Dear experts,

We have 2 separated PLCs. Lets say PLC1 connected to OP and PLC2 connected to Scada. We have a setpoint input area in Scada. Issue is, duplicating this input to OP. Physical connections are OK and I used FB14 (GET) to take this value. In general I tried to do it two steps;

IF Scada setpoint changed, move this new value to OP,
IF OP setpoint changed, move this new value to Scada.

FB request time frequencies are 150 ms for both. It is equal to functions' cycle time. I have dedicated DB900 for this communication and used 2 bits (M and N) and 6 words (A, B, C, D, X and Y) in integer form.
PLEASE SEE ATTACHED PICTURE TO SEE LOGIC.

Problem is that, when we enter a new setpoint from Scada (PLC2) it always appears same on OP and DBW always changes. However when we try same from OP side it (randomly) sometimes be copied to Scada. but usually it doesn't change or it appears sometimes for a very short time and comes back to old setpoint.

What can be the reason? How can I fix it? Could you please check the logic in attachment and tell me the probable problem?

Hello,

have looked to your problem and don't understand your point of functionality. Can you pls explain what you need control, f.ex. - 'I want change value X from Scada only when bit N is true,...). I simply prepare that your code localy on one plc and working yet strangly. Without to know what you expect from this mis-match really can't help.

Update: simply A,D are unaffected from assign any value and everything goes from B and X. Also C and Y can't change anything. I think that you missed some important condition in that CMP instructions.

Duris_I

Hello,

have looked to your problem and don't understand your point of functionality. Can you pls explain what you need control, f.ex. - 'I want change value X from Scada only when bit N is true,...). I simply prepare that your code localy on one plc and working yet strangly. Without to know what you expect from this mis-match really can't help.

Update: simply A,D are unaffected from assign any value and everything goes from B and X. Also C and Y can't change anything. I think that you missed some important condition in that CMP instructions.

 Thanks for  help. let me explain in different way. simply I want to control one set point from 2 control points. One is Scada other one is OP. but they have different PLCs and I need to communicate first. Then I need to provide the condition; sensing change point and then write new value to other one.

Is it wrong logic for this mantle?

Duris_I

What I discover (hope I hadn't wrong logic) is, that everytime I change B or X, all values change to all depended to value in B or X. If values in A or D change, nothing happen, also when values in C and Y change, but with one difference that also can't change nothing. What is meaning of that M,N bools?

 N set by OP and when setpoint changed on OP side it sets. After setting it to 1, other side PLC move the new value to related real number only for one cycle then reset itself. For M it is same but from Scada side change.

sry but if I think again and again, it looks like as I said, it's ring, when you change B, all another values change to B value. Also if change X value, all also on OP change with X value. Nothing more.

Update: if I can say something to your first post, this logic work ok, but maybe something other in other piece of code change it. Can you pls say for my sure, that is correct change that B value and all values in Scada are change to that B value, and vice-versa?