Old School Killer
I was trained on drawbridges by an Old School Drawbridge Guru. The kind of guy who could tell you off the top of his head what wire numbers to jumper across to make anything work. Fortunately for me (maybe not so fortunately for him) I was a naturally curious person and I constantly asked the “why” behind the “what” or the “how”. This helped me to gain a lot of insight into how drawbridges are designed, operated and maintained.
As confident and capable as my Old School mentor was, when our bridges started being retrofitted with PLC controls (programmable logic controller), he wanted no part of them. Quite a few of the old timers that I knew were the same. They didn’t even want to try to understand the new equipment and instead relegated the responsibility of maintaining the new control systems to the younger, less experienced technicians.
I still marvel at the design brilliance of the old relay logic systems. A relay that can be disassembled and cleaned, who’s parts can be replaced as needed and which will function as well in its 40th year as it did in its 1st is undeniably impressive. But those days are mostly over. The vast majority of new bridges or new bridge control systems are PLC controlled. The relays and contactors that are used in conjunction with the PLC are not normally designed to be disassembled or cleaned and many do not even have replaceable contacts.
However, if you were to compare the pros and cons of a PLC controlled system over a relay logic system, well to use a “Men in Black” movie quote reference… the new hotness blows away the old and busted.
Having the ability to use the same virtual relay or timer or contact for as many functions as you can dream up makes life so much easier in the world of drawbridges. Imagine two functions needing some separation; say a delay between when you have fully lowered the spans of a bascule bridge and when you could drive the locks that secure the spans. In the old days, you would have had to install a timing relay and physically wire it between the two functions. In fact, I’ve done this on several bridges.
With a PLC, however, a timer can be installed in minutes with no wiring and you can quickly change how long a delay is required before the locks are able to drive after a fully seated condition is met. This helps prevent operators from driving the locks while the spans are still bouncing a bit and greatly reduces wear and tear if not potential failures. Actually, it’s almost certain that such a timer would already be in place in modern PLC systems.
So let’s get a little creative. What if we wanted to make the fully seated indications flash during the period of time that the bridge is first fully seated and when you’re allowed to drive the locks? By using that same virtual timer, and another to make a flasher, along with a few new virtual contacts; your control desk now flashes fully seated until there is no more span bounce and then the indications turn solid green when you can drive your locks.
You could add counters that would accumulate usage data for any piece of your equipment for your maintenance records. Keep an accurate count of how many operations each gate has had, or each lock or wedge or even span motor. Get really creative and have the bridge generate an indication that maintenance is due after a certain number of operations. You are truly only limited by your imagination when working with PLC’s.
One of my bridges is a vertical lift type that experiences cable creep over the sheaves. While a slow process, because the drive train is being moved independently of the lift cables, even minutely, the span limits will eventually become far enough out of alignment that false failures begin to appear.
Luckily this bridge is PLC controlled. I utilized a spare span limit, set a few degrees before failure, and added a virtual contact that would energize and de-energize the lamp test function for the control desk. Now once or twice a year the operators will call to report that all the desk indicators are flashing. This lets me know that I have to adjust the span limits well before any failure could affect operation.
I really wish my Old School mentor hadn’t felt that technology was forcing him out of the field. If I could have helped him become comfortable with PLC’s and he was able to use his Old School genius with the ease and flexibility of the PLC programming environment, oh what wonderful bridges we would have made.
I would be interested in hearing any stories you have of PLC solutions or perhaps problems adapting to them on your bridges. Please feel free to share your comments below.