ROTRONIC HygroLab - Manual (Page 44)

IN-E-HyLab-V4_11
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
Instruction Manual
Document Type
HygroLab bench top indicator version 4:
instruction manual
Document title
Page 44 of 51
© 2006; Rotronic AG IN-E-HyLab-V4_11
17.4 General recommendations
1. Preparation of the product samples
Both the AW-DIO and the AwVC-DIO probes can be used with two different sample holders (WP-
14: shallow / WP-40: deep), corresponding to two sizes of disposable sample cups (PS-14: shallow
/ PS-40: deep). Use the shallow sample cups (PS-14) and the shallow sample holder (WP-14) 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 deep sample cups (PS-
40) and the deep sample holder (WP-40) for products in bulk (large chunks).
The disposable sample cups serve two purposes:
(a) provide a means storing product samples prior to measurements so that they can come to
the same temperature as the probe
(b) 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).
2. Other basic guidelines
To ensure accurate and repeatable results, please follow these basic guidelines:
a) Measure water activity only in a temperature stable area. 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).
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 hot samples coming straight
from the 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.