Patent GB-1230179-A (GB)
IPC: G01V3/11
Filed: 1968-10-16
Abstract: 1,230,179. Detecting objects immersed in fluid. WILLIAM H. SWAIN CO. Oct. 16, 1968, [Oct.23, 1967], No.48955/68. Heading G1N. An object immersed in a fluid medium (e.g. the sea-bed, bank of a river, mine &c. ) is detected by applying a signal to a pair of transmitter electrodes spaced apart and in contact with the fluid, and measuring the signal at at least one receiver electrode in contact with the fluid and positioned in spaced relation to the transmitter electrodes. The apparatus shown is applied to depth finding and channel following in ships, and includes transmitter electrodes 24, 30 supplied with a square-wave signal, depth finder receiver electrodes 60, 84 displaced an equal distance from the mid-point 90 between the electrodes 24, 30, and channel follower receiver electrodes 102, 104 displaced an equal distance from the centre-line 26 and closer to the electrode 30. Channel following or depth finding operation is selected by a switch 68. For channel following operation, the signal picked up by electrodes 102, 104 is dependent upon the proximity of the bank of a channel and is applied to an amplifier 72 and a phase sensitive detector 108 where it is compared with the signal from oscillator 14, the averaged product of the signals then appearing on a meter 112 which is calibrated by balancing adjustment of the detector 108. For depth finding operation, the signal picked up by electrodes 60, 84 is dependent upon the proximity of the sea-bed, and the potential between electrodes 60, 84 is balanced to provide a reference signal for the electrodes by a bridge circuit including electrodes 32, 34 adjacent transmitter electrodes 24, 30, potential divider 44, potentiometer 40, and transformer 50. An indication is obtained on the meter 112 in the same way as before. The wiper 54 of the potentiometer 40 and the gain 74 of the amplifier are used to calibrate the meter 112. The construction of the oscillator, amplifier, detector and meter is described with reference to Fig. 7 (not shown). The electrodes 32, 34 act to reduce corrosion effects of the electrodes. Either channel following or depth finding may be provided alone or may be achieved simultaneously Fig. 11 (not shown), in which case the switch 68 is replaced by a pair of transformers, the secondaries of which are each connected to their respective amplifier and meter. The primary of one transformer is connected to the channel follower electrodes, the primary of the other being connected to a centre-tap of the primary of the one transformer and to the wiper of a potentiometer connected across the electrodes adjacent the transmitter electrodes. The centre-tap has the effect of a single depth finding electrode placed between the channel follower electrodes. In further alternatives, one of the depth finder electrodes may be omitted and replaced by a potentiometer connected across the transmitter electrodes, the wiper being connected to the amplifier, Fig. 10 (not shown). For the detection of objects, such as mines, the channel follower electrodes are placed mid-way between the transmitter electrodes and are connected directly to the amplifier. The phase sensitive detector may be omitted if sensitivity and range are not important. Other forms of oscillatory signals may be used or even direct voltages and currents in special cases.