Overview of Limit Level Measurement for Bulk Materials and Liquids

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Source: Siemens 2023 | Author: Daniel Henningsen

Siemens offers a comprehensive portfolio for level measurement. This is divided into four different measurement principles:

  1. Rotation
  2. Vibration
  3. Capacitive
  4. Ultrasonic

This document aims to provide an overview of the individual measurement principles, understand the differences, and learn about their respective applications.


Technical Differences and Applications

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Rotation - Rotary Paddle Detector

  • A bearing-mounted paddle is driven by a synchronous motor.
  • The product stops the rotation.
  • Signal output indicates obstruction of the rotation.
  • Once the paddle is free from the product, it resumes rotation, and the signal output (relay) indicates "probe free".
  • Sensitivity is adjustable through the geometry of the paddle and the spring's return force.

Applications:

  • Bulk materials (grain, feedstuffs, cement, plastic granules, wood chips)
  • Food, stone/earth industry, glass, metallurgy, energy production, etc.
  • with a bulk density of at least 15 g/l
  • up to 10 m cable extension possible
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Vibration - Tuning Fork and Rod

  • The product covers the probe and dampens the vibration
  • Signal output (relay or transistor) indicates probe covered
  • When the probe is free from material pressure, it resumes vibration, and the signal output indicates "probe free"
  • Various designs for liquids and bulk solids
  • Depending on the model, extensions up to 4000 mm possible

Application Areas:

  • Food, stone/earth industry, glass, metallurgy, energy generation, etc.
  • LVS100: from 30 g/l → for free-flowing bulk solids
  • LVS200: various designs
    - Standard bulk solid (20 g/l)
    - Interface measurement (50 g/l)
    - Low bulk density (5 g/l)
    - Monitoring of material buildup through optional 4-20 mA output possible
  • LVL100: Measurements under challenging conditions (air bubbles, foam, etc.)
  • Sludges and liquids in confined installations and small pipes
  • LVL200: Full, demand, and empty signaling for bulk solids with a minimum density
    > 0.5 g/cm3
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Capacitive RF Switches

  • The probe serves as the measuring electrode of an electrical capacitor
  • When the product reaches the probe, the capacitance increases, or the frequency decreases
  • Signal output (relay or transistor) indicates probe covered
  • When the probe is free again, the capacitance decreases (frequency increases) and the signal output indicates “probe free”
  • Material build-up does not affect performance due to Active Shield Technology2
  • CLS200 / CLS300 available in standard and digital versions (PROFIBUS PA)

Applications:

  • Liquids, slurries, granulates
  • Food, pharmaceutical, chemical industries, etc.
  • CLS100/CLS200: capacitive switch with short installation length and cable extension
  • CLS300: for extreme conditions, high temperatures, and pressures
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Ultrasonic Level Switch

  • Sending and receiving an ultrasonic wave
  • The distance to the product is continuously measured
  • When a predefined product distance is reached, the signal output switches
  • If the distance increases, the signal output (relay or transistor) switches again

Applications:

  • Bulk goods, sludges, and liquids
  • Stone/earth industry, water/wastewater, etc.
  • Max 3 m for bulk goods and 5 m for liquids
  • Two switching contacts, pump control possible

Summary

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1 Separation layer: In a separation layer, there are two media with different densities in a container, for example, water and oil.
2 Active Shield Technology: Measurement is unaffected by material deposits on the shielded part of the probe.

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