Shift Buzzers

[gleblanc 1]

Attached is a small PLC program that runs the shift buzzers at work. It's in use on an FX1S-30MR here at the plant, so I know it works, but I'm still open to any comments or advice on how to make it better. I've tried to document it nearly to death, to make sure that next time I need to change it, I can figure out what's going on. I don't think the FX1S can hold comments, or maybe I've got too many for it to download, so I put a small thumb drive in the cabinet with the PLC, so that I won't lose the program and the comments. Background: We had an older "smart relay" in place, but when we went to mandatory overtime, and added a third break, we exhausted the limit on timers for that device. I had 3 FX1S CPUs sitting in a closet from a plant we shut down a few years ago, and figured they'd make a cheap alternative to buying another PLC, even though they've got FAR more I/O than is needed for this project. Shift starts at 6, half hour lunch is at 10, breaks at 8, 12:30, and 2:30 (which used to be the end of shift). There's a 2 minute buzzer before the work start bell, to remind people to get back to their stations before the line starts again. I though about using timers to do the 3s buzzers, but it turned out to be much easier to use the RTC. I also screwed up and implemented a double coil the first time through, which caused one set of buzzers not to work. Shift Buzzers.zip

[JRoss 84]

I finally got to take a look at this. I can't think of any better way to handle it! Different ways, sure. For example, you could be cute and use an indexed lookup table. But that would overly complicate things, especially for the guy who has to troubleshoot the code in ten years when the thumb drive has been "borrowed" and the program file is lost!

[gleblanc 1]

Well, I just checked today, and the RTC on the FX1S was off by more than a minute. Looks like figuring out a way to sync the RTC daily is going to have to be a priority if this keeps up!

[kaare_t 155]

Do you have anything connected to the FX1S (HMI/SCADA) that could update the RTC on the PLC? If so you could sync the HMI/SCADA to a time-server, then update the PLC clock from the HMI/SCADA....

[JRoss 84]

I've heard of RTC syncing being done on a plant-wide basis before, though using AB equipment. Pretty much everything was on Ethernet connected to Wonderware, and every PLC had a section of ladder logic to handle the RTC update from a computer on the server. I think the server pushed the time to the PLCs as an encoded word of some sort, and it was parsed in the PLC to update the time on the PLC and HMI. Sorry I don't have more information than that.