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How do humidity sensors work?

LubCos H2O 72dpi

Argo Hytos

Fluid Management


Humidity sensors take an important place in the sensor and measurement technology of ARGO-HYTOS. There, they are mainly used for quality control or improvement of fluids such as oil. They also help to automate or monitor processes in other areas. The tiny components have great versatility. Read here how they work and where the sensors can be found.

How are humidity sensors configured?

Humidity or moisture sensors have a similar structure to a capacitor. The latter consists, in simplified terms, of two electrodes with an insulating dielectric between them. It is capable of storing an electric charge in an electric field. The storage is called electrical capacitance. Humidity sensors work in the same capacitive way but require special materials for their intended function.

As with ordinary capacitors, the lower electrode is made of stainless steel. Above this are two different polymer layers. These must have hygroscopic properties - in other words, they must be able to attract and bind humidity or water. If this occurs, measurable changes in capacitance occur and the humidity sensor transmits a signal to this effect. For greater sensitivity, a thick, porous material is used as an atmospheric filter for the upper electrode.

Because of their operating principle, such humidity measuring cells are often referred to as capacitive humidity sensors. In a broader sense, they belong to the CMOS semiconductor devices. They are basically suitable for analog as well as digital data transmission for further use or processing. The analog connection option becomes particularly important in industrial applications. Because here many plants still work with analog signals due to their lower susceptibility to interference in often harsh environments.

How does ARGO-HYTOS use humidity sensors?

ARGO-HYTOS has developed its own humidity sensor: the LubCos H2O. Its task is to reliably detect water in hydraulic or lubrication media.

  • The sensor is designed for use with mineral oils, bio-oil and synthetic esther.
  • It is designed to detect relative oil humidity and temperature.
  • A capacitive transducer registers even the smallest influences of humidity.
  • The sensor has extensive compatibility with many data loggers.

You can use this sensor individually. Or you can use it as an integrated sensor in the oil condition sensors LubCos Level and LubCos H2O+ II.

Other products from ARGO HYTOS also work with these humidity sensors. The devices are part of our portfolio for Fluid Management. Our dewatering systems are particularly noteworthy here.

A brief introduction to the dewatering systems from ARGO-HYTOS

Water can penetrate hydraulic or lubricating oils due to humidity in the environment. With our mobile OPS dewatering systems, you remove this water efficiently and quickly. The devices separate free and dissolved water from hydraulic and lubricating oil. To do this, they have a reactor, our LubCos humidity sensor and a vacuum pump. The vacuum it generates causes the systems to suck in the oils.

In addition, the oil can be heated to suitable temperatures in the process. Water then simply evaporates in the reactor far below the saturation limit. The systems cool the water vapor immediately and then allow it to condense in a collecting vessel. The dewatered oil initially remains in the reactor and is then pumped to the oil outlet at the push of a button. Here, the systems also have a filter for oil cleaning.

Before this, however, you also have the option of visually checking the oil with an oil sample. If the oil sample is clear, this roughly indicates an appropriate low water content. A cloudy sample, on the other hand, indicates a water content that is too high. However, exact results on the water content in hydraulic and lubricating oils can only be obtained by laboratory analysis of the oil sample.

If necessary, you will have to repeat the dewatering or, in the worst case, even replace the oil in the system.

Why is it so important to control oils with humidity sensors?

Hydraulic devices and other systems with lubricating oil are often subjected to heavy loads in daily operation. However, systems can only cope with long service lives and constant availability if they are operated with hydraulic or lubricating oil in optimum condition. Even small amounts of water in the oils have a considerable adverse effect:

  • Acid can form, which then triggers corrosion in the plant or system.
  • The oil properties deteriorate considerably.
  • For example, the temperature resistance or load-carrying capacity of the oil can drop rapidly.
  • In general, the oil ages excessively quickly under the influence of water.
  • Expensive damage to plant and equipment is the result.

This can be easily avoided by using dewatering systems with humidity sensors from ARGO-HYTOS.

Your advantages with our humidity sensors and dewatering systems at a glance

  • Cost-effectiveness: Oil maintenance with the dewatering systems postpones oil changes and extends maintenance intervals as well as machine service life. The one-time investment in a dewatering system thus soon pays for itself.
  • Efficient, controlled dewatering: The humidity sensors from ARGO-HYTOS constantly monitor the relative humidity of the oil during dewatering.
  • Easy operation and quick filter change: The use of the systems works absolutely simple.

Further applications of humidity sensors

Humidity sensors are not only used in ARGO-HYTOS products and solutions. For example, they play a decisive role in the efficient air conditioning of offices or buildings in general. Modern and smart air conditioning systems use ambient measured values such as humidity and temperature to automatically adjust their cooling capacity.

Humidity sensors work in the same way in most smartphones. Devices from various manufacturers detect whether there is humidity or moisture in the charging socket. The phones then indicate with a warning message that the device should not be charged now. Otherwise, considerable damage to the device could easily occur.

Another application example of humidity sensors are household appliances such as washing machines and dryers. Here, the sensor technology measures the humidity in the drums, the laundry or both in parallel. This provides the automatic control of the appliances with important information for individually controlling individual dryer or washing programs. Humidity sensors also work in automobiles, where they support the automatic climate control system, for example.

Another very important field of application for humidity sensors is medical technology. Anesthesia machines, incubators and sleep apnea devices are equipped with humidity sensors. Here, they control and regulate the humidifiers in the equipment, thus ensuring optimum air quality for the patients. In the same way, anesthetic gases must be perfectly tempered and frequently humidified. Humidity sensors also help with this.

In view of these application examples, two general advantages of humidity sensors become apparent. Their design can be greatly miniaturized. For example, many sensors measure only a few millimeters in width, height or depth. In addition, only a few comparatively inexpensive components or materials are required for one of these sensors. They can also be easily manufactured in large series and thus end up being very low-cost components.

Do you still have questions about sensor technology or other products from ARGO-HYTOS?

Various articles on our website regularly show you backgrounds and information about our products or components such as the humidity sensors. Do you have any further questions? Do you need help with product selection? Are you unclear about the compatibility of our products and solutions with your plants and processes?

Then we will be happy to help you personally, quickly and competently. Please use our online contact. Here you will immediately get all the answers you are looking for.

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