GertThePLCGuy
Member
Just wondering what other peoples thoughts are on using the script code in your HMI application compared to keeping the logic in the PLC.
My answer to that is a resounding NO.
One of my design goals on anything with an HMI, is that unplugging, shutting off, rebooting, or replacing an HMI should have zero effect on the operation of the controlled equipment.
My answer to that is a resounding NO.
One of my design goals on anything with an HMI, is that unplugging, shutting off, rebooting, or replacing an HMI should have zero effect on the operation of the controlled equipment.
Auxiliary functions, such as data-logging, and report generation may be disabled while the HMI is being replaced/repaired, but the machine operation should not be affected.
For the same reason, I insist on always having hard-wired start/stop/jog buttons, even if that functionality is duplicated on an HMI.
If I have only one HMI, and it's used to set the line speed, I will have an auxiliary speed pot that can override it (I use a 'Last Change' routine in the PLC to determine what speed reference source controls a machine. In one case, I had something like 16 speed pots, any of which could control machine speed).
Troubleshooting is also much easier if you only have one 'Control Source' to deal with.
My answer to that is a resounding NO.
One of my design goals on anything with an HMI, is that unplugging, shutting off, rebooting, or replacing an HMI should have zero effect on the operation of the controlled equipment.
Auxiliary functions, such as data-logging, and report generation may be disabled while the HMI is being replaced/repaired, but the machine operation should not be affected.
Even though we have customers who try to control their entire plants with a single G306....
But, what is the value add of such a device? The single programming pacakage? Or the (minor) reduction in cost from a single enclosure, PSU etc? And what about the pain of having to run wiring around the door hinge? I've never liked these devices, but I beginning to wonder if I'm in a minority.
My answer to that is a resounding NO.
One of my design goals on anything with an HMI, is that unplugging, shutting off, rebooting, or replacing an HMI should have zero effect on the operation of the controlled equipment.
So.....
What about HMIs with integrated PLC functions? I know some of our competitors offer these, and I know we've discussed them at length in-house. We've always come down to the view that an HMI is an HMI and a PLC is a PLC, and never the twain shall meet, but obviously enough people think otherwise for these things to sell, and from what I hear from certain sources, to sell in some quantities. This is making us wonder whether we ought to get on this bandwagon. But, what is the value add of such a device? The single programming pacakage? Or the (minor) reduction in cost from a single enclosure, PSU etc? And what about the pain of having to run wiring around the door hinge? I've never liked these devices, but I beginning to wonder if I'm in a minority.