The HC2A-AW/-USB probe is designed for use with the WP-40S sample holder with removable depth reduction insert.
The WP-40S sample holder can be used with two different sizes of disposable sample cups (PS-14: shallow / PS-40: deep). Use the shallow sample cups (PS-14) together with the depth reduction insert. The PS-14 cups are suitable for calibrating the probe with the Rotronic certified humidity standards or with saturated salt solutions. In general, use the shallow cups for a liquid, a paste or a powder. Use the PS-40 deep sample cups for products in bulk (large chunks).
The disposable sample cups serve two purposes:
1)Provide a means storing product samples prior to measurements so that they can come to the same temperature as the probe.
2)Prevent contamination across samples.
Prior to measurements, fill a number of disposable sample cup with the products to be measured. Usually, filling up to 1/3 of the cup is sufficient. To avoid soiling the probe, do not fill the cup above the fill line (see below).
Additional guidelines
a)Measure water activity only in a temperature stable area. This is an essential requirement! Do not measure on a bench that is located near a heater, an AC vent or an open window. Avoid direct exposure of the probe and/or product samples to sun light (heating effect). For best accuracy, temperature should not change by more than 0.01°C / minute (0.0075 °C / minute in the case of product with a water activity > 0.80 aw)
b)Prior to measurements, place each product sample in a disposable sample cup with the cover on. Place the cups in the same general area as the probe. Allow for sufficient time for the samples to come to the temperature of the probe (usually room temperature). A frequent mistake is to measure product samples which have been kept overnight in a refrigerator without first allowing them to come to room temperature. Another mistake is to measure samples coming straight from a hot manufacturing process. To measure water activity at a temperature other than room temperature, place both the probe and the product samples in an incubator set at the desired temperature.
c)Prior to using the probe, verify the integrity and cleanliness of the sealing O-ring located under the probe.
d)Avoid warming up the probe, the sample holder or the product sample by touching or holding for too long in your hand.