Interview Question Ideas?

[ganutenator]

another question.

when is a machine the most dangerous?

when it's first turned on.
why it that?
if the machine is turned on for the first time, valves can be wired backwards, or piped backwards.

when the plc is put into run for the first time, it does what you tell it to, not what you want it to do.

how do you debug plc I/O when the plc has the program downloaded into it for the first time? have the plc in program mode and debug the I/o manually, that's how we usually do it.

james

program mode: that a good idea.

 

[janner_10]

janner_10,

taking a laptop to an interview is very risky in my opinion.
The company could claim you are stealing the laptop, copy the information, or report you to your current / former companies.

in my last position working for a defense contractor, no way am I going to carry that information somewhere! Non disclosure agreements, non-compete agreements. those can hurt you if your not careful

james

Good Points.

But I'm not sure, the whole purpose we have laptops is that they come home with us.

If I would be faced with a potential employer asking me if I stole a laptop in a job interview, it would end there and then.

That said, I didn't work for the MOD as that would be a different matter.

We are less sensitive to that kind of attitude here, the average run of the mill employer looking for a controls guy / developer / programmer, find it quite difficult to actually recruit, period. A guy turning up with documented evidence, preparing to be challenged and explaining first hand his thought process, would, to most be a god send. In my opinion, much preferable than chattering about your strengths and weaknesses, what kind of animal you would be or what would you do if a motor keeps tripping the MCB.

Horses for courses though, gents that are going for control / programmer positions tend to be, on the whole, more mature and exercise better judgement than a fresh faced kid on his way to the electrical apprentice interview.

I can only speak as I find based on my own experience. This was 9 years ago, so I don't lose much sleep lately hoping my new boss doesn't report me to the company I used to work for.

 

[boneless]

Hand them wiring diagrams (and maybe P&ID) of a typical project and ask them to name components. If they don't know, they should be able to figure out where to look up the answer from the diagrams.
To take it a step further, ask them how they would go ahead and structure the program.

 

[ganutenator]

not to keep dragging the laptop thing out, but...
I always have mine on me in case I need to help someone w/ tech support.
Of course, I'm in a dif. line of work, and it my laptop.
Been my experience most employers don't want to look at code.
Me personally, I wouldn't mind. But it better if they write it on a white board. helps to ensure they can.

Had one Engineer ask me to write a oneshot instruction for allen bradley if the processor didn't have that function. I thought that was fair. Probably because I knew how and it impressed him that i even accounted for first scan.

 

[ganutenator]

And to answer someone's good question:
I am the sole developer of the program for the machines that the OEM is selling like hot cakes.
I had a stroke. Minor one. But it got him worried w/ what if?
I comment the heck out of my code, so it shouldn't be a problem, but he wants me to train someone while I'm still alive.
It 1131. unity. i used structured text when it made sense and ladder where it made sense.
I wrote a few dfb's for stuff i used over and over. motor fail to run, analog scaling, input debounce, etc.

 

[NetNathan]

Does he understand "Examine On" and "Examine Off"?

Try.... what does PLC stand for?
I was watching an AutoCad Electrical training program and the instructor said it stood for Programmable Logic "Circuit"??

 

[bitmonkey]

"What do you do when nothing makes sense, and you are all out of guesses?
A. Blame the operator & go back to the breakroom.
B. Use logic, common sense & good judgement.
C. Ask for help from senior techs to understand the nature of the problem & improve your troubleshooting skills.
D. Call tech support & have all relevant information at hand.
E. Keep digging. Use all the available information from all resources to make educated guesses and narrow down the source of the problem.
F. Cut a P.O. and get the very skilled & very expensive techs to come in and do what you are getting paid to do.

 

[gas]

As an old retired guy I would offer this:
Knowledge and skill is certainly important but.....
Does he/she work well with others? Does he own up to mistakes? Will he/she willingly tell you about what he screwed up and what he learned from it? We all have those stories. What I have always thought most important in my later career is how fast can he learn and is he willing to. AND the really big one...the only reason that you exist anywhere is to put money in the owners pocket. Many employees resent that thought and they get an attitude, if you smell that do you want to bother with this guy?

 

[ganutenator]

"What do you do when nothing makes sense, and you are all out of guesses?
A. Blame the operator & go back to the breakroom.
B. Use logic, common sense & good judgement.
C. Ask for help from senior techs to understand the nature of the problem & improve your troubleshooting skills.
D. Call tech support & have all relevant information at hand.
E. Keep digging. Use all the available information from all resources to make educated guesses and narrow down the source of the problem.
F. Cut a P.O. and get the very skilled & very expensive techs to come in and do what you are getting paid to do.

Tell me about a problem that you were stuck on and what steps you took to resolve it?

 

[ganutenator]

As an old retired guy I would offer this:
Knowledge and skill is certainly important but.....
Does he/she work well with others? Does he own up to mistakes? Will he/she willingly tell you about what he screwed up and what he learned from it? We all have those stories. What I have always thought most important in my later career is how fast can he learn and is he willing to. AND the really big one...the only reason that you exist anywhere is to put money in the owners pocket. Many employees resent that thought and they get an attitude, if you smell that do you want to bother with this guy?

good points.

you just described me. made my day.

 

[ganutenator]

I was thinking more what happens if you XOR variable a w/ variable a.
or, what is the value of this binary word in decimal.
or, write a do while loop on the white board backing up this 2 dimensional array and then clearing it when its value changes.
et al.

 

[ganutenator]

the goal:
provide customer w/ peace of mind that someone can support the code if I fall off a cliff.

 

[L D[AR2P#0.0]]

How about working together with the interviewee on a problem that you don't know the answer to? might be risky but also might reveal what it will be like to work with them.

E.g. How would you determine how many zeroes are on the end of the number 100!

 

[cardosocea]

I was thinking more what happens if you XOR variable a w/ variable a.

Honestly, I would tell you I had to pull out a truth table. I don't think I ever used a XOR in a PLC. In microcontrollers you would use them to flip bits, which I suppose is the same on a PLC, but I never saw it. Any specific example for this instruction?

or, what is the value of this binary word in decimal.

This can be a trick question as well. If the word is 32 bits, I would ask you which processor family are we talking about as the bytes could be upside down or intertwined.
I had a similar question on this job interview for a programmer and ended up explaining to the interviewer what BCD is and how you don't have to convert it to decimal if you want it in ASCII format as you can just print directly in hex to get the value.
Not overly useful in PLC's... but very interesting in C. I think I gained Geek points by going on that diatribe.

 

[ganutenator]

Honestly, I would tell you I had to pull out a truth table. I don't think I ever used a XOR in a PLC. In microcontrollers you would use them to flip bits, which I suppose is the same on a PLC, but I never saw it. Any specific example for this instruction?


This can be a trick question as well. If the word is 32 bits, I would ask you which processor family are we talking about as the bytes could be upside down or intertwined.
I had a similar question on this job interview for a programmer and ended up explaining to the interviewer what BCD is and how you don't have to convert it to decimal if you want it in ASCII format as you can just print directly in hex to get the value.
Not overly useful in PLC's... but very interesting in C. I think I gained Geek points by going on that diatribe.

In the old modicons, would see a word XOR on itself as a way to clear the word.

as far as the base to the power of the position thing, any programmer should be able to immediately determine that 2# 1010 = decimal 10.