If an alarm keeps coming back after you’ve acknowledged it, 
9 times out of 10 the system is doing exactly what you told it to do 
Alarm keeps coming back after Acknowledged it
Acknowledge ≠ clear the condition 
Mini example:
High pressure alarm at 8 bar 
Process is actually at 9 bar 
You acknowledge on SCADA 
… but the PLC still sees PV > 8, so the alarm reappears → Correct behaviour
Typical causes I see 
Process condition still TRUE (switch made, trip active, PV beyond limit)
Chattering around setpoint because there’s no hysteresis / deadband or delay 
Comms glitches or bad tag quality that look like process trips
Alarm built as an “event” instead of a stable “state”
PLC latch + reset philosophy not aligned with HMI acknowledge
For chattering :
If a temp alarm is at 50 °C 
and PV oscillates 49.8–50.3 °C 
, you’ll see alarms flicker forever without a reset band or delay
What I’d check first 
Is the field condition genuinely cleared? (transmitter, switch, trip contact)
Is the PLC bit still TRUE even after you think it’s fixed?
Is there hysteresis / deadband and an on-delay on the alarm?
Any comms quality / timeout / bad quality flags?
Is this alarm latched in PLC and waiting for a proper reset?
Read Full Article Here: Alarms That Keep Reappearing Even After Acknowledgement
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