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NivoBob - NB 3400 Electro-Mechanical Lot System

Brand: UWT GmbH

NivoBob - NB 3400 Electro-Mechanical Lot System

  1. Introduction
  2. Overview of NivoBob® NB 3400 Electromechanical Level System
  3. Fundamental Operating Principle
  4. Key Features and Advantages
  5. Mechanical Design and Materials
  6. Technical Specifications
  7. Typical Applications and Industry Examples
  8. Pre-Installation Planning
  9. Mounting and Installation Guidelines
  10. Electrical Configuration and Control Integration
  11. System Calibration and Commissioning
  12. Operational Considerations
  13. Maintenance, Inspection, and Cleaning
  14. Common Issues, Troubleshooting, and Diagnostics
  15. Safety, Regulatory Standards, and Certifications
  16. Comparisons with Alternative Level Measurement Technologies
  17. Case Studies and Real-World Implementations
  18. Best Practices for Long-Term Reliability
  19. Future Trends and Developments
  20. Conclusion

1. Introduction

Level measurement within silos, hoppers, and bulk storage vessels is critical for maintaining uninterrupted production flows and ensuring worker safety. Overfills can cause product spillage and possible structural stress, while underfills or unexpected empty conditions can halt production and cause revenue losses. Effective, reliable level detection helps balance these risks, aiding plant operators in scheduling fill and discharge cycles without guesswork or manual intervention.

Among various level measurement solutions, electromechanical devices stand out for their relative simplicity, robust mechanical design, and suitability for a broad range of bulk solids—spanning from light powders to heavier granulates. The NivoBob® NB 3400, a product from UWT, exemplifies this category. By merging electromechanical components with user-friendly electronics, it delivers accurate continuous or spot-level readings in an easy-to-use package.


2. Overview of NivoBob® NB 3400 Electromechanical Level System

2.1 Product Description

The NivoBob® NB 3400 is an electromechanical lot (or bob) system designed for continuous level measurement of bulk solids stored in silos or hoppers. In simplistic terms, a sensor weight (or bob) is lowered into the vessel on a measuring tape or rope until it contacts the material’s surface. Once contact is detected via tension or load changes, the device retracts the weight back to its start position, calculating the distance traveled—and thus inferring the material’s level—based on cable extension length.

2.2 Purpose and Role

The NB 3400 addresses multiple operational needs:

  • Continuous Inventory Monitoring: Helps track volume changes in storage vessels, important for production scheduling and purchasing.
  • Prevent Overfill or Shortage: Though typically not a high-level “alarm” switch, a well-timed measurement can indicate nearing fill capacity or approaching empties.
  • Automated Data Acquisition: Integrates with control systems or SCADA to provide updated level readings on a regular schedule or on-demand.

2.3 Typical Outcomes

  • Safer Handling: Minimizes manual “dip-stick” or external measurements, reducing operator exposure to dust or hazards.
  • Reduced Process Interruptions: Timely detection of material top surfaces streamlines ordering or replenishment schedules.
  • Versatile Integration: With common industrial communication methods, the NB 3400 fits into varied plant control architectures.

3. Fundamental Operating Principle

3.1 Measurement Cycle

At a preset time interval or via an external request (like a PLC command), the NB 3400’s motor unwinds the measuring tape from a spool, lowering the bob into the stored product. As soon as the bob contacts the material surface, tension or load on the tape changes noticeably. The internal sensor mechanism recognizes this contact, halts further descent, and initiates retrieval. The distance the bob traveled before contact correlates to the vessel’s fill height or material level. Once retracted, the tape rewinds fully, and the device outputs the corresponding measurement data (e.g., in centimeters, or as a 4–20 mA reading, or via digital signals).

3.2 Tension/Load Sensing

The NB 3400 typically incorporates a load cell or force sensor in the winding mechanism. When the bob is suspended in air, tension is relatively low. Upon hitting the bulk surface, the tension spikes or changes abruptly. This shift indicates “material contact,” distinguishing between “free descent” (air) and “material coverage.”

3.3 Integration into Control Loops

Depending on the model variant and customer preferences, the NB 3400 can produce either:

  • Analog Output: e.g., 4–20 mA, corresponding to measured distance or fill level.
  • Digital Communication: e.g., Modbus, PROFIBUS, or a relay contact that signals measurement completion or error states.
  • Local Display: Some units feature onboard panels or can connect to external readouts for direct silo-level visualization.

4. Key Features and Advantages

4.1 Mechanical Robustness

The NB 3400’s rope or tape reel assembly is built to endure repeated lowering/lifting cycles without significant wear. The sensor weight or bob can be designed for abrasive or dusty materials, often made from stainless steel or similarly robust metals.

4.2 Broad Application Range

Electromechanical systems like the NB 3400 handle a wide variety of bulk solids—light powders (grain flours, starches), heavier granulates (corn, plastic pellets), or moderate-density lumps (sand, feed). Some models can measure bins up to tens of meters high, bridging large inventory management needs.

4.3 Minimal Sensitivity to Dust and Dielectric Changes

Unlike radar or capacitive sensors, the NB 3400’s measurement principle is unaffected by dust clouds or changes in material dielectric constants. If the material physically stops the bob, the device reliably detects it—regardless of electromagnetic or moisture changes.

4.4 Automatic or On-Demand Measurement

Users can set periodic measurements (e.g., every hour) or trigger readings on command (manually via push-button, or digitally from a PLC). This flexibility suits both inventory management (scheduled checks) and immediate fill-level inquiries.


5. Mechanical Design and Materials

5.1 Housing and Enclosure

Typically, the NB 3400’s main housing is a metal enclosure (aluminum or stainless steel) or a heavy-duty polymer ensuring strong mechanical protection. It encloses:

  • Motor and Reel Mechanism: Winds/unwinds the measuring tape or cable.
  • Load Sensing or Tension Detection: A load cell or mechanical force sensor to identify contact with material.
  • Electronic Circuitry: Translates spool rotation data into level readings, controlling motor operations.

5.2 Measuring Tape or Rope

The device uses either:

  • Metal Tape: Suitable for moderate lengths, typically with integral markings.
  • High-Tensile Rope or Cable: Serves deeper silos or heavier loads, providing flexible operation with high mechanical strength.

5.3 Sensor Weight (Bob)

The sensor weight is often:

  • Stainless Steel: For corrosion resistance and mechanical durability.
  • Shaped: Sometimes conical or cylindrical to minimize bridging or tangling with lumps in the stored material.
  • Mass Variation: Heavier bobs for denser or more compacted products, lighter for delicate materials.

6. Technical Specifications

(These vary by NB 3400 model and user options—consult official datasheets for exact figures.)

  1. Measuring Range
    • Typically up to ~30–50 meters (depending on spool capacity).
  2. Accuracy
    • Often ± a few centimeters for standard applications.
  3. Power Supply
    • AC: 90–230 V AC, typically
    • DC: 24 V (some variants)
  4. Output Signals
    • 4–20 mA (continuous level representation)
    • Relay Outputs for status, measurement complete, or error states
    • Digital Communication: e.g., Modbus RTU or PROFIBUS (optional)
  5. Enclosure Rating
    • IP65/IP66 or higher, resisting dust and mild water jets
  6. Process Temperature
    • Up to ~80°C standard near the top mounting; specialized versions for higher temps
  7. Process Pressure
    • Typically atmospheric or slight pressure; consult advanced models for pressurized vessels
  8. Approvals
    • ATEX / IECEx for dust-laden explosive zones, plus region-specific certifications if needed

7. Typical Applications and Industry Examples

7.1 Grain, Feed, and Flour Mills

Large silos storing grains or flours can benefit from scheduled NB 3400 measurements, ensuring accurate inventory management for seasonal demands, preventing overruns that can cause dust explosions or spillage.

7.2 Plastics and Resin Production

Plastic pellets or resin powders often exhibit static electricity or variable bulk densities. An electromechanical sensor is unperturbed by these factors, reliably sensing fill depth. Real-time or periodic checks align raw material consumption with extruder throughput.

7.3 Food and Beverage

Powdered ingredients in large mixing silos—for instance, sugar, cocoa, or powdered milk—can be continuously monitored. The system’s mechanical measurement remains stable under dusty conditions, reducing the guesswork of manual dip rods.

7.4 Cement and Aggregate Storage

Harsh, abrasive solids degrade many sensors. The NB 3400’s robust spool mechanism and stainless steel bob endure dust-laden cement or rough aggregates, providing near real-time stock data for logistic planning.


8. Pre-Installation Considerations

8.1 Determining Measurement Needs

Assess:

  • Measuring Range: Silo height or max fill level.
  • Measurement Frequency: Automatic intervals (e.g., hourly) or on-demand.
  • Output Integration: 4–20 mA for continuous representation, or digital signals for SCADA.

8.2 Environmental Constraints

  • Temperature: If the top of the vessel frequently exceeds standard rating (~80°C), confirm a specialized high-temp version or cooling neck.
  • Dust Explosions: Check if the vessel zone is classified as explosive (Zone 20/21/22) and confirm the NB 3400’s ATEX/IECEx marking.
  • Vessel Pressure: Some models are suitable for slight vacuum or pressurized conditions; verify specs.

8.3 Mechanical and Process Layout

  • Headroom: The device spool and motor assembly must be accommodated on the vessel top.
  • Mounting Nozzle: Typically 1½", 2" or a flanged opening. Ensure enough diameter for tape passage and bob movement.
  • Material Behavior: Does bridging near the top hamper bob descent? If so, additional mechanical flow aids or internal design modifications can be beneficial.

9. Mounting and Installation Guidelines

9.1 Mounting Interface

Depending on the model:

  1. Threaded: G1½ or NPT threads to match a coupling in the silo top.
  2. Flanged: For heavier or high-pressure setups, a standard flange (DIN, ANSI) can be used.
  3. Adapters: Additional mount adapters exist for angled roofs or thick vessel ceilings.

9.2 Physical Clearance

Ensure the reel assembly remains accessible for maintenance. The bob’s path must be unobstructed, free of cross braces or extreme internal protrusions. If the vessel roof is curved or angles downward, consider an extended standpipe or mounting bracket for vertical cable/tape deployment.

9.3 Cable or Tape Handling

  • Gentle Path: The measuring tape/cable must pass straight through the opening. If a standpipe is used, it must be wide enough and free from edges that could snag or fray the tape.
  • Tension Settings: Typically factory-set. If the rope is replaced, tension calibration might be required.

9.4 Sealing and Weather Protection

At the top mounting, ensure a robust seal:

  • Gaskets: Under flanges, O-rings in threaded couplings, preventing water infiltration.
  • Cable Glands: For power and signal lines, typically IP66 or higher to keep out rain or dust.

10. Electrical Configuration and Control Integration

10.1 Power Supply

  • AC: Usually 90–230 V AC.
  • DC: Possibly 24 V DC, check label.
    Insufficient or incorrect voltage can damage the spool motor or electronics.

10.2 Signal Outputs

Possible output combinations:

  • Analog (4–20 mA): Represents distance or fill height. Connect to a PLC analog input or stand-alone display.
  • Relay Contacts: Indicate measurement completion or fault states.
  • Digital Bus: e.g., Modbus RTU, integrated into SCADA systems for direct read of measured distance.

10.3 PLC or SCADA Integration

A typical approach:

  1. Set Device Address or Output Range: If using digital comms or 4–20 mA scaling.
  2. Program PLC:
    • Periodically issue a “measure” command or read new measurements from the sensor.
    • Process the returned level data for inventory tracking or alarm logic.
  3. Alarm Handling: Overfill threshold or “empty” threshold triggers user-defined actions (stop filling, reorder materials).

10.4 Fail-Safe Considerations

In critical processes, define how the system interprets:

  • Power Loss: Possibly a “fault” or last known measurement flagged as invalid.
  • Tape Break: The sensor typically indicates an error if tension is lost unexpectedly.

11. System Calibration and Commissioning

11.1 Initial Setup Steps

  1. Confirm Mechanical Install: Bob moves freely inside the silo, spool is not obstructed.
  2. Power On: Ensure correct supply voltage, check that the device boots without error.
  3. Zero or Reference: Some models require referencing the fully retracted position (top) as “zero” distance.

11.2 Running a Test Measurement

  • Empty or Partial Fill: Lower the bob and observe if the device recognizes contact or reaching the bottom.
  • Distance Verification: If your silo’s dimension is known, compare the sensor reading with actual distance to ensure alignment. Adjust offset if needed.

11.3 Frequency of Measurements

Configure the measuring cycle:

  • Scheduled Intervals: e.g., every 2 hours for inventory management.
  • On-Demand: A PLC or local push-button triggers an immediate measurement.
  • Hybrid: A background schedule plus manual triggers during critical production steps.

12. Operational Considerations

12.1 Material Flow Rate

If the product is actively being filled or discharged during measurement, the bob may encounter dynamic or swirling material surfaces. This can lead to slightly variable readings. Timed measurement after fill/empty can yield more stable results.

12.2 Bridging or Rat-Holing

In some products, bridging forms near the top, causing the sensor bob to report a surface that is actually suspended above an empty space. For bridging-prone materials, consider installing the NB 3400 in a location less likely to experience bridging or employing flow aids to ensure the bob contacts the true surface.

12.3 High Temperature Loads

While short exposures to heat might be tolerated, ensure the measuring tape or rope does not pass through extremely hot areas that exceed design specs (~80–120°C standard). High-heat process lines may require a cooled mounting or high-temp tolerant rope materials.

12.4 Abrasive and Cohesive Materials

While stainless steel bobs handle abrasive solids decently, repeated contact in extremely coarse or sharp aggregates could cause wear on the bob or cable over time. Periodic checks help catch early signs of mechanical damage. Cohesive or sticky materials might require shaped bobs or coatings to minimize product clinging.


13. Maintenance, Inspection, and Cleaning

13.1 Routine Checks

Despite the NB 3400’s robust design, periodic inspection ensures longevity:

  • Tape or Rope Condition: Look for fraying, kinks, or tension anomalies.
  • Bob: Check for damage or caked-on product that affects weight or shape.
  • Spool Mechanism: Confirm spool winds/unwinds smoothly. Dust or lumps in spool track can hamper retraction.

13.2 Cleaning Intervals

  1. Power Isolation: Switch off supply or set device to “maintenance mode.”
  2. External Wipe-Down: Remove dust from the spool housing, vents, or cable glands.
  3. Bob and Tape: If accessible, gently remove accumulated product from the bob. A mild detergent or brush may suffice, ensuring no strong solvents damage protective coatings or seals.

13.3 Repairs and Replacements

If the rope/tape is severely frayed, spool alignment fails, or load cell electronics degrade, replacement is often more effective than partial field repairs. Maintaining a spare rope assembly or a backup sensor is recommended for mission-critical lines, minimizing downtime in emergencies.


14. Common Issues, Troubleshooting, and Diagnostics

14.1 Inaccurate Measurements

  • Tape Slippage: The spool or tension system might slip, introducing distance errors. Check tension or spool friction.
  • Bridging: The bob lands on a false top formed by bridging. Mechanical bridging solutions or angled mounting might be required.
  • Offset Misconfiguration: If the sensor zero or scaling factor is incorrectly set, data can shift from real levels.

14.2 Bob Fails to Retract

  • Tape Jam: Material lumps in spool path or spool track misalignment.
  • Motor Overload: If the motor’s torque is insufficient to lift the bob from heavy or clingy material, consider a heavier-duty motor or ensuring the product doesn’t trap the bob.
  • Sensor Electronics Fault: Check error codes on the device’s display or control system logs.

14.3 No Measurement Trigger

  • Power Loss: Confirm supply voltage and fuses.
  • Communication Failure: If triggered from a PLC, verify digital signals or bus addresses.
  • Internal Error: The device might be in error or lockout mode if a tension sensor or spool sensor detects a malfunction.

14.4 Broken Rope or Tape

  • Material Abrasiveness: Over time, abrasive edges can weaken the rope. Inspect periodically.
  • Excess Force: The bob might be forcibly stuck in bridging, causing rope tension to exceed design limits.
  • Infrequent Maintenance: Undetected small frays or kinks escalate into a complete break.

15. Safety, Regulatory Standards, and Certifications

15.1 Dust Explosive Atmospheres

Where the NB 3400 is used in a zone with flammable dust, ensure ATEX/IECEx marking appropriate for Zone 20/21/22. Installation must follow the guidelines:

  • Grounding: Minimizes static buildup on spool/tape.
  • Cable Gland Seals: Dust-proof glands to avoid any ignition source from the device’s internals.
  • Routine Dust Removal: Keep external surfaces free of thick dust layers.

15.2 Electrical Codes

Adhere to relevant local or national standards (e.g., NEC, IEC) for wiring, conduit usage, fuse selection, and earthing. Inadequate compliance can create shock or fire hazards, or lead to insurance issues.

15.3 Protective Equipment

Operators or technicians working near silo tops or on scaffolding to service the NB 3400 must follow site PPE rules—safety harnesses, dust masks, ear protection if near loud equipment. Lockout/tagout is mandatory when servicing the spool or tape to prevent accidental motor activation.


16. Comparisons with Alternative Level Measurement Technologies

16.1 Radar (FMCW or Pulse)

Radars provide continuous level data but can be costlier and may face reading difficulties in dusty atmospheres or with low reflective materials. NivoBob’s mechanical approach remains unaffected by dust or material dielectric changes, though it measures on a cyclical basis instead of continuous real-time data.

16.2 Ultrasonic

Ultrasonic sensors can be impacted by dust, foam, or intense turbulence. The NB 3400, physically contacting the product surface, avoids many air-gap or dust cloud concerns that hamper ultrasonic signals.

16.3 Capacitive or Guided Wave Radar

Both measure dielectric or wave reflections. Changing moisture or dust buildup can hamper these readings, prompting recalibrations. NivoBob’s mechanical lot system focuses on actual physical contact, immune to dielectric shifts.

16.4 Laser or Optical

Laser-based sensors can be obscured by dense dust clouds or translucent materials. The NB 3400’s direct bob contact is unaffected by airborne particulates, ensuring robust measurement in dusty bins.


17. Case Studies and Real-World Implementations

17.1 Grain Terminal Inventory Management

A large grain terminal replaced older manual “plumb-bob” checks with multiple NB 3400 units on tall silos. Operators scheduled twice-daily measurements. The system integrated with SCADA to produce real-time inventory data, enabling better dispatch scheduling and reducing overfill incidents.

17.2 Plastic Compound Plant

In a plastic compounding facility, bridging in tall feed silos occasionally caused false high-level readings with older sensors. Installing the NB 3400 improved reliability—since the bob physically penetrated minor bridging layers and signaled the true surface. This reduced raw material guesswork and minimized extruder downtime.

17.3 Cement Loading

A cement loading depot faced extreme dust and abrasive product damaging ultrasonic and radar sensors. Switching to the NB 3400 solved these issues, as the mechanical bob consistently measured the actual fill level without the interference from cement dust clouds. Maintenance intervals dropped by 60%, saving replacement and labor costs.


18. Best Practices for Long-Term Reliability

  1. Scheduled Inspections: Monthly checks ensure spool mechanics remain smooth, and the rope/tape shows no serious wear.
  2. Clean Top Surfaces: Remove built-up dust or lumps near the spool entry port that might jam the tape path.
  3. Record Key Parameters: If tension or spool adjustments are made, log them for reference.
  4. Use Correct Bob Weight: A heavier bob may be beneficial for dense or sticky solids, while a lighter one might reduce rope stress in extremely tall silos.
  5. Train Operators: Teach them to interpret “measurement incomplete” or “error states” promptly, preventing tape damage if bridging traps the bob.

19. Future Trends and Developments

19.1 Advanced Data Communication

As Industry 4.0 evolves, next-generation electromechanical sensors might incorporate:

  • Digital Bus protocols (EtherNet/IP, PROFINET) for real-time data streaming.
  • Condition Monitoring: Tracking spool motor load or bob tension changes for predictive maintenance (e.g., rope wear detection).

19.2 Larger Measuring Ranges

Ongoing mechanical improvements could allow deeper silo coverage with minimal spool friction or specialized tension management, broadening the device’s utility in exceptionally tall bins (50–60+ meters).

19.3 Enhanced Environmental Tolerances

High-temp or high-pressure variants could become standard, facilitating usage in more extreme processes. Upgraded tapes or rope materials might handle even more abrasive or corrosive environments without frequent replacement.

19.4 Self-Cleaning Bob Designs

Future sensor weights might feature advanced coatings or self-cleaning geometries to reduce caking for extremely cohesive or sticky powders, further decreasing manual interventions.


20. Conclusion

The NivoBob® NB 3400 offers a robust electromechanical approach for continuous level measurement in a wide range of bulk solid applications. By physically lowering a bob into the stored material, it directly senses the true surface—unimpeded by dust clouds, changing dielectric properties, or moderate bridging. This results in high accuracy and reliable data for inventory management, scheduling feed operations, and preventing costly overfills or run-outs.

Key Benefits

  • Mechanical Simplicity: A spool, rope/tape, and bob design proven over decades of usage.
  • Minimal Calibration: The system’s measurement is purely distance-based, unaffected by product dielectric or moisture changes.
  • Stable Performance in Dusty/Varied Conditions: Dust-laden or low-reflectivity materials pose no reading challenges.
  • Integration Flexibility: 4–20 mA, relay, or digital bus outputs link easily to PLCs or SCADA, enabling both scheduled and on-demand measurements.

By following correct installation guidelines (ensuring adequate clearance, robust mounting, proper spool alignment), adopting sound maintenance practices (regular rope checks, spool cleaning), and calibrating the output signals to the plant’s control logic, plant engineers and operators can achieve long-term, trouble-free performance from the NB 3400. In a world of more complex and delicate sensor technologies, the straightforward electromechanical design of the NivoBob NB 3400 remains a durable, cost-effective solution for safe, reliable measurement of bulk solids across diverse industrial environments.

Features
  • Durable, simple and reliable measuring principle up to 50 m measuring range
  • Integrated belt cleaner
  • Brushless motor for many measuring cycles in short intervals

NivoBob - NB 3400 Electro-Mechanical Lot System

  1. Introduction
  2. Overview of NivoBob® NB 3400 Electromechanical Level System
  3. Fundamental Operating Principle
  4. Key Features and Advantages
  5. Mechanical Design and Materials
  6. Technical Specifications
  7. Typical Applications and Industry Examples
  8. Pre-Installation Planning
  9. Mounting and Installation Guidelines
  10. Electrical Configuration and Control Integration
  11. System Calibration and Commissioning
  12. Operational Considerations
  13. Maintenance, Inspection, and Cleaning
  14. Common Issues, Troubleshooting, and Diagnostics
  15. Safety, Regulatory Standards, and Certifications
  16. Comparisons with Alternative Level Measurement Technologies
  17. Case Studies and Real-World Implementations
  18. Best Practices for Long-Term Reliability
  19. Future Trends and Developments
  20. Conclusion

1. Introduction

Level measurement within silos, hoppers, and bulk storage vessels is critical for maintaining uninterrupted production flows and ensuring worker safety. Overfills can cause product spillage and possible structural stress, while underfills or unexpected empty conditions can halt production and cause revenue losses. Effective, reliable level detection helps balance these risks, aiding plant operators in scheduling fill and discharge cycles without guesswork or manual intervention.

Among various level measurement solutions, electromechanical devices stand out for their relative simplicity, robust mechanical design, and suitability for a broad range of bulk solids—spanning from light powders to heavier granulates. The NivoBob® NB 3400, a product from UWT, exemplifies this category. By merging electromechanical components with user-friendly electronics, it delivers accurate continuous or spot-level readings in an easy-to-use package.


2. Overview of NivoBob® NB 3400 Electromechanical Level System

2.1 Product Description

The NivoBob® NB 3400 is an electromechanical lot (or bob) system designed for continuous level measurement of bulk solids stored in silos or hoppers. In simplistic terms, a sensor weight (or bob) is lowered into the vessel on a measuring tape or rope until it contacts the material’s surface. Once contact is detected via tension or load changes, the device retracts the weight back to its start position, calculating the distance traveled—and thus inferring the material’s level—based on cable extension length.

2.2 Purpose and Role

The NB 3400 addresses multiple operational needs:

  • Continuous Inventory Monitoring: Helps track volume changes in storage vessels, important for production scheduling and purchasing.
  • Prevent Overfill or Shortage: Though typically not a high-level “alarm” switch, a well-timed measurement can indicate nearing fill capacity or approaching empties.
  • Automated Data Acquisition: Integrates with control systems or SCADA to provide updated level readings on a regular schedule or on-demand.

2.3 Typical Outcomes

  • Safer Handling: Minimizes manual “dip-stick” or external measurements, reducing operator exposure to dust or hazards.
  • Reduced Process Interruptions: Timely detection of material top surfaces streamlines ordering or replenishment schedules.
  • Versatile Integration: With common industrial communication methods, the NB 3400 fits into varied plant control architectures.

3. Fundamental Operating Principle

3.1 Measurement Cycle

At a preset time interval or via an external request (like a PLC command), the NB 3400’s motor unwinds the measuring tape from a spool, lowering the bob into the stored product. As soon as the bob contacts the material surface, tension or load on the tape changes noticeably. The internal sensor mechanism recognizes this contact, halts further descent, and initiates retrieval. The distance the bob traveled before contact correlates to the vessel’s fill height or material level. Once retracted, the tape rewinds fully, and the device outputs the corresponding measurement data (e.g., in centimeters, or as a 4–20 mA reading, or via digital signals).

3.2 Tension/Load Sensing

The NB 3400 typically incorporates a load cell or force sensor in the winding mechanism. When the bob is suspended in air, tension is relatively low. Upon hitting the bulk surface, the tension spikes or changes abruptly. This shift indicates “material contact,” distinguishing between “free descent” (air) and “material coverage.”

3.3 Integration into Control Loops

Depending on the model variant and customer preferences, the NB 3400 can produce either:

  • Analog Output: e.g., 4–20 mA, corresponding to measured distance or fill level.
  • Digital Communication: e.g., Modbus, PROFIBUS, or a relay contact that signals measurement completion or error states.
  • Local Display: Some units feature onboard panels or can connect to external readouts for direct silo-level visualization.

4. Key Features and Advantages

4.1 Mechanical Robustness

The NB 3400’s rope or tape reel assembly is built to endure repeated lowering/lifting cycles without significant wear. The sensor weight or bob can be designed for abrasive or dusty materials, often made from stainless steel or similarly robust metals.

4.2 Broad Application Range

Electromechanical systems like the NB 3400 handle a wide variety of bulk solids—light powders (grain flours, starches), heavier granulates (corn, plastic pellets), or moderate-density lumps (sand, feed). Some models can measure bins up to tens of meters high, bridging large inventory management needs.

4.3 Minimal Sensitivity to Dust and Dielectric Changes

Unlike radar or capacitive sensors, the NB 3400’s measurement principle is unaffected by dust clouds or changes in material dielectric constants. If the material physically stops the bob, the device reliably detects it—regardless of electromagnetic or moisture changes.

4.4 Automatic or On-Demand Measurement

Users can set periodic measurements (e.g., every hour) or trigger readings on command (manually via push-button, or digitally from a PLC). This flexibility suits both inventory management (scheduled checks) and immediate fill-level inquiries.


5. Mechanical Design and Materials

5.1 Housing and Enclosure

Typically, the NB 3400’s main housing is a metal enclosure (aluminum or stainless steel) or a heavy-duty polymer ensuring strong mechanical protection. It encloses:

  • Motor and Reel Mechanism: Winds/unwinds the measuring tape or cable.
  • Load Sensing or Tension Detection: A load cell or mechanical force sensor to identify contact with material.
  • Electronic Circuitry: Translates spool rotation data into level readings, controlling motor operations.

5.2 Measuring Tape or Rope

The device uses either:

  • Metal Tape: Suitable for moderate lengths, typically with integral markings.
  • High-Tensile Rope or Cable: Serves deeper silos or heavier loads, providing flexible operation with high mechanical strength.

5.3 Sensor Weight (Bob)

The sensor weight is often:

  • Stainless Steel: For corrosion resistance and mechanical durability.
  • Shaped: Sometimes conical or cylindrical to minimize bridging or tangling with lumps in the stored material.
  • Mass Variation: Heavier bobs for denser or more compacted products, lighter for delicate materials.

6. Technical Specifications

(These vary by NB 3400 model and user options—consult official datasheets for exact figures.)

  1. Measuring Range
    • Typically up to ~30–50 meters (depending on spool capacity).
  2. Accuracy
    • Often ± a few centimeters for standard applications.
  3. Power Supply
    • AC: 90–230 V AC, typically
    • DC: 24 V (some variants)
  4. Output Signals
    • 4–20 mA (continuous level representation)
    • Relay Outputs for status, measurement complete, or error states
    • Digital Communication: e.g., Modbus RTU or PROFIBUS (optional)
  5. Enclosure Rating
    • IP65/IP66 or higher, resisting dust and mild water jets
  6. Process Temperature
    • Up to ~80°C standard near the top mounting; specialized versions for higher temps
  7. Process Pressure
    • Typically atmospheric or slight pressure; consult advanced models for pressurized vessels
  8. Approvals
    • ATEX / IECEx for dust-laden explosive zones, plus region-specific certifications if needed

7. Typical Applications and Industry Examples

7.1 Grain, Feed, and Flour Mills

Large silos storing grains or flours can benefit from scheduled NB 3400 measurements, ensuring accurate inventory management for seasonal demands, preventing overruns that can cause dust explosions or spillage.

7.2 Plastics and Resin Production

Plastic pellets or resin powders often exhibit static electricity or variable bulk densities. An electromechanical sensor is unperturbed by these factors, reliably sensing fill depth. Real-time or periodic checks align raw material consumption with extruder throughput.

7.3 Food and Beverage

Powdered ingredients in large mixing silos—for instance, sugar, cocoa, or powdered milk—can be continuously monitored. The system’s mechanical measurement remains stable under dusty conditions, reducing the guesswork of manual dip rods.

7.4 Cement and Aggregate Storage

Harsh, abrasive solids degrade many sensors. The NB 3400’s robust spool mechanism and stainless steel bob endure dust-laden cement or rough aggregates, providing near real-time stock data for logistic planning.


8. Pre-Installation Considerations

8.1 Determining Measurement Needs

Assess:

  • Measuring Range: Silo height or max fill level.
  • Measurement Frequency: Automatic intervals (e.g., hourly) or on-demand.
  • Output Integration: 4–20 mA for continuous representation, or digital signals for SCADA.

8.2 Environmental Constraints

  • Temperature: If the top of the vessel frequently exceeds standard rating (~80°C), confirm a specialized high-temp version or cooling neck.
  • Dust Explosions: Check if the vessel zone is classified as explosive (Zone 20/21/22) and confirm the NB 3400’s ATEX/IECEx marking.
  • Vessel Pressure: Some models are suitable for slight vacuum or pressurized conditions; verify specs.

8.3 Mechanical and Process Layout

  • Headroom: The device spool and motor assembly must be accommodated on the vessel top.
  • Mounting Nozzle: Typically 1½", 2" or a flanged opening. Ensure enough diameter for tape passage and bob movement.
  • Material Behavior: Does bridging near the top hamper bob descent? If so, additional mechanical flow aids or internal design modifications can be beneficial.

9. Mounting and Installation Guidelines

9.1 Mounting Interface

Depending on the model:

  1. Threaded: G1½ or NPT threads to match a coupling in the silo top.
  2. Flanged: For heavier or high-pressure setups, a standard flange (DIN, ANSI) can be used.
  3. Adapters: Additional mount adapters exist for angled roofs or thick vessel ceilings.

9.2 Physical Clearance

Ensure the reel assembly remains accessible for maintenance. The bob’s path must be unobstructed, free of cross braces or extreme internal protrusions. If the vessel roof is curved or angles downward, consider an extended standpipe or mounting bracket for vertical cable/tape deployment.

9.3 Cable or Tape Handling

  • Gentle Path: The measuring tape/cable must pass straight through the opening. If a standpipe is used, it must be wide enough and free from edges that could snag or fray the tape.
  • Tension Settings: Typically factory-set. If the rope is replaced, tension calibration might be required.

9.4 Sealing and Weather Protection

At the top mounting, ensure a robust seal:

  • Gaskets: Under flanges, O-rings in threaded couplings, preventing water infiltration.
  • Cable Glands: For power and signal lines, typically IP66 or higher to keep out rain or dust.

10. Electrical Configuration and Control Integration

10.1 Power Supply

  • AC: Usually 90–230 V AC.
  • DC: Possibly 24 V DC, check label.
    Insufficient or incorrect voltage can damage the spool motor or electronics.

10.2 Signal Outputs

Possible output combinations:

  • Analog (4–20 mA): Represents distance or fill height. Connect to a PLC analog input or stand-alone display.
  • Relay Contacts: Indicate measurement completion or fault states.
  • Digital Bus: e.g., Modbus RTU, integrated into SCADA systems for direct read of measured distance.

10.3 PLC or SCADA Integration

A typical approach:

  1. Set Device Address or Output Range: If using digital comms or 4–20 mA scaling.
  2. Program PLC:
    • Periodically issue a “measure” command or read new measurements from the sensor.
    • Process the returned level data for inventory tracking or alarm logic.
  3. Alarm Handling: Overfill threshold or “empty” threshold triggers user-defined actions (stop filling, reorder materials).

10.4 Fail-Safe Considerations

In critical processes, define how the system interprets:

  • Power Loss: Possibly a “fault” or last known measurement flagged as invalid.
  • Tape Break: The sensor typically indicates an error if tension is lost unexpectedly.

11. System Calibration and Commissioning

11.1 Initial Setup Steps

  1. Confirm Mechanical Install: Bob moves freely inside the silo, spool is not obstructed.
  2. Power On: Ensure correct supply voltage, check that the device boots without error.
  3. Zero or Reference: Some models require referencing the fully retracted position (top) as “zero” distance.

11.2 Running a Test Measurement

  • Empty or Partial Fill: Lower the bob and observe if the device recognizes contact or reaching the bottom.
  • Distance Verification: If your silo’s dimension is known, compare the sensor reading with actual distance to ensure alignment. Adjust offset if needed.

11.3 Frequency of Measurements

Configure the measuring cycle:

  • Scheduled Intervals: e.g., every 2 hours for inventory management.
  • On-Demand: A PLC or local push-button triggers an immediate measurement.
  • Hybrid: A background schedule plus manual triggers during critical production steps.

12. Operational Considerations

12.1 Material Flow Rate

If the product is actively being filled or discharged during measurement, the bob may encounter dynamic or swirling material surfaces. This can lead to slightly variable readings. Timed measurement after fill/empty can yield more stable results.

12.2 Bridging or Rat-Holing

In some products, bridging forms near the top, causing the sensor bob to report a surface that is actually suspended above an empty space. For bridging-prone materials, consider installing the NB 3400 in a location less likely to experience bridging or employing flow aids to ensure the bob contacts the true surface.

12.3 High Temperature Loads

While short exposures to heat might be tolerated, ensure the measuring tape or rope does not pass through extremely hot areas that exceed design specs (~80–120°C standard). High-heat process lines may require a cooled mounting or high-temp tolerant rope materials.

12.4 Abrasive and Cohesive Materials

While stainless steel bobs handle abrasive solids decently, repeated contact in extremely coarse or sharp aggregates could cause wear on the bob or cable over time. Periodic checks help catch early signs of mechanical damage. Cohesive or sticky materials might require shaped bobs or coatings to minimize product clinging.


13. Maintenance, Inspection, and Cleaning

13.1 Routine Checks

Despite the NB 3400’s robust design, periodic inspection ensures longevity:

  • Tape or Rope Condition: Look for fraying, kinks, or tension anomalies.
  • Bob: Check for damage or caked-on product that affects weight or shape.
  • Spool Mechanism: Confirm spool winds/unwinds smoothly. Dust or lumps in spool track can hamper retraction.

13.2 Cleaning Intervals

  1. Power Isolation: Switch off supply or set device to “maintenance mode.”
  2. External Wipe-Down: Remove dust from the spool housing, vents, or cable glands.
  3. Bob and Tape: If accessible, gently remove accumulated product from the bob. A mild detergent or brush may suffice, ensuring no strong solvents damage protective coatings or seals.

13.3 Repairs and Replacements

If the rope/tape is severely frayed, spool alignment fails, or load cell electronics degrade, replacement is often more effective than partial field repairs. Maintaining a spare rope assembly or a backup sensor is recommended for mission-critical lines, minimizing downtime in emergencies.


14. Common Issues, Troubleshooting, and Diagnostics

14.1 Inaccurate Measurements

  • Tape Slippage: The spool or tension system might slip, introducing distance errors. Check tension or spool friction.
  • Bridging: The bob lands on a false top formed by bridging. Mechanical bridging solutions or angled mounting might be required.
  • Offset Misconfiguration: If the sensor zero or scaling factor is incorrectly set, data can shift from real levels.

14.2 Bob Fails to Retract

  • Tape Jam: Material lumps in spool path or spool track misalignment.
  • Motor Overload: If the motor’s torque is insufficient to lift the bob from heavy or clingy material, consider a heavier-duty motor or ensuring the product doesn’t trap the bob.
  • Sensor Electronics Fault: Check error codes on the device’s display or control system logs.

14.3 No Measurement Trigger

  • Power Loss: Confirm supply voltage and fuses.
  • Communication Failure: If triggered from a PLC, verify digital signals or bus addresses.
  • Internal Error: The device might be in error or lockout mode if a tension sensor or spool sensor detects a malfunction.

14.4 Broken Rope or Tape

  • Material Abrasiveness: Over time, abrasive edges can weaken the rope. Inspect periodically.
  • Excess Force: The bob might be forcibly stuck in bridging, causing rope tension to exceed design limits.
  • Infrequent Maintenance: Undetected small frays or kinks escalate into a complete break.

15. Safety, Regulatory Standards, and Certifications

15.1 Dust Explosive Atmospheres

Where the NB 3400 is used in a zone with flammable dust, ensure ATEX/IECEx marking appropriate for Zone 20/21/22. Installation must follow the guidelines:

  • Grounding: Minimizes static buildup on spool/tape.
  • Cable Gland Seals: Dust-proof glands to avoid any ignition source from the device’s internals.
  • Routine Dust Removal: Keep external surfaces free of thick dust layers.

15.2 Electrical Codes

Adhere to relevant local or national standards (e.g., NEC, IEC) for wiring, conduit usage, fuse selection, and earthing. Inadequate compliance can create shock or fire hazards, or lead to insurance issues.

15.3 Protective Equipment

Operators or technicians working near silo tops or on scaffolding to service the NB 3400 must follow site PPE rules—safety harnesses, dust masks, ear protection if near loud equipment. Lockout/tagout is mandatory when servicing the spool or tape to prevent accidental motor activation.


16. Comparisons with Alternative Level Measurement Technologies

16.1 Radar (FMCW or Pulse)

Radars provide continuous level data but can be costlier and may face reading difficulties in dusty atmospheres or with low reflective materials. NivoBob’s mechanical approach remains unaffected by dust or material dielectric changes, though it measures on a cyclical basis instead of continuous real-time data.

16.2 Ultrasonic

Ultrasonic sensors can be impacted by dust, foam, or intense turbulence. The NB 3400, physically contacting the product surface, avoids many air-gap or dust cloud concerns that hamper ultrasonic signals.

16.3 Capacitive or Guided Wave Radar

Both measure dielectric or wave reflections. Changing moisture or dust buildup can hamper these readings, prompting recalibrations. NivoBob’s mechanical lot system focuses on actual physical contact, immune to dielectric shifts.

16.4 Laser or Optical

Laser-based sensors can be obscured by dense dust clouds or translucent materials. The NB 3400’s direct bob contact is unaffected by airborne particulates, ensuring robust measurement in dusty bins.


17. Case Studies and Real-World Implementations

17.1 Grain Terminal Inventory Management

A large grain terminal replaced older manual “plumb-bob” checks with multiple NB 3400 units on tall silos. Operators scheduled twice-daily measurements. The system integrated with SCADA to produce real-time inventory data, enabling better dispatch scheduling and reducing overfill incidents.

17.2 Plastic Compound Plant

In a plastic compounding facility, bridging in tall feed silos occasionally caused false high-level readings with older sensors. Installing the NB 3400 improved reliability—since the bob physically penetrated minor bridging layers and signaled the true surface. This reduced raw material guesswork and minimized extruder downtime.

17.3 Cement Loading

A cement loading depot faced extreme dust and abrasive product damaging ultrasonic and radar sensors. Switching to the NB 3400 solved these issues, as the mechanical bob consistently measured the actual fill level without the interference from cement dust clouds. Maintenance intervals dropped by 60%, saving replacement and labor costs.


18. Best Practices for Long-Term Reliability

  1. Scheduled Inspections: Monthly checks ensure spool mechanics remain smooth, and the rope/tape shows no serious wear.
  2. Clean Top Surfaces: Remove built-up dust or lumps near the spool entry port that might jam the tape path.
  3. Record Key Parameters: If tension or spool adjustments are made, log them for reference.
  4. Use Correct Bob Weight: A heavier bob may be beneficial for dense or sticky solids, while a lighter one might reduce rope stress in extremely tall silos.
  5. Train Operators: Teach them to interpret “measurement incomplete” or “error states” promptly, preventing tape damage if bridging traps the bob.

19. Future Trends and Developments

19.1 Advanced Data Communication

As Industry 4.0 evolves, next-generation electromechanical sensors might incorporate:

  • Digital Bus protocols (EtherNet/IP, PROFINET) for real-time data streaming.
  • Condition Monitoring: Tracking spool motor load or bob tension changes for predictive maintenance (e.g., rope wear detection).

19.2 Larger Measuring Ranges

Ongoing mechanical improvements could allow deeper silo coverage with minimal spool friction or specialized tension management, broadening the device’s utility in exceptionally tall bins (50–60+ meters).

19.3 Enhanced Environmental Tolerances

High-temp or high-pressure variants could become standard, facilitating usage in more extreme processes. Upgraded tapes or rope materials might handle even more abrasive or corrosive environments without frequent replacement.

19.4 Self-Cleaning Bob Designs

Future sensor weights might feature advanced coatings or self-cleaning geometries to reduce caking for extremely cohesive or sticky powders, further decreasing manual interventions.


20. Conclusion

The NivoBob® NB 3400 offers a robust electromechanical approach for continuous level measurement in a wide range of bulk solid applications. By physically lowering a bob into the stored material, it directly senses the true surface—unimpeded by dust clouds, changing dielectric properties, or moderate bridging. This results in high accuracy and reliable data for inventory management, scheduling feed operations, and preventing costly overfills or run-outs.

Key Benefits

  • Mechanical Simplicity: A spool, rope/tape, and bob design proven over decades of usage.
  • Minimal Calibration: The system’s measurement is purely distance-based, unaffected by product dielectric or moisture changes.
  • Stable Performance in Dusty/Varied Conditions: Dust-laden or low-reflectivity materials pose no reading challenges.
  • Integration Flexibility: 4–20 mA, relay, or digital bus outputs link easily to PLCs or SCADA, enabling both scheduled and on-demand measurements.

By following correct installation guidelines (ensuring adequate clearance, robust mounting, proper spool alignment), adopting sound maintenance practices (regular rope checks, spool cleaning), and calibrating the output signals to the plant’s control logic, plant engineers and operators can achieve long-term, trouble-free performance from the NB 3400. In a world of more complex and delicate sensor technologies, the straightforward electromechanical design of the NivoBob NB 3400 remains a durable, cost-effective solution for safe, reliable measurement of bulk solids across diverse industrial environments.

Features
  • Durable, simple and reliable measuring principle up to 50 m measuring range
  • Integrated belt cleaner
  • Brushless motor for many measuring cycles in short intervals

Specifications

Measurement Pprinciple

  • Electromechanical Lot-Sensor

Measuring Task

  • Continuous Level Measurement
  • Interface Level Measurement

Version

  • Tape Version

Medium

  • Solids

Mounting Position

  • Top
  • On a Socket

Ambient Temperature

  • -40° C to +60° C (-40 to +140° F)

Process Temperature

  • -40° C to +80° C (-40° F to +176° F)

Process Pressure

  • -0.5 bar … +1.7 bar (-7.3 psi … +25 psi)

Minimum Sensitivity

  • > 300 g/l (> 18 lb/ft³)

Housing Type

  • Dual Chamber

Housing Material

  • Aluminum

Housing Protection Rating

  • IP66, Type 4

Flange Connection

  • ≥ 4" / ≥ DN 100

Wetted Materials

  • Aluminum
  • Stainless Steel 1.4305 (303)
  • Stainless Steel 1.4301 (304)
  • Stainless Steel 1.4310 (301)
  • PVC

Mechanical Load

  • Standard Motor: 0.8 kN
  • Brushless Motor: 3 kN

Accuracy

  • 0.5 % of max. range

Minimum Immersion Length

  • 615 mm (24.24")

Maximum Immersion Length

  • 1.66 m (5.54 ft)

Power Supply

  • 98-253 Vac
  • 20-28 Vdc

Signal Output

  • Relay
  • 0/4-20 mA
  • Modbus RTU
  • Profibus DP

Approvals

  • CE, General Purpose, ATEX, TR-CU, FM

Explosion Protection

  • Dust Ignitionproof (Ex t)

User Interface

  • LCD Display with Push Buttons

Optical Indicator

  • LED + Display

Adjustment Possibility

  • Adjustable Sensitivity
  • Self Diagnostics
  • Menu-Driven Quick Start
  • Volume Table

Applications

  • Chemicals
  • Power
  • Metal
  • Building, Cement & Quarry
  • Food & Beverage
  • Animal Feed
  • Synthetics

Documentation