In industrial plants, accurate level measurement of liquids, solids, and semi-solids is vital for process safety, quality control, and operational continuity. Among the available technologies, capacitive level transmitters stand out due to their high accuracy, robust design, and broad range of applications. These devices are widely used in industries such as food, chemicals, petrochemicals, cement, pharmaceuticals, and energy.

Capacitive Level Transmitters

WORKING PRINCIPLE

Capacitive level transmitters operate on the principle of capacitance change. Essentially, the system functions as follows:

Formula: C = ε · A / d

  • C: Capacitance (Farads)
  • ε: Dielectric constant of the medium
  • A: Electrode surface area
  • d: Distance between electrodes

A probe (electrode) inserted into a tank, together with the tank wall, forms a capacitor. As the tank fills, the dielectric constant changes depending on the medium:

  • Air → low dielectric (ε ≈ 1)
  • Water → high dielectric (ε ≈ 80)

As the fill level increases, the capacitance value changes, and the transmitter converts this variation into a level measurement.

EXAMPLE CALCULATION

For a 2 m probe with an electrode area of 50 cm² and a distance of 5 mm:

  • When filled with air: C_air ≈ 8.85 pF
  • When filled with water: C_water ≈ 708 pF

This large difference enables highly accurate level measurement.

APPLICATIONS

  • Liquids: water, acids, solvents, oils, paints
  • Solids: flour, sugar, cement, plastic granules, coal dust
  • Special media: foamy liquids, sticky substances, high-pressure or high-temperature tanks

ADVANTAGES

  • Wide applicability for liquids and solids
  • Resistant to pressure and temperature variations
  • High accuracy and repeatability
  • Corrosion-resistant coatings for aggressive chemicals
  • Easy calibration and setup

DISADVANTAGES

  • Accuracy depends on dielectric constant
  • Build-up of sticky materials may cause errors
  • Improper grounding in metallic tanks may cause faulty readings

TECHNICAL SELECTION CRITERIA

  • Dielectric constant: materials with ε < 2 require high-sensitivity models
  • Temperature and pressure: ensure compatibility with process conditions
  • Tank structure: choose appropriate probe for plastic, metal, or concrete tanks
  • Explosive environments: use ATEX or IECEx certified models

CALIBRATION AND MAINTENANCE NOTES

  • Calibrate at empty and full tank conditions
  • Regularly clean probes from dust or deposits
  • Replace damaged insulation (Teflon or ceramic)
  • Ensure proper grounding to prevent measurement errors

ENGINEERING NOTES

  • Accuracy: up to ±0.5% FS
  • Output signals: 4–20 mA, HART, Profibus, Modbus
  • Measurement range: 0.2 m – 20 m
  • Process connections: flanged, threaded, or clamped

RECOMMENDED DESIGNS BY APPLICATION

Application Dielectric Constant Recommended Design Notes
Water tank ≈ 80 Standard probe High accuracy
Oil tank 2 – 5 Insulated probe Requires calibration due to low ε
Cement silo 3 – 7 Rod/rope probe Regular cleaning required
Acid tank 50 – 70 PTFE-coated probe High corrosion resistance

CONCLUSION

Capacitive level transmitters provide a reliable, economical, and precise measurement solution. Thanks to their dielectric-based principle, they can be used effectively in both liquids and solids. With proper selection, calibration, and maintenance, they ensure long-lasting and accurate measurements in various industries.

Radar level transmitters are non-contact measurement devices that use electromagnetic waves to measure the level of liquids and solids. Compared to ultrasonic and hydrostatic measurement methods, they provide higher accuracy and ensure reliable performance even under harsh process conditions.

Radar Level Transmitters

WORKING PRINCIPLE

Radar transmitters emit microwave signals toward the material surface and measure the time taken for the reflected signal to return.

Formula: d = (c × t) / 2

Where:
d: distance (m)
c: speed of light (3 × 10⁸ m/s)
t: round-trip time (s)

The difference between the tank height and this measured distance provides the actual material level. Modern 24 GHz and 80 GHz radar technologies offer superior resolution and narrower beam angles.

TYPES OF RADAR

  • Guided Wave Radar (GWR): Uses a probe or cable to guide the signal, ideal for tanks with foam, vapor, or dust.
  • Non-Contact Radar: Uses an antenna to transmit signals, suitable for high-pressure, high-temperature, and aggressive chemical environments.

STRUCTURAL FEATURES

  • Body materials: stainless steel, PTFE coating
  • Output signals: 4-20 mA, HART, Modbus, Profibus
  • Protection class: IP67 – IP68
  • Explosion-proof versions (ATEX & IECEx)
  • Accuracy up to ±2 mm

ADVANTAGES AND LIMITATIONS

Advantages:

  • Minimal influence from foam, vapor, and dust
  • High accuracy and reliability
  • Long measuring range (up to 70 m)
  • Withstands harsh process conditions

Limitations:

  • Proper antenna alignment and mounting are critical
  • Build-up on antenna surfaces may affect accuracy
  • Generally more expensive than ultrasonic methods

SELECTION CRITERIA

  • Tank height and geometry
  • Physical properties of the measured material
  • Process conditions (temperature, pressure, vapor, dust)
  • Communication protocol requirements
  • Desired measurement accuracy

APPLICATION AREAS

  • Chemical and petrochemical industries
  • Oil and gas storage tanks
  • Power plants
  • Food and beverage industry (hygienic design models)
  • Water and wastewater treatment plants

STANDARDS

  • IEC 61326 (electromagnetic compatibility)
  • ATEX & IECEx certifications (for explosive atmospheres)
  • EHEDG (hygienic design – food industry)

CONCLUSION

Radar level transmitters are among the most preferred measurement devices in modern industry due to their non-contact measurement capability, high accuracy, and robustness under challenging process conditions.

Hydrostatic level transmitters are devices that determine the liquid level in tanks by measuring pressure. As the liquid height increases, the hydrostatic pressure at the tank bottom rises. This pressure is measured by the transmitter and converted into an electrical signal to provide continuous level monitoring. They are widely used in applications such as water, chemicals, and food production.

Hydrostatic Level Transmitters

WORKING PRINCIPLE

The principle is based on the hydrostatic pressure exerted by the liquid column.

Formula: P = ρ × g × h

Where:
P: hydrostatic pressure (Pa)
ρ: liquid density (kg/m³)
g: gravitational acceleration (9.81 m/s²)
h: liquid height (m)

The transmitter at the bottom of the tank measures this pressure, processes it electronically, and converts it into level information.

STRUCTURAL FEATURES

  • Pressure sensing elements: piezoresistive or capacitive diaphragms
  • Body materials: stainless steel, titanium, PVDF
  • Output signals: 4-20 mA, HART, Modbus
  • Protection class: IP67–IP68
  • Temperature compensation for density variations

ADVANTAGES AND LIMITATIONS

Advantages:

  • High accuracy (±0.1%)
  • Unaffected by foam, vapor, or dust
  • Reliable performance in deep tanks
  • Continuous measurement capability

Limitations:

  • Density variations may cause errors
  • Not suitable for solid materials
  • Risk of diaphragm clogging
  • Requires periodic calibration

SELECTION CRITERIA

  • Type and density of the liquid
  • Tank depth and pressure range
  • Mounting type (submersible, flanged, threaded)
  • Environmental conditions (temperature, chemical resistance)
  • Required communication protocols and integration

APPLICATION AREAS

  • Water and wastewater treatment plants
  • Chemical and petrochemical industries
  • Food and beverage production
  • Power plants (cooling water reservoirs)
  • Agriculture and irrigation systems

STANDARDS

  • IEC 61298 (pressure devices)
  • ATEX & IECEx certifications (for explosive atmospheres)
  • EHEDG (hygienic design – food sector)

CONCLUSION

Hydrostatic level transmitters are among the most widely used level measurement devices in industry due to their reliability and accuracy. With proper selection and regular maintenance, they can operate flawlessly for years while enhancing process safety.

Ultrasonic level transmitters are non-contact measurement devices that use sound waves to determine the level of liquids and solids. They provide reliable measurement in tanks, silos, and open areas. Compared to radar, capacitive, or hydrostatic methods, they are often more cost-effective and easier to install, making them highly popular across industries.

Ultrasonic Level Transmitters

WORKING PRINCIPLE

The sensor emits ultrasonic pulses toward the material surface. The time taken for the waves to return is measured, and the distance is calculated to determine the level.

Basic formula: d = (c × t) / 2

Where:
d: distance (m)
c: speed of sound (343 m/s in air)
t: round-trip time (s)

The difference between tank height and this distance gives the material level.

STRUCTURAL FEATURES

  • Measuring range: 0.2 m – 70 m
  • Body materials: PVDF, stainless steel, PP
  • Output signals: 4-20 mA, HART, Modbus, Profibus
  • Protection class: IP67 – IP68
  • ATEX and IECEx certified models

ADVANTAGES AND LIMITATIONS

Advantages:

  • Non-contact measurement, no corrosion risk
  • Easy installation and minimal maintenance
  • Suitable for dusty and aggressive environments
  • Flexible for various tank geometries

Limitations:

  • Foam and vapor can affect measurement accuracy
  • Narrow tanks may cause reflection issues
  • Temperature fluctuations influence sound velocity

SELECTION CRITERIA

  • Tank height and geometry
  • Physical properties of the measured medium
  • Environmental conditions (temperature, pressure, humidity)
  • Communication protocols
  • Explosion-proof certifications (ATEX, IECEx)

APPLICATION AREAS

  • Water and wastewater treatment plants
  • Food and beverage industry
  • Chemical industry (corrosive liquid storage)
  • Cement and mining (solid storage silos)
  • Power plants (ash, coal, and liquid tanks)

STANDARDS

  • IEC 61010 (safety for measurement devices)
  • ATEX & IECEx certifications
  • NAMUR NE 107 (diagnostic status)

CONCLUSION

Ultrasonic level transmitters are widely used in industrial facilities due to their non-contact measurement advantages and durability. Proper selection and installation help reduce operating costs while increasing process reliability.

Pressure switches are control devices that open or close an electrical contact when a preset pressure level is reached. Due to their simplicity, they are widely used in both safety and automation applications. From pump protection to industrial process safety, they play a critical role in ensuring reliability.

WORKING PRINCIPLE

When pressure is applied on the diaphragm, it causes mechanical movement that actuates an electrical mechanism. This mechanism results in the opening or closing of contacts. The fundamental principle is based on the relationship between pressure, force, and area:

Formula: P = F / A

Where P: Pressure (Pa), F: Force (N), A: Area (m²).

STRUCTURAL FEATURES

  • Body materials: stainless steel, brass, plastic
  • Diaphragm materials: NBR, EPDM, stainless steel
  • Contact types: NO (normally open), NC (normally closed), SPDT
  • Electrical connection options and IP protection classes

TYPES

  • Mechanical pressure switches
  • Electronic/digital pressure switches (with display, microprocessor controlled)
  • Vacuum switches
  • Differential pressure switches

SELECTION CRITERIA

  • Measurement range (bar, psi)
  • Maximum operating pressure
  • Contact rating (AC/DC values)
  • Process connection (threaded, flanged)
  • Environmental conditions (temperature, vibration, humidity, ATEX certification)

ADVANTAGES AND LIMITATIONS

Advantages:

  • Simple and reliable operation
  • No energy required for mechanical types
  • Cost-effective
  • Wide application range

Limitations:

  • Lower accuracy in mechanical types
  • Wear and calibration needs
  • Higher cost for electronic models

APPLICATION AREAS

  • Pump and compressor protection
  • Pressure safety in hydraulic and pneumatic systems
  • Boilers and steam systems
  • Water treatment plants
  • HVAC and automotive applications

STANDARDS

  • IEC 60947 (low-voltage switchgear)
  • EN 60947-5-1 (switches)
  • ATEX certifications (for explosive atmospheres)

CONCLUSION

Pressure switches are cost-effective, reliable, and widely used control devices in critical applications. When properly selected, they provide indispensable protection for equipment and ensure process safety.

Smart pressure transmitters represent the evolution of traditional pressure measurement devices, integrating advanced sensors, microprocessors, and digital communication protocols. They not only measure pressure but also provide self-diagnostics, remote monitoring, and seamless integration with advanced control systems, enhancing process safety, energy efficiency, and reducing maintenance costs.

Pressure Transmitters

WORKING PRINCIPLE

Smart pressure transmitters operate by converting applied pressure into an electrical signal through a diaphragm and sensing element. The most common sensor technologies include:

  • Piezoresistive sensors
  • Capacitive sensors
  • Piezoelectric sensors
  • Strain gauge elements

The analog signals are digitized by microprocessors, processed, filtered, and then transmitted to control systems.

Basic equation:
P = F / A
P: Pressure (Pa)
F: Force (N)
A: Area (m²)

STRUCTURAL FEATURES

  • High-quality diaphragm materials (stainless steel, tantalum, monel, ceramic)
  • Microprocessor-based electronics
  • Output protocols: 4-20 mA, HART, Profibus, Fieldbus, Modbus, WirelessHART
  • Protection ratings: IP65 – IP68
  • Explosion-proof models (ATEX, IECEx)

SMART FUNCTIONS

  • Self-diagnosis for malfunction detection
  • Predictive maintenance
  • Remote monitoring and calibration
  • Data logging and trend analysis
  • Automatic zero/span adjustment
  • Integration with SCADA/DCS systems

SELECTION CRITERIA

  • Measurement range and accuracy
  • Process environment (temperature, pressure, chemical compatibility)
  • Communication protocols
  • Certifications (ATEX, SIL, CE)
  • Mounting options and mechanical strength

ADVANTAGES AND LIMITATIONS

Advantages:

  • High accuracy and long-term stability
  • Remote access and data analytics
  • Reduced maintenance costs
  • Ready for Industry 4.0 and IIoT integration

Limitations:

  • Higher initial cost
  • Requires specialized configuration
  • Cybersecurity risks

APPLICATION AREAS

  • Oil and gas industry (pipelines, refineries)
  • Chemical plants (reactor pressure monitoring)
  • Power plants (boiler and turbine monitoring)
  • Food and pharmaceutical industry (hygienic processes)
  • Water and wastewater treatment facilities

STANDARDS AND CALIBRATION

  • IEC 61508 (SIL certification)
  • NAMUR NE107 (diagnostic status)
  • ISO/IEC 17025 (calibration)
  • Hart and Fieldbus compliance standards

CONCLUSION

Smart pressure transmitters are essential devices for modern industrial automation, combining safety, efficiency, and digitalization. When properly selected and applied, they offer significant long-term benefits to industries.

Pressure transmitters are essential instruments used in industrial facilities to enhance process safety and efficiency. They convert pressure into standardized electrical signals (e.g., 4-20 mA) and transmit them to control systems. They are widely applied in oil and gas, chemical, energy, food, pharmaceutical, water, and wastewater industries.

WORKING PRINCIPLE

The operating principle of a pressure transmitter is based on the deformation or electrical variation caused by applied pressure. The main measurement technologies include:

  • Strain gauge: measures resistance changes due to diaphragm deformation.
  • Piezoresistive sensors: rely on resistance changes in semiconductor materials.
  • Capacitive sensors: measure capacitance changes as the diaphragm moves.
  • Piezoelectric sensors: generate voltage proportional to applied pressure.

Basic equation:
P = F / A
P: Pressure (Pa)
F: Force (N)
A: Area (m²).

This principle ensures accurate and repeatable conversion of applied pressure into electrical signals.

STRUCTURAL FEATURES

  • Housing: stainless steel, aluminum, or special alloys
  • Diaphragm: stainless steel, monel, tantalum, ceramic
  • Electronics: analog/digital signal processing
  • Output signals: 4-20 mA, HART, Fieldbus, Profibus
  • Protection ratings: IP65 – IP68
  • Explosion-proof models (ATEX, IECEx)

TYPES OF PRESSURE TRANSMITTERS

  • Gauge pressure transmitters: measure pressure relative to atmospheric pressure.
  • Absolute pressure transmitters: measure relative to a vacuum reference.
  • Differential pressure transmitters: measure pressure difference between two points, commonly used in flow measurement.
  • Multivariable transmitters: measure pressure, temperature, and flow simultaneously.

SELECTION CRITERIA

Key factors when selecting a pressure transmitter include:

  • Measurement range (rangeability)
  • Accuracy class
  • Process temperature and pressure
  • Material compatibility
  • Output communication protocols
  • Certifications (ATEX, SIL, CE)
  • Mounting type (flanged, threaded, manifold connection)

ADVANTAGES AND LIMITATIONS

Advantages:

  • High accuracy and reliability
  • Wide measurement range
  • Digital communication integration
  • Long-term stability

Limitations:

  • Regular calibration required
  • Special diaphragms needed for abrasive or high-temperature media
  • Can be costly depending on specifications

APPLICATION AREAS

  • Pressure monitoring in oil and gas pipelines
  • Reactor pressure in chemical plants
  • Boiler pressure in power plants
  • Pump pressure in water and wastewater plants
  • Hygienic pressure measurement in food and pharmaceutical industries

STANDARDS AND CALIBRATION

  • IEC 61508 (SIL – Safety Integrity Level)
  • NAMUR NE43 (fault signal handling)
  • ISO/IEC 17025 (calibration)
  • OIML R 117 (measurement standards)

Regular calibration is essential for maintaining reliable measurement over time.

CONCLUSION

Pressure transmitters are indispensable devices for industrial automation and process safety. When properly selected, they enhance both safety and efficiency in industrial operations.

Oval gear flowmeters are one of the most common types of positive displacement flowmeters. They operate on the principle of two oval-shaped gears rotating as fluid passes through them. Each rotation corresponds to a fixed volume, enabling highly accurate volumetric flow measurement. Their reliability with high-viscosity fluids makes them popular in chemical, petroleum, food, and pharmaceutical industries.

Oval Gear Flowmeters

WORKING PRINCIPLE

As the fluid flows through the meter, it rotates two intermeshing oval gears. Each rotation displaces a constant amount of fluid, which is detected by sensors. The total flow is calculated by multiplying the number of rotations by the volume per rotation.

Basic equation:
Qv = n · Vc
Qv: volumetric flow rate (m³/s)
n: gear rotation frequency (Hz)
Vc: displaced volume per rotation (m³).

Oval gear flowmeters are particularly effective for low flow rates and viscous fluids.

STRUCTURAL FEATURES

  • Body materials: stainless steel, aluminum, cast iron
  • Measuring element: two oval-shaped gears
  • Output signals: magnetic pickup, pulse, digital signals
  • High-pressure resistance
  • Low pressure drop and wide measuring range

ADVANTAGES AND LIMITATIONS

Advantages:

  • High accuracy (±0.1% – ±0.5%)
  • Reliable measurement at low flow rates
  • Excellent performance with viscous fluids
  • Compact and durable design

Limitations:

  • Requires maintenance due to moving parts
  • Reduced lifespan with abrasive or particulate fluids
  • Limited by high-temperature conditions

APPLICATION AREAS

  • Solvent and polymer measurement in chemical industries
  • Precise fuel and oil monitoring in petroleum industry
  • Syrup, honey, and oil measurement in food industry
  • Precise dosing in pharmaceutical industry
  • Lubrication systems in energy and automotive sectors

STANDARDS AND CALIBRATION

  • OIML R 117: International standard for liquid measuring devices
  • ISO/IEC 17025: Calibration laboratory accreditation
  • ATEX-certified models for explosive environments
  • Regular calibration is necessary to maintain accuracy

CONCLUSION

Oval gear flowmeters provide high accuracy and reliability, making them one of the most trusted solutions for industrial flow measurement. They are especially advantageous for measuring viscous fluids.

Piston flowmeters are positive displacement flowmeters designed to provide high-accuracy measurement. They measure fluid volume through a reciprocating piston mechanism, making them ideal for low flow rates and high-viscosity fluids. Due to their reliability, they are widely used in chemical, pharmaceutical, food, oil, and automotive industries.

WORKING PRINCIPLE

In piston flowmeters, fluid enters a chamber where a piston moves back and forth. Each piston stroke displaces a fixed volume of fluid, which is then counted by mechanical or electronic sensors. The total volumetric flow rate is determined based on the number of cycles.

Basic equation:
Qv = n · Vc
Qv: volumetric flow rate (m³/s)
n: piston stroke frequency (Hz)
Vc: displaced volume per stroke (m³).

This principle ensures high accuracy, even at very low flow rates, and is less sensitive to pressure fluctuations.

STRUCTURAL FEATURES

  • Body materials: stainless steel, aluminum, cast iron
  • Measuring element: piston-cylinder mechanism
  • Output signals: mechanical register, magnetic pickup, pulse output
  • High-pressure resistance
  • Low pressure drop and high repeatability

ADVANTAGES AND LIMITATIONS

Advantages:

  • Very high accuracy (±0.1% – ±0.5%)
  • Effective for low flow measurements
  • Reliable for viscous fluids
  • Durable and long-lasting design

Limitations:

  • Maintenance required due to moving parts
  • Reduced lifespan with abrasive or particulate fluids
  • Limited use in large-diameter pipelines

APPLICATION AREAS

  • Solvent, resin, and polymer measurement in chemical industries
  • Precise dosing in pharmaceuticals
  • Measurement of syrup, honey, and oils in food industry
  • Oil and fuel measurement in automotive industry
  • Lubrication systems and hydraulic applications in energy sector

STANDARDS AND CALIBRATION

  • OIML R 117: International standard for liquid measuring devices
  • ISO/IEC 17025: Calibration laboratory accreditation
  • ATEX-certified models for explosive environments
  • Regular calibration is essential for maintaining accuracy over time

CONCLUSION

Piston flowmeters are highly reliable in low-flow and high-viscosity conditions. They play a critical role in industries requiring precise dosing and accurate volumetric flow measurement.

Helical rotor flowmeters are a special type of positive displacement flowmeter. They operate based on the principle of axial helical rotors being rotated by the fluid flow. Each rotation of the rotor represents a fixed and known volume, ensuring high accuracy and repeatability. They are widely used in petroleum, chemical, pharmaceutical, and food industries, particularly for measuring high-viscosity fluids.

Helical Rotor Flowmeters

WORKING PRINCIPLE

As the fluid passes through the meter, it causes the helical rotors to rotate axially. The rotation displaces a fixed volume of fluid, which is measured to calculate volumetric flow.

Basic equation:
Qv = n · Vc
Qv: volumetric flow rate (m³/s)
n: rotor rotation frequency (Hz)
Vc: displaced volume per rotation (m³).

Helical rotor flowmeters are less affected by fluid density and viscosity, providing stable and accurate performance.

STRUCTURAL FEATURES

  • Body materials: stainless steel, cast iron, aluminum
  • Measuring elements: helical (screw-type) rotors
  • Output signals: magnetic pickup, pulse, digital signals
  • Low pressure drop
  • Excellent performance with high-viscosity fluids

ADVANTAGES AND LIMITATIONS

Advantages:

  • High accuracy (±0.2% – ±0.5%)
  • Reliable performance at low flow rates
  • Suitable for viscous and dense fluids
  • Minimal pressure loss

Limitations:

  • Moving parts require maintenance
  • Reduced lifespan with abrasive fluids
  • Less suitable for fluids containing solid particles

APPLICATION AREAS

  • Fuel and oil measurement
  • Polymer and solvent monitoring in chemical industries
  • Syrup, molasses, and honey measurement in food industry
  • Precise dosing in pharmaceutical applications
  • Lubrication systems in energy and automotive sectors

STANDARDS AND CALIBRATION

  • OIML R 117: Standard for liquid measuring devices
  • ISO/IEC 17025: Calibration laboratory accreditation
  • ATEX-certified models for explosive environments
  • Regular calibration is necessary to maintain accuracy

CONCLUSION

Helical rotor flowmeters play a vital role in industries requiring precise measurement of high-viscosity fluids. With their robust design, low pressure drop, and reliable accuracy, they provide long-term and dependable solutions for demanding industrial applications.