Allen Bradly Plc 5 Deviation alarms

I am having a small problem with a deviation alarm, I am tring to get my head around what the right formula would be

What i need help with is if a level drops 5000 pounds in thirty second it will set an alarm

any help

Thanks

Sounds like you're looking for a rate-of-change alarm rather thsn a deviation alarm. Deviation alarms are only concerned with the magnitude of error in a control loop (difference between setpoint and process).
You will need to obtain the derivative of your level signal and alarm when it exceeds 10,000 lb/min or 167 lb/sec.

Thanks Gerry that sound alot more like what i need

Thanks

Programmer-in-training,

Why did you think that you needed a "deviation" alarm? Could it be that you are using a PID block with a type "PD" Control Block (which creates a deviation alarm on the PID block configure screen)? If so, then you have only 3 parameters that you can set with this type of alarm, + Deviation Alarm, - Deviation Alarm, and Deviation Alarm Deadband.

As Gerry pointed out all these parameters are based on the dirrerence between the PV (Process Variable) and the setpoint, and do not factor in a time parameter. If you need an alarm upon a 5000-pound change in 30 seconds, then you will have to create your own equations to calculate it. Hint: you can calculate the change in level divided by some time period as measured with a timer.

Thanks

Thanks For your help

I just could not get my head around what was needed!