Latching output issue

turner15429

Member
Join Date
Apr 2018
Location
Landrum, SC
Posts
13
I'm currently having issues getting an output to latch on and I don't know why i can't get it to work. I'd really appreciate it if someone could help me. The function of the routine I have attached is to check for a abrupt loss or gain in tension every second depending on the tolerance value set on the HMI. I have my logic attached. Let me know if you have any questions.

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test-1.jpg test-2.jpg test-3.jpg
 
You are comparing your saved values with the window limits. Change them to the live values. E.g. you are using Tension_1_Control in the comparison, use Tension_1 instead.
 
Last edited:
After looking at it again, I think you have your comparators backwards.

For LEQ to be true, Source A has to be Less than Source B. I would say swap your GEQ and LEQ commands on each latch rung or swap the tags in Source A & B.
 
Last edited:
You are comparing your saved values with the window limits. Change them to the live values. E.g. you are using Tension_1_Control in the comparison, use Tension_1 instead.
Well the reason I did that is because There is some jitter in my load-cell input and if I compare it every second I have a smaller chance of a false reading engaging the E-Stop. The machine test the tension of three separate cables being tightened with a 50 ton and two 25 ton screw jack. I completely broke a cable to test this function and the bit did not latch on.
 
But you are using the saved values to generate the window values using the offset from the HMI. You then compare to see samed saved values in the comparison. The saved values will never be outside the window values they just generated. In the comparisons you must use the live values.
 
After looking at it again, I think you have your comparators backwards.

For LEQ to be true, Source A has to be Less than Source B. I would say swap your GEQ and LEQ commands on each latch rung or swap the tags in Source A & B.
Yeah originally it was like that but I changed it because I thought it was backwards. I tried it both ways and still no latch. Here is the previous logic


 
I would say do the original logic like what Bernie said. Compare the live value to the set limits. As far as the jittering load cell, you could use some kind of filter as opposed to the raw value of the input. I deal with much more sensitive load cells than what I think you are talking about and we use a Low Pass Filter inside of our FBD to filter out weird spikes or drops.
 
Last edited:
But you are using the saved values to generate the window values using the offset from the HMI. You then compare to see samed saved values in the comparison. The saved values will never be outside the window values they just generated. In the comparisons you must use the live values.
Yep you are completely right. Thank you. I cant believe I got hung up on something so simple.
 

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