Inline Viscometer — LONN ND80 Vibrating Fork Viscometer-high-temp

The LONN ND80 inline viscometer is a rugged, flange-mounted industrial viscometer that delivers continuous, real-time viscosity measurement directly in the process line. Using the proven vibrating fork viscometer principle, this inline viscometer generates a viscosity reading from the damping effect of the fluid on a resonating fork — no moving parts, no bearings, no seals, and no radioactive sources.

Designed for demanding process environments, the LONN ND80 inline rotational viscometer alternative provides the same continuous inline measurement that traditional inline systems deliver, but with the reliability advantage of a solid-state vibrating sensor. The instrument simultaneously outputs viscosity and temperature via dual 4-20mA analog signals plus RS485 Modbus RTU digital communication, giving your control system both process parameters from a single flange penetration.

This tuning fork viscosity meter is housed in an explosion-proof enclosure with a flameproof Ex-rated cover, making it suitable for Zone 1 and Zone 2 hazardous areas in oil refineries, chemical plants, and gas processing facilities. The ANSI 150LB RF flange connection integrates directly into standard process piping, and the 60mm insertion depth positions the fork tines in the fluid stream for accurate real-time measurement. Whether you need a liquid viscosity meter for crude oil monitoring, polymer melt tracking, or chemical batch quality control, the LONN ND80 delivers the performance and reliability your process requires.

Why Choose the LONN ND80 Inline Viscometer?

Vibrating Fork Technology — No Moving Parts, No Maintenance

Traditional inline viscosity measurement methods rely on rotational elements, capillary tubes, or falling piston mechanisms — all of which introduce mechanical wear, fouling, and maintenance demands. The LONN ND80 vibrating fork viscometer eliminates these problems entirely. The fork tines are driven by piezoelectric crystals at their resonant frequency; as the fluid viscosity changes, the damping on the fork shifts, and the onboard microprocessor converts this shift into a precise viscosity reading. With no rotating seal, no motor bearings, and no narrow flow passages to clog, this vibrating fork viscometer runs maintenance-free for extended periods — reducing your total cost of ownership compared to rotational viscometer inline systems that require periodic seal replacement and bearing service.

Dual Parameter Output — Viscosity and Temperature Simultaneously

Process viscosity rarely tells the full story — temperature has a direct and significant effect on fluid viscosity, and accurate process control requires both parameters. The LONN ND80 delivers both: viscosity via the first 4-20mA channel and temperature via the second 4-20mA channel, plus both values available through RS485 Modbus RTU. This dual-output capability means you can monitor viscosity trends while tracking temperature correlation — invaluable for processes where viscosity specification limits shift with operating temperature.

Flange Mount Design — Direct Process Integration

The LONN ND80 features an ANSI 150LB RF flange as the standard process connection (DN50), integrating directly into existing piping without custom adapters. The flange mount eliminates the need for bypass loops, sampling lines, or specialized flow-through cells — simply install the instrument on a mating flange on your pipeline or vessel, and the fork sensor inserts 60mm into the fluid stream for representative inline measurement. This inline viscometer is designed as a direct replacement for legacy inline rotational viscometer installations using the same flange footprint.

High Temperature Capability — Up to 400°C

Process fluids at elevated temperatures — hot polymer melts, heated crude oil, distillation column bottoms, and thermal fluids — require a liquid viscosity meter that can handle the heat. The LONN ND80’s wetted parts and sensor assembly withstand continuous operating temperatures up to 400°C. The integrated heat dissipation section between the process flange and the electronics housing keeps the transmitter components within their rated temperature range while the sensor fork monitors the hot process fluid. For standard process temperatures up to 200°C, the LONN ND operates within its normal accuracy specification of ±1% FS; for extended temperature ranges up to 400°C, accuracy is maintained at ±3% FS.

Explosion Proof — Certified for Hazardous Areas

The LONN ND80 carries Ex flameproof certification (Ex d), verified by the prominent Ex marking on the enclosure cover. The heavy-duty housing contains any internal ignition, preventing propagation to the surrounding explosive atmosphere. This makes the LONN ND80 suitable for Zone 1 and Zone 2 hazardous areas in oil and gas facilities, petrochemical plants, refineries, and any environment where flammable gases, vapors, or airborne particulates may be present.

Technical Specifications — Inline Viscometer

The LONN ND80 inline viscometer is part of the LONNMETER industrial instrument family. For applications requiring a split-body design where electronics must be separated from the process connection, consider the LONN-DN100 split type viscometer. For integrated, high-viscosity-range process monitoring up to 5,000,000 cP, the LONN-DN60 online viscometer offers a wider measurement span.

Line Viscometer Applications by Industry

Oil & Gas — Inline Viscometer for Crude Monitoring

Crude oil viscosity is a critical parameter for pipeline flow assurance, pump scheduling, and refinery feed quality. The LONN ND80 inline viscometer mounts directly on crude pipelines, tank farm manifolds, and process heater inlets to provide real-time viscosity data. The ANSI flange connection mates with standard piping, and the flameproof Ex certification enables safe installation in Class I Division 1 hazardous locations.

Oil & gas applications:

• Crude oil viscosity monitoring at pipeline receiving stations
• Heavy fuel oil viscosity for burner optimization
• Lubricating oil viscosity at blending and loading
• Diluent ratio monitoring in heavy oil transport
• Asphalt viscosity at terminal storage and loading

Chemical Processing — Vibrating Fork Viscometer

Chemical reactors, blending vessels, and distillation columns demand continuous viscosity data for reaction monitoring, product quality control, and endpoint detection. The LONN ND80 vibrating fork viscometer handles aggressive chemical media with 316L stainless steel or optional Hastelloy C wetted parts. The dual 4-20mA output provides both viscosity and temperature, allowing operators to correlate the two parameters for process optimization.

Chemical applications:

• Polymerization reaction viscosity tracking
• Solvent concentration monitoring in distillation
• Acid and caustic solution viscosity verification
• Resin and adhesive viscosity during synthesis
• Surfactant and emulsifier quality control

Power Generation — Liquid Viscosity Meter

Power plants rely on heavy fuel oil, diesel, and lubricating oils that must maintain specific viscosity ranges for proper atomization, combustion efficiency, and equipment protection. The LONN ND liquid viscosity meter continuously verifies fuel and lube oil viscosity at the point of use, providing early warning of off-spec conditions before they affect boiler performance or turbine reliability.

Power generation applications:

• Heavy fuel oil viscosity for burner injection
• Diesel viscosity monitoring for emergency generators
• Turbine lube oil viscosity tracking
• Hydraulic oil condition monitoring
• Cooling tower chemical injection verification

Marine & Offshore — Inline Rotational Viscometer Alternative

Marine vessels and offshore platforms operate with limited maintenance access and harsh environmental conditions — exactly the scenario where the LONN ND80’s vibrating fork inline viscometer technology outperforms rotational viscometer inline systems. The solid-state design eliminates bearing wear and seal leaks common with rotational systems, while the IP65-rated housing resists salt spray and moisture ingress.

Marine applications:

• Bunker fuel viscosity monitoring
• Lube oil condition tracking in main engines
• Hydraulic system oil verification
• Bilge water quality monitoring
• Cooling water additive viscosity

Pulp & Paper — Inline Viscometer

Pulp slurries, coating formulations, and adhesive preparation require tight viscosity control for consistent product quality and coating uniformity. The LONN ND80 inline viscometer provides continuous measurement directly in the process line, eliminating the lag time and sampling inconsistency of laboratory testing.

Pulp & paper applications:

• Coating color viscosity monitoring
• Starch slurry viscosity at sizing presses
• Adhesive viscosity at laminating lines
• Black liquor viscosity tracking
• Bleach chemical monitoring

Installation Guidelines for Inline Viscometer

For reliable measurement with the LONN ND80 inline viscometer, follow these installation practices:

1. Flange mounting: Install the mating flange on the process pipe or vessel in a location with full pipe flow — avoid dead legs, elbows immediately upstream, and partially filled horizontal pipe sections where the sensor fork may not be fully immersed
2. Insertion orientation: Verify that the fork tines are fully immersed in the process fluid at all operating levels — the 60mm insertion depth positions the sensing element well into the pipe bore on standard DN50 and larger pipe sizes
3. Flow conditions: Install with the fork tines oriented perpendicular to the flow direction for optimal fluid exchange between the tines; avoid installation directly downstream of control valves, pump discharges, or orifice plates where turbulent flow could affect measurement stability
4. Thermal isolation: In high-temperature applications above 200°C, ensure adequate thermal dissipation through the integrated heat sink section — do not insulate the heat dissipation fins between the flange and the electronics housing
5. Electrical connections: Connect power and signal wiring according to the 8-wire wiring diagram on the instrument label — double-check polarity: 24V DC (red +, black -), RS485 (yellow +, green -), viscosity 4-20mA (brown +, gray -), temperature 4-20mA (white +, blue -)
6. Active signal warning: The viscosity and temperature 4-20mA outputs are active (self-powered) — do not short the output terminals; connect only to a passive 4-20mA input on your DCS, PLC, or display
7. Weather protection: For outdoor installations, ensure the cable gland is fully tightened and the cover is secured to maintain the IP65 protection rating

Why This Vibrating Fork Inline Viscometer is Better

The LONN ND80 vibrating fork viscometer offers a compelling set of advantages over alternative viscosity measurement technologies:

vs. Rotational Viscometers (Inline):

• No moving parts — no motor bearings to wear, no rotating seals to leak, no spindle alignment issues
• No fouling accumulation — the vibrating fork self-clears through vibration, unlike rotational spindles that accumulate deposits
• Lower maintenance — no periodic bearing replacement or seal service required

vs. Laboratory Viscometers:

• Real-time data — continuous measurement, not batch sampling with hours of laboratory delay
• Process integration — direct DCS/PLC connection eliminates manual data entry
• Immediate detection — catches off-spec conditions as they develop, not after product has left the process unit

vs. Nuclear Gauges:

• No radiation source — no regulatory permits, no source handling, no disposal costs
• No licensing — install and operate without radiation safety programs or government oversight
• Safer for personnel — no ionizing radiation exposure for operators or maintenance technicians

The vibrating fork principle used in the LONN ND80 is the same proven technology employed by major process analyzer manufacturers worldwide — reliable, repeatable, and safe for continuous industrial use.

Frequently Asked Questions

Q: Is the LONN ND80 a vibrating fork viscometer or a rotational viscometer?

A: The LONN ND80 is a vibrating fork viscometer (tuning fork technology) — it uses piezoelectric-driven fork tines that resonate in the process fluid. This is different from a rotational viscometer inline system, which uses a motor-driven spindle. The vibrating fork design offers significant advantages: no moving parts, no bearing wear, no seal leaks, and lower maintenance requirements than inline rotational viscometer alternatives.

Q: What viscosity range does the LONN ND80 cover?

A: The standard LONN ND80 covers 0 – 5,000 cP (0 – 5,000 mPa·s). The instrument can be field-calibrated to focus accuracy on specific measurement segments within this range. For higher viscosity applications, consider the LONN-V7 online viscometer with a range of 0 – 5,000,000 cP.

Q: What process connection does the LONN ND80 use?

A: The standard connection is an ANSI 150LB RF flange, DN50 size, with 60mm insertion depth. The flange has four bolt holes and a raised face sealing surface with concentric machining grooves.

Q: Can the LONN ND80 measure temperature as well as viscosity?

A: Yes. The LONN ND80 has a built-in PT100 temperature sensor and outputs both viscosity and temperature values through independent 4-20mA analog channels plus RS485 Modbus RTU digital communication. This is an 8-wire wiring configuration (2 for power, 2 for RS485, 2 for viscosity 4-20mA, 2 for temperature 4-20mA).

Q: What is the maximum process temperature?

A: The standard configuration handles -10°C to +200°C with ±1% FS viscosity accuracy. The wetted parts are rated for continuous exposure up to +400°C, with viscosity accuracy at ±3% FS for the extended temperature range. The heat dissipation section between the flange and the electronics maintains safe operating temperatures for the transmitter components.

Q: What materials contact the process fluid?

A: The standard wetted materials are 316L stainless steel. For corrosive media (hydrochloric acid, sulfuric acid, caustic solutions), optional Hastelloy C wetted parts are available. The flange material matches the wetted material specification.

Q: Is the LONN ND80 suitable for hazardous area installation?

A: Yes. The LONN ND80 carries Ex d (flameproof) certification. The heavy-duty green enclosure with Ex marking is designed to contain internal ignition and prevent propagation to the surrounding atmosphere, making it suitable for Zone 1 and Zone 2 hazardous areas.

Q: What output signals does the LONN ND80 provide?

A: The LONN ND80 provides dual 4-20mA DC active outputs (one for viscosity, one for temperature) plus RS485 Modbus RTU digital communication — all simultaneously. The 4-20mA signals can connect directly to any DCS, PLC, or SCADA analog input.

Q: How deep does the sensor insert into the process line? A: The insertion depth from the flange face to the fork tines is 60mm. This ensures the fork sensing element is positioned well into the fluid stream on DN50 (2-inch) and larger process pipe sizes.

Q: How does the LONN ND compare to the LONN-V7 online viscometer?

A: The LONN ND80 is a vibrating fork inline viscometer with a standard range of 0-5,000 cP and flange mount design. The LONN-ND60 online viscometer has an integrated screw-mount design with a wider viscosity range of 0-5,000,000 cP and is better suited for high-viscosity polymer and bitumen applications. Choose the LONN ND for lower to medium viscosity flange-mount applications, and the LONN-V7 for high-viscosity extended-range requirements.

Request a Quote

Ready to add continuous inline viscosity monitoring to your process? Contact our technical sales team for pricing, lead time, and application-specific configuration.

 Email your inquiry to: anna@xalonn.com or Fill out our RFQ form

As a specialized split type density meter manufacturer with direct-from-factory pricing, LONNMETER provides complimentary application engineering support to ensure optimal model selection for your specific installation constraints. We don’t just sell instruments — we partner with your engineering team to deliver reliable measurement solutions.