Moving from PC Software Development to PLC RSLogix

[Daryl 1]

I'm hoping to be given the opportunity at my place of work to move from developing database interfaces using Visual Basic, to becoming a PLC guy. With the job role, I don't have to be able to create projects from scratch, it's more of a role whereby a company is contracted to install and setup the PLC system and I need to be able to understand the documentation and the ladder logic. I need to then be able to make any required tweaks, or be able to troubleshoot any problems. Sort of a maintenance and modification role. The PLCs we use are mostly Allen Bradley micrologix and controllogix, and using RSLogix500 and RSLogix5000, along with 2 SCADA systems using Wonderware InTouch and RSView32. So, the question is, how easy enough would it be to pick up the knowledge required from a combination of self-study, very intelligent electrical engineers supporting me, and a laptop and test rig we have available at our site, and of course, online forum support? I've already done most of my PC software development using the previous set of 'tools'.

[Steve Bailey 118]

The ease of moving from being a VB programmer to being a PLC programmer depends on how well you understand the systems the PLC will be controlling. How well do you understand variable speed drives and how they are controlled? What do you need to do to start and stop a motor using a drive. What do you need to do to change the speed of a motor using a drive? How does a PLC handle those tasks? What do you know about pneumatic and hydraulic solenoid valves? Do you understand the different types of solenoid valves available? Do you understand how the PLC programs controlling the different types of valves might differ? A liquid level sensor outputs 4 - 20 mA over a range of zero to 10 meters. The PLC receives the 4 - 20 mA data as an integer between zero and 4095. Can you write a formula to scale that raw data to engineering units? Could you recognize the implementation in ladder logic? What would be the difference in PLC implementation between a PLC that could do floating-point calculations and one that was limited to integer arithmetic? The ease of transition also depends on your understanding of how the PLC operates "under the hood" ("beneath the bonnet"?). Misunderstanding the way a PLC "scan" cycle operates is often the biggest hurdle to overcome for a programmer making the transition from programming in VB to programming in ladder logic.

[splicer480 0]

Just to add to what Steve said... You have to really understand the "physical end" of the project too. What kind of sensors do what jobs and when they do it. Analog, voltage, frequency, current, high speed counting, etc... All of the communication devices and software. I've been working with AB plc's for about 15 years and still don't know what all the commands do....LOL

[Rodney 21]

Well Daryl No pressure ! But good luck and welcome to the world of P.L.C's and as you said very intelligent electrical engineers supporting you. Rodney

[Daryl 1]

Thanks for the replies folks, much appreciated. When it comes to understanding the various hardware to be driven, that's where I intend to use both the Electrical Engineers and C&I Engineers, and the forum too. As said, it is a very specific part I have to play, and doesn't need to go beyond understanding much more than what the PLC can and will do. I know it'll be a challenge, but it's certainly one I'm looking forward too. I've found out over the weekend that we have a budget to purchase the RSTestStand software too, so this may come in useful during my learning curve. thanks for the support folks. regards... Daryl

[Daryl 1]

PS, can anyone give me an example scenario of a difficult situation that I may encounter, just so I know what level I'd be looking to achieve? Example of systems I'll be dealing with are 1) (simpler system) Liquid filled tanks, which have around a dozen valves controlling intake, discharge, and recirc., and 2) (more complex) Package handling/storage system, sort of warehouse with location allocation, laser collision detection, and lots of conditional sequences. regards... Daryl