The dew point sensor in compressed air technology

The dew point is the temperature at which the water content of the air is saturated and starts to condense. Similarly, we speak of a pressure dew point when the pressure level of the air is above atmospheric pressure. Therefore, the pressure dew point is the temperature at which water vapour condenses at a certain pressure.

The pressure dew point is an important parameter for determining the water content in compressed air. The lower the dew point, the drier the air.

Dew point sensors in compressed air technology operate using different measurement principles. Below are the three most common types:

The dew point sensor works on the principle of condensation. The air is passed over the sensor and cooled until the dew point is reached. As soon as the dew point is reached, the water vapour condenses, and the sensor records the temperature. The dew point can be calculated based on this temperature.

Also know as capacitive metal oxide sensors, these use a thin metal oxide layer that absorbs water vapor. As moisture enters the oxide layer, its dielectric constant changes, altering the sensor’s capacitance. Electronics measure this change and calculate the dew point. Metal oxide sensors are robust and suitable for harsh industrial environments, though they typically have a slower response time compared to polymer sensors.

Similar to metal oxide sensors, polymer sensors rely on changes in capacitance. A polymer layer absorbs water vapor, causing its dielectric properties to shift. This change is converted into a humidity reading and then into dew point. Polymer sensors offer fast response times and are widely used in HVAC and meteorological applications, but they are less durable in extreme conditions.

Note: The dew point is an indirect measure of the humidity level. The higher the dew point, the higher the humidity.

Dew point sensors are important for dew point protection in compressed air systems, as they continuously monitor and control the moisture content in the air. Excess water content can cause corrosion, wear, and malfunctions, compromising the efficiency and longevity of compressed air systems.

By using dew point sensors, the water content in the compressed air can be measured and monitored. This allows suitable measures to be taken to keep the water content at an acceptable level and prevent damage to the compressed air systems.

• Protect equipment and processes: Moist air causes corrosion, contamination, and product loss. Water accelerates rust and carries impurities that compromise air quality and sensitive processes, leading to defects and downtime. Dew point monitoring keeps air dry and production safe.
• Optimization of the compressed air system: A dew point sensor can indicate leaks before its position in the air network, but leaks after the sensor won’t be detected. In long air networks, the pressure dew point (PDP) at the point of use may differ from the sensor reading. For better accuracy and easier fault detection, install PDP sensors at multiple or critical locations. This improves monitoring, efficiency, and cost control.
  
• Ensure compressed air quality: Water in compressed air can compromise quality and cause tool and machine malfunctions. ISO 8573-1 sets strict moisture limits for air quality. A dew point sensor helps meet these standards by monitoring and keeping the dew point below the required value, preventing condensation and protecting equipment.
• Save energy and costs: By accurately monitoring the dew point, you can make compressed air drying more efficient and therefore save energy.

Dew point sensors can perform a variety of tasks in different areas of compressed air technology. Their installation at certain locations makes it possible to fulfill specific functions. Here are some examples:

A dew point sensor at this point can help to monitor the quality of the dried compressed air and ensure that the dew point is below a certain level. Deviations may indicate a malfunction of the compressed air dryer.

Dew point sensors can be installed at critical points in the compressed air pipe network, e.g. where the compressed air cools down. By placing one or more sensors at these points, the formation of condensation and associated problems can be effectively prevented. With multiple dew point sensors, faults can be better localized, allowing for easier diagnosis and troubleshooting.

It is recommended to install a dew point sensor in the compressed air system when precise monitoring and control of the humidity in the compressed air is required.

Especially in environments where humidity can affect the quality of the compressed air, such as in the food and beverage industry or paint shops, the use of a dew point sensor is essential.

Experts advice: A dewpoint sensor’s accuracy will drift over time due to normal wear, electronic drift and especially contamintation from the environment. So depending on the model and make, recallibraton will be required at certain intervals to ensure reliable and accurate measurements of the dewpoint and is key for compliance with ISO 8573.

Make sure your compressed air system meets industry standards without jeopardizing product quality. Contact our experts today to discuss the best dew point sensor solution for your needs.