latch delay feed back?

[Ray.R]

Hi Craig,

That's the missing ingredient..  Thus my lengthy question...  Who has precedence / priority?

Stay tuned till we get the answer.. 😉

[Steffen595]

sorry, been away.

Priority: I have to be able to set the state on the PLC, the program running in the PLC as well and some other operator who has access to the PLC. The right way would be a flag which is read back by the PLC, but as I mentioned before we cannot change the program running on the PLC. Truth table, hm, would be endless and there is no logic to it it seams. Should try to make one. Maybe, whatever seting is made should be saved for a while, until another setting is made. As it is now, when I set the switch, it jumps back into its former postion, as soon as I release it. Maybe it should wait for 500ms for the next decision, and if nothing happens, just stay there.

Later,

Steffen.

[Ray.R]

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Steffen595 wrote:
Maybe, whatever seting is made should be saved for a while, until another setting is made. As it is now, when I set the switch, it jumps back into its former postion, as soon as I release it. Maybe it should wait for 500ms for the next decision, and if nothing happens, just stay there.

---

I think the last example I posted offers something like this.  The front panel button changes the state of the heater irregardless of the PLC.  However, the PLC remembers the state it was in, so occasionally, it may take two changes in states for it to take affect (or to be noticed), because the first state change may actually just be catching up to the one set manually by the front panel button / switch.

I agree the best way would be to provide feedback to the PLC.  That doesn't exist, does it?

RayR

[Steffen595]

Hi Ray,

no, there is just the output O0.1. Everyone can access it. So if no priority defined, who would be "right"? I? The running process/program? The other user? Makes it rather undefined.
Your last example is ok that far. The External Setting switch can control the FP Switch and the LED, but the FP switch can on only control the LED. If the FP swithc would control the LED AND the External Setting switch, then it would be perfect.

Cheers,

Steffen.

[Ray.R]

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Steffen595 wrote:
Hi Ray,

no, there is just the output O0.1. Everyone can access it. So if no priority defined, who would be "right"? I? The running process/program? The other user? Makes it rather undefined.
Your last example is ok that far. The External Setting switch can control the FP Switch and the LED, but the FP switch can on only control the LED. If the FP swithc would control the LED AND the External Setting switch, then it would be perfect.

Cheers,

Steffen.

---

The external setting switch represents the PLC, right?  And it only has an output, no input, right?   Can an input be added to the PLC?  Or does it verify the status at timed intervals?

RayR

[Steffen595]

Hi Ray,

>The external setting switch represents the PLC, right?

ja 😉

>And it only has an output, no input, right?

Yes again, basically the output could be imagined as a relais and whatever, program runnin on the PLC or operator via PC can set this ouput/switch or relais. Ok, one could wire an input to an output, but thats not really useful, isnt it. I would control the input rather then the output, would only go somewhere if I could change the program running on the PLC, but I am not meant to. Am just meant to do the SCADA thing with Labview.

Cheers,

Steffen.

[Ray.R]

Hummmmmmm.......

Okay..  That's what I understood...   Which is why I did the example in that manner.  The reason I only look at PLC transitions was because I wouldn't want it to always revert to the state that the PLC wants it to be (priority to PLC); otherwise, what's the use of the Front Panel button??  😉

Let's focus on that last example.  And let's keep the constraints in mind. We can't include wish list if it will not happen from the PLC side..

RayR

[Steffen595]

thats the point, thats why it maybe wont work. Although, quite interesting problem.

[Ray.R]

Can you find out what is an acceptable alternative?

RayR

[Steffen595]

was more curiosity, assignment is done. Would have been nice to make it work. And I guess there is a way.