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

Search This Blog

Loading...
Copyright © 2009- All Rights Reserved