Host Engineering Forum

General Category => General Discussion => Topic started by: maciek on April 14, 2019, 09:28:08 PM

Title: setting an alarm
Post by: maciek on April 14, 2019, 09:28:08 PM

in a brx plc working with a pid  i am looking for an easy way to set an alarm if the PID_0.PV gets bigger than the
 PID_0.SP by some percentage like 5 or 10

Title: Re: setting an alarm
Post by: franji1 on April 15, 2019, 06:06:13 AM

Calculate the deviation percentage to your SP PV units, then use ALDEV.

Title: Re: setting an alarm
Post by: maciek on April 15, 2019, 08:27:45 PM

i wish that the ALDEV would give me an option of deviation percentage not a number because the number for 400 deg would be way different than 1200 deg and if that is not an option any ideas on how the calculation would look.

Title: Re: setting an alarm
Post by: franji1 on April 16, 2019, 08:50:05 AM

Use a MATH instruction to calculate a variable deviation (Dev).  The percentage value should be between 0.0 and 100.0
MATH Dev "(PV * Percentage) / 100.0)"

Then use Dev as the Deviation Limit in your ALDEV:
ALDEV Input:PV Setpoint:SP DeviationLimit:Dev PosAlarm:AlarmA NegAlarm:AlarmB