7
4.3 Working principle
The working principle is as follows: a variable resistor is
mechanically connected with the upper probe. Opening the mouth
gives a change in the electric resistance, which is transformed into
mils (1/1000 of an inch) or millimeters and shown on the display.
The
sampling rate
can be set between 5-25 times per second.
The values shown on the display are dampened to avoid a rapidly
changing and therefore unreadable display.
When the instrument undergoes
temperature chances
(e.g. a relatively dry press felt, generates a lot of friction and
therefore heat during the measurement), there will be a zero-shift.
Therefore the instrument needs some time to adjust to this new
temperature (i.e. the metal parts need to expand) before the most
accurate results can be acquired.
The distance that the instrument is moved into the fabric or felt can
be read from the
linear scale
on the housing.
The
trigger
has two functions:
When pulled, the mouth opens.
When pushed, the recording of data into the memory starts/stops
5. Measuring
5.1 Finding a good position
A safe and stable position is of the utmost importance for safety.
If there are several safe positions to measure,
select one on the following criteria:
General:
Measure only on the return-run,
were the fabric/felt runs without paper.