10 Interview Questions That Distinguish Experienced Technicians
In the world of industrial automation, an interview is more than just a resume check; it is a test of your practical "tribal knowledge." While many candidates can recite definitions, hiring managers are looking for technicians who truly understand how a system operates under pressure.
The PLC Scan Cycle. Knowing that PLC stands for Programmable Logic Controller is the bare minimum. A real technician understands the scan cycle: Reading inputs, executing the program, and writing to outputs. Experienced candidates can also discuss the differences between continuous, periodic, and event tasks in modern systems.
Building a Latch Circuit. This is a test of your software familiarity. Can you build a basic seal-in circuit using ladder logic instructions, or do you rely solely on latch/unlatch commands? This shows how you handle fundamental logic and addressing.
Digital vs. Analog Signals. Do you understand the difference between a binary (0 or 1) discrete signal and a continuous process variable like pressure or temperature? Being honest about your experience with analog scaling and PIDs is better than trying to guess your way through it.
Sinking and Sourcing. This is arguably the most important question for a technician. If you don't understand the flow of current between a sensor and a PLC input, you cannot use a multimeter to troubleshoot. You must know whether you are looking for positive or negative power at a specific terminal.
Troubleshooting Methodology. What is your strategy when a machine goes down? Most people work backwards. Having a structured methodology—checking the simple things first and following the signal path—demonstrates that you can reduce downtime efficiently.
Networking Knowledge. "The IT guy handles it" is no longer an acceptable answer. You need to understand IP addresses, subnets, and industrial protocols like PROFINET and EtherNet/IP. Everything in the modern plant is networked.
Timers (On-Delay vs. Off-Delay). While this is a common "textbook" question, knowing the practical application of when to use a TON versus a TOF shows you understand how to control machine timing and safety delays.
HMI Interaction. An HMI is more than just a pretty picture. You should understand how HMI tags link to PLC data files and how the two devices communicate over the network to exchange live data.
Programming Languages. While function blocks and structured text are growing, Ladder Logic is still king. It accounts for roughly 98% of the code you will encounter in the field. Being fluent in ladder is your primary ticket to getting hired.
Lockout Tagout (LOTO) and Safety. Finally, a culture of safety is mandatory. Understanding Lockout Tagout shows you have been immersed in professional industrial environments. It proves you prioritize your life and the lives of your coworkers above just "fixing the machine."