Example of timer to switch devices

Here's what I'm trying to do: We have a watermaker that includes a UV light as part of the purification process. There are two lights, one is the main and one is the backup. As currently programmed, the backup ONLY turns on if the main faults out. I want to place a timer into the logic that switches the lights every week so the run time can be shared. I can write the timer logic easy enough, but I'd like to keep the ability to switch lights if a fault occurs and I'm really not sure how to do it.

Basically, the way I'd like it to work is that when both lights are operational, the timer switches them once a week. However, if one goes bad and a fault is generated, the light is switched automatically.


I've dug through the downloads section a bit and I'm going to continue to dig deeper, but if someone already knows an exact example to look at, I'd appreciate it if you could point me in the right direction. Thanks!


Edit: Sorry...I'm using RSLogix 500. Lol...guess you can't read my mind, can you?

check- Lancie1 Alternator thread

osmanmom said:

check- Lancie1 Alternator thread

Click to expand...

Very simple logic.

then install AC current transducer-> Analog/switch output

Thank Phuz and Osmanmom. That parallel circuit had started to develop in my mind and I was working on it. Got a little bogged down because I forgot a timer can only be preset to 32767, which pushes my time period of a week out the door, but the important thing is that they get equal run times, so I can live with that.

use counter also ok - 1 pulse = 1 hour etc

SiriusMark said:

Thank Phuz and Osmanmom. That parallel circuit had started to develop in my mind and I was working on it. Got a little bogged down because I forgot a timer can only be preset to 32767, which pushes my time period of a week out the door, but the important thing is that they get equal run times, so I can live with that.

Click to expand...

No it doesn't. There are many ways to accomplish this. You can use a counter to reset the timer every hour for 168 times (168 hours in a 7 day period).
Or....you could use a counter bit to control the lights, and just use a timer to increment the counter. I've worked on numerous applications where you have to get creative and work around the limitations of a 16-bit integer.

Counter in line with the timer? 3600 seconds gives an hour, when the counter reaches 168, a week has passed and the DN bit is set, use the counter DN but instead of the timer TT bit?

Many ways to do it.

In the logic you displayed, why use the timer's TT bit rather than the EN or DN bit? Is it because the TT bit will be active as long as the timer is actually running?

Forgive what may be dumb questions. Sometimes I know what I'm doing, sometimes I forget what my name is. Not sure what kind of day today is yet.

SiriusMark said:

In the logic you displayed, why use the timer's TT bit rather than the EN or DN bit? Is it because the TT bit will be active as long as the timer is actually running?

Forgive what may be dumb questions. Sometimes I know what I'm doing, sometimes I forget what my name is. Not sure what kind of day today is yet.

Click to expand...

Sure, use the EN bit if you want. The DN bit will only be active for one scan when it occurs, so not really a good option there.

Update: Thanks to everyone, got it done. Just learned some more on timer/counter interaction as well. Groovy.