External Hold; Hold During Wash; Tolerance Time - Vaisala PR-23 Series User Manual

Chapter 7 – Configuration and calibration
7.2.1 External hold
When a switch input is configured for external hold functionality, see Configuring input
switches (page 68), and the switch contact is closed, the measurement result is in hold. The
measurement result is kept in hold until the switch contact is opened. A status message
EXTERNAL HOLD is displayed.
7.2.2 Hold during wash
When the setting Hold during wash is configured ACTIVE, the output signal is on hold when
the instrument is washing. The signal is on hold during all three phases (preconditioning,
wash, recovery) of the wash process. This setting can be used to avoid dips in the
measurement signal during the prism wash.
For more information, see Setting prism wash parameters (page 82).
7.2.3 Tolerance time
The tolerance time setting can be used in processes with intermittent breaks in the
measurement due to non-representative sample on the prism. This typically 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, for example, NO
SAMPLE, NO OPTICAL IMAGE, PRISM COATED), the measurement is held for the given
number of seconds.
For example, a setting of 10 s ensures that any NO SAMPLE state which is shorter than 10 s
does not make a dip into the output signal. The factory setting is 5 s. To se the tolerance
time, access the 6 TOLERANCE TIME menu item.
The tolerance time counter is reset always when there is a representative sample on the
prism (for example, the n can be determined). The following figure shows this behavior
D
with an intermittent measurement signal. When the signal drop is shorter than the tolerance
time (for example, 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 is a drop in the
output signal (at t = 80 s in the figure).
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