duel compressor Logix pro

[broad bruce]

Here is what I came up with so far, still can't figure out the odd even...

 

[T Gibbs]

On rung 2, test the accumulator for a value of 0, and on rung 3 test the accumulator for a value of 1. You need a pressure switch instruction in both of those lines, otherwise the compressor will not stop when it reaches the desired pressure, and you need to reset the counter with the counter done bit. You may want to move the reset instruction to the line directly after the counter and make the counter preset a 2. (see the picture I posted) Those are just the things I see on a quick scan.

 

[Tark]

Here is what I came up with so far, still can't figure out the odd even...

1. The order of your logic is good, first is the station run logic, then the alternator logic, then the compressors logic.
2. Give a more meaningful name to Bit 0, System_Enabled or System_Run or ?
3. (As Gibbs pointed out) You need to reset the counter when the counter's count equals 2. Look at Gibbs example it is a good way of accomplishing this.
4. (As Gibbs pointed out) Rung 2 should be - If counter equals 0 then run motor 1. Rung 3 should be - If counter equals 1 then run motor 2.
5. (As Gibbs pointed out) You need to include logic in Rung 2 and Rung 3 so that the motors only run when the pressure switch is on, your current logic will run one of the motors anytime Bit 0 is on. I would put a rung in between Rung 0 and Rung 1 that would be - If System_Enabled and Pressure_Switch then Request_Lead. Then use the Request_Lead bit to increment the counter and use the Request_Lead bit in the Motor_1 and Motor_2 run logic.

 

[broad bruce]

Dc

here is where I am now, still not quit there, any suggestions?

 

[osmanmom]

Add 1 counter CTU

value 2

for m2

 

[Lancie1]

...Suggestions?

Here are a few suggestions:

1. Your idea of how the RUN light should work is flawed. When a system (any set of machinery) is in active or RUN mode, the run light should be ON, even if NO motors or other equipment is moving at the time. In other words, in RUN mode, something may, could, and probably will start up very soon. In your version, the RUN light only tries to come on when one of the motors is running. WRONG! Even if it were true, the way you have used the RUN output O:2/0 TWO different times, it will only be ON when Motor 2 is ON (double-coil syndrome). Try placing O:2/0 in a parallel branch with your Output B3:0/0. It will work correctly there.

Your comparison instructions should compare C5:0.ACC to 0 and to 1, not to N7:0 and N7:1 (which you did not define anyway). Are you trying to see how many different ways you can make this program not work?

Do not latch on your motors. There is no need for that, and it means you have to find a way to unlatch them at the right time. Go back and look at the simple program in Post #12 that is really for Exercise 3, the next one you will have to write where you use BOTH compressors for heavy loads. Then remove the rung branches for PE2, and you will have your entire program in those 4 rungs.

You should review the actual LogixPro Dual Compressor Exercise #2 problem at this point. There are several things that you are ignoring or mis-reading. For educational purposes, here is a copy of that problem:

Exercise #2 --- Alternating Compressors when Loading is Light
In this exercise, each compressor is to take it's turn bringing the storage tank pressure back up to the selected pressure setting. Pneumatic/Electric switch PE1 will continue to be utilized for this purpose and the settings will remain the same as those used in the previous exercise (120 PSI with a span of 20).

The task of alternating back and forth between loads is sometimes referred to as a load toggle function, and there are numerous methods to accomplish this in relay logic. In this exercise however, you are asked to limit yourself to using only basic relay type instructions when creating your solution.


Prior to testing your program, adjust the system's discharge flow rate again to 50% as shown. As we have already determined, this flow rate can be readily maintained by a single compressor. Adding a second compressor however, will share the loading and allow for an extended cooling period between cycles.

Once you have created your program, download it to the PLC and thoroughly test out it's operation.

Finally, adjust the flow rate which controls the amount of air leaving the storage tank to 80% and then 100% and note the effect. At higher rates of flow, a single compressor will not have the capacity to supply this system's peak needs on it's own. Obviously we will need a bit of help at times from the second compressor.

 

[Lancie1]

Change your last program to look like the attached picture. Mainly, change the counter C5:0 Preset from 1 to 2, and then change your Counter Reset rung to use XIO I:1/2 and XIC C5:0/DN. Delete all Latch instructions. Well, change it all to be the same as the picture, if you want it to work!