AOI's causing failures after releasing the E-stop Push button

[olealf]

Hi

I am having issues that I think may be associated with add-on instructions:

1, I am using AOI's in ladder logic for controlling valves (open,close,fail to open-after 5 seconds, fail to close, after 5 seconds) and pump (start, stop, alarm)

2. During the execution of the program they are working fine, however if the E-stop is pressed the outputs of the PLC are inhibited and valves are going to be closed and the pumps are going to be off.

3. if the E-stop is released some how, immediately ( remember the 5 secs timer for the valves alarm) I am seeing the alarms open or close for the valves and pump failure for the pumps, I have checked while online and the outputs associated with the alarms are 1, but inside the logic of the AOI the rungs associated with the alarms 0.


do I need to use any scan mode or something ?

I am using Compact Logix L30ER with RSlogix 5000 V20

 

[MarkNightingale]

It might help us if you can post the PLC code.

Zip it first (forum rule).

Cheers

Mark

 

[olealf]

here you have

 

[olealf]

Sorry The file size exceeds the maximum allowed!!

How can I send you the zip file ?

 

[passwordg]

Upload on dropbox and post the link ?

 

[James Mcquade]

olealf,

if I understand you correctly.
when the e-stop is pressed and stays in, the power to the outputs is killed and all is well.

if the e-stop is released immediately as you say, alarms go off.

I have a question for you.
when the e-stop is pushed, do you turn off the outputs in the plc code immediately?

if the answer is no, then when the e-stop is restored and the power to the devices is re-enabled, the plc outputs turn the devices on / off based on the plc logic.

hope this helps,
james

 

[olealf]

HI

Let me clarify the situation:

1. pressing the E-stop is going to remove the power to the PLC output cards and the power to the pump.

2. when the E-stop is released the power returns and I am seeing, in the HMI, the valves alarms fail to open or fail to close immediately ( I have programmed 5 secs timer for this alarms) the alarm will depend if the valve was open or closed prior to press the E-STOP

so basically I am getting the alarm immediately after releasing the E-stop.

any suggestions ?

 

[Greg Fowlds]

I am assuming that you have no input to the PLC from the EStop.

Your PLC does not know that the EStop is pushed.
Take an input from the EStop.
On EStop being released, start a timer for say 20 secs and use it to isolate the alarms.
This will give the system time to get back to the correct mode.

 

[ASF]

Sounds to me like the AOI does know that the e/stop has been pressed, because it doesn't generate the alarm until after it's released.

I suspect it'll be that the e/stop signal is used in the wrong spot within the AOI. Perhaps your code looks at the state of the valves, and starts a timer if the input doesn't match the output, etc. Then you say "if my timer times out, and the e/stop is not pressed, raise an alarm". The issue is that the timer times out regardless of whether the e/stop is pressed or not, so as soon as it's released, your alarm is generated. Your e/stop pressed condition also needs to be in series with the timers, so that if the e/stop is pressed, the timers will be reset, and then when the e/stop is released, you have your 5 second delay.

Does that sound plausible?