Improving plant maintenance and machinery health monitoring by simplifying the measurement task

1. Improving plant maintenance and machinery health monitoring by simplifying the measurement task Why measurements don’t need numbers, and what do we really need to measure?

2. Structure • The need, and application, of simplicity to measurements • Some case studies

3. As we progress: • Modern industry demands a wider variety of measurement methods and technologies • Contemporary thinking tends to increase technical complexity as a marketing need • Data availability tends to increase • Skill levels and staff availability tends to decrease

4. Historical problems #1Concepts of accuracy • Slide rule calculations π2 ≈ 9.88 • In 1972 Busicom introduced the first electronic calculator π2 = 9.869604403 • Actually we all know the answer is π2 ≈ 9.9 (or a bit less than 10)

5. Historical problems #2‘Real world values’ • The expansion of digital electronics has led to a situation where most readings are: i) quantified and reported ii) then acted upon • Prior to ‘modern’ instrumentation there existed many elegant solutions which combine these two functions without any intermediate analysis

6. Valuable analogue measurements • Nileometer • 2500 B.C. • Measurement: accurate analogue flood level • Result: amount of tax to be levied due to the anticipated agricultural yield

7. Measurement – the majority case • In general, 80% say, the result of a measurement task is: GO/NO GO PASS/FAIL STOP/START • Most operators (and control systems) want that binary result to cause them to undertake a binary action: DO SOMETHING or DO NOTHING

8. Some real control systems • Some typical analogue measurements and binary reactions are: IF its too dark THEN switch the light on IF its raining THEN open the umbrella IF the glass is full THEN stop pouring the beer • In an automobile, speedometers are analogue instruments which hardly anyone uses. The usual application is confined to: IF the speed limit is exceeded THEN slow down

9. The Finnish weather station • Hang a dead mouse outside of the window IF its dry THEN its good weather IF its wet THEN its raining IF its moving THEN its windy IF its stiff THEN its cold

10. The general case • Regardless whether the process is analogue or digital the actual requirement of the general control task tends towards a simple threshold decision:

11. What is really wanted? In our ‘general case’ monitoring process the requirement from an instrument system is: • Accurately monitor a process or condition using some form of sensor • Set a threshold level at which an alarm would be raised • IF the threshold is exceeded, raise an alarm

12. So What happens? • The traditional solution to this problem is over-complex and over-expensive, as well as giving far too much information to the user. • Usually the method is to take a sensor; apply some signal conditioning; quantify it (either analogue or digital) so that it becomes ‘data’ or a ‘number’; then using this data feed it into a comparator of some sort in order to make the GO/NO GO decision

13. Combining all the unknowns into a single solution • Where do you start from? • When do you trigger? (and if you quantify things) • How do you know which numbers to use?

14. DrX – simple instrument #1 • Where do you start from? • Every application has its own levels of environmental noise • By adjusting the instrument until its threshold is reached finds this level • No quantities are defined

15. DrX – the simple instrument #2 • When do you trigger? At an approximate safety margin above the threshold • How do you know which numbers to use? You don’t there aren’t any

16. Case study #1 Click detection for zero failure cable harness assembly • Push, Click, Wiggle • Environment is noisy • A click produces a wide band impulse • Numeric information would give no useful information to the operator • Detection at ultrasonic levels gives a clear indication of success or failure by means of a light

17. Case study #2 Cavitation detection in pumps • Most easily detected at constant speed by experienced personnel • High volume water pumps undergo varying speed changes • Critical cavitation occurs during change of loading • Formal vibration analysis would have to be related to the load cycle • Application of a simple ‘knock detector’ can indicate to the control room if the pump is being loaded too fast.

18. Case study #3 Partial discharge monitoring in HV/MV switchboards • PD is the main cause of long term degradation in HV/MV contacts • There are no international standards for in-field testing • Production testing legislation has led to sophisticated measuring instruments • Electricity generators and suppliers have no indication of contact health and therefore over-maintain, or fail in service

19. Case study #3 (continued)Advantages of adopting the simplification strategy • Safe, remote, online monitoring • Minimum skill level required from operators • Result is PASS or FAIL • Fine tuning available with experience • Low cost

20. Conclusions • Strength in simplification • Danger in over simplification • If we simplify instruments there is a wider user acceptance, lower cost, giving more direct results and more deployment • Assess the need to provide information • The quality of the measurement task should match the quality need of the process, and the quality of the action of the result Lyndon Owen, E2L Limited