PLC/HMI Programming Test

[kevilay]

Hey Guys,

I am looking to bring some new guys onto my team and I was pondering the idea of doing a basic test just to weed out some peoeple that might not be what they say. Maybe something written with some basic questions, or even setup a small little cell running off our test panel. What do you guys think? Have you dont this before? Any tips or suggestions? The plan is to target intermediate level people. People that should know how to connect, download, and write some basic programs.

Thanks,
Kevin Lay

 

[alan_505]

I seen to remember that some asked something similar on here a while ago, but as to how you would search for it, I don't know.

 

[alive15]

Easy way would be to print out a small pdf of a small program and show it to the person and see how quickly they can recognize it's function and purpose. Then ask them how they can improve the code to make it better. This way, you don't spend time creating an entire setup.

 

[I_Automation]

If you want to weed out the non-thinkers do it the FAA way.


A lot of questions on the pilots written test have ALL wrong answers, but they want the pilot to think which of the wrong answers is the LEAST wrong that wouldn't result in a crash.


Or see if they write in NONE OF THESE.

 

[KKleinstick]

I had an employer who had me make a pnumatic can crusher, reed switches, prox swich to detect the can and a single physical button start/stop. It also checked to see if I could do basic welding. and a little bit of trouble shooting.

By the way, the can wouldn't crush without a breather hole in the plates to let the air out of the can.

 

[geniusintraining]

Back in the day.... I had a simple test that the 'suits' would give, if they scored high enough on that and past their interview they would pass them off to me. Then I would bring them out to the floor and tell them X is not working what would you do? And some times I would move a prox and tell them what the operator would tell them...

"the machine dont work" now the operator at this point would walk outside and take a break, so I would just want to see what would they do and how to react, if they would not even open the cabinet or ask a few questions (like what should happen next) or would they just say "dont know" and not even try.

It also depends on what the position on your team is for, programmer, tech, troubleshooter, start up?

 

[geniusintraining]

I seen to remember that some asked something similar on here a while ago, but as to how you would search for it, I don't know.

Reading material....

http://www.plctalk.net/qanda/showthread.php?t=26532
http://www.plctalk.net/qanda/showthread.php?t=102758
http://www.plctalk.net/qanda/showthread.php?t=84179
http://www.plctalk.net/qanda/showthread.php?t=48878

 

[kevilay]

Back in the day.... I had a simple test that the 'suits' would give, if they scored high enough on that and past their interview they would pass them off to me. Then I would bring them out to the floor and tell them X is not working what would you do? And some times I would move a prox and tell them what the operator would tell them...

"the machine dont work" now the operator at this point would walk outside and take a break, so I would just want to see what would they do and how to react, if they would not even open the cabinet or ask a few questions (like what should happen next) or would they just say "dont know" and not even try.

It also depends on what the position on your team is for, programmer, tech, troubleshooter, start up?

Thanks for the good feedback. The position would be a programmer/designer for a machine builder

 

[I_Automation]

How about ask them how they would do a task, but instead of the easy/normal way management wants to use components sitting on the shelf and not purchase the correct items. [This happens quite a lot, actually]



Say you need an encoder position of a conveyor but aren't going to get an encoder. See if they can think of how to do it with a Conveyor Base Home prox and a pulsed prox off a sprocket or gear on the drive to calculate the correct position.

 

[arpus4KM]

Thanks for the good feedback. The position would be a programmer/designer for a machine builder

best way to get who you want is to test for who you want.

if you want a guy who can program something from scratch, then ask them to do a small program based on some parameters for what you want it to do and then test it with a small machine.

Have the machine ready in back, maybe a servo drive, connected to a belt or ball screw that drives a plate, and multiple sensors along the way with a couple of cylinders that have reed switches for extend and retracted positions.


then you can ask for a program that does a simple operation like " have the startup of the machine home the assembly. send the screw plate out 3 inches, extend cylinder 1, move the screw plate to sensor 2, extend cylinder 2, move the screw plate to home, retract both cylinders."

Include some info for fault conditions.


Something that might take 30 minutes for someone really good, and up to 2 hours if they struggle, by the time you get to the limit then you'll have a good idea if they are in the categories of

A+ - finished in 20 minutes, working program
A- - Finished in an hour working
B - Finished in less than 2 hours, working program, some problems
C - Didn't finish, looks like they were on the right track
D - Didn't finish, not very close, they probably know what a PLC is, but shouldn't touch one.
F - Something caught fire, or they just walked out after given the test.

 

[geniusintraining]

if you want a guy who can program something from scratch, then ask them to do a small program based on some parameters for what you want it to do and then test it with a small machine.

A+ - finished in 20 minutes, working program
A- - Finished in an hour working
B - Finished in less than 2 hours, working program, some problems
C - Didn't finish, looks like they were on the right track
D - Didn't finish, not very close, they probably know what a PLC is, but shouldn't touch one.
F - Something caught fire, or they just walked out after given the test.

This should be really easy but some people have real issues with it

http://www.plctalk.net/qanda/showpost.php?p=569702&postcount=3

 

[PLCDontUQuitOnMe]

I have a very basic test:


PLC with 3 inputs wired up to 3 pushbuttons, two NO and one NC. A corresponding rung underneath with a mix of NO/NC contacts. They have to tell me which pushbuttons must be physically pressed to turn the rung on. This shows me that they can read an electrical schematic, understand NO vs NC and shelf state vs actuated, And that they can accurately translate that to ladder logic and make the connection between a PB being pressed and what the input will do.


That's the basic test, and you'd be suprised how many people struggle with a NC push button wired up to an input but it being represented by a NO contact in the program.



If I am feeling evil, I ask them to do the next test which is convert a short STL network into ladder logic. We have a lot of Siemens PLCs here so this weeds out the guys who have never used Siemens before.


You cannot trust resumes these days as everyone writes that they are "great" at programming multiple platforms.



Once I give them the test and they fail miserably, they usually admit that instead of having actual programming experience, they "watched" over someone's shoulder a few times while they were programming.

 

[diat150]

I did a interview with a fortune 5 company. They presented a logic printout and asked if I could explain what the logic did. I looked over the rungs and determined that the logic as written wouldnt function. I dont know to this day if the answer was right as I was really just getting started programming but they did give me the job offer. I was already working as contractor so they knew I was very good and the interview was just a formality... but I still wonder to this day if I gave the right answer or if I was nervous and overlooked something. I ended up turning the job down and went into more of a Admin role and now own my own company. My old boss at the fortune 5 company was devastated he wanted me to come on so bad. I might call him this evening it has been many years since we talked.

 

[I_Automation]

A shop in the Detroit area was hiring a controls guy.


After a short interview I was taken out to the shop for a "test"


Took me to a broken machine and asked me to figure out what the problem was and see if it's what his maintenance tech found.


Talking to the tech he knew absolutely nothing about controls or electrical, was all mechanical.


Told the owner I knew what it was and could have it fixed by Monday afternoon when I started.



Turns out this guy puts an ad out to hire someone every-time one of his machines goes down to get a free service call.

 

[Blue92]

Interviewing for a maintenance tech position I was asked to draw and describe a simple 3 wire motor starter circuit. Then describe how to connect to a SLC 500 via RSLinx.

Interviewing for an engineering gig I was asked to do a lead/lag pump ladder program using 5 float control, all NO floats. I can see where that could trip someone up using a NO float for the off signal instead of NC. Next task was to write a simple analog scaling function block. That one could weed those that dont have a clue about analog resolution.

In school we would partner up and have our partner move wires around on our trainers without the oher guy knowing. Fun times.