What is the NRE-4 non-contact radar level transmitter?
The NRE-4 is a radar level transmitter that uses 80 GHz FMCW (frequency modulated continuous wave) radar to measure the level of liquids and solids without touching the medium. It reports distance and calculates level, volume, mass, and flow, with a range up to 98.5 ft (30 m) and accuracy up to ±0.078" (±2 mm).
Operating at 80 GHz (W-band) gives a smaller antenna, better focusing, and a narrower beam than lower-frequency 5 to 12 GHz and 25 GHz radars. The compact antenna eases installation, and a plug-in NRM-300P graphic display module can be added.
How the 80 GHz FMCW radar works
The transmitter emits a continuous, frequency modulated 80 GHz signal and calculates distance from the time of flight of the echo returned by the product surface. Because millimeter waves travel at a nearly constant speed in air, gases, and vacuum, the measured distance does not depend on process temperature or pressure.
Reflection depends on the medium's dielectric constant, which must be above 1.9. Because no medium is needed for the waves to propagate, the NRE-4 can also operate in a vacuum.
Measuring range, accuracy, and resolution
The NRE-4 measures up to 98.5 ft (30 m) with accuracy up to ±0.078" (±2 mm) and a resolution of 0.0039" (0.1 mm). The minimum beam angle is 7 degrees and the measuring cycle is about 1 second. Range and accuracy depend on the selected model and antenna:
- 1 inch antenna (NRE-41xx R25 or N25): up to 33 ft (10 m), accuracy ±0.197" (±5 mm), 12 degree beam angle.
- 1½ inch antenna (NRE-41xx R40 or N40): up to 33 ft (10 m), accuracy ±0.197" (±5 mm), 7 degree beam angle.
- 1½ inch antenna (NRE-42xx R40 or N40): up to 66 ft (20 m), accuracy ±0.078" (±2 mm), 7 degree beam angle.
Stated accuracy assumes an ideal reflecting surface and can be limited by low dielectric constant or non-perpendicular, non-planar media.
Media, applications, and industries
The NRE-4 is designed to measure liquids, emulsions, chemicals, and large-particle bulk solids, including substances prone to vapor formation and liquids under a gas blanket. It suits storage tanks, open pits, sumps, and wells, can measure through a plastic tank roof, and supports open-channel flow measurement.
- Water and wastewater
- Energy and plant utilities
- Food and beverage
- Chemical and pharmaceutical
- Agriculture
- Construction materials
- Heavy industry
- Packaging
Millimeter-wave measurement is less suited to media with a dielectric constant below 1.9, to highly agitated surfaces, and to narrow tanks with internal obstructions.
Ratings, materials, and connections
The standard design operates from -40 to +176°F (-40 to +80°C), and a high-temperature design extends to +356°F (+180°C). Process pressure reaches -14.5 to 580 psi (-1 to 40 bar) with stainless steel antennas, or -14.5 to 43.5 psi (-1 to 3 bar) with PP, PVDF, and PTFE antennas. Ingress protection is IP 67.
Antennas come in 1.4571 stainless steel or plastic (PP, PVDF, PTFE), sized 1 inch (25.4 mm) or 1½ inch (38.1 mm). Threaded connections cover 1 inch and 1½ inch BSP or NPT, with flanges from 3 to 12 inches in DIN, ANSI, and JIS. Housings are plastic (PBT), painted aluminium, or stainless steel.
Power, output, and communication
The NRE-4 is a 2-wire device with a supply voltage of 12.5 to 36 VDC and a 4 to 20 mA output with HART. An optional SPDT relay is rated 30 V / 1 A DC and 42 V / 0.5 A AC, and the recommended HART loop resistance is 250 ohms.
In current mode the NRE-4 works as a point-to-point HART device, and in multidrop mode up to 15 units can share one HART loop.
Installation and positioning
The NRE-4 mounts in a fixed, antenna-down position. On a cylindrical tank the suggested location is at 0.3 to 0.5 of the tank radius, with the process connection parallel to the product surface within about 2 to 3 degrees, and set away from the inlet.
- Keep pipes, ladders, and other obstacles out of the radiation cone; up to four interfering echoes can be masked in the threshold settings.
- Allow at least 3.9 inch (100 mm) of product over convex or conical tank bottoms and bottom-mounted equipment for reliable measurement.
- Protect the sensor from direct sunlight to keep it within the permitted temperature.
- Mount where foam formation is smallest, since foam can interfere with millimeter-wave measurement.
Hazardous-area approval
The NRE-4 is available in ATEX intrinsically safe (Ex ia) versions for gas and dust atmospheres. Standard versions are marked II 1 G Ex ia IIC T6 Ga and II 1 D Ex ia IIIC T85°C Da, and high-temperature versions cover temperature classes T6 through T3, up to a +356°F (+180°C) process temperature. IECEx options are also available.
Common Questions about NRE-4 - Non-Contact Radar Level Transmitter - Expert Line
It transmits a frequency modulated 80 GHz beam and analyzes the frequency shift of the echo returning from the surface, converting the signal's travel time into a distance. The electronics then turn that distance into a level reading and, where configured, into volume, mass, or open-channel flow values.
Depending on model and antenna, the device reaches up to 98.5 ft (30 m). The 20 m and 30 m versions offer accuracy of ±0.078" (±2 mm), while the 10 m versions offer ±0.197" (±5 mm). Measurement resolution is 0.0039" (0.1 mm).
Because the reading relies on a reflected signal, the medium should have a dielectric constant (εr) above 1.9. For reference, water sits near 80, ethyl alcohol near 24, acetone near 21, and LP gas near 1.6 to 1.9. Media below 1.9 may reduce range or accuracy.
Standard builds cover -40 to +176°F (-40 to +80°C); the high-temperature version reaches +356°F (+180°C). Stainless steel antennas allow -14.5 to 580 psi (-1 to 40 bar), while plastic PP, PVDF, and PTFE antennas are rated -14.5 to 43.5 psi (-1 to 3 bar).
The transmitter runs on a 2-wire loop at 12.5 to 36 VDC and delivers a 4 to 20 mA signal with HART. A relay option (SPDT) switches 30 V / 1 A DC and 42 V / 0.5 A AC. For HART, a loop resistance near 250 ohms is recommended.
Antenna choices are 1.4571 stainless steel or plastic in PP, PVDF, or PTFE, sized 1 inch (25.4 mm) or 1½ inch (38.1 mm). Threaded ports are 1 inch or 1½ inch in BSP and NPT, and flanges span 3 to 12 inches across DIN, ANSI, and JIS standards.
Fit it facing down in a fixed spot, ideally at 0.3 to 0.5 of a cylindrical tank's radius, with the antenna face aligned to the surface within roughly 2 to 3 degrees. Keep it away from the fill inlet and from any obstacle that would sit inside the beam.
Yes. Intrinsically safe ATEX (Ex ia) versions are offered for both gas and dust zones, with IECEx variants also available. Standard units carry a T6 (T85°C) rating, and high-temperature units span classes T6 through T3, reaching +356°F (+180°C). Each must be powered from a circuit that matches its intrinsic-safety data.
The code sets model, range (1 = 10 m, 2 = 20 m, 3 = 30 m), version (S standard or H high-temperature to +180°C), antenna and housing material, process connection, and the output, display, and approval option. Some connections are range-specific: R25 and N25 serve 10 m, and D75 serves 30 m.
Programming is done with the plug-in NRM-300P graphic display or with KOBOLD NUS-NTB-NRM-SW software over HART. These show distance, level, volume, and mass and open the threshold and echo settings. As many as 15 devices can run together in one multidrop HART loop.