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[File Name or Event]Emerson Confidential27-Jun-01, Slide 2
Emerson ConfidentialSlide 2
Why On-Line Validation?Why On-Line Validation?“Occasionally, a thermocouple may fail in a manner that gives randomly
high temperature readings.”
“..the temperature alarm and shutdown systems should reliably distinguish between these false readings and an actual runaway. Otherwise needless risk and expense are introduced by unnecessary reactor shutdowns.”
“Perhaps even more important is the loss of confidence in the shutdown systems by operations personnel – the shutdown interlock might be bypassed at a time it is most needed”
From an article by Arthur Smart, Jr., Celanese Chemical Co. (1981)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 3
Emerson ConfidentialSlide 3
Measurement Validation:What is it?Measurement Validation:What is it? Industry First Diagnostic Provides online validation of data during
measurement Approximates standard deviation of the input
error in relation to a measurement trend Allows the user to understand abnormal
deviations in the measurement Also calculates PV rate of change – to detect
abnormally fast process changes
Provided in 848T Fieldbus
[File Name or Event]Emerson Confidential27-Jun-01, Slide 4
Emerson ConfidentialSlide 4
Measurement Validation:Why use it?Measurement Validation:Why use it? Measurement qualification before control
– Only use valid measurements in the process control strategy Allows for validation of data to detect degraded conditions
– Provides alerts to the user of the abnormal temperature behavior– Online Sensor failure can be detected before the sensor actually
fails. Proactively change-out sensors before failure. Avoid Shutdowns
Know process rate of change– Detect abnormally fast process increases or decreases, and be
alerted before they become unsafe– Alerts allow unsafe condition detection BEFORE upper or lower
limits are reached
[File Name or Event]Emerson Confidential27-Jun-01, Slide 5
Emerson ConfidentialSlide 5
Measurement Validation Diagnostic-Industry First on the 848T Fieldbus-Measurement Validation Diagnostic-Industry First on the 848T Fieldbus-
Industry first diagnostic provides validation of measurement data which can help identify the following issues:– On-scale Errors- when the output of a transmitter is within process alarm limits yet
does not accurately indicate actual process information.– Invalid measurement readings that lay outside of alarm limits when actual process
variable is within acceptable range– Abnormally fast process rates of change.
Issues are usually due to failing sensors (most common), electronic interference, corroded termination points, loose electrical connections and runaway reactions
[File Name or Event]Emerson Confidential27-Jun-01, Slide 6
Emerson ConfidentialSlide 6
Prevent Unnecessary Shutdowns, Optimize Processes And Increase SafetyPrevent Unnecessary Shutdowns, Optimize Processes And Increase Safety
Avoid unnecessary process shutdowns– Detect measurement abnormalities and take preventative action before shutdown is
necessary• Avoid loss of revenue and safety concerns associated with shutdown process
– Determine validity of measurement points that are outside of alarm limits Avoid on-scale failure related issues
– Identify on-scale failures and take action before process efficiency and safety is compromised
• Improve Energy Efficiency• Increase Product Quality• Improve Product Yield and Throughput
– On-scale failure can lead to process shutdown Avoid unsafe process conditions
– Detect abnormally fast process rates of change
before alarm state is reached– The earlier unsafe conditions are identified the
more manageable they are
[File Name or Event]Emerson Confidential27-Jun-01, Slide 7
Emerson ConfidentialSlide 7
A Closer Look: How Measurement Validation WorksA Closer Look: How Measurement Validation Works
By evaluating sample to sample deviations over an averaged trend, Measurement Validation can detect abnormal deviations in measurements which in turn can be related to a specific issue
Sample to sample deviation is calculated as follows:– A rolling average of raw process measurements is taken to create a trend line– the difference of the most current measurement to the average is calculated, generating a pseudo rate of
change value– This value is then compared to a rolling average of pseudo rate of change values- the difference of the two
values resulting in the deviation output which is then compared to customer selected alert limit– The deviation output is then compared a customer selected limit which, depending on severity setting, will
generate a status that the user can use to take action.
• Process Rate of Change is calculated bymeasuring the time and difference between
samples and applying a moving filter to eliminate high frequency noise.
[File Name or Event]Emerson Confidential27-Jun-01, Slide 8
Emerson ConfidentialSlide 8
Case StudyCase Study Amoco made these calculations for a particular
Hydrocracker unit During study, 78 “incidents” occurred The measurement validation analysis helped the
operators differentiate between– 12 valid high temperature excursions and 66
malfunctions• One malfunction due to multiplexor failure• 2 were due to radio interference• 63 were due to the failure of 63 Thermocouples.
– Operators were able to perform preventative maintenance instead of process shutdowns
[File Name or Event]Emerson Confidential27-Jun-01, Slide 9
Emerson ConfidentialSlide 9
Measurement Validation:ConfigurationMeasurement Validation:Configuration Alert Limits
– Deviation and Rate of change Increasing and Decreasing limits
Alert Severity– Failure, warning, advisory, or not used
Deadband– Decide how sensitive your alerts are, i.e. how much
they have to go down before the alarm is surpressed.
[File Name or Event]Emerson Confidential27-Jun-01, Slide 10
Emerson ConfidentialSlide 10
Measurement Validation:Status HandlingMeasurement Validation:Status Handling Advisory Plant Web Alerts available
– Excessive Deviation and Excessive Rate of Change Four levels of validation severity for both Rate of
Change and Deviation– Failure – Sets PV to fail status, triggers Failed plant
web alert (sensor failure)– Warning – Sets PV to uncertain status, triggers
Maintenance plant web alert (sensor degraded)– Advise – No change to PV status, triggers Advisory
plant web alert – Not Used – Provides Rate of Change or Deviation
output with no status handling
[File Name or Event]Emerson Confidential27-Jun-01, Slide 11
Emerson ConfidentialSlide 11
Measurement Validation:Dashboard DDMeasurement Validation:Dashboard DD
[File Name or Event]Emerson Confidential27-Jun-01, Slide 14
Emerson ConfidentialSlide 14
848T New Model Option Codes848T New Model Option CodesNew Option Codes 848T
D04 Measurement Validation Diagnostic
[File Name or Event]Emerson Confidential27-Jun-01, Slide 15
Emerson ConfidentialSlide 15
Key TakeawaysKey Takeaways High Density transmitters provide a cost effective
method of measuring moderate to large numbers of measurement points
New input options allow the 848T to be used in more applications
Appropriate installation practices allow the 848T to be used in critical applications
Measurement validation provides a new level of integrity for a highly reliable measurement.