New to Beckhoff PLCs

Thread Starter


Joined Nov 6, 2019
Hi guys,

Next year our company will start a project with Beckhoff PLCs. We are a small company and all new to Beckhoff hardware, so I thought I'd ask here. Does anybody have experience with Beckhoff, and if so, what are your thoughts when compared to suppliers like Siemens and Rockwell?

Another question: For the general input modules ( EL1124 | EtherCAT Terminal, 4-channel digital input, 5 V DC, 0.05 µs | Beckhoff USA, EL1008 | EtherCAT Terminal, 8-channel digital input, 24 V DC, 3 ms | Beckhoff USA ) do we need to add pull ups and pull downs ourselves or are these built in?

We will be collaborating with a third party who has a lot of experience programming control system with beckhoff / twincat but no one has experience with the actual hardware.

Thanks in advance!

panic mode

Joined Oct 10, 2011
I have used many brands including three you mention. I like Beckhoff PLCs. Very capable, scalable, nice IO too...

EL1xxx are digital inputs
EL2xxx are digital outputs
EL3xxx are analog inputs
EL4xxx are analog outputs etc.

Most of the time we use EL1809 for inputs since it is higher density (16pts). EL1008 is 8 points.
The cards themselves have internal loads (sensing circuit equivalent to pull resistors).
When selecting IO cards you need to watch things like polarity and voltage. Do not use external resistors to bias inputs. Technically you could do that too but it is only going to open can of worms so... don't do that except if testing something on the bench or as a last resort and short term fix.

there are many reasons, including messy wiring, sensed would be inverted and less reliable... there is a reason stop button on a machine is using NC contact even through all other buttons are using NO.

another thing to watch include isolation, consumption etc. some modules take more power and there are limits on how many modules one can gang together. it is a good idea to add separate power terminal so one can inject power at multiple places. also not all modules can be directly side by side, they may require different order or power terminals for separation.

next you need to plan the fieldbus architecture. EtherCat is not like regular Ethernet where you plug ten things into same ethernet switch and forget about it. with EtherCat you need to follow design guidelines and topology. daisy chaining coupe of IO groups is straight forward on paper but in field it may be much more reasonable to use star topology and for that you need to choose correct hardware.

panic mode

Joined Oct 10, 2011
about other brands... i do not care much about hardware... Once selects hardware and have it connected rather quickly, The time is spent developing software and I can tell that i am not happy working with Siemens... it is probably the last brand on my list. They do have capable platform(s) but their software is really poor in my opinion. Ask around and most people will tell the same unless they don't know anything else.
It is better if you are in Europe and speak German because there is a large user base and that means better support (check SPS forum). but it is not just Siemens product ugly user interface, it is also that they are very fragile system designed to just push code from PC to PLC/HMI but ... not really the other way around. And I don't know how many times user lost the symbols etc. And on top of that monitoring capabilities are really poor. On common platforms (small, medium and large PLCS) one can monitor only one file... you need to go up to a really large S400 to monitor just two files at the same time. meanwhile every other PLC brand lets you monitor EVERY file in your project at the same time - even on a cheapest little PLC. and if you think oh well, one file is not so bad, think again. most of the time you would actually be happy to see half of your screen refresh. one may have to scroll and click around in hope that S7 will start refreshing on one instruction that you are looking at... The quirky memory order and endianness are least of the worries...

AB is very nice. one thing unique to AB is that communication software is not built into the programming software, it is separate and shared for all products (PLC HMI,...). software is pricey and needs frequent updates.