Honeywell Experion PKS R430.3, Cascade Loop Initialization


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Just ended up converting a Kamyr digester from Foxboro I/A to Honeywell Experion PKS. The issue we are currently facing in our diffuser process is the upstream controller output initializes to a reset value (say 60% to 40%) every time our process cycles/strokes.

The OP of this block is tied to the SP of a Ratio control block, whose output then feeds to another PID block which then feeds into an AO channel.

We have secondary initialization enabled on the block, but haven't been able come up with any sort of hold to prevent the block from resetting each time the process cycles (approximately every 80 seconds). When the process does cycle, the AO channel (an auto valve) is moved from its current position, down to zero, and then back to its last position.

I know in Foxboro I/A there was a HOLD parameter that we could end up tying logic to, but I am not familiar enough with Honeywell's blocks to be able to identify how to accomplish what we want here. A fellow coworker mentioned the use of a PIDER block as a potential solution, but I wanted to pick a couple other brains to see if we are missing anything.

<b>Moderator's Note:</b> check out thread
How are you cycling the AO output to zero?

All the function blocks in the cascade loop's chain must be regulatory blocks to ensure that initialization and tracking work and are not broken.
Dear mcwv,

If i am not misunderstood about your issue, you can use shed feature in case of bad control or safety interlock option for shedding the OP to low, high, hold or your desired value (Safe) which could be defined in Output tab.

Also PIDER can handle it. Or as our friend dwpatterson stated you can limit your OP by OPHILM.
Bear in your mind that as dear depatterson said, you should use regulatory blocks in your chained loops.

With respect
Any DCS should have a "track and hold" function, you just have to find it.

Search the function block manual for the word 'track' or 'tracks'

Honeywell's Process Automation Controller, the HC-900, has a function block named TAHD, Track and Hold, that "provides an output that tracks the value of the input (X), when a digital input signal (TC) is On; or when TC is OFF, holds output at last value of X."