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Calibration of Industrial Hygiene Instruments. David Silver, CIH. Industrial Hygiene Issues. Accurate & repeatable measurements. Analytical results and confidence limits. Uncover the mystery of annual calibrations. Field calibrations vs. annual calibrations. Successful Outcomes.

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industrial hygiene issues
Industrial Hygiene Issues
  • Accurate & repeatable measurements.
  • Analytical results and confidence limits.
  • Uncover the mystery of annual calibrations.
  • Field calibrations vs. annual calibrations.
successful outcomes
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
presentation outline
Presentation Outline
  • Calibration & metrology defined.
  • Primary Standards.
  • Uncertainty.
  • How industrial hygiene instruments are calibrated.
metrology defined

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

significance of metrology
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.

quality systems
Quality Systems
  • Say what you do, do what you say.
    • Standard operating procedures (SOPs)
    • Calibration Procedures
    • Work instructions
  • International Standards Organization (ISO)
  • ANSI Z540
calibration procedures
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
time line
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
measurement philosophy
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.
absolute values
Absolute Values
  • Electric constant
  • Magnetic constant
  • Speed of light in a vacuum


clear communication of data
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.

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 kg·m/s2

Time: second (s)

Voltage: 1 volt = 1 m2·kg/s3·A

Electric current: ampere (A)

Frequency: 1 hertz = 1/s

Thermodynamic temperature: Kelvin (K)

Power: 1 watt = 1 kg·m2/s3

Electric Charge: 1 C = 1 A·s

Amount of substance: mole (mol)

Luminous intensity: candela (cd)

standards accuracy
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.
    • Avogadro’s number - # of atoms in a kilogram, count them (not possible).
clocks atomic time
Clocks: Atomic time

One part per quadrillion accuracy!!!

Accurate frequency gives accurate distance and time.

artifact vs quantum standards
Artifact vs. quantum standards:

The modern meter:

A metal bar:1889-1960

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

the modern kilogram
The modern kilogram

The SI kilogram drifts!

mass possible replacements
Mass - possible replacements

Goal: 10 parts per billion accuracy

Avogadro’s number6.0221415 × 1023


temperature kelvin celsius and fahrenheit
Temperature: Kelvin, Celsius, and Fahrenheit

294 K

Room temperature

21 C

70 F

0 C

32 F

273.15 K

Water freezes

-196 C

-321 F

77 K

Air liquefies

Helium liquefies

-269 C

-452 F

4.2 K

-273.15 C

-459.67 F

0 K

Absolute zero

the kelvin the si unit
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)


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;”

  • 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.
  • Reference to SI units (National Primary Laboratory).
  • Re-calibration at appropriate intervals to ensure accuracy of test instruments.
calibration standards
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).
calibration standards1
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.
equipment specifications
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.
  • 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.
step 1 determine the uncertainty contributors
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.
step 2 determine contribution
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%.
95 uncertainty
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.
measurement methods
Measurement Methods
  • Direct
  • Differential
  • Indirect
  • Ratio
  • Reciprocity
  • Substitution
  • Transfer
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
industrial hygiene measurements
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.
flow calibration
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.
flow calibration1
Flow Calibration
  • High-speed, hands-free measurements.
  • 3 Cells
  • ±1% per reading volumetric calibrations.
calibration of flow calibrators
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.
calibration of velocity meters
Calibration of Velocity Meters
  • Wind Tunnels
  • Laminar Flow
  • Comparative
  • Referent velocity pressure
calibration of heat stress monitors
Calibration of Heat Stress Monitors
  • Chamber – cold/hot
  • NIST traceable Instrulab platinum resistance thermometer
platinum resistance thermometer
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.
calibration of sound level meters noise dosimeters
Calibration of Sound Level Meters & Noise Dosimeters
  • ANSI Standards.
  • Accuracy of dB measurements, response time and frequency.
  • Anechoic Chamber
acoustic laboratory
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.
calibration of mass concentration meters
Calibration of Mass Concentration Meters
  • Arizona Road Dust Standard.
  • Laminar flow chamber.
  • Comparative Standard – R&P 1400A
r p 1400a
R&P 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.
calibration of optical particle counters
Calibration of Optical Particle Counters
  • ASTM Standard
  • Spherical Latex Particles
  • Aerosol Generator
  • Mini-Chamber
  • Classifier.
  • Bi-polar ion generator.
  • Referent CNC / OPC.
polymer particle standards
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.
calibration of gas meters
Calibration of Gas Meters
  • “Canned Gas” – most common.
  • Permeation gas – advantages:
    • Long shelf life.
    • Physical principals.
    • Repeatable.
permeation tubes
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.