PLC Help required

Discussion in 'Homework Help' started by lomax1, Feb 19, 2014.

  1. lomax1

    Thread Starter New Member

    Feb 6, 2014
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    Hi all, I have this question which I need assistance on an assignment:

    A PLC analogue input module is described as: 8-bit, 0 - 10 v dc
    What is the smallest change in voltage that this input can detect (i.e. the resolution)?
    What changes would need to be made to enable the input module to detect a change of at least 3mV for a 0 – 10v dc input?
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    So, how many steps can be represented by 8 bits? What happens if you divide the highest voltage this device handles by this number of steps? What are your units?

    How many steps does it require before you get a step of =< 3mV. How many bits are required to represent that number of states?
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    8 bits represents a resolution of 255.
    So you can calculate the smallest change that 10v will represent.
    Max.
     
  5. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    256, not 255.
    "Resolution limits the precision of a measurement. The higher the resolution (number of bits), the more precise the measurement. An 8-bit ADC divides the vertical range of the input amplifier into 256 discrete levels. With a vertical range of 10 V, the 8-bit ADC cannot ideally resolve voltage differences smaller than 39 mV."
    From NI: http://www.ni.com/white-paper/4806/en/
     
    anhnha likes this.
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