Editing Cathode-ray tube (section)

===Oscilloscope CRTs===
[[File:Lissajous-Figur 1 zu 3 (Oszilloskop).jpg|thumb|An oscilloscope showing a [[Lissajous curve]] ]]
[[File:Kathodestraalbuis2.jpg|thumb|The electron gun of an oscilloscope. A pair of deflection plates is visible on the left.]]
In [[oscilloscope]] CRTs, [[electrostatic deflection]] is used, rather than the magnetic deflection commonly used with TV and other large CRTs. The beam is deflected horizontally by applying an [[electric field]] between a pair of plates to its left and right, and vertically by applying an electric field to plates above and below. TVs use magnetic rather than electrostatic deflection because the deflection plates obstruct the beam when the deflection angle is as large as is required for tubes that are relatively short for their size. Some Oscilloscope CRTs incorporate post deflection anodes (PDAs) that are spiral-shaped to ensure even anode potential across the CRT and operate at up to 15&nbsp;kV. In PDA CRTs the electron beam is deflected before it is accelerated, improving sensitivity and legibility, specially when analyzing voltage pulses with short duty cycles.<ref>{{cite book | last=Trundle | first=E. | title=Newnes TV and Video Engineer's Pocket Book | publisher=Elsevier Science | series=Newnes Pocket Books | year=1999 | isbn=978-0-08-049749-5 | url=https://books.google.com/books?id=SSP06tjOO0QC | access-date=2020-12-11 }}</ref><ref name="auto69"/><ref>{{cite book | last=Boyes | first=W. | title=Instrumentation Reference Book | publisher=Elsevier Science | year=2002 | isbn=978-0-08-047853-1 | url=https://books.google.com/books?id=sarHIbCVOUAC&pg=PA697 | access-date=2020-12-11 | page=697}}</ref>

====Microchannel plate====
When displaying fast one-shot events, the electron beam must deflect very quickly, with few electrons impinging on the screen, leading to a faint or invisible image on the display. Oscilloscope CRTs designed for very fast signals can give a brighter display by passing the electron beam through a [[micro-channel plate]] just before it reaches the screen. Through the phenomenon of [[secondary emission]], this plate multiplies the number of electrons reaching the phosphor screen, giving a significant improvement in writing rate (brightness) and improved sensitivity and spot size as well.<ref>{{cite book |last= Williams |first= Jim |title= Analog circuit design: art, science, and personalities |publisher= Newnes |year= 1991 |pages= 115–116 |url= https://books.google.com/books?id=CFoEAP2lwLEC&pg=PA115 |isbn= 978-0-7506-9640-1}}</ref><ref>{{cite book |author1=Yen, William M. |author2=Shionoya, Shigeo |author3=Yamamoto, Hajime |title= Practical Applications of Phosphors |publisher= CRC Press |year= 2006 |page= 211 |url= https://books.google.com/books?id=cKMSf0iRVSgC&pg=PA211 |isbn=978-1-4200-4369-3}}</ref>

====Graticules====
Most oscilloscopes have a [[oscilloscope#Graticule|graticule]] as part of the visual display, to facilitate measurements. The graticule may be permanently marked inside the face of the CRT, or it may be a transparent external plate made of glass or [[acrylic glass|acrylic]] plastic. An internal graticule eliminates [[parallax error]], but cannot be changed to accommodate different types of measurements.<ref>{{cite book |author1= Bakshi, U. A. |author2= Godse, Atul P. |title= Electronic Devices And Circuits |publisher= Technical Publications |year= 2008 |page= 38 |url= https://books.google.com/books?id=uJaQML8-MggC&pg=PA38 |archive-url= https://web.archive.org/web/20201207015004/https://books.google.com/books?id=uJaQML8-MggC&pg=PA38 |url-status= dead |archive-date= 7 December 2020 |isbn= 978-81-8431-332-1 }}</ref> Oscilloscopes commonly provide a means for the graticule to be illuminated from the side, which improves its visibility.<ref>{{cite book |last= Hickman |first= Ian |title= Oscilloscopes: how to use them, how they work |publisher= Newnes |year= 2001 |page= 47 |url= https://books.google.com/books?id=O2oj04vbQqgC&pg=PA47 |isbn=978-0-7506-4757-1}}</ref>

====Image storage tubes====
{{Main|Storage tube}}
[[File:Tektronix 564 Analog Storage Oscilloscope.jpg|thumbnail|The Tektronix Type 564: first mass-produced analog phosphor storage oscilloscope]]
These are found in ''analog phosphor storage oscilloscopes''. These are distinct from ''[[digital storage oscilloscope]]s'' which rely on solid state digital memory to store the image.

Where a single brief event is monitored by an oscilloscope, such an event will be displayed by a conventional tube only while it actually occurs. The use of a long persistence phosphor may allow the image to be observed after the event, but only for a few seconds at best. This limitation can be overcome by the use of a direct view storage cathode-ray tube (storage tube). A storage tube will continue to display the event after it has occurred until such time as it is erased. A storage tube is similar to a conventional tube except that it is equipped with a metal grid coated with a [[dielectric]] layer located immediately behind the phosphor screen. An externally applied voltage to the mesh initially ensures that the whole mesh is at a constant potential. This mesh is constantly exposed to a low velocity electron beam from a 'flood gun' which operates independently of the main gun. This flood gun is not deflected like the main gun but constantly 'illuminates' the whole of the storage mesh. The initial charge on the storage mesh is such as to repel the electrons from the flood gun which are prevented from striking the phosphor screen.

When the main electron gun writes an image to the screen, the energy in the main beam is sufficient to create a 'potential relief' on the storage mesh. The areas where this relief is created no longer repel the electrons from the flood gun which now pass through the mesh and illuminate the phosphor screen. Consequently, the image that was briefly traced out by the main gun continues to be displayed after it has occurred. The image can be 'erased' by resupplying the external voltage to the mesh restoring its constant potential. The time for which the image can be displayed was limited because, in practice, the flood gun slowly neutralises the charge on the storage mesh. One way of allowing the image to be retained for longer is temporarily to turn off the flood gun. It is then possible for the image to be retained for several days. The majority of storage tubes allow for a lower voltage to be applied to the storage mesh which slowly restores the initial charge state. By varying this voltage a variable persistence is obtained. Turning off the flood gun and the voltage supply to the storage mesh allows such a tube to operate as a conventional oscilloscope tube.<ref>The [[Great Soviet Encyclopedia]], 3rd Edition (1970–1979)</ref>