Hi am a very new to PLC programming, and have been asked to test a program for first out alarming. I am waiting for a PLC to test the code but in the mean time I have received the code offline and am trying to figure it out. I have attached the file to this and have some questions on how instructions execute.
My initial question is if a PLC execution is from left to right, top to bottom when an alarm comes in
how will Rung 6 ever execute.
Note:1 to alarm (cannot see how this would work if 0 to alarm)
Rung 5: Say an alarm comes in, First_out_sd_in becomes a 1, first_out_sd_on is already 0,
so 0 or 1 =1 which makes first_out_sd_on a 1.
then this rung stops executing as input bit FO_SD_BIT is set to 1 (if rung 6 executes)
if the logic is execute left to right, top to bottom
Rung 6 first_out_sd_in & first_out_sd_on will always be equal when an alarm came in, because first_out_sd_in and
first_out_sd_on are both 1 from OR instruction on Rung 5 already???
I have some other questions but once I can understand how the PLC executes these intructions hopefully they will get
cleared up.
My initial question is if a PLC execution is from left to right, top to bottom when an alarm comes in
how will Rung 6 ever execute.
Note:1 to alarm (cannot see how this would work if 0 to alarm)
Rung 5: Say an alarm comes in, First_out_sd_in becomes a 1, first_out_sd_on is already 0,
so 0 or 1 =1 which makes first_out_sd_on a 1.
then this rung stops executing as input bit FO_SD_BIT is set to 1 (if rung 6 executes)
if the logic is execute left to right, top to bottom
Rung 6 first_out_sd_in & first_out_sd_on will always be equal when an alarm came in, because first_out_sd_in and
first_out_sd_on are both 1 from OR instruction on Rung 5 already???
I have some other questions but once I can understand how the PLC executes these intructions hopefully they will get
cleared up.
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