Connecting sensors and execution devices Programmable Logic Controllers ( PLC )

Introduction

Connecting external devices to a PLC controller regardless whether they are input or output is a special subject matter for industry. If it stands alone, PLC controller itself is nothing. In order to function it needs sensors to obtain information from environment, and it also needs execution devices so it could turn the programmed change into a reality. Similar concept is seen in how human being functions. Having a brain is simply not enough. Humans achieve full activity only with processing of information from a sensor (eyes, ears, touch, smell) and by taking action through hands, legs or some tools. Unlike human being who receives his sensors automatically, when dealing with controllers, sensors have to be subsequently connected to a PLC. How to connect input and output parts is the topic of this chapter.

Sinking-Sourcing Concept

PLC has input and output lines through which it is connected to a system it directs. Input can be keys, switches, sensors while outputs are led to different devices from simple signalization lights to complex communication modules.

This is a very important part of the story about PLC controllers because it directly influences what can be connected and how it can be connected to controller inputs or outputs. Two terms most frequently mentioned when discussing connections to inputs or outputs are "sinking" and "sourcing". These two concepts are very important in connecting a PLC correctly with external environment. The most brief definition of these two concepts would be:

SINKING = Common GND line (-)
SOURCING = Common VCC line (+)

First thing that catches one's eye are "+" and "-" supply, DC supply. Inputs and outputs which are either sinking or sourcing can conduct electricity only in one direction, so they are only supplied with direct current. According to what we've said thus far, each input or output has its own return line, so 5 inputs would need 10 screw terminals on PLC controller housing. Instead, we use a system of connecting several inputs to one return line as in the following picture. These common lines are usually marked "COMM" on the PLC controller housing.


  PLC

Input lines

Explanation of PLC controller input and output lines has up to now been given only theoretically. In order to apply this knowledge, we need to make it a little more specific. Example can be connection of external device such as proximity sensor. Sensor outputs can be different depending on a sensor itself and also on a particular application. Following pictures display some examples of sensor outputs and their connection with a PLC controller. Sensor output actually marks the size of a signal given by a sensor at its output when this sensor is active. In one case this is +V (supply voltage, usually 12 or 24V) and in other case a GND (0V). Another thing worth mentioning is that sinking-sourcing and sourcing - sinking pairing is always used, and not sourcing-sourcing or sinking-sinking pairing.

PLC

If we were to make type of connection more specific, we'd get combinations as in following pictures (for more specific connection schemas we need to know the exact sensor model and a PLC controller model).


  PLC

Output lines

PLC controller output lines usually can be:

-transistors in PNP connection
-transistors in NPN connection
-relays

The following two pictures display a realistic way how a PLC manages external devices. It ought to be noted that a main difference between these two pictures is a position of "output load device". By "output load device" we mean some relay, signalization light or similar.

PLC  

How something is connected with a PLC output depends on the element being connected. In short, it depends on whether this element of output load device is activated by a positive supply pole or a negative supply pole.


 

author: Nebojsa Matic

Hopefully this article can add your insights.
Please follow me:

ShareTo
Share on Facebook Tweet this Share to Google Plus Stumble this article
CLOSE

Enter Your Email Address




All Labels

  1. ABB PLC
  2. Allen Bradley PLC
  3. Allen-Bradley MicroLogix
  4. Allen-Bradley PLC
  5. Analog Input
  6. Android
  7. Android and PLC
  8. Android Bluetooth
  9. Arduino
  10. Arduino Microcontroller
  11. Audio and PLC
  12. Automatic Gates using PLC
  13. Baldor PLC
  14. Battery Level Indicator using PLC Analog
  15. BMS
  16. Build a Simple PLC
  17. Building Management System
  18. Car Ticketing Machine using PLC
  19. CIMON PLC
  20. Click Series PLC
  21. Computer Vision
  22. Computer Vision and PLC
  23. Control Seven Segment Display with PLC
  24. Conveyor Control Using PLC
  25. CPU PLC
  26. CV and PLC
  27. CX-One
  28. DCS
  29. DDC
  30. DELMIA V5
  31. DeltaV
  32. Digital Input
  33. DirectLogic PLC
  34. DirectSOFT PLC
  35. Eaton PLC
  36. Elevator with PLC Program
  37. EPICS PLC
  38. Fatek PLC
  39. Festo PLC
  40. Fieldbus
  41. Forex Trading and PLC
  42. FPGA PLC
  43. GE Fanuc PLC
  44. GP proface
  45. GX Developer
  46. Heater Controller with PLC
  47. Hitachi PLC
  48. HMI
  49. Home Automation
  50. Honeywell PLC
  51. IDEC PLC
  52. Internet of Things
  53. IoT
  54. Keyence PLC
  55. Koyo PLC
  56. LED Display
  57. LG PLC
  58. Lock Unlock Door Using PLC
  59. Logixpro PLC
  60. Maple OIT
  61. Matsushita PLC
  62. MELSEC A
  63. MELSEC Q
  64. Memory PLC
  65. Micro PLC
  66. Microcontroller
  67. MicroLogix 1000
  68. MicroSmart PLC
  69. Mitsubishi PLC
  70. Mobile Application
  71. Modbus
  72. ModBus Communication
  73. ModBus RTU
  74. ModBus RTU Communication
  75. Modicon PLC
  76. Momentum PLC
  77. Motion Control
  78. National Instruments PLC
  79. Omron PLC
  80. OPC
  81. PAC
  82. Panasonic PLC
  83. Parking Information using PLC
  84. Password Using PLC
  85. PLC
  86. PLC Analog Input Module
  87. PLC and Android
  88. PLC and Arduino
  89. PLC and CNC
  90. PLC and Computer
  91. PLC and Facebook
  92. PLC and PC
  93. PLC and Servo
  94. PLC and Visual Basic
  95. PLC Application Project
  96. PLC Battery
  97. PLC Beginner Guide
  98. PLC Book
  99. PLC Cable
  100. PLC Codesys
  101. PLC Companies List
  102. PLC Computers
  103. PLC Design
  104. PLC for 3 Movement
  105. PLC for Assembly Line
  106. PLC for Automatic Welding
  107. PLC for Binding Machine
  108. PLC for Cutting Machine
  109. PLC for Filling Machine
  110. PLC for Fountain Application
  111. PLC for Injection Molding
  112. PLC for Marking
  113. PLC for Packing
  114. PLC for Rotary Bottle Washing
  115. PLC for Snack Vending Machine
  116. PLC for Sorter Machine
  117. PLC for Water Treatment
  118. PLC Hardware
  119. PLC Hybrid
  120. PLC Information
  121. PLC Knowledge
  122. PLC Language
  123. PLC Link Model
  124. PLC Mitsubishi Download
  125. PLC Model
  126. PLC Modules
  127. PLC Real Time Clock
  128. PLC Simulator
  129. PLC Software
  130. PLC Supplier
  131. PLC Types
  132. PLC using Arduino
  133. PLC Wiring
  134. PLC WorkShop
  135. PLC-ANALYZER
  136. PLCSIM
  137. Power Supply for PLC
  138. Profibus
  139. Programmable Logic Controller
  140. ProSafe PLC
  141. Push ON Push OFF with PLC
  142. Quickpanel Operator Interfaces
  143. Raspberry Pi
  144. Raspberry Pi and PLC
  145. Read Data
  146. RTU
  147. RTU and PLC
  148. SAS
  149. SCADA
  150. Schneider PLC
  151. Sensor
  152. SHARP PLC
  153. Siemens PLC
  154. Simple ModBus
  155. Simple PLC
  156. SINUMERIK CNC
  157. Small Modular PLC
  158. Standard Sequence Programming for PLC
  159. Substation Automation System
  160. Teco PLC
  161. Telemetry
  162. TEP PLC
  163. Texas Instruments PLC
  164. Timer Countdown with PLC
  165. Toshiba PLC
  166. Touch Screen PLC
  167. Traffic Light with PLC
  168. TWIDO PLC
  169. Types of PLC
  170. Ultrasonic Sensor
  171. Unitary PLC
  172. Unitronics PLC
  173. USB Keyboard and PLC
  174. VIPA PLC
  175. Vision PLC
  176. Weighing Machine Using PLC
  177. Write Data
  178. Yokogawa PLC
  179. Zelio PLC

Search This Blog

Loading...
Copyright © 2009- All Rights Reserved