RAC 207 | Fundamentals of Humidity Measurement Apparatus

The measurement of air humidity plays an important role in many branches of industry, e.g. during drying or in the air conditioning of buildings and vehicles. There are different measuring methods to determine humidity. The trainer enables the measurement of air humidity with four different instruments which can be directly compared to each other: two different hygrometers, a capacitive hygrometer and a psychrometer. Psychrometers operate based on the principle of evaporation cooling and compare the ambient temperature with the wet bulb temperature to determine the humidity. Hygrometers utilize the property of specific fibers, e.g. hair, to expand with increasing air humidity. In the capacitive sensor the electricity constant of a layer and with it its capacity changes due to the water molecules absorbed.The core element of the trainer is a climatic chamber with transparent door. This chamber can be humidified and dehumidified and contains the four instruments. A Peltier cooling element is used for dehumidification. An ultrasonic atomizer is used for humidification. To circulate the air and ensure good mixing a fan is used.

Experimental Capabilities

• Measuring methods for air humidity measurement.
• Psychometric humidity measurement.
• Hygrometric humidity measurement.
• Capacitive humidity measurement.
• Characteristic variables to describe air humidity.
• Changes of the state of humid air in the h-x diagram.
• Determination of the relative air humidity with:
• Hair hygrometer
• Hygrometer with synthetic fiber.
• Capacitive humidity sensor.
• Design and operation of the instruments.

Labelled Diagram

• Capacitive humidity sensor.
• Displays and controls.
• Humidifier.
• Psychrometer.
• Hair hygrometer.
• Dehumidifier.
• Hygrometer with synthetic fiber and combined temperature sensor.

Graphical Representation

Relative humidity (r. h.) over time (t) with rising content of humidity; blue: capacitive sensor, orange: hygrometer with synthetic fiber, red: psychrometer, green: hair hygrometer