ACADs (08-006) Covered

KeywordsProcess 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

1.1.2.1 5.1.2.1.9 5.4.1.7

NIA97ADVANCED PROCESS AND MEASUREMENT CONTROL

Any sufficiently advanced technology is virtually indistinguishable from magic.

Arthur Clark

Path to becoming an I&C Techat Palo VerdePlant Systems

Advanced Process

NIA97

Foxboro

NIA98

Technical Skills

NIB43

Loops

NIA02

In Field (OJT)

Loop Calibration

The ‘100’ card

GPI

I&C

Tech

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

Seismic

DFWCS

Fire Protection

PPC/PLC

GR

EHC/TSI

Gas Turbine

NIA97 Lessons• Measurement Fundamentals• Pressure instrumentation• Level instrumentation• Flow instrumentation• Temperature instrumentation• Pneumatic instrumentation• Calibrating & maintaining flow control

valves

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.

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"

Measurement is

• 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?

Imperial or English Customary Weights & Measurements

1 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

U.S. Customary Units• Similar to the old Imperial system• Based 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.

The SI System1 meter = the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second

1 second = 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

1 Kelvin = The Kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water."

1 kilogram = the mass of the international prototype of the kilogram

The Second• Same unit in nearly every system• Originally 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

Unit systems we do not use

• MKS-Meter/Kilogram/Second• CGS-Centimeter/Gram/Second• Both were replaced by the SI system in 1960

Bureau International des Poids et Mesures

The BIPM at Le Pavillon de Breteuil in Sevres, France

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

KPa

• 1 Pascal = 1 Newton x 1 meter2

• 1 Newton = 1 kilogram x 1meter/sec2

• 1000 Pascal x 1 meter2 = 1 KPa

• 1 Kilopascal = 0.145 psi

• 1000 Kilopascal = 145 psi

Range Vs. Span

What is the range of the output of a Rosemont transmitter? What is the span?

Range: The region between the limits within which a quantity is measured

Span: The algebraic difference between the upper and lower limits of a range expressed in the same units as the range.

• URV – Upper Range Value – the highest quantity a device is adjusted to measure

• LRV – Lower Range Value – the lowest quantity a device is adjusted to measure

Terms• Accuracy• Precision• Resolution• Inaccuracy• Linearity• Scale• Total loop uncertainty• Repeatability• Tracability •Sensitivity

•Conformity

Accuracy 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

Resolution: The resolving power of a system, the smallest increment in a measurement

Zero, Span, Angularity & Gain

Static Calibration Errors

Input Ideal Output

(psig) (ma) (ma)

0 4 4

25 8 8

50 12 12

75 16 16

100 20 20

Ideal Calibration

05

10152025

0 25 50 75 100

Pressure

Cur

rent

Zero Adjustment Span Adjustment

Angular Error

05

10152025

0 25 50 75 100

Pressure

Cur

rent

Input Output

(psig) (ma)

0 4

25 8.25

50 12.5

75 16.75

100 21.0

Angular or Span Error

Angular Error

05

10152025

0 25 50 75 100

Pressure

Cur

rent

Input Ideal Output

(psig) (ma) (ma)

0 4 4

25 8 7.75

50 12 11.5

75 16 15.25

100 20 19

Would you adjust zero or span?

Zero Shift

05

10152025

0 25 50 75 100

Pressure

Cur

rent

Input Ideal Output

(psig) (ma) (ma)

0 4 3

25 8 7

50 12 11

75 16 15

100 20 19

Would you adjust zero or span?

Zero Shift

05

10152025

0 25 50 75 100

Pressure

Cur

rent

Input Ideal Output

(psig) (ma) (ma)

0 4 5

25 8 9

50 12 13

75 16 17

100 20 21

Would you adjust zero or span?

Zero

Based

Linearity

• 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

• 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.

Hysteresis

Uncertainty

222 %75.0.25%00.5%ncertaintyTotalLoopU

Transmitter +/- 0.5%

I2V

Converter +/- 0.25%

Indicator +/- 0.75%

Total Loop Uncertainty = 0.935%

On to Measuring Pressure