1 Advanced Process & Measurement ControlACADs (08-006) Covered Keywords Process measurement, control, zero error, angular error, units of weight, units of measurement, SI Measurements, range, span, upper range, lower range, accuracy, precision. Description Supporting Material
2 NIA97 ADVANCED PROCESS AND MEASUREMENT CONTROLAny sufficiently advanced technology is virtually indistinguishable from magic. Arthur Clark
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4 Path to becoming an I&C Tech at Palo VerdePlant Systems Advanced Process NIA97 GPI I&C Tech Loops NIA02 In Field (OJT) Loop Calibration The ‘100’ card Foxboro NIA98 Other required training: Site Access Training RWP & Dress out Respirator training & fit test Conduct of Maintenance Prints & Plant Drawings Tagging Electrical Safe Work Practices Industry Events I&C Select Training: PPS, Excore BOP/NSSS ESFAS SESS/RK RRS/SBCS QSPDS CEDMCS DAFAS VLPMS Technical Skills NIB43 Seismic DFWCS Fire Protection PPC/PLC GR EHC/TSI Gas Turbine
5 NIA97 Lessons Measurement Fundamentals Pressure instrumentationLevel instrumentation Flow instrumentation Temperature instrumentation Pneumatic instrumentation Calibrating & maintaining flow control valves
6 Terminal Objective From memory the I&C Technician will define concepts and terminology related to the process measurement and control industry. Mastery will be demonstrated by successful completion of Lab Performance Exercises and written Exam.
7 Enabling Objectives Define the term "measurement“List two common engineering measurement systems Define the following terms as they relate to process measurement and control: a. Range b. Span c. Linearity d. Dead band e. Hysteresis f. Sensitivity g. Conformity h. Accuracy i. Resolution Differentiate between "Zero Error" and "Angular Error"
8 Measurement is Who decides which units we will use?the determination of the size or magnitude of something. An observation that reduces the amount of uncertainty about the value of a quantity. A comparison of a quantity to some standard, called a unit Who decides which units we will use?
9 Imperial or English Customary Weights & Measurements1 inch = the length of 3 barleycorns (the word ‘inch’ comes from the word ‘thumb’ in some languages) 1 yard = the distance from the nose to the fingertip of Henry I 1 mile = the length of 1000 paces of a Roman legion 1 acre = a field of a size that a farmer can plow in a single day 1 grain = the weight of 1 barleycorn 1 pound = 7000 grains (The Latin word for pound is Libra, hence the abbreviation LB) 1 gallon = the volume of 8 pounds of wheat 1 cubit - the distance from the elbow to the tip of the middle finger - from the Latin word for elbow or lower arm (cubare - to lean - for the part of your arm you lean on) So a royal cubit would be that measurement for a king An egyptian cubit is longer than an english cubit. A roman inch is shorter than an english inch Barley:Beer 1 stadium = 1/4 of a roman mile Inch - actually came from ‘thumb’ standards varied through the years until international conferences and proclamations by kings standardized the units.
10 U.S. Customary Units Similar to the old Imperial systemBased on many old local units derived over centuries, often based on old Anglo-Saxon and Roman units Length: The inch, foot, yard, and mile are declared units based on historical customs Volume: The ounce, quart, cup, pint, gallon, and barrel are declared units based on custom Weight: The ounce, pound, and ton are Avoirdupois weights based on custom Temperature: Degrees Fahrenheit based on historical custom. Tell the story of how Fahrenheit came up with his scale: Took Romer’s scale (his friend and danish astronomer who set zero to as cold as it gets in Denmark) and multiplied it times 4, then adjusted it so that body temperature was 96. Originally he had set body temperature at 100 but inaccuracies showed that body temperature is actually 98.6. So in the Fahrenheit scale water freezes at 32 and boils at 212, 100 and 96 used to be body temperature, and zero is as cold as it gets in Denmark. Recall that early thermometer builders may have had significant exposure to mercury.
11 The SI System 1 meter = the length of the path travelled by light in vacuum during a time interval of 1/ of a second 1 second = the duration of periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom 1 Kelvin = The Kelvin is the fraction 1/ of the thermodynamic temperature of the triple point of water." 1 kilogram = the mass of the international prototype of the kilogram Story about Thomas Jefferson proposing a metric-like system in 1790, ordering a set of metric standards from France but the ship sank in a storm, and that may be why we don’t use kilometers and liters today. The triple point of any substance is that temperature and pressure at which the material can coexist in all three phases (solid, liquid and gas) in equilibrium. Specifically the triple point of water is K at Pa. (example: Ice skates on an ice skating rink - water exists as a solid, but the pressure from the ice skates turns it to a liquid. It also exists as vapor)
12 The Second Same unit in nearly every systemOriginally 1/86,400 of a mean solar day Earth’s rotation is not sufficiently uniform With the development of atomic clocks, the second was redefined in terms of atomic time. the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom
13 Unit systems we do not useMKS-Meter/Kilogram/Second CGS-Centimeter/Gram/Second Both were replaced by the SI system in 1960
14 Bureau International des Poids et MesuresInternational territory Sevres is a suburb of Paris Basic units: meter kilogram second ampere kelvin mole candela All other units derived from these 7 basic units Our equivalent is the NIST (national institute of standards and technology) which operates in Maryland and in Boulder, Co. The BIPM at Le Pavillon de Breteuil in Sevres, France
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16 Base quantity Name Symbol length meter m mass kilogram kg SI base units Base quantity Name Symbol length meter m mass kilogram kg time second s electric current ampere A thermodynamic temperature kelvin K amount of substance mole mol luminous intensity candela cd All other units are based on these standards
17 KPa 1 Pascal = 1 Newton x 1 meter2 1 Newton = 1 kilogram x 1meter/sec21000 Pascal x 1 meter2 = 1 KPa 1 Kilopascal = psi 1000 Kilopascal = 145 psi
18 Range Vs. Span Range of -20 to +80 psi Span of 100 psi What is the range of the output of a Rosemont transmitter? What is the span?
19 Range: The region between the limits within which a quantity is measuredSpan: The algebraic difference between the upper and lower limits of a range expressed in the same units as the range. From the high end to the low end (not the difference)
20 URV – Upper Range Value – the highest quantity a device is adjusted to measureLRV – Lower Range Value – the lowest quantity a device is adjusted to measure
21 What is the range of this gauge? 0-30 PSI or 0-830 in. h2oWhat is the span? 30 psi or 830 in h20
22 Range? 0-30 inches of vacuumspan? 30 inches vacuum
23 Range? psi or Kpa Span? 15 psi or 100 Kpa
24 Terms Sensitivity Conformity Accuracy Precision Resolution InaccuracyLinearity Scale Total loop uncertainty Repeatability Tracability Accuracy and Precision next slide Resolution - the smallest change that can be seen Inaccuracy - the deviation of a measurement from a standard value or true quantity. Scale - how much is hiding in the thing you’re talking about. If your scale is very small, not much is hiding. If your scale is very large, a great deal of detail may be hiding in or under the data you’re looking at. Total Loop uncertainty - later slide Inaccuracy vs. uncertainty. (Inaccuracy (imprecision, bias) is characteristic of the Measurement Process, whereas error and uncertainty are characteristics of a Result.) a very subtle difference. Repeatability - The closeness of agreement between independent results obtained in the normal and correct operation of the same method on identical test material, in a short space of time, and under the same test conditions Tracability - the property of a measurement result whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons, each step in the chain having stated uncertainties Conformity – the closeness to which the output curve approximates a specified curve such as a parabolic or logarithmic. Sensitivity – The ratio of the change in output magnitude to the change in input that caused it. Sensitivity Conformity
25 measure with a micrometer, mark with chalk cut with an axAccuracy vs. Precision measure with a micrometer, mark with chalk cut with an ax Precision: How much you care to say about a particular item Accuracy: How correct you are when you say something about that item Any instrument can be precisely inaccurate" if it is set wrong. It is never more accurate than the original calibration. But it can tell you to 10 decimals precisely an inaccurate reading. I&C techs are all gifted with calibrated eyeballs. But you can get in trouble by being too precise just as easily as by being to vague. The rule of significant digits: Use no more than one significant digit greater than the least significant of all the numbers used in the work How precisely can we read a gauge? Our standard is: Half the smallest division on the gauge! Reading a gauge more precisely is not more correct. The number of significant digits recorded for a measurement includes all of those digits known with certainty plus the first digit about which there is some uncertainty. The first digit in which there is some uncertainty is the first digit which is estimated One cannot read seconds on a sundial, nor inches with an odometer.
26 Precision: How much you care to say about a particular item Accuracy: How correct you are when you say something about that item Resolution: The resolving power of a system, the smallest increment in a measurement
27 Zero, Span, Angularity & GainStatic Calibration Errors Zero, Span, Angularity & Gain
28 Input Ideal Output (psig) (ma) (ma) 0 4 4 25 8 8 50 12 12 75 16 160 4 4 Ideal cal - 0 to 100 psi in equals 4 to 20 ma out This slide is for comparison to later slides
29 Span Adjustment Zero Adjustment
30 Angular or Span Error Input Output (psig) (ma) 0 4 25 8.25 50 12.50 4 Span error. Span is low and needs to be raised. Zero is fine Angular or Span Error
31 Would you adjust zero or span?Input Ideal Output (psig) (ma) (ma) 0 4 4 Same as previous - span is low and must be tweeked up Discuss span and zero adjustment interactions both in electronic and pneumatic instruments Would you adjust zero or span?
32 Would you adjust zero or span?Input Ideal Output (psig) (ma) (ma) 0 4 3 Zero is low Would you adjust zero or span?
33 Would you adjust zero or span?Input Ideal Output (psig) (ma) (ma) 0 4 5 Zero is high Would you adjust zero or span?
34 Zero Based Linearity
35 Linearity-a behavior of a system in which the output varies in direct proportion with the input. In a linear circuit the output/input ratio is always the same Sensitivity-The ratio of the change in output magnitude to the change in input that caused it
36 Conformity-(used when output is not linear from input) the closeness to which the output curve approximates a specified curve, such as a parabolic or logarithmic. Conformity is specified as independent, terminal-based, or zero based Repeatability Repeatability is the closeness of agreement among a number of consecutive measurements of the output for the same value of the input under the same operating conditions, approaching from the same direction. It does not include hysteresis.
37 Hysteresis Hysteresis - The lagging of an effect behind it’s causeEspecially exhibited in pneumatic instruments or instruments with mechanical linkages such as indicators. Slop or play in mechanical linkages causes hysteresis. Also present to some degree in electronic components due to the voltages required to overcome material boundaries. If you push on something, it will yield: when you release, does it spring back completely? If it doesn't, it is exhibiting hysteresis, in some broad sense. Commonly applied to magnetic materials that exhibit a residual magnetic field even after turned off. Hysteresis
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39 Uncertainty Total Loop Uncertainty = 0.935% Transmitter +/- 0.5%I2V Transmitter +/- 0.5% Converter +/- 0.25% Indicator +/- 0.75% Total loop uncertainty - the square root of the sum of the squares method Take a basic loop. Transmitter, I2V converter and indicator. There are 3 sources of uncertainty in the loop. Transmitter has +/- 0.5% I2V has +/- 0.25% Indicator has +/- 0.75% What is the total loop uncertainty? Not the sum of all the uncertainty, but the square root of the sum of the squares. Draw squares on whiteboard and add their area to illustrate Total Loop Uncertainty = 0.935%
40 On to Measuring Pressure