InstroTek
81
Since the above density equation used in the gauge contains
three constants, it is necessary to use three known density
blocks at the factory to provide an original calibration. There
are many different methods of calibrating the gauge by
assuming certain criteria or by using historical data.
However, the bases of all these methods depend on having a
minimum of three different counts for three different known
density blocks.
Moisture Calibration
- Gauge moisture calibration is
performed by utilizing at least two blocks of known hydrogen
density covering a range of moisture in the construction
materials. The two blocks routinely used for moisture calibration
are magnesium (0 lb./ft³, 0 kg/m3) and a combination block of
magnesium and polyethylene (~ 35 lb./ft³, ~560 kg/m³). The
gauge standard count and the counts on these blocks are
used in a linear equation such as the one below to calculate
the parameters E (intercept) and F (slope).
M= A* MCR - B
MCR is the moisture count ratio, which is the ratio of the
measured moisture count and the daily moisture reference
standard count. The daily reference standard count is
performed on a high-density polyethylene block provided with
each gauge. M is the moisture content of the material in PCF or
kg/m3. The A and B parameters are placed in the gauge
memory and are used in the field with the count ratio obtained
on the test material to calculate the moisture content from the
above equation.
