848T High Density Temperature Measurement Validation Diagnostic

848T High Density Temperature848T High Density Temperature

Measurement Validation Diagnostic

[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)



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



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



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



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



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.



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



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.



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



Measurement Validation:Dashboard DDMeasurement Validation:Dashboard DD



848T New Model Option Codes848T New Model Option CodesNew Option Codes 848T

D04 Measurement Validation Diagnostic



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.

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848T High Density Temperature Measurement Validation Diagnostic