GB2186993A - Viewing systems with variable field of view - Google Patents

Abstract

A system for viewing in pipework or space containing radioactive material comprises a video camera for receiving light through an optical arrangement which is movable to change the field of view angularly. In an embodiment a video camera 63 receives light from a lens 64 in a containment wall 60, a prism deflector 65, a telescope 66, a prism unit 68 and a prism 67. The unit 68 has two prisms and one or both these and/or prism 67 can be rotated to change angularly the field of view through window 69. A roof-mounted arrangement is described. <IMAGE>

Description

SPECIFICATION Viewing systems This invention relates to viewing systems and in par ticular systems for viewing space containing radioactive material or emissions from radioactive material. Such material is often in a so-cailed cell or cave.

In the past, the viewing of in-cell equipment has been restricted to looking through viewing windows of either the zinc-bromide or the solid stabilised glass blocktypes; the cost in general has limited their use to the control face of a cell. The view ofthe in-cell equipment obtained from the resultant window positions is limited, generally to a plan ora viewto one side of the equipment with, in some cases, a plan or side view as an option from another window. The requirements to see other faces leads to ad-hoc methods, eg. mirrors placed in-cell. It is also advantageous in some cases to obtain a closeup view of specific small areas when a problem arises, and past practice has been to use a pair of binoculars looking through a cell window, which incurs the same limitations as normal window viewing.

According to this invention an optical system comprises a video camera for receiving lightthrough an optical arrangement, the arrangement being movable to change the field ofviewangularly.

The optical arrangement may comprise a prism which can be rotated about two axes transverse to eachothertogiveascan andtilteffect.

The optical arrangement may comprise two prisms.

The two prisms may be movable relative to each otherto effectthe change in the field of view.

The system may include a telescope device between the optical arrangement and the camera for moving the light path sideways. Such a construction is particularlysuitableforwhen the system isto be used to view the interior of a containment for radioactive material; the telescope device can be mounted in an aperture in a shield wall and the camera positioned laterally of the aperture to avoid radiation passing through the aperture falling on the camera optical inlet.

The invention may be performed in various ways and some specific embodiments with possible modifications will now be described by way of example with reference to the accompanying drawings, in which: Figure 7A to lCshow an optical shift system; Figure 2 shows another optical shift system; Figure3A to3Cshowa prism optical shift system; Figure4shows a radiation shielded optical system; Figure 5shows a viewing system mounted in a cell orcontainment roof orwall; and Figure 6shows a viewing system mounted in a cell or containment rooforwall.

Referring to Figures 1Ato 1 C, an optical shift system 10 including rotating prism system 14,15 is shown, for use with a video orTV camera 1 to provide a scanning motion to an optical path without moving the camera 11.

Two identical wedge or triangular-section prisms 12, 13 are shown, preferably right-angle prisms, having longer and shorter sides orfaces 14, and hypo tenuse or face 16 (as seen in the drawing) with the sides 14 parallel and adjacent (Figure 1A) and sides 15 coplanar. The sides 14 need not be parallel, the sides 15 need not be coplanar.

Light is focussed at 20 at the light sensitive faceplate of the camera 11. Rotating the two wedge prisms either singly or together, relative to the camera or relative to one another, enables a deviation or movement of the line of sight to be obtained.

Both prisms can be co-rotated or contra-rotated (Figure 1Ato Figure 1C) which follows a straight line deviation of the field or either prism can be rotated separately (Figure 1Ato Figure 10) which produces a complex circular deviation of the field. One operative angle of each prism is typically less than 30". The limitation with this system isthe amount of optical distortion produced by a deflection, . Atypical wedge angle is approximately 12". With larger deviation angles there is a variable amount of refraction when light passes through such a prism, ie. there will be a limitation of viewing angle due to the dispersion of white light.Chromatic prisms which are corrected for this dispersive error can reduce this effect, but the thickness of the prisms is increased to such an extent that the effect of viewing "through a tube" results (see Figure 2) unless the field angle is kept small.

This principle can however be used where a small deflection is required, and so becomes a practical arrangement when the optical system is mounted a large distance away from the viewed object. In all incell applications this is the case, the distance from the viewing plane orviewed object two the optical system is relatively large and the deviation angle necessary to cover the required area is small.

The prisms are preferably but not necessarily placed concentrically on the camera axis 30.

Rotating the prisms gives a pan and tilt effect ie.

the field of view given by the camera can be moved so as to be directed to a selected position.

The prisms can be driven in synchronism by stepper motors controlled by a pulsed current gener- ator, to give a linear panning motion. The deflection or pan angle is dependent on the shape ofthe prisms and their distance from the camera.

Atilting and swivelling prism system is shown in Figures 3Ato 3C. A prism is used to "bend" the optical path as required and keeps the camera shielded from the radiation field, the near 90" deflection increasing the effect of given shielding. Using the prism a view is given which can be from normal to the rooforwall into which the system is placed to parallel to the roof orwall. If the prism may also rotate about a centreline which is to the normal to the roof orwall, panning in all directions then becomes possible. There is an advantage with this method over the rotating prism system since a greater total field of view is available.However, this type of panning tends to rotate the picture as seen relative to the monitor, whereas the rotating prism method (Figure 1 ) keeps the view in the same orientation on the screen. This disadvantage can be overcome by employing a camera rotation facility which has the added advantage that irrespective of where the camera is mounted relative to the field ofviewrequi- red, the field of view can always be presented in the required manneronthemonitororvariedasapp- ropriate at will.

The prism 31 Figure 3A can be rotated about an X-X axis (to give a tilt angle) passing through the mid-points of parallel longer sides 32,33 of the hypo tenuse surface 34, and aboutthe Y-Y axis (to give a 'scan' angle) at right angles to the mid point of one side of the right angled 45" prism. As can be seen from Figures 3B,3Cthe prism 31 is placed in front of the camera lens and/or an optical telescope system (see below) and rotated either about the centre line ofthe camera (Y-Y) or about an axis at 90" to the centre line,which runs parallel to the largest surface of the prism (X-X).The rotations can be obtained with stepper or other motor drives to give a remote tilt and pan facility and so achieve a total field of view covering a full hemisphere without moving the camera 11.

The telescope system as shown in Figure 4 provides a solution to the difficulty of placing the shield in front of the TV camera lens. This system consists of a field widening telescope 50 which is placed in the shielding block 51 but displaced relative to the TV camera 11 so that the optical path is shifted through the offset distance by means oftwo reflecting prism faces 12. This principle enables the field angle ofthe TV camera lens offor example 34 , or other angle as desired,to be obtained on the hotside of the cell wall, whilstthe camera is kept behind the appropriate amount of shielding. Radiation 53 misses the lens.

Another advantage ofthe optical system is thatthe spread of the optical field is kept to a minimum when passing through the shielding and when used in conjunction with a swivelling prism the required panning movement ofthe optical path is simultaneously obtained.

A standard closed circuit TV camera 11 and a zoom lens with non-stabilised glass lenses is used. Afield widening telescope 50 reduces the size of the optical pathway so that a relatively small aperture is required in the shielding 51.

In a modificationtheTVcamera is placed in line with the telescope and the telescope is designed with shielding glass between the front and back lens distance.

The aperture may alternatively be filled with glass.

The telescope optics are matched to the zoom lens and glass plug characteristics so that focussing is possible overthe entire zoom range ofthe lens.

Because the longitudinal magnification ofthefield widening telescope is the square of the angular magnification, there is the additional advantage in this configuration thatobjects very close to the prism may be focussed.

Figure 5 illustrates a wall-mounted system. An aperture in wall 60 has a liner 61 and a camera plug or rear biological shielding 62 mounts a standard closed circuit TV camera unit 63 and a zoom lens 64.

Zoom magnification may vary, for example up to 10:1. Atwo-sided 45 prism 65 and lens 64 as in Figure 4 receives light through an optical telescope 66 comprising a circular section tube 66 with lenses which receives light from a pivotable prism 67. In a modification in the case where prism 67 is omitted a pairof rotarywedge prisms68asin Figure 1Amay optionally be provided. The light is admitted through a window 69 which provides an alpha and beta seal in housing 70. In a modification that part of housing 70 infrontofwall 60 may be omittedto giveafull hemispherical field of view.

In-cell lighting should be such as to provide for photometric losses before reaching the camera. If a vidicon camera is used, attenuation may be needed to avoid burn-in.

In one example forward end shielding will protect the TV camera and lens, attenuating the radiation by a factor of 5 x 103 to give a ievel of about R/hr atthe lens. Behind the camera, supplementary shielding is fitted to give full biological shielding equivalentto the shielding wall thickness of 1500mum of normal concrete. The radiation attenuation levels are dependent on the physical sizes of the system.

Since the unit is in general capable of looking at a field nearto the normal of its assembly centre line it can also be used for some roof camera positions where a large deflection angle is also needed.

The unit can be mounted approximately a minimum offorexample3 metresfromtheviewing plane and the optical system allows for a field coverage offor example nearly 2 metres width at this distance; thustheviewing field coverage is somewhat similartothat obtained with a normal shielding window mounted nearer to the viewing plane, but pan and tilt extends the range considerably and the TV system typically enables at 10:1 zoom rangeto be employed.

It meansthereforethatthe useful full screen view on the 30.5cm (across diagonal) TV monitor can be concentrated on area offorexample400mm cell width if required, ie providing an enlarged view of a specific detail. It should also be recognised thatthe system enables true part plan orientated views of the equipment in the cellto be obtained which givethe operational and maintenance staff greatly improved interpretation of the views they need compared to the restricted front angularviews they normally obtain from the normal cell viewing windows.

Figure 6 shows a roof mounted system. This system consists of a TV camera 80 and zoom lens 81 placed behind a for example 300mm of solid block glass shielding 82, the first 150mm being stabilised (82a).Withthislayoutthezoom lens can be of any power, for example a 6:1 magnification ratio may be used, the glass blocks act as an alpha seai and also ensure cell containment, as well as providing gamma shielding to the TV camera and prisms. The roof thickness is at 83 and the aperture liner sleeve at 84. The optical field mainly gives a "straight through" view with a limited deviation to for example approximately 12 . Because of the tunnel effect of the shielding glass blocks the deviation ofthe line of sights limited iflargefrontwindows areto be avoided. This effect, combined with the inherentdef lection limitations of the unachromatized wedges means the most natural application of the system is where a nearly straight through view is required.

The forward end shielding 82, 82a will protectthe TV camera, its lens and rotating prisms, attenuating the radiation by a factor of for example 5 x 103 to give a level of for example about 1 R/h at the lens. Behind the camera supplementary shielding is fitted to give full biological protection equivalent to the roof thick ness, offor example 1 ,000mm of barytes concrete.

It should be noted that the unit may be mounted at a distance oftypicallyfour metres from the viewing plane and the optical system allows for a typical field coverage offor example nearly two metres width at this distance. Thus the viewing field coverage is somewhat similar to that of a normal shielding window mounted nearerto the viewing plane, but the TV system enables a zoom lens to provide enlar gedviews. For example a 6:1 zoom lens can be used on the system and enables a full screen view on the 30.5cm (across diagonal) monitor two include a viewing field of some 330mm width in the cell, ie. virtually a full size presentation.Similarto the other system described, it gives a part plan view of equipment which cannot be obtained from the normal cell viewing windows.

The systems described give a userthefollowing possibilities: a. To employ standard TV camera units and lenses, thus keeping replacement costs to a minimum.This requires the dose rate seen by the camera and lens to be reduced to the order of for example 1 R/hr, by incorporation of appropriate shielding.

b. To employ a zoom lens over any point within a given maximum viewing field or area, to obtain an enlarged picture of a particular piece of equipment, as compared with that seen through the normal cell window.

c. To obtain views ofequipmentfrom angles or positions which cannot normally be obtained through cell windows.

d. To development optical systems which would enable a useful viewing field to be covered, since appropriate pan and tilt facilities on the TV camera cannot be obtained inside the shielding due to the limited size available.

e. To design an easily maintainable shielded unit of a modularform so thatthe camera and optics can be removed from the heavy environmental shielding without breaking containment ofthe cell. They may then be treated as a normal on-bench instrument maintenance job for both electronics and optics, with alignment and quality testing done before the unit is returned to the shielded cell or unit. The systems can be used in the following situations: A. Permanent active viewing facilities forusein production caves or cells This type is required in the Cells or Caves orshielded zones, to be housed in the walls and/or roof of each facility, the unit being inserted in a stepped encastre liner in the shielding wall or roof section. The system consists of a TV camera placed behind a cer tain amount of shielding material, which reduces the dose rate to the lens to for example about 1 R/hr, with an optical arrangement which allows itto "see through" the shielding, without the TV camera and lens being exposed to high dosage of damaging radiation. Also optical equipment to "pan", "tilt" and "zoom" the view field are provided.

B. Viewing facilities for active area maintenance For use in such places as the active pipework ducts and transfer corridors or any closed zones for use under maintenance conditions. The facilities provided by this system are similartothose given by the type described but modified for the lower radiation sources and possibly a wider field of viewing requirements.

Claims (7)

1. An optical system comprising a video camera for receiving light through an optical arrangement, the arrangement being movable to change the field of view annularly.

2. A system as claimed in claim 1, in which the arrangement comprises a prism which can be rotated about two axes transverse to each other to give a scan and tilt effect.

3. A system as claimed in claim 1 or claim 2, in which the arrangement comprises two prisms.

4. A system as claimed in claim 3, in which the two prismsaremovable relativetoeachothertoef- fectthechange in the field of view.

5. A system as claimed in any preceding claim, including a telescope device between the optical arrangement and the camera for moving the light path sideways.

6. A system as claimed in claim 5, for viewing the interior of a containment, in which the telescopic de- vice is mounted in an aperture in a shield wall ofthe containment and the camera is positioned laterally ofthe aperture.

7. An optical system substantially as herein before described with reference to and as shown in the accompanying drawings.