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Retrofitable Tilt Apparatus

IP.com Disclosure Number: IPCOM000116650D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 110K

Publishing Venue

IBM

Related People

Beeteson, JS: AUTHOR [+3]

Abstract

An add-on accessory for CRT displays is described that allows the user to control the tilt of the image with a single control. The device has the advantage of being fitted by the user without the need to open the display.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Retrofitable Tilt Apparatus

      An add-on accessory for CRT displays is described that allows
the user to control the tilt of the image with a single control.  The
device has the advantage of being fitted by the user without the need
to open the display.

      It has been found that some monochrome displays suffer from
excessive image tilt.  On site measurements indicate that this is due
to very high ambient magnetic fields in certain buildings, and the
tilt varies as the display is rotated.

      Monochrome displays are more sensitive to image shifts due to
external fields than colour, due to their lower EHT (Electron Beam
deflection is proportional to 1/-EHT voltage).  Tilt arises when the
horizontal ambient field is in the direction of the gun axis of the
CRT.

      Tilt can be controlled by a coil mounted on the neck of the CRT
with current controlled by a pot.  Another possibility is magnetic
shielding, but this is only a partial solution since it is not
possible
to totally block fields entering from the screen of the display.

      Devised is a solution that can be retrofitted to displays in
the field, and that allows the user full control of the tilt
characteristic of the display image.

      If a coil is mounted round a display then an axial field is
created as shown in Fig. 1, which will cause a picture tilt with
magnitude dependent on the current level in the coil.

The questions to be asked were:
  1.  What is the tilt deflection sensitivity at different positions
of
       the coil along the box?
  2.  Are there any edge distortions when the coil is near the bell
of
       the CRT?

For a 5mm tilt at one side we measured the following coil currents in
a 60 turn coil:
  o  76 ma at 5.31 V for the coil on the bezel
  o  79 ma at 5.5 V for the coil half way down the box
  o  242 ma at 10.15 V for the coil at the back of the box

      The coil may be positioned anywhere along the display, with
best sensitivity from the front to half way.  A mechanical
construction that can create a complete coil and...