Water Activity Instruments Overview
About Water Activity:

The measurement of water activity or equilibrium relative humidity is a key parameter in the quality control of moisture-sensitive products or materials. Water activity, by definition, is the measurement of water vapor pressure generated by the free or non-chemically bound water in foods and other products. (Bound water and moisture content cannot be measured with this method)

The "free water" in a product influences its microbiological, chemical and enzymatic stability. This is especially important in the case of perishable products such as foodstuffs, grain, seeds etc. as well as in many products in the pharmaceutical and cosmetic industries. If there is too much free water available, the products spoil, and if there is too little, other properties of the product can be influenced negatively.

The Aw value (range: 0.00...1.00 aw) is an important indicator for the shelf life of foods, pharmaceutical and cosmetic products and it strongly influences the occurrence and growth of microorganisms.

The table shows typical growth thresholds below which the specified organism cannot reproduce and therefore spoil the product. Therefore water activity has a significant impact on the shelf life of a product.

Regular Aw measurement takes about an hour to determine exact Aw value. The Aw Quick function allows Aw measurement results in 5 minutes or less. The function is nearly as precise as the regular measurement method. It requires an environment with stable temperatures variations which is mostly given in laboratory and indoor applications. The bench-top unit HygroLab C1, the handheld device HP23-AW-A and the software HW4-P-QUICK-Vx all include the Aw Quick capability. For additional time saving up to 4 probes can be connected to the HygroLab C1. For applications with a large amount of measurements up to 64 USB probes can be directly connected to the HW4 software which also provides the Aw Quick function. All measurement results are saved in log files either directly in the device or via the HW4 software on the PC.

Both Aw and ERH (equilibrium relative humidity) are an expression of the amount of free water vapor present on a product, both at its surface and within its structure, and are practically the same measurement expressed in a slightly different way. Throughout this brochure we will refer to water activity, but this can be interchanged with ERH.

Software calibration:
It's essential that instruments have regular calibration checks traceable to national standards ensuring optimum performance at all times. HW4 software provides convenient, easy to use control of the calibration process, and if required, the sensor adjustment sequence:

• Full software control of calibration or adjustment sequence and timing
• Single or multiple points adjustment / calibration
• Precise adjustment to 0.001 Aw (0.1 %RH) and 0.1 K
• Automatic generation of adjustment, calibration and configuration reports
• User configurable calibration and adjustment process


HP23-AW-A Portable Water Activity Instrument

  • Portable with rechargeable batteries
  • 2 input channels for HC2 sensor heads or HP2 insertion probes can be connected for measurement of water activity, relative humidity and temperature
  • Aw Quick function for fast measurement results (typically 4-5 minutes)
  • Audible alarm to indicate completed measurement
  • Saves up to 2,000 data records with %RH, °C/°F, date and time
  • Battery charging function
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HygroLab C1 Bench-Top Water Activity Instrument

  • Laboratory Unit
  • 4 input channels for HC2 sensor heads or HP2 insertion probes can be connected for measurement of water activity, relative humidity and temperature
  • Aw Quick function for fast measurement results (typically 4-5 minutes)
  • Audible alarm to indicate completed measurement
  • Saves up to 10,000 data records with %RH, °C/°F, date and time

HC2-AW Sensor Heads for Water Activity of Most Products

The sensor head is used for most products. It fits over the sample cup holder to form a sealed chamber so that the equilibrium relative humidity can be obtained.

Sensor heads are used in conjunction with the different meters either the portable or bench top types above

Sample Cup holders

water activity sample holder water activity sensor head

The sensor cup holder holds the disposable sample cups - the sensor head sits on top of the holder to form a sealed container. There are 2 different sizes of sensor cup holders, 14mm and 40mm deep with corresponding disposable sample cups of the same size.

The 40mm dual can be used for both depths by using an insert with the 14mm cups.

Disposable Sample Cups

water activity sample cup water activity sample cup

Disposable sample cup offer a convenient way to load the samples into sample cup holder. Come in 2 depths 14mm and 40 mm.

 

Insertion Probes for Water Activity of bulk materials

Compatible with either the HygroLabC1 or the HP23-AW-A meters Inserrtion probes are suitable for certain kinds of bulk materials such as grain. When the probe tip is buried in the bulk material the local environment in the region of the tip is effectively isolated (sealed off) from the atmosphere and a local ERH can be obtained as if it were in a sealed chamber.