Det-Tronics SW9200x Slickwatch IR Oil Detection System - Manual (Page 4)

TRANSMITTER
The transmitter projects a beam of light onto the water
surface to be monitored. A tungsten halogen lamp is
mounted at the focal point of an aluminum parabolic
reflector in the transmitter housing.
RECEIVER
The receiver contains the optical and mechanical com-
ponents and electrical circuits that receive the light emit-
ted by the transmitter and process the signal to obtain
an oil film/no oil film output.
Receiver Lens
Light enters the receiver through the infrared transmitting
lens located within the lensholder. The lens focuses the
incoming light onto the face of the infrared photodetec-
tor.
Filterwheel Motor
This motor is a small 115 VAC shaded pole ball-bearing
motor. The filterwheel is attached to the motor shaft.
Filterwheel
The filterwheel is located between the receiver lens and
the photodetector. It contains the DENOMINATOR
(active) and NUMERATOR (reference) optical interfer-
ence filters. Rotating at a rapid rate, the filterwheel
chops the incoming light beam and alternately passes
infrared light at the two distinct wavelengths to the pho-
todetector.
Sync Pickoff
The sync pickoff is a small, “U”-shaped optical switch
mounted on the Rear Panel printed circuit board and
straddling the filterwheel. It employs a light source and
a silicon photodetector at opposite ends of the “U” to
sense when each filter is in front of the infrared photode-
tector. Light emitted by the sync pickoff passes through
slots in the outer edge of the filterwheel and generates
the synchronization signal.
Photodetector
The infrared photodetector is mounted at the focal point
of the receiver lens. The photodetector converts the
intensity of the incoming infrared light to a proportional
electrical signal. It alternately senses the light intensity
at both wavelengths during each revolution of the filter-
wheel. The photodetector is thermo-electrically cooled
to increase the sensitivity to infrared light.
Amplifiers
The signal at the photodetector is amplified by the
preamplifier circuitry. The gain of the preamplifier can
be adjusted with an internal potentiometer to optimize
the signal strength for long or short operating distances.
The amplified signal is fed to the AGC amplifier, which
maintains the signal within the proper operating range.
Signal Processing Electronics
The signal from the AGC amplifier is separated into two
outputs: active (DENOMINATOR) and reference
(NUMERATOR).
Ratiometer
The ratiometer circuit generates an analog output by cal-
culating the ratio of the NUMERATOR (reference) signal
to the DENOMINATOR (active) signal.
Optional Film Thickness Discriminator
This option converts the 0 to 10 VDC voltage into a posi-
tive voltage (approximately +1.0 VDC) for “thin” oil films
(average thickness of less than 10 micrometers) and a
negative voltage (approximately -15.0 VDC) for “thick” oil
films (average thickness greater than 10 micrometers).
With this option the oil alarm relay is energized when a
“thick” film is present and inhibited when a “thin” film is
present.
Optional Selectable Criteria Alarm
With this option the oil alarm relay activates only if either
of the following conditions are met:
1. The time of uninterrupted oil observation exceeds a
preset duration between 1 second and 999 sec-
onds.
2. The percentage of accumulated time during which oil
is observed exceeds a preset percentage between
10% and 90% measured over a 1000 second interval.
Optional 4-20 mA Converter
This option converts the 0 to 10 VDC voltage into a 4 to
20 mA current when a load resistor is connected
between the RATIO output and the signal ground. The
loop resistance cannot exceed 500 ohms.
Threshold Detector: Oil Alarm Relay
This threshold detector activates when the voltage of the
RATIO increases above a preset value. Activation of this
threshold detector causes the oil alarm relay to energize
indicating that oil is present on the water surface within
the instrument’s field of view. The threshold level at
which the oil alarm relay is energized can be adjusted
and tested on the front panel.
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