Fast Water Activity Measurements using the Rotronic AwQuick Algorithm

Introduction

Water activity measurements are used in many industries as critical quality or control measurements. The main benefit of water activity measurements is that they are quick to provide results. Microbial or physical tests can take many days or require highly specialized equipment, whereas water activity can give results within 10-60 minutes, ensuring excellent return on investment. However, even this speed of measurement can be problematic in fast processes; therefore, all Rotronic water activity products include the option to use our AwQuick algorithm. This blog looks to explain the algorithm and how to use it.

Basic concept

The Rotronic AwQuick Water Activity Measurement algorithm provides an accurate prediction of the water activity of a product sample well before actual equilibrium has been reached.

The basic idea is to monitor the equilibration process of the sample to rapidly develop a mathematical approximation, which is, in turn, being used to make an early projection of the process end result.

The underlying assumption is that the equilibration process of different samples of the same product follows the same pattern if the samples are subjected to the same conditions during measurement.

AwQuick uses a pre-existing mathematical model of the sample equilibration process. When a sample is left to equilibrate in a water activity station, the humidity data obtained from the sample is read at regular intervals. The parameters that define the mathematical model of the sample are computed based on this data. A curve-fitting method is being used for that purpose.

With each new data point, an entirely new computation is being made. Each computation results in a prediction of the equilibrium value of humidity. A stability test evaluates successive predictions and determines when the prediction process can be ended.

Prepare for AwQuick measurement

Before starting the AwQuick measurement, it is important to follow the “How to carry out a Water Activity (aw) Measurement” steps. In addition, when conducting water activity measurements, it is essential to ensure that the samples to be measured are conditioned to room temperature (around 23-25 °C or 73-77 °F), especially for non-temperature controlling measuring devices such as the HC2A-AW(-USB) and AwEasy. Conditioning the samples to a consistent temperature helps obtain accurate and reliable water activity readings.

Additionally, regular calibration of the water activity measurement device is crucial. Calibration ensures that the instrument is providing accurate and precise readings. Regular checks and calibrations help maintain the reliability of the measurements over time.

Setting up the AwQuick measurement

All Rotronic devices have two input parameters for the AwQuick mode: temperature stability and dwell time. Temperature stability is defined in °C per minute and is commonly expressed in the default setting of 0.1°C/min (for the HygroLab and AwEasy). This means that the temperature should not fluctuate by more than 0.1°C per minute for the measurement to be concluded.

Simultaneously, a dwell time is required, which uses minutes as a parameter and is required before the AwQuick algorithm can initiate the measurement process. The dwell time is also preset (for HygroLab and AwEasy) to 4 minutes, which is a good guideline for the initial measurement using AwQuick mode and can then serve as a basis for optimizing future measurements.

Finding the right dwell time for the AwQuick measurement

In water activity, the rate at which a product releases or absorbs moisture depends on several factors, including the product's physical and chemical characteristics. These factors influence how quickly the product reaches equilibrium with the surrounding environment, impacting its overall water activity level. For this reason, the dwell time for the AwQuick measurement can be adjusted for the different products.

In more than 90% of all cases, the dwell time of 4 minutes is sufficient, but there are a few instances where this is not so. For these cases, it is possible to adjust the dwell time. To determine whether the AwQuick measurement is as accurate as possible, the following steps should be carried out:

1. Measure your sample with the standard AWE measurement:

   

   In this measurement, the water activity for your sample is measured by waiting for the equilibrium. This measurement takes the longest time (up to 45–60 min) but is the most precise. The result of this measurement then serves as a reference value for the AwQuick measurement.

2. Start the first AwQuick measurement:

   For the first AwQuick measurement, the default setting of 0.1°C/min for temperature stability and 4 minutes for dwell time should be selected, as mentioned above. During the measurement, each of the new data points is repeated, each time yielding a new estimate. The process is stopped if three successive estimates differ by less than 0.04 %rh.

3. Evaluate the AwQuick measurement:

   To evaluate the AwQuick measurement correctly, the measurement inaccuracy of the AwQuick algorithm must be considered, which is ±0.005 aw compared to the Standard AWE measurement. This means that if the standard AWE measurement gives a result of 0.753 aw, the AwQuick measurement should be at least 0.748 aw or, at most, 0.761 aw.

   If this is not the case, increase the dwell time, ensure good temperature stability, and re-evaluate the AwQuick measurement.

The Rotronic AwQuick algorithm is a useful and reliable tool for water activity predictions, as it offers an early insight into a sample's equilibrium state, allowing for swift decision making.

By leveraging a pre-existing mathematical model and real-time data, AwQuick generates rapid and trustworthy projections. While the default parameters suit many cases, the flexibility to adjust dwell time ensures adaptability to diverse product characteristics. Regular calibration and adherence to measurement protocols further guarantee the accuracy and consistency of the results. The AwQuick algorithm is part of our 60-year history of humidity and water activity measurement, and ensures our instruments continue to provide valuable measurements to industries where precision and efficiency are paramount.

To discover more about our range of water activity products please follow this link or watch our Explain-it Videos:

We belong to the world’s leading experts in water activity, humidity and temperature monitoring and measurement of relative humidity. To learn more, talk to one of our application specialists today.

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