Ultrasonic Level Transmitter for Tanks – NUS-4

The NUS-4 is an ultrasonic level transmitter that provides non-contact, continuous measurement of level, volume, and open-channel flow using time-of-flight ultrasonic technology. A compact sensor and integrated electronics measure how long an ultrasonic pulse takes to reach the surface and return, then convert that time into level. Wetted parts are polypropylene or PVDF, so the transmitter is designed for corrosive, contaminating, or adhesive liquids where contact sensors are difficult to use.

How the NUS-4 ultrasonic level transmitter works

The sensor emits an ultrasonic pulse train and receives the echoes reflected from the surface. The integrated electronics select the surface echo and calculate distance from the time of flight, then output the level. A narrow beam of 5 to 7 degrees at -3 dB is designed to keep measurement reliable in narrow silos and in tanks with protruding objects.

Because it is non-contact, the transmitter suits applications where no physical contact can be established with the medium, including corrosive acids, contaminated or sewage-bearing liquids, and adhesive materials. The focused beam helps the signal penetrate gases, vapor, and foam.

Measuring range, accuracy, and resolution

The NUS-4 measures liquids up to 80 ft (25 m) and solids up to 33 ft (10 m), with accuracy of ±(0.2% of reading + 0.05% of full scale) at 68°F (20°C). Six sensor versions cover progressively longer spans, and resolution tightens at shorter distances.

NUS-4x04: 0.66 to 13.1 ft (0.2 to 4 m)
NUS-4x06: 0.82 to 19.7 ft (0.25 to 6 m)
NUS-4x08: 1.15 to 26.2 ft (0.35 to 8 m)
NUS-4x10: 1.15 to 32.8 ft (0.35 to 10 m)
NUS-4x15: 1.48 to 49.2 ft (0.45 to 15 m)
NUS-4x25: 1.97 to 82 ft (0.6 to 25 m)

Resolution is 0.04 in (1 mm) below 2 m, 0.08 in (2 mm) from 2 to 5 m, 0.2 in (5 mm) from 6 to 10 m, and 0.4 in (10 mm) above 10 m.

Wetted materials, temperature, and pressure

Wetted parts are polypropylene or PVDF and the housing is powder-coated aluminum. Process temperature ranges from -22°F to 194°F (-30°C to 90°C) and pressure reaches 40 PSIA. Ambient temperature is -22°F to 158°F (-30°C to 70°C), or -13°F to 158°F (-25°C to 70°C) with the plug-in programming unit. Sensor ingress protection is IP 68 and the housing is IP 67.

Outputs and electrical connection

The transmitter provides a 4-20 mA, 2-wire analog output (3.9 to 20.5 mA), with HART and an SPDT relay rated 30 Vdc, 1 A available. Power is 12 to 36 Vdc with reverse-polarity protection, and the output is galvanically isolated and surge protected with a maximum load of 600 ohms. Wiring uses two M20 x 1.5 cable glands for 0.24 to 0.47 in (6 to 12 mm) cable plus two 1/2 in NPT entries, with 0.5 to 1.5 mm² conductors.

Volume and open-channel flow measurement

Beyond level, the NUS-4 can be set for volume using pre-programmed tank shapes and for open-channel flow using pre-programmed primary elements. A 32-point linearization table supports custom tank profiles and flow curves. Flow accuracy depends on the primary element and is lower than the distance-measurement figure.

Supported primary elements include the Parshall and Khafagi-Venturi flumes, Palmer-Bowlus flumes in D/2, D/3, and rectangular forms, and V-notch (Thomson 90 degree), suppressed rectangular or BAZIN, trapezoidal, special trapezoidal, bottom-step, and circular weirs.

Installation and mounting

Process connections range from 1-1/2 in and 2 in NPT and G threads to ANSI 3, 5, and 6 in and DN 80, DN 125, and DN 150 flanges. Mount the sensor vertical to the product surface and high enough that the block, or dead-zone, distance is never entered at full tank. Position the sensor on the tank radius, keep its face parallel to the surface within about 2 to 3 degrees, keep the beam cone clear of pipes, ladders, and other obstacles, and shield the transmitter from direct sun. Tightening torque is 20 Nm and the housing rotates up to 350 degrees.

Display, programming, and diagnostics

An optional NUS-400P plug-in unit adds a 6-digit LCD with symbols and a bar graph for local display and configuration. Programmable functions include engineering units, 4 and 20 mA assignment, damping of 10, 30, or 60 seconds, measurement mode, close-end and far-end blocking, linearization, totalizers, simulation, and keyword protection. Read-out parameters report the echo map, transducer temperature, and a signal-to-noise ratio, and error codes cover echo loss, sensor or mounting faults, and linearization conditions.

Applications

The NUS-4 is used for continuous level and volume monitoring in open and closed vessels and for flow measurement in open channels. Typical applications include chemical storage, water and wastewater treatment, fuel and petroleum storage, food and beverage tanks, clarifiers, buffer tanks, and CIP systems, as well as corrosive, viscous, contaminated, and hygienic media. For heavy foam, dense fumes, or windy outdoor service, lower-frequency versions (40 or 20 kHz) are designed to help, and a stilling pipe or well can improve reflection.

Common Questions about NUS-4 - Ultrasonic Level Transmitter

The NUS-4 is a 2-wire, 12 to 36 Vdc device delivering 4-20 mA (3.9 to 20.5 mA). Options add HART communication and a relay (SPDT, 30 Vdc, 1 A). The signal is galvanically isolated and surge protected, driving up to 600 ohms of loop resistance.

It operates from -22°F to 194°F (-30°C to 90°C) at pressures up to 40 PSIA. Environmental protection is rated IP 68 at the sensor and IP 67 at the housing. A threaded unit weighs about 2.5 lb and a flanged unit about 5.6 lb.

Directly below the sensor is a dead zone where echoes cannot be received, so the device must sit above it at full tank. The minimum block distance runs from 0.66 ft (0.2 m) on the shortest version to 1.97 ft (0.6 m) on the longest, and programming can extend it.

Threaded models use 1-1/2 in or 2 in NPT, or G 1-1/2 or G 2. Flanged models use ANSI 3, 5, or 6 in, or DN 80, DN 125, or DN 150. G-thread versions include a counter-nut and EPDM gasket. The connection pairs with the sensor range you order.

Yes. It supports pre-programmed weirs and flumes selected through the programming unit, and a 32-point linearization table handles profiles outside the standard set. Because the primary element sets the accuracy, flow readings are less precise than direct level, and the sensor mounts just above the maximum expected water level.

An optional NUS-400P plug-in provides a 6-digit LCD and bar graph for on-site readings and setup. You can set units, span, damping, tank and channel forms, linearization, totalizers, and simulation, and lock access with a secret code. Up to 15 transmitters can share one HART multidrop network.

An order number sets sensor material (0 = polypropylene, 9 = PVDF), the range and connection (for example N8 = 1-1/2 in NPT), the power (3 = 12 to 36 Vdc), and the output (40 = 4-20 mA; R0 adds a relay; 4H adds HART; RH adds both; 4P or RP add the plug-in display). A sample code is NUS-4004 N8 340.

No Echo indicates that no reflection returned, often from foam, a highly disturbed surface, or a mounting issue. Try relocating the sensor for a clear line of sight, confirm its face is within 2 to 3 degrees of the surface, and recheck the programmed measuring range. A signal-to-noise ratio below 30 signals unreliable conditions.