Free Trial

Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.


  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL
Help

4.2. Signal Conditioning

4.2. Signal Conditioning

When connecting sensors that generate digital or discrete signals to an input unit, care has to be taken to ensure that voltage levels match. However, many sensors generate analog signals. To avoid having a multiplicity of analog input channels to cope with the wide diversity of analog signals that can be generated by sensors, external signal conditioning is often used to bring analog signals to a common range and so allow a standard form of analog input channel to be used.
A common standard that is used (Figure 4.12) is to convert analog signals to a current in the range 4 to 20 mA and thus to a voltage by passing it through a 250 Ω resistance to give a 1 to 5 V input signal. Thus, for example, a sensor used to monitor liquid level in the height range 0 to 1 m would have the 0 level represented by 4 mA and the 1 m represented by 20 mA. The use of 4 mA to represent the low end of the analog range serves the purpose of distinguishing between when the sensor is indicating zero and when the sensor is not working and giving zero response for that reason. When this happens the current would be 0 mA. The 4 mA also is often a suitable current to operate a sensor and so eliminate the need for a separate power supply.

  

You are currently reading a PREVIEW of this book.

                                                                                                                    

Get instant access to over $1 million worth of books and videos.

  

Start a Free 10-Day Trial


  
  • Safari Books Online
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint