Calibration of industrial hygiene instruments
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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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Calibration of industrial hygiene instruments

Calibration of Industrial Hygiene Instruments

David Silver, CIH


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

    Etc..


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.


Calibration of industrial hygiene instruments

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

Watt-balance


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)


Calibration of industrial hygiene instruments

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;”


Traceability

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.


Traceability1

Traceability

  • 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.


Uncertainty

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.


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

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.


Differential

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.


Indirect

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.


Reciprocity

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.


Substitution

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.


Transfer

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.


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.


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