RSLogix 500 ML1400 Alterate pumps based on contactor

[bearsgone]

Hello
I have two blowers that alternate every day at midnight. Additionally I have contractors that tell me if pump 1 fails, start pump 2. However my logic seems to to have fault because only last pump in ladder logic works correctly but first pump does not even come on?

Any help would be greatly appreciated!

 

[Christoff84]

It looks like you are using the same output on multiple rungs (B3:2/12 and B3:2/15). You can't do this as the ladder code is read top to bottom so whatever logic is the last to get processed using that output will always win.

Try using different addresses and then trigger the output with those addresses using only one rung.

Example rung would be:

BST XIC B3:10/0 NXB XIC B3:10/1 BND OTE B3:2/12

(No logix available so just double click a rung and paste this into the text box)

 

[bearsgone]

Thank you Christoff84 for the feedback

I am not sure I understood your suggestion. I have two ouputs B3:2/12 and B3:2/13.
Here is the complete code:

BST EQU RTC:0.DOW 1 NXB EQU RTC:0.DOW 3 NXB EQU RTC:0.DOW 5 NXB EQU RTC:0.DOW 7 BND OTE B3:4/8


BST EQU RTC:0.DOW 2 NXB EQU RTC:0.DOW 4 NXB EQU RTC:0.DOW 6 BND OTE B3:4/9

XIC B3:4/8 BST OTL B3:2/12 NXB OTU B3:2/13 NXB TON T4:14 1.0 3 3 BND

XIC T4:14/DN XIO I:0.0/13 BST OTL B3:2/13 NXB OTU B3:2/12 NXB OTE B10:0/0 BND

XIC B3:4/9 BST OTL B3:2/13 NXB OTU B3:2/12 NXB TON T4:15 1.0 3 3 BND

XIC T4:15/DN XIO I:0.0/14 BST OTL B3:2/12 NXB OTU B3:2/13 NXB OTE B10:0/1 BND

Thanks again

 

[Tharon]

In the picture you gave, those don't look like OTU or OTL instructions. They only look like OTE instructions.

 

[harryting]

The picture you posted doesn't match with the code you posted later. Which is it? Might as well print out your entire program in PDF then posted it here.

 

[bearsgone]

Hello
I have attached a pdf. The issue is that if contractor does not confirm start up of the first blower, logic fails over to the second blower, however when first blower comes back on line, second blower does not stop and first blower does not start.

 

[Christoff84]

From what you posted, I can see the day of week switch overs should be working, but there was no fail over logic posted or anything to do with the outputs for the pump/blower.

Can't really help you anymore with what you have posted, if you post all the relevant code then maybe we can help you with something. I assume you've checked for broken wires/proven that all the I/O is working?

 

[bearsgone]

Hello

Maybe what I am calling fail over logic is a bit misleading. In the example posted, I have feedback from contractors. So if on day 1, blower 101A does not come on based on contactor feedback, turn pump 2 and set the alarm. Which works fine until pump 1 comes back online. Pump 2 stays latch for almost 2 days until it is pump 1's turn again. I am struggling with trying to figure out how to monitor if pump1 is ready to run and how to go back to it from pump2 being latched as a result of pump1 initial failure or maintenance. Maybe there is a better way to go about this?

Thank you

 

[harryting]

I failed to find where the blowers are actually getting turned on. In any case, the switchover will not happen until the next time Pump A should be running because it only do a 3 second fail check at the beginning of the switchover.

If the blower A fails to start in 3 seconds then it fails to blower B. Comes next day, it still goes to blower B, because that's when Blower B are supposed to run anyway.

Is this what you are seeing?

 

[Bob A.]

I have done this in discrete components a long time ago, but never in a PLC. However, if you search for the logic design for a "MultiStable Multivibrator", you will get a good place to start. This is basicially a flip flop memory circuit that reverses state on each succeeding pulse.
Remember that an Output Command should only occur once in the program as the last one is the only one that will make it to the actual output hardware.