Alarm rates will be much lower than you have experienced before and are likely to decrease further as operators come to believe in and trust the new alarm limits and start to use less of the Operating Envelope than before. Process Capability will increase and you could redefine the Operating Envelope and Alarm Limits to capture the improvement for the future.
But, unfortunately, many other factors are working to reduce Process Capability. This includes heat exchangers fouling, furnace efficiencies dropping, catalyst activity decrease with age, and with the number of regeneration cycles. You will need a slightly different Operating Envelope to be able to achieve your Operating Objectives without having an increase in alarm rates.
You could simply recalculate all the alarm limits just as you did when you rationalized to get a perfect Operating Envelope and set of alarm limits again. However, you probably don’t want to take the whole set of alarm limits through the Management of Change process just because of the time it takes.
Many of the value changes to the limits would be small and only some would be big enough to justify being changed. To get around this CVE provides the “Consistentizer” function. It lets you specify the alarm limits that are not to be changed and gives you a new slightly compromised operating envelope that will change only a few alarm limits to maintain your achievement of operating objectives with very little change to alarm rates. You can use CVE’s Alarm Performance Prediction on the new alarm limit set to predict the new alarm rate and adjust by changing which limits are held constant until you are confident. Now you only have a few limits to take through Management of Change.
This three-way relationship between Operating Objectives, Operating Envelope, and Process Capability is why you must use CVE for alarm performance monitoring and subsequently making changes to the operating envelope because it is a multi-variable method that understands “Consistency”. If you use the old ‘Bad Actor’ method of changing the values of individual limits in the hope of improving alarm performance you will steadily destroy the three-way relationship, your Operating Envelope will grow larger and lose consistency and you will destroy all the good work you did by rationalization.
You can continue using the nice alarm reports and dashboards produced from the alarm logs but must not use them to make changes to alarm limits.