PLC Interview Questions Help

[chickenkiller 0]

Hello

I am  a Robot Programmer. Fortunately  I would be beginning the PLC Programmer Interview Process. From Initial CV Screening and first round of Interview. Screening was easier. But unfortunately I am not good with PLC tech questions apart from that is involved with Robot Programming. I need a few questions to judge whether the applicant is faking his experience or does he has the qualities.

If any PLC Programmers can help me, It would be a great help for me.

 

Thank You

[panic mode 245]

i don't see many Germans in this forum. what do "PLC programmers" actually do in Germany? only programming?

i ask because i worked with several integrators from Europe (Germany, Italy, Czech republic etc.) and was a bit surprised. so far my impression is that everyone on their team is very narrowly specialized...  do they require teams or can they function individually? and if they are indeed mainly focused on PLC (and only one brand like Siemens), they better be dang good with it, i would want to some real magic and fast.

also what kind of experience you need - low, medium, high?

robot and plc programming has a lot in common:

+ both use I/Os, fieldbusses, networks and programs

+ both use same simple data types and arrays, data conversion/casting is a very common thing

+ ask about SCAN, in case of KUKA robots, background process (Submit interpreter) is "SPS" or PLC. but there are differences in regularity of scan

+ robots only rarely use analogs, but on PLCs this is quite common, Siemens has some quirky configuration for this

etc.

 

for entry level positions maybe just go with basic questions like toggle (flip-flop) where button is used to change state of output, using timers, combinational logic etc. 

for mid level i would expect to see some math, including custom data types (structures), custom functions, parameter transfer, using arrays (recipes for example), sequential logic etc.

for high level i would expect to see some serious data manipulation skill in any programming language that target platform supports, sorting arrays, (at least one dimension), using ring buffers, stack, optimization, processing large blocks of data efficiently (for example processing data at word-level, not bit-level) 

 

[kaare_t 155]

It was a good thing you are a "chickenkiller", and NOT a "catkiller", as I can imagine by panic_mode's picture he/she would be quite upset...! 

I agree with everything that @panic mode writes, and would emphasize SCAN: PLC's are scan-based and NOT event-based. This is basically often the first pitfall of many non-PLC programmers. A returning "issue" for people not familiar with scan-based programming is how to correctly debug for example a bit that is constantly set to a state (high or low), without the use of breakpoints. I normally recommend to use a temporary bit and a SET/RST or alternatively a MOV instruction together with the "problem" device, so that you can see if, in the specific line of code, the state is what you expect and if the device is being modified later down the code.

[panic mode 245]

he may be chickenkiller but i am a chickenconsumer