GB2110501A - Housings for underwater measuring equipment - Google Patents

Abstract

A method of reducing weight and increasing operational reliability of underwater measuring equipment, e.g. a hydrophone or fluorimeter, characterised in that the part of the equipment to be protected is situated in an inert liquid such as a silicon compound in a housing that is not pressure-tight but that is liquid-tight and that is elastic, or has an elastic zone, to provide pressure equalization.

Description

SPECIFICATION A method of reducing weight and increasing reliability of underwater measuring equipment Equipment for use in underwater measurements, for example in situ fluorimeters, and hydrophones, are usually accommodated in appropriate pressure-tight housings suitable to the water depth in order to protect the circuitry, electronics, photodiodes or microphones from effects of salt water and from corrosion.

The disadvantage of all equipment having a pressure-tight housing is the great weight of the housing in relation to the weight of the instruments, so that any operation for taking measurements from a small vessel is often very tedious, since it may involve manual lowering of the equipment. Another disadvantage is that after the equipment has been opened on board the vessel, e.g. for replacement of an optical filter, even a small grain of sand in the region ofthe seal is enough to enable water to penetrate at high pressure, e.g. 10 bars at a water depth of 100 m.

It has now been found that the commercially available inert liquids (usually silicon compounds with saturated valencies) are both chemically inert and optically transparent in the visible spectral range, and are also highly insulating from the electrical stand point.

According to the present invention there is provided a method of reducing weight and increasing operational reliability of underwater equipment, characterised in that the part of the equipment to be protected is situated in an inert liquid that is in turn accommodated in a housing that is not pressure-tight but that is liquid-tight and that is itself or at a suitable point provided with an elastic zone that equalizes the different compressibility between water and the inert liquid Clearly some structural changes must be made particularly in the case of optical measuring instruments with lenses. These modifications relate mainly to the lens system.Depending upon the optical refractive index of the inert transparent liquid, the glass or quartz material must be made much thicker-a specific focal length must be maintained-in order to obtain the same focal length in the liquid. Glasses are available with a considerably increased refractive index.

To ensure that the hydrostatic pressure is substantially equalized inside and outside the equipment, the latter may itself be accommodated in a cylindrical tube and a metal suspension member or a diaphragm movable to some degree in both directions may be provided, in order to equalize the different compressibility movements between water and the inert liquid.

It is to be understood that flashlamps often used in such equipment will advantageously be provided with a curved and preferably thickwalled light exit window and, if necessary, the internal pressure will be increased somewhat, since the flashlamps often have a plane window and a xenon filling pressure of about 1 bar when used in a laboratory atmosphere or a pressuretight casing. Again, thyristor packages and transistors are usually pressure-tight to above 30 bars as shown by measurements that have been taken, and these require no special steps.

Very sensitive components which do not withstand storage and operation in an inert liquid can be provided with an elastomeric coating, that may if required be sprayed on, or some other protective coating with respect to the inert liquid, before final assembly. Measurements show that the method is particularly suitable for providing simplified and operationally reliable equipment in water depths down to about 100 to 200 m for use in connection with chlorophyll measurement by fisheries personnel and in the monitoring of pipelines.

Claims

1. A method of reducing weight and increasing operational reliability of underwater equipment, characterised in that the part of the equipment to be protected is situated in an inert liquid that is in turn accommodated in a housing that is not pressure-tight but that is liquid-tight and that is itself or at a suitable point provided with ari elastic zone that equalizes the different compressibility between water and the inert liquid.

2. The method as claimed in claim 1, wherein the inert liquid is radiation-transparent in the optical wavelength range.

3. The method as claimed in Claim 2, wherein depending upon the refractive index of the inert liquid those components of the optical measuring equipment which are in the form of lenses allow for the specified focal lengths together with said liquid and, if necessary, also allow for chromatic correction of the focal length.

4. The method as claimed in Claims 1 to 3, wherein electronic or optical components that are not fully insensitive to the inert liquid are provided with a protective film of elastic structure applied by immersion or spraying before assembly.

5. The method as claimed in Claims 1 to 3, wherein a gas discharge lamp is used in the measuring equipment for protection, such lamp is provided with a more intensely curved light exit area and, if necessary, an increased xenon filling pressure.

6. The method as claimed in Claim 1 , wherein a metal bellows provides pressure equalization between the water and the inert liquid, and such bellows may additionally be so devised as to bear the filling aperture for the complete system.

7. The method as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A method of reducing weight and increasing reliability of underwater measuring equipment Equipment for use in underwater measurements, for example in situ fluorimeters, and hydrophones, are usually accommodated in appropriate pressure-tight housings suitable to the water depth in order to protect the circuitry, electronics, photodiodes or microphones from effects of salt water and from corrosion. The disadvantage of all equipment having a pressure-tight housing is the great weight of the housing in relation to the weight of the instruments, so that any operation for taking measurements from a small vessel is often very tedious, since it may involve manual lowering of the equipment. Another disadvantage is that after the equipment has been opened on board the vessel, e.g. for replacement of an optical filter, even a small grain of sand in the region ofthe seal is enough to enable water to penetrate at high pressure, e.g. 10 bars at a water depth of 100 m. It has now been found that the commercially available inert liquids (usually silicon compounds with saturated valencies) are both chemically inert and optically transparent in the visible spectral range, and are also highly insulating from the electrical stand point. According to the present invention there is provided a method of reducing weight and increasing operational reliability of underwater equipment, characterised in that the part of the equipment to be protected is situated in an inert liquid that is in turn accommodated in a housing that is not pressure-tight but that is liquid-tight and that is itself or at a suitable point provided with an elastic zone that equalizes the different compressibility between water and the inert liquid Clearly some structural changes must be made particularly in the case of optical measuring instruments with lenses. These modifications relate mainly to the lens system.Depending upon the optical refractive index of the inert transparent liquid, the glass or quartz material must be made much thicker-a specific focal length must be maintained-in order to obtain the same focal length in the liquid. Glasses are available with a considerably increased refractive index. To ensure that the hydrostatic pressure is substantially equalized inside and outside the equipment, the latter may itself be accommodated in a cylindrical tube and a metal suspension member or a diaphragm movable to some degree in both directions may be provided, in order to equalize the different compressibility movements between water and the inert liquid. It is to be understood that flashlamps often used in such equipment will advantageously be provided with a curved and preferably thickwalled light exit window and, if necessary, the internal pressure will be increased somewhat, since the flashlamps often have a plane window and a xenon filling pressure of about 1 bar when used in a laboratory atmosphere or a pressuretight casing. Again, thyristor packages and transistors are usually pressure-tight to above 30 bars as shown by measurements that have been taken, and these require no special steps. Very sensitive components which do not withstand storage and operation in an inert liquid can be provided with an elastomeric coating, that may if required be sprayed on, or some other protective coating with respect to the inert liquid, before final assembly. Measurements show that the method is particularly suitable for providing simplified and operationally reliable equipment in water depths down to about 100 to 200 m for use in connection with chlorophyll measurement by fisheries personnel and in the monitoring of pipelines. Claims

1. A method of reducing weight and increasing operational reliability of underwater equipment, characterised in that the part of the equipment to be protected is situated in an inert liquid that is in turn accommodated in a housing that is not pressure-tight but that is liquid-tight and that is itself or at a suitable point provided with ari elastic zone that equalizes the different compressibility between water and the inert liquid.

2. The method as claimed in claim 1, wherein the inert liquid is radiation-transparent in the optical wavelength range.

3. The method as claimed in Claim 2, wherein depending upon the refractive index of the inert liquid those components of the optical measuring equipment which are in the form of lenses allow for the specified focal lengths together with said liquid and, if necessary, also allow for chromatic correction of the focal length.

4. The method as claimed in Claims 1 to 3, wherein electronic or optical components that are not fully insensitive to the inert liquid are provided with a protective film of elastic structure applied by immersion or spraying before assembly.

5. The method as claimed in Claims 1 to 3, wherein a gas discharge lamp is used in the measuring equipment for protection, such lamp is provided with a more intensely curved light exit area and, if necessary, an increased xenon filling pressure.

6. The method as claimed in Claim 1 , wherein a metal bellows provides pressure equalization between the water and the inert liquid, and such bellows may additionally be so devised as to bear the filling aperture for the complete system.

7. The method as hereinbefore described.