Vaisala K-PATENTS PR-23 AX Series, Instruction Manual

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44 PR-23 instruction manual
6.2.3 Tolerance time
The tolerance time setting can be used in processes where there are intermittent
breaks in the measurement due to non-representative sample on the prism. This typ-
ically occurs when there are large voids in the process liquid.
If the optical image can be interpreted, the tolerance time setting does not have any
effect. When the optical image can no longer be interpreted (status messages, e.g.,
NO SAMPLE
,
NO OPTICAL IMAGE
,
PRISM COATED
), the measurement is held for the given
number of seconds.
For example, a setting of 10 seconds ensures that any
NO SAMPLE
state which is shorter
than 10 seconds will not make a dip into the output signal. The factory setting is 5
seconds, access the
6 TOLERANCE TIME
menu item to set the tolerance time.
The tolerance time counter is reset always when there is a representative sample on
the prism (e.g., the nD can be determined). Figure 6.4 illustrates this behaviour with
an intermittent measurement signal. When the signal drop is shorter than the toler-
ance time (e.g. at t = 10 s or t = 35 s in the figure), the output signal does not drop. If
the signal drop is so long that the tolerance time counter reaches zero, there will be a
drop in the output signal (at t = 80 s in the figure).
CONC [%]
Signal with tolerance
Original signal
Filtered (damped) output
0 10 20 30 40 50 60 70 80 90 100
Time [s]
Tol. time counter
Figure 6.4 Effect of tolerance time on output
6.2.4 QF threshold
The QF threshold setting can be used to prevent the instrument from measuring when
the image quality is below a certain limiting value. When QF value becomes less than
the user defined value the image status changes to
NO OPTICAL IMAGE after the user