Logic circuits


Logic circuits 1

• Produce a truth table for the following logic circuit

Logic circuits 2

• A safety system uses three inputs to a logic circuit. An alarm, X, sounds if input A represents ON and input B represents OFF, or if input B represents ON and input C represents OFF.
• Produce a logic circuit and truth table to show the conditions which cause the output X to be 1.

Logic statement

X = 1 if (A = 1 AND B = NOT 1) OR (B = 1 AND C = NOT 1) this equates to A is ON and B is OFF
this equates to B is ON AND C is OFF

Boolean algebra

$X=(A\cdot \bar{B})+(B\cdot \bar{C})$

Logic circuits 3

• A wind turbine has a safety system which uses three inputs to a logic circuit. A certain combination of conditions results in an output, X, from the logic circuit being equal to 1. When the value of X = 1, the wind turbine is shut down.
• The following table shows which parameters are being monitored and form the three inputs to the logic circuit.
• The output, X, will have a value of 1 if any of the following combination of conditions occur:
  • either turbine speed ≤ 1000 rpm and bearing temperature > 80 °C
  • or turbine speed > 1000 rpm and wind velocity > 120 kph
  • or bearing temperature ≤ 80 °C and wind velocity > 120 kph

TIP

1 turbine speed 1000 rpm and bearing temperature > 80 °C logic statement: (S = NOT 1 AND T = 1) 2 turbine speed > 1000 rpm and wind velocity > 120 kph logic statement: (S = 1 AND W = 1) 3 bearing temperature 80 °C and wind velocity > 120 kph logic statement: (T = NOT 1 AND W = 1)