Hydronix Hydro-View HV02, Руководство пользователя

Страница: 45 / 82

CALIBRATION AND SAMPLING TECHNIQUES
HYDRO-VIEW USER GUIDE
D0022
REV 1.06
45
⇒
Calculate the ‘dry-reading’ moisture value by calculating back based on the wet-
reading, water added, and dry weight of material.
⇒
Enter both sets of values into the Hydro-View calibration table.
Continuous system sampling method
In this case you will need to take samples passing the face of the sensor at the same time
as recording the
unscaled input
display.
It is normally impossible with this type of system to take a series of samples for mixing
together before drying as it is the instantaneous value of moisture content passing the
sensor which is required.
The preferred procedure here is to take several spot samples at different moisture
contents and plot these on a graph against the corresponding unscaled input. A ‘best-fit’
calibration line would then be obtained using a linear-regression algorithm (most
spreadsheet programs will do this for you). Two points on this line would then be used for
entry into the calibration table of the Hydro-View.
Drying the samples
An electric hot-plate (small portable models are available), camping gas burner, electric
oven, or microwave oven are suitable.
Proceed as follows...
⇒
Weigh the empty container to obtain its tare weight. Record this as value A.
⇒
Add the sample of material to the container and weigh again. Record this as value
B.
⇒
Dry the material using the heat source, checking periodically by weighing until two
measurements taken three minutes apart show no significant change. If an open
tray is used, the material may be stirred carefully to assist evaporation.
⇒
Weigh the container again. Record this as value C.
Normally the drying process for one sample takes approximately 15 minutes.
Recommendations for best performance
A
LWAYS
try to dry materials as quickly as possible to prevent reactions which may affect
the results. This is particularly true of wet-mix concrete which will produce quite different
results when dried overnight in an electric oven compared with drying quickly over a hot-
plate.
A
LWAYS
wear safety glasses during the drying process.
N
EVER
use excessive heat during the drying process. This can result in violent expulsion
of small pieces of material from the drying tray which are potentially dangerous.
Calculating the moisture percentage
It is customary to express moisture present by weight as a percentage of the
dry weight
of
material. Hence the following formula is used:-
M
B C
C A
=
−
−
×
( )
( )
% 100
Where...