Vgo 21
Vgo 21
In the landscape of industrial automation, precise level measurement is a cornerstone of process efficiency and safety. The Vgo 21 series represents a specialized category of ultrasonic level transmitters designed to provide non-contact measurement for liquids and certain granulated solids. As a compact and integrated solution, it is frequently employed in water treatment, chemical storage, and light industrial applications where space is limited and reliability is paramount.
Understanding the technical nuances of the Vgo 21 requires a deep dive into ultrasonic physics, material compatibility, and the specific environmental factors that influence sensor performance. This guide serves as a practical engineering reference for selecting, installing, and maintaining Vgo 21 level sensors within a modern industrial framework.
Measurement Principle of the Vgo 21
The Vgo 21 operates on the "Time of Flight" (ToF) principle. This method relies on the propagation of high-frequency sound waves—typically above the range of human hearing (20 kHz to 70 kHz)—to determine the distance between the sensor and the material surface.
The Pulse-Echo Cycle
1. Emission: The sensor's transducer contains a piezoelectric crystal that converts electrical energy into mechanical vibrations, emitting a short ultrasonic pulse.
2. Propagation: The sound wave travels through the air (or vapor space) toward the target medium.
3. Reflection: Upon hitting the surface of the liquid or solid, a portion of the acoustic energy is reflected back toward the sensor as an echo.
4. Detection: The transducer receives the echo and converts the mechanical vibration back into an electrical signal.
5. Calculation: The internal microprocessor measures the time elapsed ($t$) between emission and reception. Using the known speed of sound in air ($c$), the distance ($D$) is calculated using the formula:
$$D = \frac{c \times t}{2}$$
Because the sensor is mounted at a fixed height, the system subtracts the measured distance from the total tank height to determine the actual level of the medium. To ensure accuracy, Welk integrates temperature compensation within the Vgo 21, as the speed of sound varies significantly with air temperature (approximately 0.6 m/s per degree Celsius).
Technical Specifications and Selection Criteria
When evaluating the Vgo 21 for a specific project, engineers must match the sensor's capabilities with the physical constraints of the vessel. For a broader overview of how ultrasonic technology compares to radar or hydrostatic options, professionals can refer to the Main Page for detailed product hierarchies.
Key Performance Parameters
| Feature | Specification (Typical Vgo 21) | Notes |
| :— | :— | :— |
| Measurement Range | 0.4m to 10m (standard) | Varies by model and medium density. |
| Blind Zone | 0.25m to 0.5m | The area directly below the sensor where measurement is impossible. |
| Accuracy | ±0.25% to ±0.5% of full scale | Depends on environmental stability. |
| Output Signal | 4-20mA, RS485 Modbus | Standard industrial communication protocols. |
| Power Supply | 24V DC (2-wire or 4-wire) | 2-wire is preferred for loop-powered efficiency. |
| Operating Temp | -20°C to +60°C | Standard range for outdoor/indoor use. |
| Enclosure Rating | IP65 / IP67 | Suitable for wash-down environments. |
| Process Connection | G1½" or M66×2 thread | Flange adapters are often available. |
Material Compatibility
The wetted parts of the Vgo 21 are typically constructed from ABS or Polypropylene (PP). For highly corrosive environments involving concentrated acids or aggressive solvents, specialized PVDF versions may be required. Engineers should always verify the chemical resistance of the housing material against the specific vapors present in the tank headspace.
Application Engineering: Where to Use Vgo 21
The Vgo 21 is optimized for "clean" liquid applications. Its compact form factor makes it ideal for the following scenarios:
* Water and Wastewater: Monitoring levels in open channels, wet wells, and chemical dosing tanks (e.g., sodium hypochlorite or alum).
* Food and Beverage: Non-contact measurement in storage tanks for oils, juices, or water, ensuring no contamination of the product.
* Chemical Industry: Level control in intermediate bulk containers (IBCs) and atmospheric storage tanks.
* Agriculture: Monitoring liquid fertilizer levels and irrigation water reservoirs.
Limitations to Consider
While versatile, the Vgo 21 is not a universal solution. It should be avoided in the following conditions:
* High Pressure/Vacuum: Ultrasonic waves require a medium (air/gas) to travel. In a vacuum, sound cannot propagate. Under high pressure, the speed of sound changes unpredictably.
* Heavy Foam: Foam absorbs acoustic energy rather than reflecting it, leading to "loss of echo" errors.
* Extreme Turbulence: Rapidly fluctuating surfaces can scatter the signal, requiring heavy software damping which slows response times.
* High Dust: In solid applications with significant dust during filling, the sound waves can be attenuated before reaching the surface.
Installation Best Practices
Correct physical installation is the most critical factor in ensuring the longevity and accuracy of a Vgo 21 sensor. Improper mounting accounts for the majority of field failures and measurement inaccuracies.
1. Managing the Blind Zone
Every ultrasonic sensor has a "blind zone" (also known as the blocking distance) near the transducer face where the crystal is still vibrating from the emission pulse and cannot yet receive an echo. If the liquid level enters this zone, the sensor will report an incorrect value or a failure. Always mount the sensor high enough so that the maximum possible liquid level remains at least 100mm below the blind zone limit.
2. Positioning and Beam Angle
The Vgo 21 typically has a beam angle of 8° to 12°. The sensor must be mounted such that the "cone" of the ultrasonic signal does not intersect with tank walls, ladders, pipes, or agitators.
* The 1/10 Rule: A common rule of thumb is to mount the sensor at a distance from the wall equal to at least 1/10th of the tank height.
* Perpendicularity: The transducer face must be perfectly parallel to the liquid surface. A tilt of even a few degrees can cause the reflected echo to miss the receiver, especially at longer ranges.
3. Avoiding Interference
* Inflow Streams: Do not install the sensor directly above the point where liquid enters the tank. The turbulence and air entrainment will disrupt the signal.
* Sun Shields: For outdoor installations in hot climates, a sun shield is recommended to prevent the internal temperature sensor from being skewed by solar radiation, which would lead to inaccurate temperature compensation.
Configuration and Commissioning
Modern Vgo 21 units are commissioned via on-board buttons and an LCD or through a digital interface (RS485). The setup process generally involves defining the following parameters:
1. Empty Distance: The distance from the sensor face to the bottom of the tank (corresponds to 4mA).
2. Full Distance: The distance from the sensor face to the maximum liquid level (corresponds to 20mA).
3. Damping/Response Time: Adjusting how quickly the sensor reacts to level changes. Higher damping is useful for turbulent surfaces but slower for process control.
4. Safe Value: Determining what the output should be (e.g., 22mA or 3.6mA) in the event of a lost echo.
Maintenance and Troubleshooting
Because the Vgo 21 has no moving parts, maintenance requirements are minimal. However, environmental factors can necessitate periodic checks.
Common Issues and Solutions
* Condensation/Buildup: In humid applications, water droplets or crystallized chemicals may form on the transducer face. While many Welk sensors feature a self-cleaning vibration effect, heavy buildup should be wiped away with a soft, damp cloth.
* Intermittent Signal: This is often caused by electrical noise. Ensure that the signal cable is shielded and that the shield is grounded at the controller end only.
* Inaccurate Readings in Summer/Winter: Check the placement of the temperature sensor. If the sensor body is heated by the sun but the air in the tank is cool, the compensation will be incorrect.
Comparison: Vgo 21 vs. Radar
In some applications, users may debate between the Vgo 21 and a 26GHz or 80GHz radar transmitter. While radar is immune to temperature fluctuations and vapors, the Vgo 21 remains a preferred choice for many due to its lower cost and effectiveness in simple, atmospheric water-based applications. Radar is typically reserved for high-temperature, high-pressure, or chemically aggressive environments where ultrasonic technology reaches its physical limits.
Frequently Asked Questions (FAQ)
Q: Can the Vgo 21 measure the level of solids like sand or grain?
A: Yes, but with caveats. Solid surfaces are often angled (angle of repose), which scatters the signal. The effective range for solids is typically 50% of the rated range for liquids. A swiveling flange may be needed to aim the sensor at the material surface.
Q: What happens if the sensor is submerged?
A: Most Vgo 21 units are IP67 or IP68 rated, meaning they can withstand temporary submersion. However, while submerged, the sensor cannot measure level. Once the liquid recedes, the transducer face must be clear of debris to resume operation.
Q: How long can the signal cable be?
A: For 4-20mA analog signals, the cable can extend up to several hundred meters, depending on the wire gauge and the power supply voltage. For RS485 Modbus, distances up to 1,200 meters are possible with appropriate twisted-pair cabling.
Q: Does the Vgo 21 work in tanks with internal agitators?
A: It can, provided the beam angle is narrow enough to avoid the blades. Advanced units also offer "false echo suppression," allowing the software to "learn" and ignore static reflections from internal tank structures.
For technical support regarding specific mounting adapters or to request a quote for bulk industrial projects, visiting the Main Page provides access to the full Welk product catalog and engineering documentation. Selecting the right Vgo 21 configuration ensures a long-term, maintenance-free solution for your level monitoring needs.
