Define the Right Humidity Probe for Industrial Applications

Humidity & Temperature Measurement in Harsh Environments

In the world of industrial humidity and temperature measurement, precision is crucial, especially in environments characterized by high temperatures, aggressive chemicals, and harsh conditions.

Rotronic products set standards for quality and reliability in measurement technology. Our industrial portfolio is designed to provide accurate and exact data in any situation.

Careful selection and implementation of humidity and temperature sensors can make industrial processes more efficient, improve product quality, and minimize safety risks. In this blog, we provide some insider tips for measurements in an industrial environment and look at how Rotronic and PST can help you monitor, and even control, your processes if needed!

Robust construction structure of industrial probes

There are many considerations when talking about harsh environments and reliable measurements. Therefore, Rotronic has various solutions; amidst the variety of requirements and considerations, it is crucial to understand the core elements that make our sensors indispensable tools in demanding applications.

For reliable relative humidity measurement at higher temperatures to be possible, the sensors and evaluating electronics must be protected, and the materials used must be designed to be dustproof, temperature resistant, and chemical resistant.

Remote electronics – distance the main application

In order to measure humidity accurately, the evaluation electronics (1) must be distanced from the sensorics (2) and thus protected from the higher temperatures, which directly influence the evaluation of the measured humidity values.

Note: Temperatures above 40 °C can affect the accuracy of the measurement.

Linearization of humidity readings

The AirChip3000 keeps in memory a set of two tables (A1% and A2%) consisting of corrections (linearization) to be applied at 23 °C ± 5 °C to the raw humidity data generated by the humidity sensor. Each table holds 101 values (from 0 to 100 %rh, in steps of 1 %rh) to achieve a very precise linearization of the humidity sensor. Table A1% holds the factory default values. Table A2% holds the additional corrections generated during adjustments made by the user. The linear humidity value is obtained by adding to the raw humidity value the corresponding corrective values from both tables. An interpolation is used for intermediate raw values. Table A1% cannot be modified by the user. This table is used to return the AirChip3000 to its original factory settings at any time after zeroing the values generated by the user in table A2%.

Temperature compensation

In many applications, especially in industrial environments, temperatures can change significantly. Correct temperature compensation ensures that humidity measurement remains reliable and accurate, regardless of ambient temperatures.

With remote electronics, it is essential to ensure that temperature compensation is considered for both the electronics and the humidity sensor itself. Rotronic sensors have algorithms to perform compensation automatically and ensure stable and accurate measurements.

Practically every relative humidity sensor requires compensation for the effect of temperature on the humidity output signal to maintain accurate measurements over a wide range of temperature conditions.

In the specific case of a capacitive sensor, compensation is required because the dielectric characteristics of both the water molecule and the hygroscopic polymer used in the sensor vary with temperature. The AirChip3000 holds a set of 31 tables corresponding to temperature values within the range of -100 to +200˚C (see note below). Each table holds compensation data between 0 and 100 %rh in steps of 10 %rh. A temperature of 23˚C is used as the reference.

Based on the humidity and temperature data provided by the sensors, the AirChip3000 uses the values from the tables to apply a correction for the effect of temperature on the humidity sensor. Intermediate correction values are interpolated.

Calibration and adjustment

The additional calibration and adjustment at 23 °C and 10 %rh/35 %rh and 80 %rh is carried out for the best measurement accuracy possible up to ± 0.5 %rh at 23 °C.

Contaminants/pollutants

Although Rotronic humidity sensors are very durable, they can be damaged by some gases and contaminants/pollutants.

The contaminants/pollutants can be divided into two categories: gases without influence and gases with an influence on the humidity sensors.

For contaminants/pollutants with an influence on the sensors and, therefore, with an impact on the measurement result, the maximum constant concentration must be known.

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Drying Processes

Pasta Manufacturing

During the manufacturing of pasta, it is very important that the temperature and humidity values are stable; unwanted temperature and moisture fluctuations that occur in the pasta production will lead to quality defects of the final product – for example, so-called post-cracking: the pasta would dry unevenly and break during preparation. For this reason, a sample of each product is taken from the first three and the last three pallets for quality assessment.

The temperature and humidity of the individual production stages must be recorded precisely. It is, therefore, crucial that the implemented sensors measure very accurately and are checked regularly to ensure the right quality.

Tablet-coating process

In modern pharmaceutical plants, many tablets require coating before they are pressed. These tablet coatings are usually polymer and polysaccharide in nature and need to be strong and stable enough to survive handling. The surface and finish of the tablets need to be smooth in order for them to be swallowed easily. The coating also helps mask any unpleasant tastes or odors associated with the active ingredients. Colorings are added to improve their appearance, and the coating allows an identifying mark of the manufacturer to be stamped into the tablet – a common requirement of regulatory authorities.

Coatings are also important in other industries, such as confectionery, where they are made up of sugar or vegetable oil and are used to seal off the softer cores of the candies.

Tablet coating usually takes place within a perforated rotating drum. Angled baffles are placed in the drum that, along with the airflow inside, help mix the tablet bed. This allows the tablets to be lifted and turned from the peripheries to the centers of the drum to ensure that all surfaces of the tablets are evenly and uniformly coated with the sprayed coating or deposited coating. The atmosphere within this rotating drum needs to be closely controlled for temperature and dew point or relative humidity to ensure that the coating is uniform and smooth in appearance.

Once the coating is applied, the drying of the coating takes place by drawing heated air through the tablet bed from a fan. This airflow also requires temperature, humidity, and volume control to ensure controlled drying and extraction. Monitoring the dew point of both the inflow and outflow of this air gives an indication of the progress of the drying process. This allows the drying time to be kept to a minimum, reducing the overall costs of the drying process.

Rotronic is a Swiss company specializing in developing and manufacturing humidity measurement devices and belongs to the Process Sensing Technologies (PST) Group. Founded in 1965, the company has a long history of providing high-quality measurement technology for monitoring relative humidity (RH) and other parameters.

Rotronic sensors are manufactured in the company's headquarters and, besides the sensor, the probe itself is assembled, calibrated, and adjusted in Bassersdorf.

Rotronic humidity and temperature probes are known for their quality, precision, and durability, and customers can use the probe for many years.

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