Ladder logic question

[Philippe Parmentier]

Good day everyone,

I'm creating some rung to handle emergency hammer buttons. The idea is when the N.C. hammer button is hit, a relay keep the status (latch) and when the hammer button is resetted, a timer start to clear the error status and also a reset error request... the idea is to avoid removing the alarm directly.

The current logic is working fine up to the point when the timer reach 0 (elapsed reset time), the system is waiting a realise relay hit to clean the emergency.

when, under ITrilogi V6.47 I quickly hit the Stop_button_Rel (R71), it's going back in the timer waiting loop...
if I longer hit the Stop_button, then it's correcly clearing the alarm and working as expected.

I cannot explain why a short hit is not clearing the alarm and where it's happening in the ladder. Is it a ladder logic mistake? Where is the fault?

Description of the differents inputs/relay/timers

I1    : INPUT : Emergency_Butt ( N.C. circuit)
R72 : RELAY : Stop_Button_Ok ( Use to be N.C / N.O independant from the INPUT logic)
R70 : RELAY : Stop_Button (Latch that keep that an emergency event happend)
R71 : RELAY : Stop_Button_Rel (Request for cleaning the alarm (If the Stop_button_Ok is not ok, the R71 is opened)
R73 : RELAY : Stop_Button_Tim (Closed when the T2 timer is running)
T32 : TIMER : StopButtonDelay (Set to a amount of waiting time and activated when the physical alarm is cleared)

[garysdickinson]

The problem is with the ladder rung that enables the TIMER, StopButtonDelay.
You must press Emergency_Butt for a time period that is longer that the time period of the StopButtonDelay TIMER or the output of the TIMER will not go TRUE.

I think that you need to take a step back and a deep breath.  Your code is a lot significantly more complex than what you described.

I think that you can get most of what you want with 2 lines of ladder logic and one RELAY.

In this example the first ladder rung is a typical, PLC style, latch.  The RELAY, Stop_Button, is latched when the Emergency_Butt is pressed.  The RELAY is cleared when the TIMER, StopButtonDelay, expires.

The 2nd rung controls the  TIMER, StopButtonDelay.  I added the NC version of Emergency_Butt to not allow the TIMER to run until the StopButtonDelay is released.

Best of luck,

Gary D.

[Philippe Parmentier]

Thanks for your reply Gary

I've noticed that on my original message there was a mistake in the description
-
"when, under ITrilogi V6.47 I quickly hit the Stop_button_Rel (R71), it's going back in the timer waiting loop...
if I longer hit the Stop_button_REL, then it's correcly clearing the alarm and working as expected"

The problem here is that I cannot automaticaly clear the alarm after a time out only.

I used the stop button for this example, but mainly this logic will be used for a vibration switch that start an emergency stop of the machine and I don't want to have the operator just cleaning the alarm without an visual inspection to see what caused this alarm. Just resetting automaticaly after a time out is not enough. I would like to avoid him just cleaning the alarm and let the marchine restarting. The delay 'behing' is to force them to go to a visual inspection anyway and not being 'obliged' by performance manager/financial people to bypass the procedure. Because i'm pretty sure in that domain, productivity can overpass procedures and warranty.