 1200Hz and is piezo electrical energized
• The frequency of the fork changes when the fork is submerged in
the media and this change is detected by the internal oscillator, so
• The denser the liquid, the lower the frequency.
• Converted into a digital out put signal
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Cont.…
• Features
- they are cost effective and compact
• Specification
- they are easy to install and maintenance free
However;
- they are invasive and the number of uses is limited.
• Application
- level control of liquids
- powders and fine grained solids
- mining, food and beverage industries
- chemical processing industries
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5. Float switch sensor
• It is a well proven technologies for liquid level
sensing
• It utilizes a float, a device that will raise or lower when
a product is applied or removed.
• A float switch includes a magnet within a float and a
magnetic reed switch contained within a secure
housing.
• The float changes with the change in liquid and will
cause the reed switch to either open or close depending
on if it is in air or liquid.
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• Features
- relatively inexpensive
- has various outputs
- float switches are non powder devices
- has direct indications.
And but ;
- they are invasive to the product
- they have moving parts
- they are big in size and large amount of liquid has to be
present before the float makes contact
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Cont..
• Applications
• Tank level application where
- water and oil
- hydraulic fluids
- and chemicals are used.
** all the above sensors we tried to explore are point level measurement sensors.
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6. Ultrasonic level sensor
• Are used to detect level of the sticky liquid
substance and bulkiness material as well.
• They work based on emitting and receiving
ultrasonic waves ~ 20 to 200khz
• The wave are then replicated back to transducer.
• And then the distance is measured by the time it
takes for the wave to reflect back.
• The length of the time in which the sensor takes to
react is affected by various elements such as ,
pressure, temperature, moisture, foam and
turbulence.
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Cont.…
• Features
- they are reliable and cost effective
- have no moving parts
- they are compact
- relatively they are not costly
but; -needs self cleaning
- performance can be affected by various elements from the
environment.
• Applications
- non contact applications with highly viscous and bulk solids
-used in systems that requires remote monitoring.
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7. Microwave/radar level sensors.
• They work similarly to ultrasonic sensors.
• But incase of this sensor, the pulses travel at the speed of light and
again
• The repeatability and reliability cab be exaggerated, and uses the
dielectric constant of the fluid.
• These sensors sends microwave by an antenna on the radar sensor
• And then the product being sensed reflects these micro waves back
to the antenna
• And then the time from the emission to receiving of the signal is
proportional to the level of the liquid.
• The radar sensors are unaffected by dust, temperature or pressure.
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Cont..
• Features
- they are very accurate and no calibration
is needed
- they have multiple output options
- Measuring range: 100 to 20.000mm.
- Fastest reaction time with 0.5 sec
- Power requirements: 12 to 30VDC.
And yet - they are expensive
- have limited detection range
• Applications : most commonly used in
- moist and vaporous
- dusty environment and in systems that temperature is vary.
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Reference
1. https://instrumentationtools.com/types-level-measurement/
2. https://forumautomation.com/t/basics-of-levelmeasurement-working-principle-and-types-of-levelmeasurement/495
3. https://www.academia.edu/41284287/Liquid_Level_Measure
ment
4. https://www.plantautomation-technology.com/articles/7main-types-of-industrial-level-sensors
5. https://www.globalspec.com/search/products?page=ms#sqid
=90437922&comp=1791&show=products
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Thank you
and question ??
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