The right level measurement in process engineering

Why the right level measurement is crucial

Choosing the right level measurement method in process engineering is no easy task. Different requirements - whether chemical resistance, process pressure, temperature fluctuations or movement in the medium - significantly influence the selection. No method is universally perfect; the right choice always depends on the specific conditions of the application. In this article, we highlight the most important influencing factors and explain which measuring principles work best under which conditions.

What factors determine the choice of level measurement?

The right choice starts with a clear analysis of the framework conditions. The following questions help to identify the right measurement method:

1. What are the physical properties of the medium?
2. Is the liquid conductive or non-conductive?
3. Is it an aggressive or viscous medium?
4. Is there steam, foam or strong turbulence?
5. What are the container and process conditions?
6. Is the tank open or closed?
7. Is the tank under pressure or vacuum?
8. Are there agitators or strong movements?
9. How high are the requirements for measuring accuracy and maintenance effort?
10. Does the measurement have to be highly precise?
11. Do hygienic requirements have to be taken into account (e.g. CIP/SIP)?
12. What are the long-term maintenance costs?

Only after these questions have been answered can a decision be made in favor of a specific measuring method.

Comparison of different measuring principles: When is which method suitable?

1. Transit time measurement with radar - non-contact and versatile

Radar is one of the most widely used methods for measuring liquids in process plants. There are free-radiating radar sensors and guided radar systems.

Suitable for:

• Tanks with high temperature, high pressure or aggressive media
• Media with heavy foaming (guided radar is the better choice)
• Large measuring ranges (up to 30 m and more)

Please note:

• Free-radiating radar can be affected by steam or strong turbulence
• Guided radar requires mechanical mounting in the tank (unsuitable for strong currents or agitators)
  

2. Differential pressure measurement - robust, but temperature-dependent

The differential pressure principle uses the hydrostatic pressure to determine the fill level. It is particularly suitable for atmospheric tanks or containers with a constant density.

Suitable for:

• Standard liquids without strong temperature fluctuations
• Process tanks with moderate accuracy requirements

Please note

• Temperature or density changes can lead to deviations
• High maintenance effort required due to regular calibration
  

3. Capacitive level measurement - for conductive and non-conductive media

Capacitive sensors measure the change in electrical capacitance between a probe and the container wall. They are particularly advantageous for highly viscous or pasty media.

Suitable for:

• Sticky or foamy liquids
• Small and medium container sizes

Please note:

• Build-up on the probe can lead to incorrect measurements
• Medium must have a sufficient dielectric constant
  

4. Load cells - when mass is more important than volume

Instead of measuring the fill level directly, load cells record the total weight of the container and use this to calculate the fill level.

Suitable for:

• Applications with maximum accuracy
• Processes in which the density of the medium changes

Please note:

• Mechanical decoupling required
• Higher installation costs
  

5. Optical and laser measurement methods - precise but sensitive

Modern optical sensors and laser-based systems measure the fill level without contact and with high precision. However, they are heavily dependent on ambient conditions.

Suitable for:

• High-precision measurements in a clean environment
• Applications with transparent or translucent media

Please note:

• Sensitive to dirt, condensation or foaming
• High acquisition costs
  

6. Radiometric measurements - for extreme conditions

If all other methods fail, radiometric measurement technology can be used. Gamma radiation is used to determine the fill level.

Suitable for:

• High-temperature and high-pressure tanks
• Corrosive, toxic or extremely aggressive liquids

Please note:

• Strict regulatory requirements
• High costs for approvals and maintenance
  

Step-by-step: How to choose the right level measurement

Step 1: Media analysis

Determine physical and chemical properties

Step 2: Check process conditions

Pressure, temperature, agitators and hygiene requirements

Step 3: Determine measuring accuracy

High-precision or coarse monitoring?

Step 4: Evaluate maintenance costs

Include long-term operating costs

Step 5: Clarify technical feasibility

Consider installation, sensor positioning and data connection

Every measuring method has its strengths and weaknesses - a well-founded analysis of the requirements is the key to making the best choice.

Conclusion: No universal solution, but individual customization

Choosing the right level measurement requires technical expertise and in-depth process analysis. While radar and differential pressure measurements can be used universally, capacitive or optical methods offer specific advantages for particular media. The optimum solution always depends on the process conditions, measuring accuracy and maintenance requirements.

Let us advise you! Our experts will support you in the selection, implementation and maintenance of customized solutions for your processes. Contact us for an individual analysis - we will help you find the perfect measuring method for your applications.