PLC Question 3

Broadley

Member
Join Date
Mar 2018
Location
Abroad
Posts
7
Hi there all,
I have been asked to complete some PLC related tests for a job. I have completed them and they are fairly basic. I just need someone to run their eyes over them and see if I was in the ball park or out of the grounds.

I have had some Allen Bradley experience, but I have not been had the chance to program anything for about 6 years now.

Any feedback will be greatly appreciated :)
 
In your first rung of test #3, why did you use the false condition of the opened LS instead of the true condition of the closed LS? The job spec called for both purge valves in the closed position.
In rung #3, as soon as the top purge valve opened LS is true, the Permission to Start bit will go false, so the timer will never begin timing.
 
In your first rung of test #3, why did you use the false condition of the opened LS instead of the true condition of the closed LS? The job spec called for both purge valves in the closed position.
In rung #3, as soon as the top purge valve opened LS is true, the Permission to Start bit will go false, so the timer will never begin timing.
I was thinking - and not open - as the input would only indicate when it was open.
Ah... good call... well that doesn't work :(
It has been submitted so I can't go back on that... guess I need to re-think it and come up with a solution... thanks for looking over it Steve
 
When you have limit switch indication of both ends of travel, it is almost always better to use them. The specification for pre-conditions was "Top Purge Valve Closed", not "Top Purge valve not Opened". Being off the closed limit is not the same thing as being on the opened limit.
 

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