Industrial Electrician exam: PLC basics

Key points

• The scan reads inputs, solves the logic, then updates outputs, over and over.
• An XIC (examine if closed) is true when its input is on.
• An XIO (examine if open) is true when its input is off.
• Timers include on-delay (TON) and off-delay (TOF).
• Field wiring of a normally closed stop button changes how the ladder rung must be written.

Study tip

When a rung behaves backward, check whether the field device is NO or NC.

Try these

1. The order of a PLC scan is:

   1. Outputs, logic, inputs
   2. Inputs, logic, outputs
   3. Logic, inputs, outputs
   4. Inputs, outputs, logic
   Show answer

   B. Inputs, logic, outputs Read, solve, write.

2. An XIC instruction is true when:

   1. The input is off
   2. The input is on
   3. The output is on
   4. The PLC is in program mode
   Show answer

   B. The input is on Examine if closed.

3. A TON timer starts timing when:

   1. Its rung goes false
   2. Its rung goes true
   3. The PLC powers up
   4. The accumulator resets
   Show answer

   B. Its rung goes true On-delay times while true.

Keep going

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