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My company, AMPS Industrial Controls, recently finished the installation and start-up on a control system for the Custar Stone Quarry project we mentioned late last year. This quarry is located in northwest Ohio and it supplies stone for road projects all over the region. We are pleased to say that everything went very well and the quarry is now up and running with wireless Ethernet communication between all three control stations. This was really a fun project so we would like to take this opportunity to explain it in some detail... Background – Unitronics Vision System With Wireless Ethernet from Westermo The stone quarry in Custar, Ohio is quite old. It has been crushing stone and providing northwest Ohio with rock for over 100 years! One problem, though, is that the numerous expansions and upgrades which have happened over the decades have resulted in control stations positioned all over the place. Our job was to integrate all the conveyors and crushers into one central PLC-based control system that could be operated from any location in the quarry. Ideally, this would be done wirelessly so as to simplify installation. Of course, reliability was a great concern. This quarry runs year-round and downtime is very costly. We must ensure that any breakdown in wireless communication would not result in shutting down the quarry. Safety was also a big concern. Great care would need to be taken to safely control crushing equipment remotely. AMPS Industrial Controls would also build the electrical control panels which must hold up to harsh outdoor conditions and be very reliable. We decided a control system based upon the Unitronics Vision line of PLCs would be a good solution. These controllers could be coupled with wireless Ethernet radio modems from Westermo to allow control from anywhere in the quarry. AMPS would handle the programming of the PLCs and would design the system to be reliable, easy to use and intuitive for the operators. Unitronics V570 to Control Main Operator Station The 5.7″ color touch-screen on the Unitronics V570 could serve as the HMI for the main control station. The new V1040 may have been an even better product but it had not quite been released when we started the job. This station is located at the highest point in the quarry inside a booth with a window so the operator can see everything that’s going on. It’s a small booth, though, so we didn’t want to take up too much space. The Unitronics V570 was a perfect fit. From this perch, the operator can control all the conveyors and crushers that wind through the quarry. In the photo below, you can see the main control station circled in red. Unitronics V350 to Control Other Stations The other two control stations only really required small HMI screens because the operators are not used as often. Most of the everyday control will take place from the main station. Because the large color touch-screens were not needed here, we selected the V350. Still part of the Vision series of controllers, the V350 provides full Ethernet capability with extensive I/O options but packaged with a smaller color touch-screen. The photo below shows the small booth where one of the V350 electrical control panels is installed. Not fancy but very nice accommodations in cold weather. Wireless Ethernet Communication Details The Westermo RM-240 was perfect for this application. These devices were easy to configure with a web browser. They formed their own WiFi network on site and were very reliable. The antennas were installed at each location and have been very reliable in all weather conditions. Each Vision PLC from Unitronics was installed with an Ethernet module to connect to the Westermo devices. Modbus IP is the protocol we used. I can’t speak highly enough of both the Unitronics and Westermo products. This control system has been in use for a couple months now and we haven’t had a single phone call from the customer. It is controlling every conveyor and crusher in the quarry. Even a crusher that draws 4,000 starting Amps! As always, it was nothing but pleasure working with the Unitronics Vision controllers.
Twelve years ago when I started writing basic ladder programs for PLCs I made a lot of mistakes. Seemed like I was always getting halfway through a project only to realize I'd taken the wrong approach and needed to take two steps back before I could move forward. Frequently this resulted in me scrapping the entire program and starting over. I told myself that was fine. I was learning, right? Well... a dozen or so years later I'm still learning. Now I say, "You never want to stop learning," but I'm not sure I believe myself. I mean, wouldn't it be better to stop making mistakes, altogether? I suppose that's not likely to happen so here's the tale of my latest misstep:One of my projects for an OEM control system uses several data tables. Even though we've already built hundreds of these electrical control panels and the machines work great, we're constantly updating and improving the PLC/HMI program. Some of these changes affect the data tables. No problem, except...Two of the data tables are frequently accessed by a third-party wireless, handheld device called SynTrack. Here's where my mistake comes in: I should have put these data tables first in the list. Whenever you make a change to a data table, the starting location of all the data tables following it will change. The starting location of your first data table will never change, though, so it would have been a good idea for me to put one of these two first in the list of 7 or 8 tables. It wasn't a big deal to change this but there is an issue with the second data table that Syntrack needs to access.I can only have one table in the first position. What happens, though, when I make a change to the first data table? The starting location of table number two will change but I don't want to force changes to the software in SynTrack. An easy solution is to add a column in the first data table which holds an offset value to tell SynTrack what the starting location of table two is. SynTrack always knows where to find the first table and that first table will tell it where to find the second table. Simple but effective. Now I can make changes to any data table and SynTrack can keep up with my changes without the need to revise its software. I just need to remember to change the value of this offset integer.You can bet I'll remember this in future projects. It was aggravating to make the change this time around because changing the order of data tables required me to delete the originals and then search them all out in ladder, point to the new tables and then re-address all the fields in each of those DT function blocks.Hopefully my time-consuming mistake will help you, though.As always, I encourage you to stop by my primary website and visit my company blog where we regularly discuss Unitronics and other controls news.
Well, I never thought it would happen but people have convinced us to enter the world of Twitter. We'll be tweeting often about Unitronics, control system design and the electrical control panels we build. We'd be honored to have you follow us @matthew_AMPS.