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Innovative inline material moisture sensors
Moisture sensors for measuring material moisture are of great importance for optimized process control in many industries. Optical methods are becoming increasingly important because they have the advantage of working without contact and having no influence on the measurement object.
Our fiber-optic moisture sensors also offer the advantage that they can be used in areas that are difficult to access and under harsh environmental conditions!
Learn more about our humidity sensors, how they work and their applications
Inline humidity sensors for different applications
| Technical Specifications (Optimized) | tr²dent "moist" | SensoWeb "moist" |
|---|---|---|
| Peculiarity | Standard design | “Heavy-duty” version especially for paper production |
| Measuring principle | Near-infrared (SWIR) | Near-infrared (SWIR) |
| Measuring range | 0..~60% humidity (outside wet phase) | 0..~60% humidity (outside wet phase) |
| Accuracy | product-dependent | product-dependent |
| Resolution | 0,1% | 0,1% |
| measuring time | einstellbar | einstellbar |
| Measuring distance | Depending on the application, up to 200 mm | Depending on the application, up to 200 mm |
| Air purge | - | integrated |
| fiber optics | to 5 m | to 15 m |
| Ambient temperature | Sensor up to 45 °C, sensor head up to 200 °C | Sensor up to 50 °C, sensor head up to 200 °C |
| tension | 24 VDC | 24 VDC |
| outputs | up to 4 analog (4…20 mA) | up to 4 analog (4…20 mA) |
| Class | IP54 | IP65 |
| Learn more | Learn more |
How do our humidity sensors work?
Optical humidity sensors are based on the principle of stimulating water molecules to oscillate using electromagnetic waves and thus absorbing electromagnetic energy at specific wavelengths (absorption bands).
Our humidity sensors feature integrated light sources with high-performance LEDs that emit pulsed light in the near-infrared (SWIR) range. The emitted light is reflected by the measurement object to varying degrees: Water exhibits high absorption in specific SWIR wavelength ranges, meaning less reflection occurs in this range than in other wavelength ranges.
This absorption in water-dependent wavelengths is compared with that in water-independent reference wavelengths and converted to % humidity using predefined models. relative humidity can be tracked via the browser and output via analog output (4-20mA) and transferred to the controller.
Our tri²dent “moist” humidity sensors work according to the same time/same spot principle: The sensor sends out three light signals of different wavelengths, which can be identified and evaluated by the receiver thanks to their special modulation. High-quality lock-in amplifiers prepare the signals in the detector with precise frequency and phase. The LED technology used guarantees a long service life for the light sources. Robust fiber optic technology with hundreds of individual fibers enables long-term use even in industrial environments.
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Advantages of continuous inline moisture measurement
In many industries, material moisture control is traditionally carried out by taking regular samples and determining the moisture content of the samples in the laboratory. While this method allows for a precise assessment, this data is always available with a significant delay: if the laboratory measurement reveals unacceptable deviations from the target values, any intervention in production is only effective for future production batches, while rejects continue to be produced in the meantime.
Due to these disadvantages of laboratory measurements, continuous, inline moisture measurement is becoming increasingly important. Our optical or fiber-optic NIR sensors enable continuous moisture measurement of materials, thus enabling 100% monitoring of product or process quality. Thanks to inline moisture sensors, deviations can be responded to immediately, preventing unnecessary waste. This not only reduces costs but also energy and raw material consumption, thus contributing to improved eco-efficiency.
Optical and fiber optic material moisture sensors: the technology and its advantages in production
Humidity measurement is often used synonymously with the measurement of air humidity and material moisture. Please note that our sensors are generally used for material moisture measurement, not air humidity.
There are different technologies for measuring material moisture – optical moisture measurement using so-called NIR sensors has the great advantage of being contactless, i.e. the product/substrate, etc. has no contact with a measuring sensor – thus preventing damage to or interference with the parameter actually being measured.
Not only this – in contrast to capacitive methods, for example, the measurement can also be taken from a much greater distance: depending on the model, our sensors work with measuring distances of several centimeters or more.
Our fiber optic sensors offer a special advantage: The fiber optics (also called optical waveguides or light guides) make it possible to separate the measuring head from the sensor electronics – which can then be mounted in a “normal” and accessible environment – the fiber optics guides the light from the sensor to the measuring point and the reflected light back to the sensor.
In this way, it is possible to measure even under conditions where humidity measurement would otherwise not be possible, such as high temperatures or cramped space or hard-to-reach measuring locations!
This technology makes it possible to place a moisture measurement at almost any desired process step: for example, in a paper machine, a moisture measurement can be carried out after the press as well as within the drying group.
Sensor technology Humidity sensors: Resistant to ambient light and precise
Incidentally, only the light emitted by the sensor itself is evaluated, which makes our sensors resistant to external light, i.e. they are not affected by fluctuations in the ambient light during the day, for example, and do not need to be shielded.
The accuracy of the measurement results depends on the specific application and the measurement conditions; unfortunately, measurements in the ppm range are not possible with the sensors.
In this context, it must also be noted that the reflection of the light occurs primarily at the surface (plus a material-dependent penetration depth in the µ-range) – the SWIR moisture measurement therefore ultimately reflects the surface moisture, and a measurement inside the material is therefore not possible.