Det-Tronics SW9200x Slickwatch IR Oil Detection System - Manual (Page 23)

The final output stage of the Film Thickness
Discriminator compares the RATIO voltage conditions
from the first processing stages. If the RATIO voltage is
within the “window” and is steady (the conditions
required for a thick film), the blue test point voltage is
negative and the oil alarm is activated. If the RATIO volt-
age is above or below the “window” or is not steady
(either condition indicating a thin film), the blue test point
voltage will be negative and the oil alarm will not be acti-
vated.
SPECIFICATIONS
Specifications of the optional Film Thickness
Discriminator printed circuit board are tabulated below:
Power Consumption: less than 0.1 Watts
Alarm: Alarm relay is activated
and contacts open.
Alarm Response Time - ON: approximately 70 sec-
onds for an abrupt
change from clean water
to a continuous thick film
– longer if the thick film
has breaks in it.
Alarm Response Time - Off: approximately 5 seconds
for an abrupt change
from a continuous thick
film to clean water.
INSTALLATION
If the Film Thickness Discriminator board is ordered with
the instrument, the optional printed circuit board is
installed and ready for operation. If this option has been
ordered after the delivery of the instrument, one opera-
tional amplifier (A211) on the inside of the Rear Panel
p.c. board must be removed prior to installation of the
Film Thickness Discriminator board. Removing A211
disables the normal oil alarm condition where the relay is
activated on either thin films or thick films. The Film
Thickness Discriminator board is then plugged into the
Options p.c. board connector (see Figure 3 and P.C.
Board and Assembly Replacement procedure in the
MAINTENANCE Section of this manual).
SELECTABLE CRITERIA ALARM
OPTION
GENERAL DESCRIPTION
An optional printed circuit board for the Oil Slick
Detector, the Selectable Criteria Alarm option adds con-
siderable flexibility in selecting the criteria and condi-
tions under which the oil alarm will activate. This option
delays activation of the oil alarm relay until either of the
following conditions is met:
1. The time of uninterrupted oil observation* exceeds a
preset duration between 1 and 999 seconds. The
duration of oil observation is set in one second
increments by direct reading thumbwheel switches
labeled OIL DURATION (SECS) on the printed cir-
cuit board.
2. The percentage of accumulated time during which
oil observation* exceeds a preset percentage mea-
sured over a 1000 second interval. The percentage
of accumulated time is set in increments of 10% by
a direct reading thumbwheel switch labeled %OIL
(X10) on the printed circuit board.
*Oil observation is defined by the oil alarm threshold set-
ting.
NOTE
When either of the above conditions is met, the oil
alarm relay activates (contact open) for approxi-
mately 60 seconds, then deactivates (contacts
close). If oil film is constantly present in the detec-
tor’s field of view, the oil alarm will close twice
(once for each criteria) for approximately 60 sec-
onds every 1000 seconds.
For example, if the OIL DURATION switches are set for
20 seconds, the oil alarm relay will activate after the
instrument observes any continuous slick that exceeds
20 seconds in duration. However, if a large spill occurs
where the resulting slick observed by the instrument has
small 1 second breaks of clean water every 15 seconds
(due to turbulence, wind action, etc), the oil alarm relay
will not activate because no continuous period of oil
observation exceeds 20 seconds in duration. The inter-
nal timer is reset every time clean water is observed.
The alarm will not activate even though the water surface
is covered with oil 94% of the 1000 second measure-
ment cycle (15 out of every 16 seconds).
Following the same example, if the %OIL switch is set at
10%, the oil alarm relay will activate after the total accu-
mulated time of oil observation exceeds 10% of the 1000
second measurement cycle or 100 seconds. The oil
alarm relay will activate 106 seconds after the oil slick
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