15
Note: To establish representative values for the re-wetting factor
compare the actual weight from lab reports which are
made later to the calculated F
current
7.2 Sources of error
•
wrong felt weight
is being used, due to wrong data or because
the felt has lost weight.
In particular in combination with CaCO
3
a loss of weight of the
felt of 15 to 20% due to wear is common. In case of a very high
calculated compaction (> 85%) it’s likely that the felt has lost
fibers
-> A low water content and high airspeeds at the Uhle
boxes can confirm this.
• The measured caliper was affected by some
local wear
,
for instance caused by a suction box edge
-> measure again
• The
measurement
was done
outside the sheet’s run
-> measure
again
•
No ‘set zero’ performed
just before the measurement.
The temperature difference between a 1st press position in the
basement and a 3rd press position near the drying hood can be
substantial
-> set zero, and measure again
8. Maintenance
Cleaning
For accurate measurements the two stainless steel
probes
must be
cleaned with a cloth or tissue. The aluminum frame and the
polycarbonate display window can be cleaned with a humid cloth
and, if necessary, some mild detergent.