HMD CRT Assembly

Technical Information

Catalogue No:	C1542
Category:	Head-Mounted Equipment [HMD/NVG/Glasses]
Object Type:	Module/Sub-Assembly/Component
Object Name:	HMD CRT Assembly
Part No:	M0220R-S6
Serial No:	OMB91300
Manufacturer:	Brimar
Division:	Unknown
Platform(s):
Year of Manufacture:	2000
Dimensions:	Width (mm): 50 Height (mm): 31 Depth (mm): 210 Weight (g): 65
Location:	Cupboard CA (CRTs) [Main Store]

Inscription(s):

Brimar Limited
Viewed as the finest i the World
Cathode Ray Tube
Made in England
Type No. xM0220R-S6
Serial No. 0MB91300
Date Code 0048 L
NSCM U3008
―――――――――――
CRT RIGHT HANDED
(LEFT EYE) K0662
3887/59157 Iss. AB
NSN 506-99-123-1235
Spec SPE-J-950-B-0221
―――――――――――

Notes:

This is the right-hand Cathode Ray Tube (CRT) Assembly for a binocular Helmet Mounted Display (HMD). A CRT Assembly comprises the CRT, its deflection coil, its magnetically shielding housing and its fully connectorised connection leads.
This particular CRT Assembly design uses a fibre optic faceplate to tilt the image plane of the its screen. The tilt alows the CRT and its optical relay chain to bend between the curves of the helmet shell and the skull of the helmet wearer.
The nature of the design requires that this type of CRT Assembly is produced in left-haded and right-handed versions. The HMD's binocular optical paths cross, such that the left eye views the image from the right-hand CRT and vice versa.
History and application unknown.

HMD Cathode Ray Tube

A CRT can run in 2 modes:
Cursive- this is where lines are vector drawn on the screen. Only a small area of the screen is illuminated but very high luminance levels are achievable (~10,000fL)
Raster- this is where the whole screen is covered by scanning – as in conventional TV. Luminance is lower (~3,000fL)
The two can be mixed by doing the cursive writing during the flyback of the raster scan.
On the down side, high resolution CRTs are generally limited to one colour (usually green), are based on valve technology, involve high voltage (up to 13kV) and are heavy (a 1” CRT weighs about 80g)
A nominal 1” CRT can (just) achieve SXGA resolution, they are obsolescent resistant, and have a good temperature range. They are not a pixilated device so any distortion correction (to offset any optical distortion elsewhere) can be achieved without necessarily losing resolution.

A CRT in a Helmet Mounted Display will often have a fibre-optic faceplate which is a coherent fibre optic plate that precisely transmits an image from its input surface to its output surface. A fibre-optic faceplate (FOP) is composed of millions of fibres fused together in parallel array. It is capable of transferring high-resolution image from on end to another. So it is widely used in high-resolution image transferring, magnification, reduction and inverting in image intensifiers and CRTs. In this case it is used for field-flattening and distortion correction.

The latest HMD now use solid state displays.