STATIC CONTROL OF MACHINES 259

STATIC CONTROL OF MACHINES 259

The second statement is: Statement 1 will be true only if LS2 and T2 are open . The graphical picture for second statement is obtained by ORing inputs from LS2 and T2 followed by a NOT element as shown in Fig .  11 . 19 ( b ).

The next step is to combine the circuits for the above two statements .  This is done as shown in Fig .  11 . 19 ( c ) . Further ,  next step is to simplify the circuit ,  if possible .  In this case it is

done by using a NOR gate instead of an OR gate followed by a NOT gate .  The last step is to analyse the circuit whether it works according to the specifications .  According to Fig . 11 . 19 ( d ),

when PB1 is pressed ,  it sends a signal to OR gate through its signal converter .  There is an output from OR gate ,  which is fed through an amplifier for energisation of contactor M .

If LS1 and T1 are both closed ,  there are two inputs at the AND gate .  The third input is provided by the inputs from LS2 and T2 .  If these two are open ,  there is no input to the NOR

element ,  and therefore it will have an output which is the third input to the AND gate .  When all the three inputs are present at the AND element it will have an output .  The output of AND

gate provides an input to the OR element and thus there is an output for energising contactor M .  WITH REGARD

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