GRey (Customer) asked a question.
I have a vision of using an HMI device like a C-more micro from inside a skid loader. To wirelessly control a PLC in a building. I would prefer to not have any ongoing dependency on an active internet connection. In my mind, I am picturing a relatively simple wireless touchscreen in the cab of the skid loader. Linked by Wi-Fi or similar technology. Only when the skid loader is actually inside the building, will a connection ever be needed.
The only way I can tell this would be possible, would be the HMI directly connected to a Wi-Fi-enabled Click Plus (or similar) in the cab. Then that PLC, would wirelessly control the PLC in the building.
For context, the system would be used to control a variety of motors related to fertilizer blending. The blenders themselves, conveyors, and outflow gates. Possibly use mathematical calculations to meter liquid additives relative to the weight of the fertilizer (electronic scale output x a set volume per pound) or by manually entered volume.
Any other ideas/hints?
I would use something much more robust and meant for bridging, such as the Ubiquiti AirMax line. You could use something like the Rocket Prism 5AC and mount it near the middle of your building with omni antennas:
https://store.ui.com/us/en/category/all-wireless/products/rocket-5ac-prism
And mount the Bullet AC IP67 on the skid loader up near the top of the loader with a single omni antenna:
https://store.ui.com/us/en/category/all-wireless/products/bulletac-ip67
Then you set up the Prism to be a PtMP access point mode, and it can connect to multiple skid loaders roaming around the building that are set as PtP station mode.
Your PLC and HMI can connect into a network switch, and the network switch goes into a 24v passive PoE injector which then goes into the Bullet AC unit.
I don't use those specific units, I use the PowerBeam5AC models which are bigger and directional, but I have been using them for around 15 years now without a single hiccup. These devices are very reliable
You probably already know this, but since you would be controlling motors remotely over wifi while you drive around, you probably will also want to build in some sort of watchdog handshake into your PLC programs so that when you initiate a motor run from the skid loader the PLCs check back and forth once a second or two and check if they get a reply from each other. If they ever dont get a reply after a motor has been turned on then the building's PLC should be set to stop the motor. That way, if you for some reason you ever happen to lose communication between the loader and building the motor isn't unable to be turned off when you want it to be. Having a motor left on while you aren't in range of shutoff controls is generally considered bad practice due to safety. Probably also build an error flasher LED into the skid loader so that if that comm loss happens you see an easy notification letting you know you lost connection.
This could be done some simple way, like the loader PLC writes a 1 to some memory address every 500ms. The building PLC checks every 2 seconds that same address, if it sees a 1 then keep the motor running and set the memory to 0. The loader will keep writing 1 and if it ever looses comms then the building will see it within 2 seconds by the memory address still being a 0. Same goes for checking comms the other direction.
I've attempted using Bullets on a similar application where there was 20' between the machine and operator cab. It worked okay, but one little obstruction causes a lot of issues.
For fixed PtP or PtMP, great success with UI products, but mobile left a little to be desired.
How about something much more simple and compact to have in a skid loader than a PLC and HMI? Use a phone or tablet to access the HMI or RHMI that is at the building PLC, and connect to it via Wi-Fi. That way you don't have to do much to install in the mobile machine.
that is exactly how i would do it. mount a CM5-RHMI where ever it is convient on the floor and use a rugged tablet on the fork truck
https://www.automationdirect.com/adc/shopping/catalog/hmi_(human_machine_interface)/graphical_hmi_devices/headless_hmi_devices/cm5-rhmi
One issue I see with your plan, the Click cannot act as a Wi-Fi AP, you cannot connect an HMI directly to it, you need to create a Wi-Fi network with both devices on it.
Not to mention having to deal with the loss of connection and reconnection lag that is sure to annoy operators. Unless the machine will always be within the building and not in/out during operation.
if you don't actually need the full functionality of the HMI and just need a few buttons I have used these wireless push buttons on fork trucks to advance a conveyor and rotate a carousel. They have an impressive range for having no batteries.
https://www.se.com/us/en/product-range/60642-harmony-22-mm-xb5r-xb4r-wireless-push-buttons/?parent-subcategory-id=81654&filter=business-1-industrial-automation-and-control#products