{"id":399,"date":"2015-08-08T14:16:00","date_gmt":"2015-08-08T14:16:00","guid":{"rendered":"http:\/\/machineryequipmentonline.com\/video-equipment\/uncategorized\/timebase-circuits\/"},"modified":"2015-08-08T14:16:00","modified_gmt":"2015-08-08T14:16:00","slug":"timebase-circuits","status":"publish","type":"post","link":"http:\/\/machineryequipmentonline.com\/video-equipment\/timebase-circuits\/","title":{"rendered":"TIMEBASE CIRCUITS."},"content":{"rendered":"<div class=\"mryfo6a0dbadddea8d\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '61e5902552e2353963d8d2f1bd1f4a8f',\n\t\t'format' : 'iframe',\n\t\t'height' : 250,\n\t\t'width' : 300,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/61e5902552e2353963d8d2f1bd1f4a8f\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.mryfo6a0dbadddea8d {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.mryfo6a0dbadddea8d {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.mryfo6a0dbadddea8d {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.mryfo6a0dbadddea8d {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.mryfo6a0dbadddea8d {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<h3 align=\"justify\"><em><u>TIMEBASE CIRCUITS<\/u><\/em><\/h3>\n<p align=\"justify\">Every picture-tube must have a means of de\ufb02ecting its scanning spot to all parts of the screen or target. Except in oscilloscope displays the electron beam is de\ufb02ected by magnetic \ufb01elds in the neck of the tube. These are generated by de\ufb02ection coils wound on a ferrite former and securely \ufb01tted to the tube neck. One pair of coils is used for vertical spot de\ufb02ection, and between them make <i>hori<\/i><i>z<\/i><i>onta<\/i><i>l <\/i>lines of magnetic \ufb02ux in the tube neck: these de\ufb02ect the beam vertically, in a direction determined by the polarity of the \ufb02ux lines, and to a degree proportional to the intensity (or number of lines) of \ufb02ux. For horizontal de\ufb02ection of the electron beam a second pair of coils is used, this time generating <i>v<\/i><i>e<\/i><i>r<\/i><i>tica<\/i><i>l <\/i>lines of force through the tube neck. Again beam de\ufb02ection is proportional to strength and direction of the magnetic \ufb01eld. The complete assembly of coils and moulded ferrite former is called a <i>scan yoke<\/i>. Each yoke is manufactured speci\ufb01cally to match, physically and magnetically, the tube type with which it is intended to be used; this is particularly true of colour tubes, as was made clear in Chapter 5.  <\/p>\n<p align=\"justify\">The intensity of magnetic \ufb01eld developed by an electromagnet is proportional to the current \ufb02owing in it. Since beam de\ufb02ection is exactly proportional to \ufb01eld strength, the basic requirement for linear image scan is a sawtooth <i>current <\/i>waveform in each pair of de\ufb02ection coils. Unless the coils behave as a pure resistor, the voltage appearing across them will not be in sawtooth form \u2013 in fact, to create a saw- tooth (linearly rising) current in a <i>pure <\/i>inductor, a constant d.c. volt- age must be applied to it.  <\/p>\n<p align=\"justify\">At very small de\ufb02ection angles such as those used in camcorder view\ufb01nder tubes a linear de\ufb02ecting current for line and \ufb01eld scans will result in the required constant velocity of the scanning spot over the target. In large \ufb02at-faced display tubes, especially 110\u00b0 de\ufb02ection types, a linear de\ufb02ection characteristic will not impart constant scan- ning speed over the screen, however: the differing beam path lengths between screen centre and screen edges tends to speed up the \u2018linear\u2019 progress of the beam towards picture extremities, and correction must be made for this in the shape of the scanning current waveform passed through the de\ufb02ection coils.  <\/p><div class=\"memsz6a0dbadddec24\" ><script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-0778475562755157\"\n     crossorigin=\"anonymous\"><\/script>\n<!-- 300x600 television-and-video -->\n<ins class=\"adsbygoogle\"\n     style=\"display:inline-block;width:300px;height:600px\"\n     data-ad-client=\"ca-pub-0778475562755157\"\n     data-ad-slot=\"6549443290\"><\/ins>\n<script>\n     (adsbygoogle = window.adsbygoogle || []).push({});\n<\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.memsz6a0dbadddec24 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.memsz6a0dbadddec24 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.memsz6a0dbadddec24 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.memsz6a0dbadddec24 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.memsz6a0dbadddec24 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<div class=\"tvgsl6a0dbadddeb66\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '0c1eb4c533eaedb7b996f49a5a4983a9',\n\t\t'format' : 'iframe',\n\t\t'height' : 300,\n\t\t'width' : 160,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/0c1eb4c533eaedb7b996f49a5a4983a9\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.tvgsl6a0dbadddeb66 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.tvgsl6a0dbadddeb66 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.tvgsl6a0dbadddeb66 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.tvgsl6a0dbadddeb66 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.tvgsl6a0dbadddeb66 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n\n<p align=\"justify\">At \ufb01eld frequency (50 Hz) the scanning coils behave almost as a resistance during the forward stroke, so the required voltage drive approximates to a sawtooth, with compensatory shaping to correct for scan coil inductance and where applicable the \u2018\ufb02at-face\u2019 effect. Here the scan output stage acts in similar fashion to a conventional ampli\ufb01er, e.g. an audio output stage. On the other hand, the line scan- coil pair represent almost pure inductance at the much higher (15625 Hz) horizontal scanning rate; to correctly drive these, then, a constant voltage in one direction must be applied for the 52 \u03bcs of the active picture period, then a higher constant voltage in the opposite direction for 12 \u03bcs to achieve a complete reversal of magnetic \ufb01eld and a complete traverse of the screen by the scanning spot on its \ufb02yback stroke.  <\/p>\n<p align=\"justify\">Time bases, then, consist of three basic sections: a timing source (in practice some form of oscillator, locked to incoming sync pulses); a shaping stage, consisting of ramp generator for \ufb01eld applications or a pulse generator for line time bases; and a power output stage as a means of driving rapidly changing currents through the scan coils.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>TIMEBASE CIRCUITS Every picture-tube must have a means of de\ufb02ecting its scanning spot to all parts of the screen or target. Except in oscilloscope displays the electron beam is de\ufb02ected by magnetic \ufb01elds in the neck of the tube. These are generated by de\ufb02ection coils wound on a ferrite former and securely \ufb01tted to the [&hellip;]<br \/><a href=\"http:\/\/machineryequipmentonline.com\/video-equipment\/timebase-circuits\/\" class=\"more-link\" >Continue reading&#8230;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"aioseo_notices":[],"views":584,"_links":{"self":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts\/399"}],"collection":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/comments?post=399"}],"version-history":[{"count":0,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts\/399\/revisions"}],"wp:attachment":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/media?parent=399"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/categories?post=399"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/tags?post=399"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}