{"id":1735,"date":"2019-10-15T20:49:12","date_gmt":"2019-10-15T14:49:12","guid":{"rendered":"https:\/\/us.rs-online.com\/expert\/?p=1735"},"modified":"2023-10-18T13:59:02","modified_gmt":"2023-10-18T18:59:02","slug":"industrial-communications-4-20-ma-current-loop","status":"publish","type":"post","link":"https:\/\/us.rs-online.com\/expert\/industrial-communications-4-20-ma-current-loop\/","title":{"rendered":"Industrial Communications: 4-20 mA Current Loop"},"content":{"rendered":"<div class=\"wpb-content-wrapper\"><div id=\"tdi_1\" class=\"tdc-row\"><div class=\"vc_row tdi_2  wpb_row td-pb-row\" >\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_2,\r\n                .tdi_2 .tdc-columns{\r\n                    min-height: 0;\r\n                }.tdi_2,\r\n\t\t\t\t.tdi_2 .tdc-columns{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_2 .tdc-columns{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}\n<\/style><div class=\"vc_column tdi_4  wpb_column vc_column_container tdc-column td-pb-span12\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_4{\r\n                    vertical-align: baseline;\r\n                }.tdi_4 > .wpb_wrapper,\r\n\t\t\t\t.tdi_4 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_4 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_4 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_4 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_column_text]<em>The basic 4 to 20 milliamp current loop is by far the most prevalent method of industrial automation analog measurement and control, so designers need a solid understanding of their operation.<\/em><\/p>\n<p>Analog process signals are those used to measure or control values that are not just on or off like discrete signals, but instead vary over a range. Another Expert article, called <a href=\"https:\/\/us.rs-online.com\/expert\/plc-analog-programming\/\" target=\"_blank\" rel=\"noopener noreferrer\">PLC Analog Programming<\/a>, covers how analog signals are handled in PLC programming.<\/p>\n<p>Each 4\u201120 mA current loop conveys just one analog value and is commonly used to get analog I\/O points into and out of PLCs. These loops can also be hardwired directly between instruments and devices without a PLC, but this article will focus on PLC connections. Regardless, it is necessary for automation system designers to understand the basics of how analog signaling works.[\/vc_column_text]<\/div><\/div><\/div><\/div><div id=\"tdi_5\" class=\"tdc-row\"><div class=\"vc_row tdi_6  wpb_row td-pb-row\" >\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_6,\r\n                .tdi_6 .tdc-columns{\r\n                    min-height: 0;\r\n                }.tdi_6,\r\n\t\t\t\t.tdi_6 .tdc-columns{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_6 .tdc-columns{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}\n<\/style><div class=\"vc_column tdi_8  wpb_column vc_column_container tdc-column td-pb-span12\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_8{\r\n                    vertical-align: baseline;\r\n                }.tdi_8 > .wpb_wrapper,\r\n\t\t\t\t.tdi_8 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_8 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_8 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_8 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_single_image source=&#8221;external_link&#8221; external_img_size=&#8221;500&#215;267&#8243; alignment=&#8221;center&#8221; custom_src=&#8221;https:\/\/res.cloudinary.com\/mktg-allied-electronics-automation\/image\/upload\/v1571071875\/Expert%20Advice\/4-20_m_Current_Loop.jpg&#8221;][vc_column_text]Every 4-20 mA current loop consists of a power source, loop wiring, a sensor\/transmitter\/receiver at the field end, and a PLC I\/O module at the control panel end.<\/p>\n<h2><strong>What Are Analog I\/O Points and What Do They Measure?<\/strong><\/h2>\n<p>[\/vc_column_text]<\/div><\/div><\/div><\/div><div id=\"tdi_9\" class=\"tdc-row\"><div class=\"vc_row tdi_10  wpb_row td-pb-row\" >\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_10,\r\n                .tdi_10 .tdc-columns{\r\n                    min-height: 0;\r\n                }.tdi_10,\r\n\t\t\t\t.tdi_10 .tdc-columns{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_10 .tdc-columns{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}\n<\/style><div class=\"vc_column tdi_12  wpb_column vc_column_container tdc-column td-pb-span3\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_12{\r\n                    vertical-align: baseline;\r\n                }.tdi_12 > .wpb_wrapper,\r\n\t\t\t\t.tdi_12 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_12 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_12 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_12 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_single_image source=&#8221;external_link&#8221; external_img_size=&#8221;250&#215;219&#8243; alignment=&#8221;center&#8221; css_animation=&#8221;slideInUp&#8221; custom_src=&#8221;https:\/\/res.cloudinary.com\/mktg-allied-electronics-automation\/image\/upload\/v1571079944\/Expert%20Advice\/Dwyer_insertion_electromagnetic_flow_transmitter.jpg&#8221; caption=&#8221;Insertion electromagnetic flow transmitter&#8221;]<\/div><\/div><div class=\"vc_column tdi_14  wpb_column vc_column_container tdc-column td-pb-span3\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_14{\r\n                    vertical-align: baseline;\r\n                }.tdi_14 > .wpb_wrapper,\r\n\t\t\t\t.tdi_14 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_14 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_14 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_14 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_single_image source=&#8221;external_link&#8221; external_img_size=&#8221;250&#215;219&#8243; alignment=&#8221;center&#8221; css_animation=&#8221;slideInUp&#8221; custom_src=&#8221;https:\/\/res.cloudinary.com\/mktg-allied-electronics-automation\/image\/upload\/v1571079944\/Expert%20Advice\/Flowline_ultrasonic_level_transmitter.jpg&#8221; caption=&#8221;Ultrasonic level transmitter&#8221;]<\/div><\/div><div class=\"vc_column tdi_16  wpb_column vc_column_container tdc-column td-pb-span3\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_16{\r\n                    vertical-align: baseline;\r\n                }.tdi_16 > .wpb_wrapper,\r\n\t\t\t\t.tdi_16 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_16 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_16 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_16 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_single_image source=&#8221;external_link&#8221; external_img_size=&#8221;250&#215;219&#8243; alignment=&#8221;center&#8221; css_animation=&#8221;slideInUp&#8221; custom_src=&#8221;https:\/\/res.cloudinary.com\/mktg-allied-electronics-automation\/image\/upload\/v1571079944\/Expert%20Advice\/Sick_pressure_transmitter.jpg&#8221; caption=&#8221;Pressure transmitter&#8221;]<\/div><\/div><div class=\"vc_column tdi_18  wpb_column vc_column_container tdc-column td-pb-span3\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_18{\r\n                    vertical-align: baseline;\r\n                }.tdi_18 > .wpb_wrapper,\r\n\t\t\t\t.tdi_18 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_18 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_18 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_18 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_single_image source=&#8221;external_link&#8221; external_img_size=&#8221;250&#215;219&#8243; alignment=&#8221;center&#8221; css_animation=&#8221;slideInUp&#8221; custom_src=&#8221;https:\/\/res.cloudinary.com\/mktg-allied-electronics-automation\/image\/upload\/v1571079944\/Expert%20Advice\/IFM_temperature_transmitter.jpg&#8221; caption=&#8221;Temperature transmitter&#8221;]<\/div><\/div><\/div><\/div><div id=\"tdi_19\" class=\"tdc-row\"><div class=\"vc_row tdi_20  wpb_row td-pb-row\" >\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_20,\r\n                .tdi_20 .tdc-columns{\r\n                    min-height: 0;\r\n                }.tdi_20,\r\n\t\t\t\t.tdi_20 .tdc-columns{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_20 .tdc-columns{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}\n<\/style><div class=\"vc_column tdi_22  wpb_column vc_column_container tdc-column td-pb-span12\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_22{\r\n                    vertical-align: baseline;\r\n                }.tdi_22 > .wpb_wrapper,\r\n\t\t\t\t.tdi_22 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_22 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_22 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_22 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_column_text]Most analog inputs to a PLC come from transmitters for one of the \u201cbig four\u201d sensing parameters:<\/p>\n<ul>\n<li><a href=\"https:\/\/us.rs-online.com\/sensors\/flow-sensors\/\" target=\"_blank\" rel=\"noopener noreferrer\">Flow<\/a><\/li>\n<li><a href=\"https:\/\/us.rs-online.com\/sensors\/liquid-level-sensors\/\" target=\"_blank\" rel=\"noopener noreferrer\">Level<\/a><\/li>\n<li><a href=\"https:\/\/us.rs-online.com\/sensors\/pressure-sensors\/\" target=\"_blank\" rel=\"noopener noreferrer\">Pressure<\/a><\/li>\n<li><a href=\"https:\/\/us.rs-online.com\/temperature-sensors\/temperature-transmitters-transducers\/\" target=\"_blank\" rel=\"noopener noreferrer\">Temperature<\/a><\/li>\n<\/ul>\n<p>But there are many other signal options generated by <a href=\"https:\/\/us.rs-online.com\/sensors\/\" target=\"_blank\" rel=\"noopener noreferrer\">various types of instruments and transmitters<\/a>, here are just a few:<\/p>\n<ul>\n<li>Weight<\/li>\n<li>Electrical voltage, current, or power<\/li>\n<li>Rotational speed<\/li>\n<li>Analyzer values such as pH, conductivity, or dissolved oxygen<\/li>\n<li>Distance<\/li>\n<li>Potentiometer knob on a control panel<\/li>\n<\/ul>\n<p>For analog outputs commanded by a PLC, some of the leading targets include:<\/p>\n<ul>\n<li>Valve position<\/li>\n<li>Variable frequency drive motor speed<\/li>\n<li>Setpoints to other instruments and devices<\/li>\n<li>Digital or analog display on a control panel<\/li>\n<\/ul>\n<p>Whatever the signal type, it needs to be wired from the field device to the PLC I\/O module.<\/p>\n<h2><strong>Analog Signal Options<\/strong><\/h2>\n<p>Analog signals for industrial automation operate at low voltages, generally under 24 VDC. Many ranges may be allowable for various PLC I\/O modules, but here are the most common:<\/p>\n<ul>\n<li>Current: 4-20 mA, 0-20 mA, \u00b120 mA<\/li>\n<li>Voltage: 0-5 V, 0-10 V, \u00b15 V, \u00b110 V<\/li>\n<li>Millivolt or resistance: thermocouple (TC), resistance temperature detector (RTD)<\/li>\n<\/ul>\n<p>Bi-directional signals (those with the \u201c\u00b1\u201d symbol) are useful with reversing devices (like a motor speed ranging from 100% reverse to 100% forward), or dual-function systems like a heating\/cooling package.<\/p>\n<p>Voltage signals are convenient to use with potentiometers, but as we will see this signal type suffers some downsides such as voltage drop over distance and more susceptibility to noise. Potentiometers are largely being replaced by graphical human-machine interfaces. Sensing elements and I\/O modules for TCs and RTDs are specialized for direct connection, but many times designers will use field-located transmitters to convert these signals into 4-20 mA to obtain the benefits of this signal type.[\/vc_column_text]<\/div><\/div><\/div><\/div><div id=\"tdi_23\" class=\"tdc-row\"><div class=\"vc_row tdi_24  wpb_row td-pb-row\" >\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_24,\r\n                .tdi_24 .tdc-columns{\r\n                    min-height: 0;\r\n                }.tdi_24,\r\n\t\t\t\t.tdi_24 .tdc-columns{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_24 .tdc-columns{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}\n<\/style><div class=\"vc_column tdi_26  wpb_column vc_column_container tdc-column td-pb-span12\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_26{\r\n                    vertical-align: baseline;\r\n                }.tdi_26 > .wpb_wrapper,\r\n\t\t\t\t.tdi_26 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_26 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_26 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_26 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_column_text]<\/p>\n<h2><strong>Benefits of 4-20 mA Analog I\/O Signals<\/strong><\/h2>\n<p>Many industries use 4-20 mA signals because of the following benefits:<\/p>\n<ul>\n<li>Simple to design, connect, configure, and troubleshoot<\/li>\n<li>Can travel long distances, typically hundreds or even thousands of feet<\/li>\n<li>Relatively immune to electrical noise<\/li>\n<li>The \u201clive zero\u201d at 4 mA makes it easy to detect many failure types<\/li>\n<\/ul>\n<p>Since these signals drive to a specific current regardless of the resistance in the circuit, they can travel long distances with good resistance to noise.<\/p>\n<p>The final point regarding a \u201clive zero\u201d deserves more explanation. For 4-20 mA loops, 4 mA=0% signal and 20 mA=100% signal. This means there should always be at least 4 mA traveling through the loop. A portion of this 4 mA can be consumed by the field device to power its electronics, so no other separate power is needed. While 0-20 mA is possible, this would mean that 0 mA=0% and therefore the control system couldn\u2019t differentiate between a failed signal or a true 0% signal.<\/p>\n<p>Also, if a loop wire is cut or disconnected, or if a field device totally fails, the current will drop to 0 mA and the connected PLC can detect this as a \u201copen loop\u201d failure. Furthermore, some intelligent devices can be configured to send a high current (perhaps 21.5 mA) upon certain failures, which could also be detected by the PLC.<\/p>\n<h2><strong>Loop Power Source, Sinking, and Sourcing<\/strong><\/h2>\n<p>Each 4-20 mA loop must be powered, typically by 24 VDC. Sometimes I\/O modules can initiate this power, other times a separate power supply is needed. A \u201csourcing\u201d configuration occurs when the PLC or the panel it resides in generates the power to the field; a \u201csinking\u201d configuration occurs when the field device supplies the loop power.<\/p>\n<p>Many modern systems use one field device connected to one PLC I\/O point. However, it is possible to wire many indicators or output devices in series within one loop. If this is done, users need to make sure the total impedance in the loop does not exceed allowable values.[\/vc_column_text]<\/div><\/div><\/div><\/div><div id=\"tdi_27\" class=\"tdc-row\"><div class=\"vc_row tdi_28  wpb_row td-pb-row\" >\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_28,\r\n                .tdi_28 .tdc-columns{\r\n                    min-height: 0;\r\n                }.tdi_28,\r\n\t\t\t\t.tdi_28 .tdc-columns{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_28 .tdc-columns{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}\n<\/style><div class=\"vc_column tdi_30  wpb_column vc_column_container tdc-column td-pb-span8\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_30{\r\n                    vertical-align: baseline;\r\n                }.tdi_30 > .wpb_wrapper,\r\n\t\t\t\t.tdi_30 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_30 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_30 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_30 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_column_text]<\/p>\n<h2><strong>Wiring 4-20 mA to Avoid Electrical Noise and Ground\u00a0Loops<\/strong><\/h2>\n<p>Basic 4-20 mA loops are relatively resistant to electrical noise because they usually have shielded cables and any noise affects both conductors equally. However, best practice is to ground the cable shield at only one end, otherwise a stray current could run through the shield and introduce electrical noise via a ground loop. Also, in certain cases, it is preferred to install optical isolators at one or both ends of the loop to protect against noise. A final consideration for loop cables installed outdoors and subject to lightning is installation of surge suppressors at each end.<\/p>\n<p>Using 4-20 mA current loops for transmitting analog signals to and from PLCs is a straightforward and reliable design method. Following the basic considerations outlined above will provide successful implementations.[\/vc_column_text]<\/div><\/div><div class=\"vc_column tdi_32  wpb_column vc_column_container tdc-column td-pb-span4\">\n<style scoped>\n\/* custom css - generated by TagDiv Composer *\/\n\n\/* custom css - generated by TagDiv Composer *\/\n\/* custom css - generated by TagDiv Composer *\/\n.tdi_32{\r\n                    vertical-align: baseline;\r\n                }.tdi_32 > .wpb_wrapper,\r\n\t\t\t\t.tdi_32 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    display: block;\r\n\t\t\t\t}.tdi_32 > .wpb_wrapper > .tdc-elements{\r\n\t\t\t\t    width: 100%;\r\n\t\t\t\t}.tdi_32 > .wpb_wrapper > .vc_row_inner{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t}.tdi_32 > .wpb_wrapper{\r\n\t\t\t\t    width: auto;\r\n\t\t\t\t    height: auto;\r\n\t\t\t\t}\n<\/style><div class=\"wpb_wrapper\" >[vc_single_image source=&#8221;external_link&#8221; external_img_size=&#8221;250&#215;155&#8243; alignment=&#8221;center&#8221; css_animation=&#8221;slideInRight&#8221; custom_src=&#8221;https:\/\/res.cloudinary.com\/mktg-allied-electronics-automation\/image\/upload\/v1571073143\/Expert%20Advice\/Typical_4-20mA_shielded_cable_70004847.jpg&#8221; caption=&#8221;Cables used for 4-20 mA current loop service are usually 2\u2011conductor with an overall shield&#8221;]<\/div><\/div><\/div><\/div>\n<div style='text-align:left' class='yasr-auto-insert-visitor'><\/div><\/div>","protected":false},"excerpt":{"rendered":"[vc_column_text]The basic 4 to 20 milliamp current loop is by far the most prevalent method of industrial automation analog measurement and control, so designers need a solid understanding of their operation. 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