Vannaktivitetmålere

Vannaktivitetmålere are instruments used to measure the water activity of a substance. Water activity, often abbreviated as aw, is a fundamental property of moist foods, pharmaceuticals, and other materials that indicates the amount of "free" water available for microbial growth, chemical reactions, and enzymatic activity. It is distinct from moisture content, which measures the total amount of water present.

The measurement is typically performed by determining the equilibrium relative humidity (ERH) of the air in a sealed chamber containing the sample. When the sample is placed in a sealed environment, water will evaporate from or condense into the sample until the partial pressure of water in the air above the sample reaches equilibrium with the water in the sample. The water activity is then calculated as the ERH divided by 100.

Modern vannaktivitetmålere are generally electronic and employ various sensing technologies. Capacitive sensors are common, where the dielectric constant of a sensing material changes with absorbed water vapor, altering the capacitance. Resistive sensors, which measure changes in electrical resistance as water vapor is absorbed by a hygroscopic material, are also used. Isothermal methods, where the sample is brought to a constant temperature before measurement, are preferred for accuracy.

Accurate water activity measurements are crucial for ensuring product safety and quality. In the food industry, controlling water activity helps prevent the growth of spoilage microorganisms and pathogens, extending shelf life. In pharmaceuticals, it is vital for the stability and efficacy of drugs. Cosmetics and other industries also utilize these devices to manage product integrity. Calibration of these instruments using standard solutions of known water activity is essential for reliable results.