HMI or NOT

[Boorabee Parker]

Forty I/O I would have a HMI. Machine stop / start and safety can still be hard wired. You could use the HMI for I/O diagnostics, run hours, alarms etc etc.

 

[ktmtragic]

Thanks guys for giving me some food for thought

 

[ktmtragic]

This machine has approximately 12 switches / buttons that are used frequntly

 

[boneless]

It depends on the client. I am a PLC guy, so I would go for PLC/HMI.

Many of our clients swear by relay logic (especially on older ships). Easier to spot errors, easier to replace parts (generally a relay is a relay).

As mentioned, a nice intermediate would be PLC control with an alternative relay logic.

 

[JesperMP]

Many of our clients swear by relay logic [..] Easier to spot errors,

?

I disagree. A PLC program can be "self-monitoring" if written properly, and it can log alarms and other information that will assist greatly in pinpointing error causes.
With a relay-based logic, intermittent errors can be nasty to troubleshoot.

 

[ktmtragic]

Agree Jesper

 

[boneless]

My assumption is that the user/client does not have access to the program and thus has to rely on the inputs/outputs.

 

[JesperMP]

My assumption is that the user/client does not have access to the program and thus has to rely on the inputs/outputs.

I think you mean that if there is a PLC but no HMI, then in order to trace errors, the end-user would have to try and interpret what the inputs and output does, and without knowing what the internal memory bits are doing.
If there was a relay based control, the end-user could also observe the "internal" relays, which could be an advantage.
Well, that is another argument that if there is a PLC there should also be an HMI.

 

[boneless]

Partially yes, but even with an HMI. If there is something wrong, in the code, even if you get an alarm, it will be hard to fix if you do not have access to the PLC.

Don't get me wrong, I am pro-PLC, but I know clients that have a relay based machine, that has been in service for a 100 years, often are very skeptical about PLC's. The way the original question was put, it sounds that was the case here. If the end-user really doesn't want it, and someone else makes the decision to put it in anyway, they will make sure they find something to proof you wrong.

 

[shooter]

stick with the buttons for operation, and have a HMI for timing and alarms.

 

[JesperMP]

It is quite typical that E-stop and E-Stop Reset are hardwired (because they have to be), and then a few buttons for start/stop sequence (because you can locate them without looking at the screen).

 

[janner_10]

It is quite typical that E-stop and E-Stop Reset are hardwired (because they have to be), and then a few buttons for start/stop sequence (because you can locate them without looking at the screen).

E-Stop does, but the reset does not have to be. You can go through the HMI and out of a digital output.