How to choose the correct filter for humidity probes. 

choosing the correct filter

Humidity measurement plays a critical role in many industries. It impacts processes, product quality, and storage conditions. An essential tool in humidity measurement is the humidity probe. To ensure accurate measurements, a filter or filter cap might sometimes be required. This guide will focus on the nuances of selecting the right filter, especially when using Rotronic humidity sensors and probes.

Why are filters necessary?

  1. Protection of the Sensor: Some environments might contain contaminants or impurities that could harm the sensor. A filter protects the sensor from physical particles and can prolong its lifespan. Rotronic probes, known for their precision, equally benefit from such protection to maintain their accuracy over time.

  2. Chemical Defense: Rotronic probes, like many others, can be affected by chemical contaminants. Some filter types can protect the sensor from these contaminants, ensuring accurate readings.
  3. Condensation and Dripping Water: Especially in environments with a high risk of condensation, a filter can prevent water from dripping directly onto the sensor, a concern that Rotronic probes are not exempt from.

Filter Material for Rotronic Probes: Deep Dive

As a prominent manufacturer in the realm of humidity measurement, Rotronic offers a range of filter materials suited for various environments. The type of filter materials chosen can influence the probe's accuracy, response time and longevity.

  1. PE (Polyethylene) Filter

    • Temperature Range: Typically -50°C to 100°C, though specific models might vary.
    • Pore Size: Ranges from 20 to 50 microns. Suitable for blocking larger particles such as dust.
    • Air Velocity: Moderate air velocity capabilities, suitable for most standard applications.
    • Applications: General-purpose protection, especially in environments where dust is the primary concern.
  2. PTFE (Polytetrafluoroethylene) Filter

    • Temperature Range: Broad temperature resistance, from -100°C to 200°C.
    • Pore Size: Typically 0.2 to 4 microns. The fine pore structure offers protection from smaller particles and certain chemical contaminants.
    • Air Velocity: High air velocity handling, making it ideal for fast-changing environments.
    • Applications: Environments where chemical resistance is necessary or oil and grease are present. Its hydrophobic nature also makes it suitable for areas with moisture concerns.

  3. Stainless Steel Filter

    • Temperature Range: Extremely broad, usually from -200°C up to 200°C or even higher.
    • Pore Size: Varies widely, from 5 to 25 microns or more.
    • Air Velocity: Exceptional air velocity handling due to the strength and rigidity of the material.
    • Applications: Harsh conditions where maximum durability is needed, such as high-temperature environments or places with potential for physical damage to the probe.

Overview of the Rotronic Filter and Filter Carriers:

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relative humidity transmitter

relative humidity transmitter

Choice of filters for the right application

Selecting the appropriate filter for your humidity probe is not just about choosing a brand or material; it's about understanding the specific needs of your application and environment. Here, we'll explore key considerations to help you make an informed choice:

  1. Understand Your Environment

    • Ambient Conditions: Consider the general atmosphere where the probe will be used. Is it dusty, humid, or does it contain chemical vapors? This understanding will guide you toward a filter material that best suits these conditions.
    • Temperature and Humidity Levels: Some filters are better suited to extreme temperatures or high humidity levels. Ensure the filter you choose can withstand the environmental conditions without compromising the probe’s functionality.

  2. Application-Specific Requirements

    • Industrial Applications: In industrial settings, where probes might be exposed to harsh conditions, a sturdy filter like stainless steel may be necessary for durability.
    • Laboratory Settings: In controlled environments like labs, where the air is cleaner, a less robust filter like PE may suffice, focusing more on precision than protection against harsh elements.

  3. Filter Material Characteristics

    • Polyethylene (PE) Filters: Ideal for environments where dust is the main concern, offering a balance between protection and airflow.
    • Polytetrafluoroethylene (PTFE) Filters: Best for chemical resistance and in settings with oil, grease, or moisture concerns.
    • Stainless Steel Filters: Optimal for extreme environments, offering the highest durability and resilience against physical and chemical challenges.

  4. Maintenance and Longevity

    • Cleaning and Replacement: Understand the maintenance requirements of each filter type. Some may be easier to clean and maintain, while others might need regular replacement.
    • Cost vs. Lifespan: Consider the cost of the filter in relation to its expected lifespan and the frequency of replacement. A more expensive filter that lasts longer and offers better protection might be more cost -effective in the long run.

  5. Consult Manufacturer Guidelines:

    Always refer to the guidelines provided by the manufacturer. For instance, Rotronic offers detailed documentation on which filters best suit their range of humidity probes.

  6. Trial and Adaptation:

    If feasible, testing different filters in your specific environment can provide practical insights into which filter performs best under your unique conditions.

Rotronic Filter Selection Guide

relative humidity transmitter


Choosing the right filter is crucial, even more so when precision instruments like Rotronic humidity probes are in use. By factoring in specific requirements and environmental conditions, and understanding the specifics of each filter material, you can ensure the optimal functioning and longevity of the Rotronic probe. Always refer to Rotronic's official product documentation for the most accurate specifications and recommendations.

Related Content
Define the Right Humidity Probe for Your Applications
Differences and Benefits of Transmitters with Interchangeable Probes vs. Fixed Instrumentation
How to Choose the Most Suitable Humidity Transmitter

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Humidity Measurement & Monitoring Relative Humidity Product Catalogue

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