GB2057156A

GB2057156A - Thermal protective device for a lens

Info

Publication number: GB2057156A
Application number: GB8024076A
Authority: GB
Original assignee: WOOLEN D
Current assignee: WOOLEN D
Priority date: 1979-08-13
Filing date: 1980-07-23
Publication date: 1981-03-25

Abstract

A device, for protecting a lens against exposure to high temperatures e.g. at an opening in a furnace wall, comprises an open-ended duct (10) positioned in front of the lens (17) having a rear heat shield (15) with a small aperture (16) and a compressed air or other gas inlet (25,26) which directs a blast of air across the aperture (16) and then along the length of the duct away from the lens. <IMAGE>

Description

SPECIFICATION Thermal protective devices This invention relates to devices for protecting sensitive equipment from exposure to high temperatures.

The invention is partly though not exclusively applicable to apparatus for protecting the lens of a television camera used to observe the interior of a furnace kiln or the like.

Attempts have been made to protect cameras in such situations and one such proposal involves an elongated duct to be positioned in front of the lens with a series of internal transparent screens and means for passing a stream of compressed air over the screens in series. One of the great disadvantages of such a system is that compressed air supplies available in steelworks and the like are extremely dirty and depositis of oils and dirt form rapidly on the screens, necessitating frequent laborious cieaning operations.

Accordingly it is an object of the invention to provide an improved thermal protective device which will be reliable in operation and will not require frequent maintenance.

Broadly stated, the invention consists in a thermal protective device for the lens of an optical instrument comprising an elongated straight duct open at its front end and having a small aperture at its rear end to be located over the optical lens and including means for introducing a flow or compressed air or other gas adjacent the rear end of the duct to flow axially through the duct towards its front end.

According to a preferred feature of the invention the small aperture at the rear end is less than 2 mm in diameter.

According to another preferred feature of the invention the aperture is less than 1 mm in diameter.

Preferably the apparatus includes means for providing a closed chamber around the actual lens of the instrument and communicating with the ducts through the small aperture.

It is also desirable that the gas entry port at the rear end of the duct is designed to cause a stream of gas to flow rapidly across the small aperture.

According to another preferred feature of the invention the apparatus includes a device mounted at or supported by a collapsible support having a connection to the same compressed gas supply and so arranged that if the supply pressure fails, the supply also fails and the whole device, including the optical instrument, is moved clear of the furnace opening.

The invention may be performed in various ways and one preferred embodiment will now be described, with reference to the accompanying drawings, in which: Figure 1 is a somewhat diagrammatic side elevation illustrating a protective device according to the invention in place in front of the lens of a television camera, Figure 2 is an end view of the device according to Figure 1, and Figure 3 is a diagrammatic side elevation illustrating the complete equipment in position against a furnace wall.

In this example the apparatus comprises a steel duct 10 of approximately 50 mm diameter with an open front end 11 designed to be inserted with a slight clearance within an opening 12 in a furnace wall 13.

At the rear end of the ductthere is a steel plate 15 with a small central aperture 16to be centrally positioned overthe lens 17 of a closed circuit T.V.

camera 18. This lens may be, for example, a 25 mm fixed focus lens such as a Dallmeyer Super Six. The aperture 16 is preferably less than 2 mm in size and in this example is .7 mm diameter. The steel heat shield plate 15 is mounted clear in front of a rear annular mounting plate 20 provided with mounting bolts 21 by which the unit is secured with an interposed gasket 22 to the front face of the T.V.

camera. This provides an annular sealed space 23 surrounding the T.V. lens and communicating with the aperture 16.

Compressed air from the normal plant supply (which may therefore be extremely oily and dirty) is connected by a flexible hose to an air inlet 25 which communicates via an elbow bend with an inlet port 26 at the rear end of the main duct 10. The high velocity air stream flows across a small aperture 16 and then axially along the length of the duct towards the furnace opening. It is found in practice that this arrangement practically eliminates or greatly reduces the deposit of dirt on the T.V. camera lens and the small size of the aperture 16 is in fact a suprising benefit. The images produced of the interior of the furnace at high temperatures are much improved.

In the general assembly arrangement illustrated in Figure 3, a camera 18 combined with the protective duct system 10 is shown mounted for vertical movement on a pair of vertical supports or guides 30 and is normally maintained in its operative upper position by means of a pneumatic jack 31 connected by a pipe 32 to the same compressed air supply line 33 which is also connected by a flexible hose 34 to the air inlet 25. If the compressed air pressure fails, the pneumatic jack 31 will collapse and the camera is automaticaly moved clear of the furnace opening 12.

If this were not so, the failure of the compressed air supply would make the protective device inoperative and the camera would be rapidly destroyed.

1. A thermal protective device for the lens of an optical instrument comprising an elongated straight duct open at its front end and having a small aperture at its rear end to be located over the optical lens and including means for introducing a flow of compressed air or other gas adjacent the rear end of the duct to flow axially through the duct towards its front end.

2. A device according to claim 1 in which the small aperture at the rear end is less than 2 mm in diameter.

3. A device according to claim 2, in which the aperture is less than 1 mm in diameter.

4. A device according to any of the preceding

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Thermal protective devices This invention relates to devices for protecting sensitive equipment from exposure to high temperatures. The invention is partly though not exclusively applicable to apparatus for protecting the lens of a television camera used to observe the interior of a furnace kiln or the like. Attempts have been made to protect cameras in such situations and one such proposal involves an elongated duct to be positioned in front of the lens with a series of internal transparent screens and means for passing a stream of compressed air over the screens in series. One of the great disadvantages of such a system is that compressed air supplies available in steelworks and the like are extremely dirty and depositis of oils and dirt form rapidly on the screens, necessitating frequent laborious cieaning operations. Accordingly it is an object of the invention to provide an improved thermal protective device which will be reliable in operation and will not require frequent maintenance. Broadly stated, the invention consists in a thermal protective device for the lens of an optical instrument comprising an elongated straight duct open at its front end and having a small aperture at its rear end to be located over the optical lens and including means for introducing a flow or compressed air or other gas adjacent the rear end of the duct to flow axially through the duct towards its front end. According to a preferred feature of the invention the small aperture at the rear end is less than 2 mm in diameter. According to another preferred feature of the invention the aperture is less than 1 mm in diameter. Preferably the apparatus includes means for providing a closed chamber around the actual lens of the instrument and communicating with the ducts through the small aperture. It is also desirable that the gas entry port at the rear end of the duct is designed to cause a stream of gas to flow rapidly across the small aperture. According to another preferred feature of the invention the apparatus includes a device mounted at or supported by a collapsible support having a connection to the same compressed gas supply and so arranged that if the supply pressure fails, the supply also fails and the whole device, including the optical instrument, is moved clear of the furnace opening. The invention may be performed in various ways and one preferred embodiment will now be described, with reference to the accompanying drawings, in which: Figure 1 is a somewhat diagrammatic side elevation illustrating a protective device according to the invention in place in front of the lens of a television camera, Figure 2 is an end view of the device according to Figure 1, and Figure 3 is a diagrammatic side elevation illustrating the complete equipment in position against a furnace wall. In this example the apparatus comprises a steel duct 10 of approximately 50 mm diameter with an open front end 11 designed to be inserted with a slight clearance within an opening 12 in a furnace wall 13. At the rear end of the ductthere is a steel plate 15 with a small central aperture 16to be centrally positioned overthe lens 17 of a closed circuit T.V. camera 18. This lens may be, for example, a 25 mm fixed focus lens such as a Dallmeyer Super Six. The aperture 16 is preferably less than 2 mm in size and in this example is .7 mm diameter. The steel heat shield plate 15 is mounted clear in front of a rear annular mounting plate 20 provided with mounting bolts 21 by which the unit is secured with an interposed gasket 22 to the front face of the T.V. camera. This provides an annular sealed space 23 surrounding the T.V. lens and communicating with the aperture 16. Compressed air from the normal plant supply (which may therefore be extremely oily and dirty) is connected by a flexible hose to an air inlet 25 which communicates via an elbow bend with an inlet port 26 at the rear end of the main duct 10. The high velocity air stream flows across a small aperture 16 and then axially along the length of the duct towards the furnace opening. It is found in practice that this arrangement practically eliminates or greatly reduces the deposit of dirt on the T.V. camera lens and the small size of the aperture 16 is in fact a suprising benefit. The images produced of the interior of the furnace at high temperatures are much improved. In the general assembly arrangement illustrated in Figure 3, a camera 18 combined with the protective duct system 10 is shown mounted for vertical movement on a pair of vertical supports or guides 30 and is normally maintained in its operative upper position by means of a pneumatic jack 31 connected by a pipe 32 to the same compressed air supply line 33 which is also connected by a flexible hose 34 to the air inlet 25. If the compressed air pressure fails, the pneumatic jack 31 will collapse and the camera is automaticaly moved clear of the furnace opening 12. If this were not so, the failure of the compressed air supply would make the protective device inoperative and the camera would be rapidly destroyed. CLAIMS

4. A device according to any of the preceding claims, including means for providing a closed chamber around the actual lens of the instrument and communicating with the ducts through the small aperture.

5. A device according to any of the preceding claims, in which the gas entry port at the rear end of the duct is designed to cause a stream of gas to flow rapidly across the small aperture.

6. A device according to any of the preceding claims, mounted at or supported by a collapsible support having a connection to the same compressed gas supply and so arranged that if the supply pressure fails the supply also fails and the whole device, including the optical instrument, is moved ctearofthefurance opening.