Reliable continuous and point level measurement under real process conditions
PVC powder is one of the more demanding bulk solids in the chemical industry. Fine, highly dusty, electrostatically charged and with a low dielectric constant (DK value) of 1.6 to 2.0, it places high demands on level measurement technology.
In this case study, a plant operator from Eastern Europe was looking for a reliable solution for continuous and point level measurement in an existing plant. The solution had to reliably meet ATEX requirements and withstand local environmental influences over the long term.
Especially during winter, severe frost, ice and snow are common. Under these conditions, sensors must operate precisely, be mechanically robust and resistant to extreme temperatures. Maintenance interventions, particularly on the bridge above the silos, also needed to be reduced to a minimum for safety reasons.
Low-maintenance measurement solutions that function reliably even under harsh environmental and process conditions were therefore required. To determine the most suitable solution for this application, a multi-stage test phase was carried out in close cooperation with the operator.
Typical challenges when handling PVC powder
Before looking at the individual measurement tasks, it is worth taking a closer look at the general boundary conditions of this application:
- very fine, occasionally fluidized bulk solid with a low dielectric constant (DK value)
- heavy dust generation in tall, narrow silo
- material build-up and electrostatic charging
- ATEX Zone 20 and 21
- year-round operation with silo roof installation, including temperature fluctuations, frost and snow
How these challenges can be successfully addressed in practice is demonstrated by two specific measurement tasks within the same application.
Measurement Task 1
Continuous level measurement in PVC powder
Initial situation: In 22-meter-high steel silos, radar sensors from another manufacturer had previously been used. In practice, however, they delivered fluctuating and unreliable measurement results. The likely cause was the very low dielectric constant (DK value) of the PVC powder which, in combination with the dusty atmosphere, led to insufficient radar reflection.
A maintenance-free sensor was therefore required that would provide stable and reliable measurement results even under these conditions.
Individually configured rotary paddle level switch and electromechanical lot system ensure reliable level measurement and overfill protection
The electromechanical lot system is used for continuous level measurement in storage silos containing a wide variety of bulk solids. Its simple and robust measuring principle has proven highly reliable in practice, particularly for solids with a low dielectric constant (DK value).
A sensing weight is lowered on a belt to the material surface and then returned to its upper end position. The measured belt length corresponds to the level and is output as an analog signal. Modbus and Profibus interfaces are also available.
A key factor for this application is the integrated belt cleaner. After each measurement, it reliably removes PVC dust from the measuring belt. This prevents dust from entering the mechanical chamber and largely avoids contamination.
Although the mechanical and electronic chambers of the NivoBob® are hermetically separated, the belt unit leading into the mechanical chamber is not hermetically sealed by design. Due to the strongly fluidized material and the overpressure that may occur under certain process conditions during filling, an existing compressed air connection was used. Occasional air purging of the mechanical chamber provides additional protection and ensures long-term, reliable operation.
Additional safety is provided by the integrated heater, which protects the housing chambers from moisture caused by condensation and the associated risk of frost.
Result: Stable and reproducible level values without maintenance effort, even in dusty atmospheres, with material build-up and bulk solids with low DK values.
Why the NB 3200 excels in this application:
- reliable measurement in dusty atmospheres, with material build-up and low dielectric constant (DK value)
- belt version for measuring ranges up to 40 m (≈ 131 ft)
- ATEX II approval for Zone 20/21
- DN100 PN16 flange – fast replacement without modification of the plant
- PVC sensing weight with spikes, particularly suitable for fine bulk solids
- integrated housing heater down to −40 °C (−40 °F)
- version designed for increased process overpressure
NivoBob® NB 3200 with belt version
Measurement Task 2
Point level detection / overfill protection
Initial situation
For overfill protection, the operator had previously used vibrating fork level switches from another manufacturer. In daily operation, however, a recurring problem became apparent:
- fine PVC powder tends to cause heavy material build-up
- poor flow characteristics
- monthly cleaning intervals, as blocked vibrating forks no longer provided reliable signals
- cleaning was particularly time-consuming due to the sensor position on the silo bridge
- maintenance during winter was additionally complicated by cold temperatures, snow and ice
A point level sensor was therefore required that would operate reliably even in the presence of material build-up – and eliminate the need for regular cleaning.
The rotary paddle level switch RN 3002 with extension tube is primarily used as a full detector in storage and process vessels. Its measuring principle is unaffected by dust generation and material build-up, making it ideally suited for use in PVC powder.
To ensure optimal alignment of the rotary paddle level switch, an additional sliding sleeve was used during the test phase to adjust the mounting height and determine the ideal installation depth. This allowed the extension tube to be individually adapted to the silo geometry, ensuring that the switching point is positioned exactly where required.
Thanks to the adjustable sensitivity of the rotary paddle, the sensor could be precisely matched to the material properties of the challenging PVC powder in the area of the material cone, thereby reliably preventing overfilling.
The rotary paddle and the extension tube are made of stainless steel, providing long-term protection against the abrasive properties of PVC powder. Even during long-term operation, the sensor remains mechanically stable and reliable.
Why the RN 3002 is superior in this application
In contrast to vibrating forks, the rotary paddle remains fully functional even when material adheres to the paddle. Blockages do not occur, eliminating the need for regular cleaning. At the same time, the robust stainless steel design ensures that abrasive influences of the PVC powder do not affect the sensor’s functionality or service life.
Rotonivo® RN 3002 with individually adjustable extension tube up to 4000 mm for precise switching point definition
Key features of the individually configured rotary paddle level switch:
- double-sided folding paddle for restricted process connections and materials with low bulk density
- vertical extension tube and support arm made of stainless steel
- extension length 2800 mm (≈ 110 in) – up to 4000 mm (≈ 157 in / 13.1 ft) possible
- additional bearing at the tube end for high mechanical stability
- ATEX approval for Zone 20 / 21
- process overpressure up to 5 bar (≈ 73 psi)
- G 1 ½" stainless steel threaded connection – for easy retrofit in existing plants
- integrated housing heater down to −40 °C (−40 °F)
Functional features:
- adjustable sensitivity to match material properties
- adjustable signal output delay
- selectable switching logic (Fail Safe High / Fail Safe Low)
- height adjustment for variable installation depth
- rotation monitoring
Result: Reliable overfill protection without monthly cleaning and without risky maintenance interventions during winter operation.
„Throughout the entire test phase – and beyond – the sensors measured with a very high level of accuracy. The measurement values were closely monitored during filling and emptying and manually verified several times. All measurements matched exactly. Issues we had experienced in the past no longer occurred. For this application, these are the best devices we could use," the plant operator confirmed.
Conclusion:
PVC powder requires measurement technology that remains stable even under real process and environmental conditions. By using the NivoBob® NB 3200 for continuous level measurement and the Rotonivo® RN 3002 for point level detection, the operator relies on proven, robust solutions that reliably handle dust, material build-up, frost and ATEX requirements.
The result: stable process operations, high confidence in the measurement values and significant time savings due to the elimination of regular maintenance work.
At UWT, we develop measurement technology that proves itself not only under ideal conditions – but in everyday operation.
UWT. LEVEL. UP TO THE MAX.
Silo bridge with filling and venting equipment and level monitoring sensors
Discover More Applications in the Chemical Industry
Whether for the storage and processing of powders, granulates, liquids, or aggressive chemicals – UWT offers robust and safe sensor solutions for a wide range of chemical industry processes.
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