GB2230862A - Depth gauge - Google Patents

Abstract

A depth gauge comprises a first unit in the form of a housing attached or attachable to a line to enable its retrieval and being of a weight to sink to the bottom of water when cast therein. The housing incorporates a pressure transducer 14 producing a pressure-dependent output signal, a power source 20 and a memory 22 for storing sample values of the transducer output signal at regular intervals as the housing is pulled across the bed of the water during retrieval of the housing at a uniform rate by means of the line. A second unit in the form of a display device connectable to the first unit after retrieval of the latter enables transfer of the sample values in a manner which displays the profile of the bed of the water. <IMAGE>

Description

Title Depth Gauqe Field of the invention This invention relates to a depth gauge, and more especially to a gauge for measuring the changing depths of the bottom of a river, pond, lake or analogous limited stretch of water, and also relates to a method of depth measurement.

Background to the invention Anglers, in particular, would like to know the profile of the bottom of a river, pond or lake in which they are fishing, because this profile is indicative of the best position at which to cast a fishing line in order to catch particular species of fish.

Anglers fishing in the sea from a beach, are very interested in the depth of water. Locating the best depth of water, or the drop-off point where the water deepens rapidly would be very useful.

One object of the present invention is to enable the profile of the bottom of a river, pond or lake to be determined without leaving the bank or water's edge.

While being especially suited to use by anglers, the gauge in accordance with the invention may also be useful in other fields, for example to assist investigation of silting up of a river or harbour mouth or the like.

River and reservoir managment regularly require bottom mapping usually done from a boat with an echo sounder. It is a further object of the invention to provide a device which can be cast from a moored boat, and retrieved to give a profile of the bottom.

The invention According to one aspect of the invention, there is provided a depth gauge comprising a first unit in the form of a housing attached or attachable to a line to enable its retrieval and being of a weight to sink to the bottom of the water when cast therein, the housing incorporating a pressure transducer for producing a pressure-dependent output signal and, in addition to a power source, a memory for storing sample values of the transducer output signal at regular intervals as the housing is pulled across the bed of the water during retrieval of the housing at a uniform rate by means of the line; and a second unit in the form of a display device connectable to the first unit after retrieval of the latter to enable transfer of the sample values in a manner which displays the profile of the bed of the water.

According to another aspect of the invention, therefore, there is provided a method of water depth measurement according to which a unit incorporating a pressure transducer is cast into the water to sink to the bottom thereof, the unit is retrieved by use of a line from the water's edge at a uniform rate, during retrieval sample values of a depth-dependent output signal from the transducer are regularly stored, and after retrieval the stored values are displayed in a manner which reveals the profile of the bed of the water across which the unit has been dragged during retrieval.

A suitable memory may be a FIFO (first-in/first-out) storage device capable of storing, for example, one hundred values of the transducer output signal. Thus, with a cast of say 50 metres and a retrieval time of 25 seconds, storage of a sampled value every 0.25 of a second would record the depth every 0.5 metre of movement across the water bed.Generally, rivers, ponds or lake edges to be gauged will not exceed 5 metres in depth, and if an accuracy within 0.5 metre depth is accepted, the total bit storage required would be sufficiently modest to be well within the capacity of a relatively inexpensive FIFO memory. after retrieval, plugging the fifo memory into a suitable LCD display device would give a reasonably accurate profile of the bed of the river, pond or lake, certainly of sufficient accuracy to enable an angler to know where best to cast a fishing line for fishing purposes.

However, it will be appreciated that the above-described proposal for use of a simple FIFO memory does not preclude from the invention the use of different types of memory means with greater capacity and accuracy allowing depth measurement to 0.2m or 0.lm accuracy for example, should this be required.

Description of embodiment The apparatus and method in accordance with the invention is exemplified in the following description, making reference to the accompanying drawings, in which: Figure 1 shows a pressure transducer unit; Figure 2 shows a display unit; and Figure 3 is a circuit diagram.

The illustrated depth gauge in accordance with the invention comprises a pressure transducer unit (Figure l) and a display unit (Figure 2).

The pressure transducer unit comprises a generally sausage-shaped housing 10 tapering towards one end, and weighted at the other end.

A line (not shown) is attached to the ring 12 at the tapered end so that the unit can more easily be drawn by or through obstructions, eg weeds, reeds, etc. The housing has adjacent the tapered end a window sealed by a pressure sensitive transducer 14 and an exposed sealed in place socket 16 for receiving a plug 18 forming part of the display unit (to be described).

The housing is preferably rigid, but may possibly have flexible walls which transmit pressure from the exterior to the interior, so that the transducer can be fitted within the housing interior. A suitable transducer is sensitive in the range 0 - 15 p.s.i., such as a Mullard Sensym (Trade Mark) 5P x 100 DN.

Within the housing 10 is incorporated a 6V battery power source 20 and a FIFO memory device 22 connected to the transducer output by the circuit shown in Figure 3. A suitable FIFO memory is one capable of storing one hundred values of any combination of the digits 0 to 9.

The circuit shown in Figure 3 comprises the pressure transducer 14 energised by the source 20, which is only switched on by a pressure sensitive switch 24 below a water depth of about 0.3 m at the transducer. The output of the transducer 14 is reduced to the range 0 to 60 mV by a resistive divider 26, and this reduced level output is taken to a differential amplifier 28 having an associated blocking diode 30. The output of the differential amplifier 28 is fed to the fifo memory device 22, which is stepped by a variable frequency oscillator 32 controlling a pulse generator 34, and also powered from the battery source 20.

The unit may be attached to the end of a fishing line.

In use, the unit is cast by hand or by use of a fishing rod into the water, whereupon it sinks to the bottom. The unit is then retrieved by use of the line at a uniform rate. Given a cast of 50 m, for example, and retrieval at a uniform rate during a period of 25 seconds, then if the oscillator 32 is adjusted so that a stepping pulse for the FIFO memory 22 is produced every 0.25 sec, the pressure and therefore water depth is stored in the memory 22 every 0.5 m of movement while the unit is being dragged across te bed of the water, e.g. a river, pond or lake, during its retrieval. One hundred sample values of the depth are stored during retrieval, within an accuracy of 0.5 m, which is sufficiently accurate to define the profile of the bed of the river or the like sufficiently closely for most purposes, and certainly for the purpose of an angler as an aid to efficient fishing.

However, it will be appreciated that the accuracy of profile definition achieved is dependent on the distance by which the unit is cast from the water's edge and the number of samples taken during retrieval, and it is for this reason that the frequency of generation of the pulses for stepping the FIFO memory is adjustable. By initially making an experimental cast and retrieval, the frequency of pulse generation can be adjusted to the value which ensures full utilisation of the capacity of the FIFO memory, so that in any given circumstance the most accurate possible definition is achieved. Moreover, if greater accuracy is required, a memory device of greater capacity, possibly of a type other than a FIFO memory, can be employed, in which case it may also be possible to store more precise values of the depths at the sampling positions or sampling times.In any case, it is important to note that the depth measurement and sampling circuitry is only operative when the unit is below a depth of 0.3 m (or any other selected depth predetermined by the characteristic of the pressure sensitive switch), so that depth values during casting and final reeling in are not stored.

The display unit shown in Figure 2 comprises an LCD display area 38 conventionally activated by successive signals read out from the FIFO memory when the display unit is connected by means of the plug 18 to the socket 16 of the pressure transducer unit following retrieval of the latter. Transfer of sampled values is initiated by a switch 40 and, after all the sampled depth values have been transferred, the display area shows a profile 42 of the bed of the river or other stretch of water, albeit in steps rather than a continuous curve. The horizontal axis of the displayed profile is, of course, with respect to distance cast (assuming a constant retrieval rate) and must be interpreted accordingly.

If desired, the pressure transducer unit may have a manually operable switch for switching on power, the pressure sensitive switch serving only to control the period for which the memory is operative.

Various other modifications of the above described arrangement are possible within the scope of the invention hereinbefore defined.

Claims (8)

Claims

1. A depth gauge comprising a first unit in the form of a housing attached or attachable to a line to enable its retrieval and being of a weight to sink to the bottom of the water when cast therein, the housing incorporating a pressure transducer for producing a pressure dependent output signal, a power source and a memory for storing sample values of the transducer output signal at regular intervals as the housing is pulled across the bed of the water during retreival of the housing at a uniform rate by means of the line; and a second unit in the form of a display device connectable to the first unit after retrieval of the latter to enable transfer of the sample values in a manner which displays the profile of the bed of the water.

2. A gauge according to claim 1 in which the memory is a FIFO (first-in/first-out) storage device.

3. A gauge according to claim 2 in which the FIFO Storage Device is capable of storing 100 values of the transducer output signal.

4. A gauge according to any of the preceding claims in which the second unit comprises an LCD display.

5. A gauge according to any of the preceding claims in which the first unit includes a pressure sensitive switch operable to activate the first unit only when the latter is suitated below a predetermined minimum depth of water.

6. A method of water depth measurement comprising the steps of: a) casting a unit, which is attached to a line and which incorporates a pressure transducer, into the water to sink to the bottom thereof; b) retrieving the unit by means of the line from the water's edge at a uniform rate; c) sampling values of a depth-dependent output signal from the transducer at regular intervals during retrieval, and storing the sampled values; d) displaying the stored values in a manner which reveals the profile of the bed of the water across which the unit has been dragged during retrieval.

7. A gauge substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

8. A method as substantially described herein with reference to the accompanying drawngs.