4
■
Detector
(Fig.4-1)
(a) Way of detection
When all of the detecting electrodes come in contact with oil at an oil depth from 3 to 5
mm, this device functions to detect the presence of oil there.
When any of the electrodes, even only one electrode, is in contact with water, no detection
signal is sent out from the device.
The purpose of this design is to prevent the device from giving out erroneous signals
influenced by the force of waves, wind, etc. when there is no abnormal existence of oil.
(b) Theory
Detector floats on water with its electrode points in touch with water surface about 2 mm.
(in case of 3-5 mm range detection depth).
Inside the detector are set high frequency wave oscillation circuit, AC bridge circuit,
switching circuit and constant voltage power source circuit To the AC bridge circuit is
impressed high frequency (approx. 1 MHz) power, and part of the bridge is connected in
parallel to the three electrodes.
Namely, the AC bridge circuit monitors the changes in electrostatic capacity around the
electrodes.
When oil flows out on water surface, and it comes to contact the electrodes, the
electrostatic capacity around them largely varies to cause the balance in the AC bridge
circuit to be reversed.
This variation is caught and amplified at the switching circuit subsequently, it is turned
into current signal at the constant voltage power source circuit and this signal is sent to
transducer. When oil is detected at approx. 14 mA DC under ordinary conditions, this
signal becomes approx. 4 mA DC.
Fig. 4-1 Detector
∞
N
B
A
i
P'
N'
Between B &Earth Impedance
High frequency wave
oscillator
Detecting electrodes
Oil depth
Water
Earth
Switching
circuit
Power source
Functional theory of “Apolarm-C”
