Guided Wave Radar

Guided wave radar (GWR) level measurement is a technology that uses electromagnetic pulses guided along a probe to continuously measure the level of liquids, slurries, or light solids inside a tank or vessel. The technology relies on time domain reflectometry (TDR), a proven measurement principle used across industrial process control.

How it differs from other level technologies:

• Contact-based: The probe extends into the process medium
• Guided Signal: Pulses travel along a physical probe instead of through open air
• Continuous output: Real-time level readings, not just point detection

Common industry terms for this technology include:

• Guided radar level transmitter
• TDR level sensor
• GWR transmitter

Guided wave radar is especially well-suited for tanks containing foam, turbulence, vapor, or fluctuating media — process conditions where alternative methods often struggle to deliver consistent accuracy. Its versatility and proven reliability make it a preferred choice across nearly every industrial sector. KOBOLD offers two distinct models in the NGM and NGR.

A guided wave radar level transmitter generates low-energy, high-frequency electromagnetic pulses along a probe that extends into the tank. When a pulse reaches the surface of the liquid or solid being measured, a portion of the energy is reflected back up the probe to the transmitter electronics.

The measurement sequence:

1. The transmitter emits a microwave pulse along the probe
2. When it contacts the material surface, part of the signal reflects back
3. Electronics measure the pulse's travel time (time-of-flight)
4. The transmitter converts this time into a precise level value

Because the pulse is physically guided along the probe, signal strength stays strong and the measurement remains stable even in challenging process conditions.

Time domain reflectometry (TDR) is the measurement principle that is utilized by guided wave radar level instruments. Originally developed to locate faults in telecommunications cables, TDR works by sending an electrical pulse down a conductor and analyzing the timing of any reflected signals.

In level measurement applications, TDR works like this:

• A low-energy electromagnetic pulse is sent down the probe
• When the pulse encounters a change in dielectric — typically the surface of a liquid or solid — part of the energy reflects back
• The instrument calculates distance by measuring the round-trip travel time

Why TDR is well-suited for level measurement:

• Speed of pulse propagation is well-known and predictable
• Reflection occurs at any dielectric discontinuity
• Pulse energy stays concentrated along the probe
• Accuracy holds regardless of medium density or pressure

Guided wave radar level transmitters offer a unique combination of accuracy, versatility, and low-maintenance operation that makes them well-suited for a wide range of industrial process applications.

Performance advantages:

• Independence from media properties — measurement is unaffected by density, temperature, pressure, humidity, and conductivity
• High accuracy — typically capable of measurements with millimeter-level precision
• Strong performance in tough conditions — handles foam, vapor, dust, and turbulent surfaces better than many alternatives

Operational advantages:

• No moving parts — eliminates mechanical wear and reduces failure modes
• Low maintenance — minimal calibration and servicing required after installation
• Versatile media compatibility — measures liquids, slurries, and light solids with a single instrument technology

Installation and integration advantages:

• Compact electronics housings simplify mounting in tight spaces
• Standard 4-20 mA output integrates with virtually any PLC or DCS
• Quick commissioning reduces startup time and labor costs

Guided wave radar is a contact-based level measurement technology. The probe physically extends into the tank and is in contact with the process medium during measurement. This distinguishes it from non-contact radar (also called free-space radar), which transmits microwaves through open vapor space above the liquid.

Why the contact-based design is an advantage:

• Concentrated signal energy along the probe means stronger, more reliable reflections
• Less affected by tank geometry — internal obstructions, agitators, and other tank components cause fewer interference issues
• Better with low dielectric media — the guided pulse retains energy better than free-space transmission
• More tolerant of foam, vapor, and turbulence — common deal-breakers for non-contact methods

When contact-based may not be ideal:

• Highly viscous, sticky, or crystallizing media that coat the probe
• Tanks with strong internal agitation or surface disruption
• Installations that physically stress the probe or tanks with moving internals that could damage the probe

For most industrial liquid-level applications, however, the contact-based approach delivers superior performance with high reliability.

Guided wave radar level transmitters typically come with a variety of different output options. 4-20 mA analog outputs are the most common but 0-10 V analog outputs, switching outputs, or IO-Link are also possible.

Standard output options found on most GWR transmitters:

• 4-20 mA analog — direct integration with PLC and DCS analog input cards
• 0-10 VDC analog — alternative analog signal option offered by some devices
• HART digital communication — overlaid on the 4-20 mA loop for diagnostics and configuration with the NGM
• Switching output (PNP) — for high/low level alarm or pump control functions
• IO-Link — Continuous level and multiple switching outputs with bidirectional communication for device parametrization and status alarms.
• Display interface — local indication and configuration without additional tools

Power supply considerations:

• Most units operate on 12-30 VDC with two-wire or four-wire configurations
  • Two-wire loop-powered designs simplify field wiring on the NGR
  • Four-wire designs typically support higher output flexibility on the NGM

Integration benefits:

• Compatible with virtually any modern process control system
• Compliant with NAMUR NE 43 fault signaling on the analog output (NGR)

Guided wave radar level transmitters are among the most accurate continuous level measurement technologies available, with modern instruments typically delivering precision in the millimeter range for most industrial applications.

Typical accuracy specifications:

• ±3 mm or ±0.03% of the measured value for the NGM
• ±5 mm for the NGR
• Specific accuracy varies by model, probe type, and process conditions

Factors that affect measurement accuracy:

• Dielectric constant of the medium — higher dielectric materials produce stronger reflections and better accuracy
• Probe type selected — coaxial probes generally deliver the highest accuracy
• Installation quality — proper mounting away from obstructions improves performance
• Medium conditions — heavy foam or severe turbulence may reduce precision

To achieve optimal accuracy:

• Follow manufacturer installation guidelines for nozzle size and clearance
• Follow procedures for configuration and calibration

The NGM can potentially be used for interface measurement between two immiscible liquids but with important limitations.

How interface measurement works with the NGM:

The lighter layer on top of the bottom layer attenuates signal detection, which causes the NGM to underestimate the total fill level. When the top layer exceeds 50 mm in thickness, a clear and reproducible separation layer can be detected.

Requirements for successful interface measurement:

• No mixing can occur — a stable, well-defined interface must be present
• The liquids must fully separate after filling, so a distinct interface forms
• The dielectric constant (DC value) of the upper liquid must be known
• The densities of the two liquids must differ sufficiently; densities that are too similar tend to form an emulsion rather than a clean separation
• The upper liquid layer must be greater than 50 mm thick for the interface to be reliably detected
• Gain parameters must be adjusted whenever fluid properties change

One of guided wave radar's greatest strengths is its ability to maintain reliable measurement in conditions that disrupt other level technologies. The guided pulse keeps signal energy focused along the probe, allowing the instrument to "see through" many common process disturbances.

Foam tolerance:

• Light, airy foam is generally transparent to the radar pulse — measurement continues uninterrupted
• Wet, conductive foam reflects the pulse, and the instrument typically measures the foam surface
• Heavy, dense foam may absorb signal energy and challenge measurement reliability

Vapor performance:

• Vapor space conditions have minimal effect on accuracy
• Pressure, humidity, and condensation do not interfere with the guided pulse
• The technology works reliably in steam, gas blankets, and inert vapor environments

Turbulence handling:

• Mild surface agitation is well-tolerated by most GWR probe types
• Severe agitation or vortex conditions may benefit from a stilling well or chamber
• Coaxial probes provide additional protection against lateral disturbances

The dielectric constant of the medium being measured is one of the most important parameters in guided wave radar applications. It determines how strongly the radar pulse reflects when it hits the material surface — and therefore how reliably the instrument can detect the level.

How dielectric constant affects measurement:

• High dielectric materials (e.g., water with a dielectric constant of ~80) produce strong, clean reflections and excellent measurement performance
• Medium dielectric materials (e.g., alcohols, solvents) work very well with most GWR probe configurations
• Low dielectric materials (e.g., light oils, hydrocarbons with values around 1.5–2.5) require careful probe selection
• Very low dielectric materials (below ~1.5) may need a concentric probe or stilling well

Practical guidance:

• Select a probe type that is suitable for the dielectric of the media being measured
• Account for dielectric variation with temperature in some applications
• For interface measurement, the upper layer's dielectric constant should be lower than the bottom layer's dielectric constant

Guided wave radar level transmitters are deployed across virtually every industrial sector that requires accurate continuous level measurement of liquids, slurries, or light solids. The technology's versatility makes it a go-to solution in a variety of industries.

Chemical processing:

• Storage tanks for raw materials, intermediates, and finished products
• Reactor vessels and batch processing tanks
• Solvent and acid storage where reliability is critical

Water and wastewater treatment:

• Clarifier and settling tank monitoring
• Chemical dosing tanks for treatment additives
• Sludge holding tanks and digesters

Oil and gas:

• Crude oil storage and separator vessels
• Produced-water tanks with oil-water interface measurement
• Refined product terminals and tank farms

Other common industries:

• Pulp and paper manufacturing
• Power generation, including feedwater tanks
• Mining and minerals processing

Yes — guided wave radar can measure a wide range of solid and bulk materials, though probe selection and installation must be tailored to the specific application. The technology is particularly effective for powders, granular materials, and other light solids.

Solids commonly measured with GWR:

• Powders like cement, flour, and chemical additives
• Granular materials including plastic pellets, grain, and fertilizer
• Aggregate materials such as sand and small-particle ores

Why GWR works well on solids:

• Immune to dust generated during filling and emptying
• Not affected by humidity, temperature, or bulk density variations
• Concentrated signal energy provides reliable echoes from material surfaces
• Continuous level reading enables accurate inventory management

Application considerations for solids:

• Cable probes are typically used for taller silos and bins
• Probe loading from material flow must be evaluated during selection
• Force exerted on the probe from the material weight must be considered
• Avoid materials with extremely low dielectric or heavy buildup tendencies

Guided wave radar level transmitters perform reliably across a remarkably wide range of vessel types, from compact day tanks to large storage silos. Their concentrated signal and contact-based probe design make them especially valuable in vessels where non-contact technologies struggle.

Ideal vessel applications:

• Tall, narrow tanks and silos — guided pulse holds signal strength over long distances
• Vessels with complex internal geometry — agitators, ladders, and supports cause minimal interference
• Bypass chambers and stilling wells — for tanks with strong agitation to separate the measurement from the tank conditions

Process conditions where GWR excels:

• High and low pressure vessels
• Tanks with significant temperature variation
• Vessels containing foaming, vaporous, or turbulent media
• Storage tanks with stratified layers requiring interface measurement

Less ideal applications include:

• Vessels with extreme agitation or moving parts that could damage probes
• Tanks containing sticky, crystallizing, or polymerizing media

Probe selection is one of the most important decisions in a guided wave radar application. The right probe matches your medium's properties, measurement range, and vessel geometry — and it directly impacts accuracy, reliability, and maintenance.

Rigid rod probes work best for:

• Liquids with moderate to high dielectric constants (typically ≥1.8)
• Measurement ranges generally up to about 20 feet
• Applications requiring high accuracy in clean, non-viscous media
• Smaller vessels where mechanical rigidity is needed

Flexible cable probes are ideal for:

• Tall vessels and silos where longer measurement ranges are required
• Bulk solids and powders
• Applications where rigid probe installation is impractical
• Larger ranges, often up to 65 feet or more

Coaxial probes are the best choice for:

• Very low dielectric media where signal concentration is essential
• Clean liquids without particles or coating possibility
• Applications with turbulence or wavy surfaces

Material selection for guided wave radar probes is critical because the probe contacts the process medium continuously. The right materials ensure long service life, chemical compatibility, and accurate measurement.

Standard wetted parts materials:

• 316L stainless steel — the most common probe material, with excellent corrosion resistance for general industrial use
• PTFE (Teflon) — used for seals and as a probe coating for highly corrosive media

Process connections commonly available:

• 3/4" NPT or G3/4 threaded — economical and quick to install
• ANSI flanges (1½" through 4") — for industrial process connections
• DIN flanges (DN40 through DN100) — for metric applications

The maximum measuring range of a guided wave radar transmitter depends on probe type, the dielectric properties of the medium, and the specific model. Modern GWR units offer ranges suiting applications from small day tanks to tall silos.

Typical measurement ranges by probe type:

• Rigid rod probes: generally up to about 10 feet for most models
• Flexible cable probes: available up to 65 feet for the NGM and up to 13 feet for the NGR, ideal for tall vessels and installations with limited clearance above the tank.
• Coaxial probes: Maximum lengths from 6.5 feet up to 20 feet depending on the model

Factors that affect achievable range:

• Dielectric constant of the medium — higher dielectrics support longer ranges
• Vessel internal conditions — heavy turbulence or foam may reduce effective range
• Probe loading in solids applications — physical stresses limit probe length
• Vapor space conditions — extreme pressure or temperature may affect performance

Proper installation is essential for accurate, reliable guided wave radar performance. While most modern GWR instruments are designed for straightforward installation, following best practices ensures optimal long-term operation.

Mounting considerations:

• Install the transmitter at the top of the vessel with the probe extending downward
• Maintain clearance above the vessel for probe insertion or removal
• Mount at least 6 inches from tank walls and away from agitators or inlets
• Use manufacturer-specified nozzle size to avoid signal interference

Probe positioning:

• Avoid mounting directly above inlet or outlet streams
• Keep the probe end at least 1–2 inches from the tank bottom
• For long flexible probes, anchor or weight the end to minimize swaying
• Position away from internal obstructions like ladders, baffles, or coils

Electrical and commissioning steps:

• Connect power and signal wiring per the diagram (typically 12-30 VDC, 4-20 mA)
• Configure the probe according to the specific operating manual. The basic configuration of the NGM is achieved by performing a disturbance signal scan and setting the lower range and upper range values. The NGR has an automatic configuration function for initial setup. The upper and lower range values can be set up by the user. Both models have advanced configuration options for low dielectric media, interfering tank components, extreme agitation, foam, or other deviations from ideal installations.

Guided wave radar level transmitters are engineered to operate across an exceptionally wide range of process temperatures and pressures, making them suitable for applications from cryogenic storage to high-temperature reactors.

Typical operating temperature ranges:

• Standard models: roughly -4°F to 212°F (-20°C to 100°C) for compact, general-purpose units
• Industrial models: approximately -40°F to 300°F (-40°C to 150°C) for demanding process environments
• Specialty configurations: available for cryogenic service down to extremely low temperatures of -328°F
• High-temperature designs: with extended electronics housings or remote separation for temperature up to 482°F

Typical operating pressure ranges:

• General-purpose units: atmospheric up to 145 PSIG for the NGR
• Process-grade transmitters: vacuum service up to roughly 580 PSIG or higher for the NGM

Important considerations:

• Temperature and pressure ratings depend on the probe materials and the process seal design
• Combined extreme conditions may require derating from individual maximums
• Verify that wetted parts, gaskets, and seals meet your specific requirements

Guided wave radar (GWR) and non-contact radar (also called free-space radar) are closely related technologies that solve different challenges. The right choice depends on your process conditions, vessel geometry, and measurement priorities.

Guided wave radar advantages:

• Better with low dielectric media — concentrated signal handles weak reflections
• Tolerant of foam and vapor — guided pulse cuts through interference
• Stronger in complex vessel geometries — obstructions cause less trouble
• Excellent for interface measurement between liquid layers

Non-contact radar advantages:

• No contact with media — preferred for sticky or sensitive products
• Longer measurement ranges — often suitable for very tall tanks
• Simpler installation — no probe insertion or anchoring required
• Easier maintenance — no submerged components to clean

When to choose which:

• Choose GWR for foam, vapor, low-dielectric liquids, interfaces, or complex tanks
• Choose non-contact radar for large open vessels, very tall tanks, or media that fouls probes

Choosing a Made-in-USA guided wave radar level transmitter offers tangible advantages that go beyond country-of-origin labeling. For industrial buyers, US manufacturing means faster delivery, better support, and federal compliance.

Practical benefits of US manufacturing:

• Shorter lead times — domestic production avoids overseas shipping delays
• Better technical support — US-based engineering and service teams in your time zone
• Faster spare parts availability — replacement components ship from domestic stock
• Easier customization — proximity simplifies engineered modifications

Regulatory and procurement advantages:

• BABA (Build America, Buy America) compliance — required for many federally funded infrastructure projects
• Domestic supply chain visibility — reduces tariff exposure and geopolitical risk

Quality and engineering value:

• US manufacturing standards for materials, machining, and assembly
• Application engineering support from teams familiar with US codes, standards, and industry practices