Calibration of Industrial Hygiene Instruments

1
Calibration of Industrial Hygiene Instruments
David Silver, CIH
2
Industrial Hygiene Issues

• Accurate repeatable measurements.
• Analytical results and confidence limits.
• Uncover the mystery of annual calibrations.
• Field calibrations vs. annual calibrations.

3
Successful Outcomes

• Confident that instruments are performing as they
  should.
• Results are accurate and repeatable.
• The analysis holds up to litigation.
• Accurate data provides a mean to establish
  effectiveness of controls
• Ventilation
• Work practices

4
Presentation Outline

• Calibration metrology defined.
• Primary Standards.
• Uncertainty.
• How industrial hygiene instruments are
  calibrated.

5
Metrology Defined
Metrology establishes the international standards
for measurement used by all countries in the
world in both science and industry
Examples distance, time, mass, temperature,
voltage, values of physical and chemical constants
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Significance of Metrology

• Measurement calibration procedures are
  essential for quality control.
• Quality minimize uncertainty in measurements.
• Quality control system
• Direct reading instrument, sampling.
• Measurement or analysis.
• Results variability.

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Quality Systems

• Say what you do, do what you say.
• Standard operating procedures (SOPs)
• Calibration Procedures
• Work instructions
• International Standards Organization (ISO)
• ANSI Z540

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Calibration Procedures

• Performance requirements specs
• Measurement standards accuracy std
• Preliminary operations intrinsic safety
• Calibration process tolerances
• Calibration results- documentation
• Closing operation labeling
• Storage handling to ensure accuracy

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Time Line

• Ancient Measurement need to standardize
  weights, weapons
• 732 A.D. King of Kent standard acre
• 1585 Decimal system in Europe
• 1824 George IV Weights Measures Act
• 1958 All countries agree on length and mass

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Measurement Philosophy

• Standardization is paramount.
• True value of a dimension.
• Speed of light, electron mass.
• Absolute units are a foundation for
  standardization.
• Primary laboratories provide the standards that
  are closest to the true value. Has the least
  uncertainty.

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Absolute Values

• Electric constant
• Magnetic constant
• Speed of light in a vacuum
• Etc..

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Clear Communication of Data

• Scientific Data in units understandable to all in
  the scientific community.
• Allows for greater understanding, compliance with
  occupational, safety and health laws.

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SI The International System of Units
Lots of derived units
Seven base units
Area m2
Length meter (m)
Speed m/s
Mass kilogram (kg)
Force 1 Newton 1 kgm/s2
Time second (s)
Voltage 1 volt 1 m2kg/s3A
Electric current ampere (A)
Frequency 1 hertz 1/s
Thermodynamic temperature Kelvin (K)
Power 1 watt 1 kgm2/s3
Electric Charge 1 C 1 As
Amount of substance mole (mol)
Luminous intensity candela (cd)
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Standards Accuracy

• More accurate methods to measure a unit than
  intuitive common methods.
• Example 1 kilogram
• Subjective hold in hand guess weight.
• Pan or spring balance more accurate.
• Watt-balance even more accurate.
• Avogadros number - of atoms in a kilogram,
  count them (not possible).

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Clocks Atomic time
One part per quadrillion accuracy!!!
Accurate frequency gives accurate distance and
time.
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Artifact vs. quantum standards
The modern meter
A metal bar1889-1960
The meter is the length of the path traveled by
light in vacuum during a time interval of
1/299,792,458 of a second
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The modern kilogram
The SI kilogram drifts!
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Mass - possible replacements
Goal 10 parts per billion accuracy
Avogadros number6.0221415 1023
Watt-balance
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Temperature Kelvin, Celsius, and Fahrenheit
294 K
Room temperature
70 F
21 C
273.15 K
32 F
0 C
Water freezes
77 K
-321 F
-196 C
Air liquefies
Helium liquefies
4.2 K
-452 F
-269 C
0 K
-459.67 F
-273.15 C
Absolute zero
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The Kelvin the SI unit
The Kelvin, unit of thermodynamic temperature, is
the fraction 1/273.16 of the thermodynamic
temperature of the triple point of water.
(0.006 atm)
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Primary Laboratories
Most technologically advanced countries.
From Article I, section 8 of the U.S Constitution
The Congress shall have Power To fix the
Standard of Weights and Measures
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Traceability

• Unbroken chain of comparison to national
  standard.
• Measure uncertainty for each step in the
  calibration chain.
• Documentation of procedures and results for each
  step in the chain.
• Competence of each lab performing calibrations.

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Traceability

• Reference to SI units (National Primary
  Laboratory).
• Re-calibration at appropriate intervals to ensure
  accuracy of test instruments.

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Calibration Standards

• National standard provides the basis for fixing a
  value.
• Primary standard highest metrological standard
  (NIST).
• Secondary based on comparisons to primary.
• Reference standard at a location (metrology
  labs with NIST calibrated stds).

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Calibration Standards

• Working standard a standard not reserved as a
  reference standard but intended to verify test
  equipment.
• Transfer standard the same as a reference
  standard and transfers a measurement parameter
  from one organization to another for traceability
  purposes.

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Equipment Specifications

• Tolerance a design feature that defines the
  limits of a quality characteristic.
• Specification defines the expected performance
  limits of a large group of identical test units.

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Uncertainty

• Goal minimize measurement uncertainty.
• Measurement validity depends on random
  distributions, fixed models, fixed variation and
  fixed distribution curves.
• Central tendency.
• Linear and non-linear interpolation.

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Step 1 Determine the uncertainty contributors

• Each element in the chain of calibration.
• Example soap film calibrator.
• Dimensional volume.
• Timer.
• Operator start stop timer at bubble mark.
• Variable flow in air mover.
• Drag on soap bubble.

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Step 2 Determine Contribution.

• Dimensional error Type B buret is 6 ml/1000ml
  0.6.
• Timer /1 one minute per year negligible.
• Stop Start operator /- 0.5 seconds x 2 1
  second. 10 for 10 second run.
• Variable flow in air mover 0.1 lpm for 5 lpm
  pump 2.

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95 Uncertainty

• Combined standard deviation sq.rt. (0.62 102
  22) 10.21
• Uncertainty 95 k s
• 2 10.21 20.42
• By using an electro-optical sensor we reduce the
  10 operator error.

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Measurement Methods

• Direct
• Differential
• Indirect
• Ratio
• Reciprocity
• Substitution
• Transfer

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Direct

• Direct Measurement that is in direct contact
  with the measurand and provides a value
  representative of the measurand as read from an
  indicating device.
• Example measuring electrode resistance of a
  moisture meter.

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Differential

• Differential A measurement made by comparing an
  unknown measurand with a standard.
• Example comparing reading from a heat stress
  monitor and compare to a NIST traceable
  thermometer.

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Indirect

• Indirect a measurement made of a non-targeted
  measurand that is used to determine the value of
  the targeted measurand.
• Example measuring the time a piston traverses a
  cylindrical volume in a piston prover and
  calculating flow.

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Reciprocity

• Reciprocity makes use of a transfer function
  relationship in comparing two or more measurement
  devices subject to the same measurand.
• Example determination of microphone sensitivity
  via the response of another microphone.

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Substitution

• Substitution using a known standard to
  establish a measurand value after the known
  standard is removed and the test unit is
  inserted to determine the test unit response.
• Example measuring weight using a single pan
  scale.

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Transfer

• Transfer an intermediate device used for
  conveying a known measurand value to an unknown
  test device.
• Example generating a known volume of gas to a
  test gas meter.

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Industrial Hygiene Measurements

• Flow bell prover, flow test stand, flow
  calibrator.
• Frequency time bases, frequency standards.
• Humidity environmental chamber, salts.
• Luminance calibrated light source.
• Temperature chamber, triple point of water.

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Flow Calibration

• Soap bubble meter.
• Pump is attached to the top of a volumetric glass
  tube containing a small amount of liquid soap.
  While the air flow causes the soap film to move
  from one volume mark to another, the travel time
  is measured with a stopwatch. The flow rate can
  then be directly calculated using the travel time
  and the known tube volume.
• 2 per reading volumetric calibrations.

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Flow Calibration

• High-speed, hands-free measurements.
• 3 Cells
• 1 per reading volumetric calibrations.

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Calibration of Flow Calibrators

• Brooks Vol-U-Meter
• Precision bore borosilicate glass cylinder
  combined with photo-electric switches.
• Mercury O-ring piston seal is virtually
  frictionless. Accuracy 0.2 of indicated volume.

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Calibration of Velocity Meters

• Wind Tunnels
• Laminar Flow
• Comparative
• Referent velocity pressure

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Calibration of Heat Stress Monitors

• Chamber cold/hot
• NIST traceable Instrulab platinum resistance
  thermometer

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Platinum Resistance Thermometer

• Platinum RTD sensor, 100 ohms.
• Instrument sensor accuracy up to 0.08ºC.
• Resolution up to 0.01ºC.
• Wide range -60º to 300ºC, -76ºF to 572ºF.
• Self-check calibration.
• Traceable to NIST.

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Calibration of Sound Level Meters Noise
Dosimeters

• ANSI Standards.
• Accuracy of dB measurements, response time and
  frequency.
• Anechoic Chamber

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Acoustic Laboratory

• Sound level meters, noise dosimeters,
  microphones, octave filters and microphones.
• Frequency response calibration of microphones
  using electrostatic and acoustical method
• Sensitivity calibration of microphones using the
  insert voltage method.
• Sound level meter calibration in ANSI 1.4
• Test of fractional octave filters.

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Calibration of Mass Concentration Meters

• Arizona Road Dust Standard.
• Laminar flow chamber.
• Comparative Standard RP 1400A

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RP 1400a

• TSI 3400 Fluidized Aerosol Generator maintains
  Arizona road dust concentrations in laminar flow
  chamber.
• Particle Mass is proportional to frequency of
  tapered element.
• Highly precise and accurate.
• Mass calibration is NIST traceable.

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Calibration of Optical Particle Counters

• ASTM Standard
• Spherical Latex Particles
• Aerosol Generator
• Mini-Chamber
• Classifier.
• Bi-polar ion generator.
• Referent CNC / OPC.

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Polymer Particle Standards

• Duke Scientific's standards contains a
  Certificate of Calibration and Traceability to
  NIST which includes a description of the
  calibration method and its uncertainty, and a
  table of chemical and physical properties.

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Calibration of Gas Meters

• Canned Gas most common.
• Permeation gas advantages
• Long shelf life.
• Physical principals.
• Repeatable.

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Permeation Tubes

• Permeation devices provide a stable concentration
  of a specific trace chemical, including those
  with low vapor pressures. Calibration gas
  generators, used with their respective permeation
  devices, generate known concentrations of various
  gases and liquid vapors.