Guided Wave Radar Level Transmitter – NGM

The KOBOLD NGM is a guided wave radar level transmitter that uses Time Domain Reflectometry (TDR) to measure liquids and light solids up to 65.6 ft (20 m), independent of density, temperature, pressure, humidity, or conductivity.

Made in the USA, with BABA compliant models available, the NGM pairs a programmable 4-20 mA analog output with an active PNP switching output, making it the perfect solution for industries requiring reliable continuous level measurement and point level detection in bypass chambers, stilling wells, and tanks with difficult geometries.

The NGM can be mounted in small tanks and in tall, narrow nozzles, and it measures precisely even in proximity to interfering structures. Fully modular probes, factory configuration, and complete galvanic isolation keep installation and startup simple.

How Guided Wave Radar Level Measurement Works

Guided wave radar works by propagating low-energy, high-frequency electromagnetic impulses along a probe immersed in the liquid or solid being measured. When the impulses hit the surface of the media, part of the impulse energy is reflected back up the probe, and the circuitry calculates the level from the time difference between the impulses sent and the impulses reflected.

This measuring principle enables direct, precise, and highly reliable measurement in almost every liquid or light solid application, independent of changing process conditions such as density, conductivity, temperature, pressure, or air humidity. A 4-wire design and innovative signal analysis with disturbance signal suppression contribute to dependable readings, according to specifications.

NGM Performance According to Specifications

The NGM measures with an accuracy of plus or minus 3 mm or 0.03% of measured distance, whichever is greater, with repeatability under 2 mm and resolution under 1 mm. Response time is 0.5 seconds by default, with 2 second and 5 second settings selectable.

Measuring length: up to 9.8 ft (3 m) with the single rod probe, 19.5 ft (6 m) with the concentric probe, and 65.6 ft (20 m) with the wire rope probe
Media temperature: -40 to 302 °F (-40 to 150 °C) for standard versions, depending on probe and O-ring; -328 to 482 °F (-200 to 250 °C) for high temperature versions
Operating pressure: -14.5 to 580 PSIG, or 0 to 58 PSIG for the PTFE coated NGM-19
Minimum media dielectric constant: greater than 1.8 for rod and rope probes, greater than 1.4 for the concentric probe
Viscosity: up to 5,000 cP with rod and rope probes, up to 500 cP with the concentric probe
Ambient temperature: -10 to 176 °F (-23 to 80 °C) for electronics and housing, with IP68 protection
Wetted parts: 316 grade stainless steel and PEEK, with PTFE and O-ring options set by order code

Three Probe Types, One Modular Design

The NGM has a flexible modular concept: single rod, wire rope, and concentric probes are joined to the housing by one universal feed-through, so any probe can be used with any housing, and probe types are interchangeable without any special tools or welding. Choosing the right probe matches the sensor to the tank geometry and the media.

Single rod, to 9.8 ft (3 m): recommended for liquid applications in bypass chambers and stilling wells, and well suited to viscous, fibrous, or particle-laden liquids
Wire rope, to 65.6 ft (20 m): recommended for light solids and for liquids in tall tanks where limited headroom is available
Concentric, to 19.5 ft (6 m): the measurement signal is completely contained within the outer tube, making the probe immune to external conditions and interfering objects; recommended for clean liquids only, and the ideal choice for low reflectivity liquids such as oils and hydrocarbons

Outputs, Wiring, and Configuration

The NGM is a 4-wire system powered by 12 to 30 VDC, with one pair of wires for the power supply and a separate pair for each output. It provides a 4-20 mA analog output programmable by HART modem and an active DC PNP switching output, configurable normally closed or normally open.

Every unit is supplied factory-set with the specific operating parameters given at ordering, so the physical installation is essentially a plug and play operation. Basic in-field configuration uses an internal DIP switch, a single push button, and visual LED feedback; advanced setup and extensive diagnostics run through the HARTCOM-0 HART modem with a provided spreadsheet.

The electronics are completely galvanically isolated from the inputs, outputs, and tank potential, which helps avoid problems with the electrochemical corrosion protection of the tank.

Made in the USA and BABA Compliant

The NGM guided wave radar level transmitter is made in the USA, and BABA (Build America, Buy America) compliant models are available. For projects that must document compliance, KOBOLD USA can identify the specific model configurations that meet BABA requirements as part of a quote.

Common Questions about NGM - Guided Wave Radar Level Transmitter

TDR stands for Time Domain Reflectometry, a measuring principle also known as Guided Microwave or Guided Wave Radar. The sensor's electronics generate the impulses, evaluate the portion of energy returned from the media surface, and can output the analysed level as an analog signal or convert it into a freely programmable switching signal.

Measuring length depends on the probe: 65.6 ft (20 m) for wire rope, 19.5 ft (6 m) standard for concentric, and 9.8 ft (3 m) for single rod. Probe length and measuring range are not equal: TDR sensors have small inactive areas at the top and bottom of the probe, so the measuring range sits between them.

KOBOLD's application guide recommends the concentric probe when mounting close to tank walls, internal structures, or non-stationary interference targets such as agitator blades; the wire rope probe for bulk solids and tall tanks with limited headroom; and the rod or rope probes for viscous, fibrous, sticky, or particle-laden liquids where probe cleaning matters.

Yes. Performance in low reflectivity media, meaning a low dielectric constant, is a strength of the design: rod and rope probes measure media with dielectric constants above 1.8, and the concentric probe, which concentrates the signal inside its tube, measures media down to dielectric constants above 1.4, including oils and hydrocarbons.

According to specifications, an oil layer less than 2.8 in (7.1 cm) on top of water is not detected, and the sensor reads the level at a slightly lower position than actual. For an oil layer greater than 2.8 in, the sensor detects the total level, including the oil layer.

Two outputs run on separate wire pairs: an analog 4-20 mA signal adjustable via a HART modem, and a DC PNP transistor switch, normally closed by default or normally open, short-circuit protected, with load current under 200 mA and switching response time under 100 ms.

Standard versions cover media from -40 to 302 °F, with exact limits set by probe type and O-ring, while high temperature versions extend the range to -328 to 482 °F. Pressure ratings run from -14.5 to 580 PSIG, and the PTFE coated NGM-19 is rated 0 to 58 PSIG.

Yes. Ordering the E4 output option provides an ATEX version carrying gas and dust markings, including II 1/2G Ex ia/db IIC T6 Ga/Gb and II 1/2D Ex ia/tb IIIC T86 °C IP68 Da/Db. Every version of the transmitter also carries IP68 ingress protection.

Yes. KOBOLD manufactures the NGM in the USA, and versions that comply with BABA (Build America, Buy America) are available. When requesting a quote, ask KOBOLD USA to identify the compliant model configuration that matches your measuring length, probe type, and process connection.

The transmitter installs vertically, and each unit arrives configured at the factory with the parameters given at ordering, so startup is essentially plug and play. Rod and rope probes need nozzle diameters over 2 in (50 mm) and at least 3.9 in (100 mm) of clearance to tank internals; the concentric probe has no such restrictions.