Wednesday, December 13, 2017

Ladder Diagram Design : Huffman Method

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Huffman method is classical method for planning a sequential system. This method is more complicated but the result will have a minimal relay. 

There are two kinds of state, Stable and Unstable. Stable state is where the output state is equal to input state. While unstable state is transition where the output is not same as input.
  1. Build primitive flow table
  2. Merge flow table row
    -   Row can be merged as long as there is no different number in same column
    -   If there is unstable and stable state in same column, merged row get stable state
    -   If there is number and don't care in same column, merged row get number
    -   If there is only don't care, merged row get don't care
    In merging a row, output column ignored
  3. Create a state
  4. Decrease excitation and output function
  5. Add START signal
  6. Draw the ladder diagram

START, A+, A-, A+, A-
  1. Build primitive flow table
    First, create a table with number of columns is 2^n, where n is number of input. Also add other column at the left for all state and at right for the output.
    Then fill each stable and unstable state also the don't care state.
  2. Merged flow table row
    Need to merge because it will decrease the number of components.
  3. Create state
    To avoid race, there is an important rule to ensure only one state is changed each moving state.
    The state flow are,
  4. Decrease excitation
    And the Set Reset function are,
    And the output function for A+ is
  5. with that output function, it will looping forever, so add a "START" to S1 and modify the output function to,
    so the final output function is, 
  6. Draw the Ladder Diagram

[1] PPT System Automation (M. Rameli & Eka Iskandar)

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