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{"id":1485,"date":"2021-08-05T07:07:00","date_gmt":"2021-08-05T07:07:00","guid":{"rendered":"https:\/\/www.wikitechy.com\/interview-questions\/?p=1485"},"modified":"2021-09-07T11:08:25","modified_gmt":"2021-09-07T11:08:25","slug":"why-we-dont-use-2-20ma-1-20ma-3-20ma-or-10-50ma-signal-instead-of-4-20ma","status":"publish","type":"post","link":"https:\/\/www.wikitechy.com\/interview-questions\/instrumentation\/why-we-dont-use-2-20ma-1-20ma-3-20ma-or-10-50ma-signal-instead-of-4-20ma\/","title":{"rendered":"Why we don\u2019t use 2-20mA, 1-20mA, 3-20mA or 10-50mA signal instead of 4-20mA ?"},"content":{"rendered":"<div class=\"TextHeading\">\n<div class=\"hddn\">\n<p class=\"color-pink\">Why we don\u2019t use 2-20mA, 1-20mA, 3-20mA or 10-50mA signal instead of 4-20mA ?<\/p>\n<\/div>\n<\/div>\n<div class=\"Content\">\n<div class=\"hddn\">\n<ul>\n<li>Generally, in a transistor some amount of voltage is required for turning it on.<\/li>\n<li>This voltage is the cut in voltage. Up to this voltage it exists a nonlinearity in its characteristics. Beyond this cut in voltage the characteristics of transistor is linear.<\/li>\n<li>This nonlinear region lays between 0-4mA, beyond 4ma it linear. That&#8217;s why 4-20 mA range is used.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"subheading\">\n<p><strong>Due to some following reasons 4-20mA signal is used,<\/strong><\/p>\n<\/div>\n<div class=\"Content\">\n<div class=\"hddn\">\n<ul>\n<li>4-20mA has an inherent &#8216;live zero&#8217;. Zero engineering unit is 4mA not 0.0mA indicates an open circuit, fault in the line which is not valid.<\/li>\n<li>4-20 mA has little, if any, signal loss in its circuit; current regulation compensates for minor resistances in terminal boxes, whereas voltage drop across resistances for voltage signals creates an error.<\/li>\n<li>S 4-20 mA signal is less susceptible to noise pickup than a voltage circuit. So it is free from interference from other signals.<\/li>\n<li>4-20 mA works at a relatively long distance(&gt;1 Km ) boosting the power supply voltage will drive the signal further.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Answer : Generally, in a transistor some amount of voltage is required for turning it 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