RSlogix 500 confusion

I am modifying a program on RSLogix 500 for a generator control panel. I was asked to try to simplfy this program so it would not be so complicated.
Midway through the program I encountered something I find very hard to comprehend.




The previous person who did the program really got me confused. It seems pretty long-winded. Sometimes I have no idea which I/O signifies the desired function, because he add description to some inputs and outputs only. And I do not have the schematics to follow on.

I believe the above rungs are for the fault relay to give a blinking signal to the indicating lights so they will flash, whenever a fault is detected and the relay activated. After that the user will have to push the alarm acknowledge button to acknowledge the fault and still the indicating light.

I'm appealing to someone who could help me out on this portion. Is there a simpler way to do the same function?

regards
Sherine T.

Didn't try to follow your code, but the attached file may give you some ideas. I only used two fault conditions, but you can add additional ones. It's a RSlogix 500 file. Did this from home and don't have PDF option, and it's too big for one screen capture.

Might point you in the right direction. It's just one way of doing this, I use a different method when there are many conditions. But this one is easy to follow.

Sherine T,

Wow! This is a good example of poor programming techniques. All elements should be labeled. If all it does is flash an alarm light, then it could be done more efficiently.

What I couldn't see is: Where is the input for the acknowledge pushbutton? What is the output that causes the light to flash? If you could answer those two questions, perhaps I or someone could re-write your logic to eliminate all the unnecessary elements. Perhaps there are some other things being done here.

Ken
Thank you for the tip. I couldn't open the file yet at home (Shouldn't have got WinXP Home; Big mistake!), but I'll take a look at it tml at work. I print out the whole program onto recycled paper so there's no hassle to carry the laptop, and managed to solve some parts in the program.

I realized that some of the I/Os came from a remote module 1746-SN. For my current project, there are only 4 D.Is and 4 D.Os, managed by a RTU 5/03. So I think I can remove the rungs that are associated totally with those I/Os.

I need a little clarification on the move command. Say for example:

   B3:150/0                       MOV

-----][-------------------------|Move   0 |

                                |Source 0<|

                                |Dest N7:0|

 

   B3:150/1                       MOV

-----][-------------------------|Move   1 |

                                |Source 1<|

                                |Dest N7:0|

And so it goes on for till 

   B3:153/12                      MOV

-----][-------------------------|Move   61|

                                |Source 61|

                                |Dest N7:0|

So from the node N7:0/0 to N7:0/6, each NO contact goes to an output.

 

   N7:0/0                         O:6/0

-----][----------------------------< >

 

   N7:0/1                         O:6/1

-----][----------------------------< >

until...

   N7:0/6                         O:6/6

-----][----------------------------< >

I have 62 memory bits all move to N7:0, why is it only N7:0/0 to N7:0/6? Does it mean of the 62 bits, I only used 7 of them? It's my first time doing these kind of instructions on RSLogix so I'm a tad bit confused. It's quite different from Twido software that I'm a little more familiar with.

regards
Sherine T.

edit: Lancie, I didn't show the ack PB because it's on another ladder file. I got the alarm part figured out somehow but I do not quite get the concept this person has entered for the blinking function with relation to the fault relay 74 being activated.

Previous attachment in pdf format.

Sherine T,

The MOVE comand is "what you see is what you get". It moves a 16-bit word from the Source memory location to the Destination memory location. The last value in the Destination is shown at the top right of the command. The first 3 rungs set some values (0, 1, and 61) to the bits in word N7:0

It appears that the last 3 rungs you listed are nothing more than part of the "mapping" between the original PLC and the 1746-SN Scanner Module. For the PLC to see the remote I/O rack, it is necessary that the Scanner Module inputs and outputs be assigned to some memory locations in the PLC. The last 3 rungs are probably the Outputs to the remote rack, which shows as Slot 6. The programmer probably only "mapped" the bits that he actually needed, instead of the entire range of the scanner module. This is common to save on memory space in the original PLC.

Thank you, Ken and Lancie, for the explainations. I can understand better now!:nodi:

Lancie, there are actually 2 outputs OR together from the N7 contact. The output I entered is for the digital output module. The other output I omitted is the scanner module, which I think there's only 1 in the chasis ('cause it shows as O:1/68, for example). So if I do not have the scanner module now in slot, replaced by the RTU processor with modbus, will it be necessary to use the Move instructions still? The outputs on the schematics only showed wired output signals to the other panels. Only use for the modbus is for input signals only. Or does the move command necessary for modbus communiction?
Thank you for the advices!

regards
Sherine T.

No, the move command is not a communications command. Every place where MOVE is used to "map" a Scanner Module (and you are deleting the Scanner Module), then you can safely delete that MOVE command.

Originally posted by jolio ST:

I have 62 memory bits all move to N7:0, why is it only N7:0/0 to N7:0/6? Does it mean of the 62 bits, I only used 7 of them?

Click to expand...

You aren't really moving 62 bits into N7:0. You are moving a value into N7:0 based on the condition of some bit. Your maximum value listed is 61, which fits into six bits of a binary value (2^6 = 64). The original programmer is using 7 bits total for a maximum value 127 (2^7 - 1). It looks to me like the original programmer wanted to pass information to another processor using digital I/O OR they wanted to display an error code as a light pattern on a panel.

Keith

Thank you for all the replies. I had a discussion with my boss. There had been some slight changes, and it doesn't seem very pleasant. But at least it's more simpler now.

A 10 slot chasis with an RTU 5/03 with modbus for communications. The only informations which will be transmitted by modbus are all faults and status signals received from this control panel. I have 30 modbus signals in all.

What I find a relief is that the only output signal from the plc to the SPMD (Digital synchronizer)is only the contact signals from the circuit breaker relay and the synchronizing relay. The idea to send all fault signals to display on the SPMD has been drop.

Anyway, I have attached a zipped RSL500 program on a project-gone-wrong done by one other guy. I was told it works fairly well. It's pretty messy and unclear in labellings, making it look complicated. I finally understand most of the program now. SO anyone interested can take a peek.
As for my current working-on, I'll change a little here and there and test it out by next week.

regards
Sherine T.