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

6. 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.

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

8. 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

9. 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

10. 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.

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

12. 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.

13. 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)

14. 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).

15. Clocks: Atomic time One part per quadrillion accuracy!!! Accurate frequency gives accurate distance and time.

16. 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

17. The modern kilogram The SI kilogram drifts!

18. Mass - possible replacements Goal: 10 parts per billion accuracy Avogadro’s number6.0221415 × 1023 Watt-balance

19. 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

20. 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)

21. 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;”

22. 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.

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

24. 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).

25. 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.

26. 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.

27. 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.

28. 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.

29. 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%.

30. 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.

31. Measurement Methods • Direct • Differential • Indirect • Ratio • Reciprocity • Substitution • Transfer

32. 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.

33. 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.

34. 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.

35. 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.

36. 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.

37. 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.

38. 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.

39. 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.

40. Flow Calibration • High-speed, hands-free measurements. • 3 Cells • ±1% per reading volumetric calibrations.

41. 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.

42. Calibration of Velocity Meters • Wind Tunnels • Laminar Flow • Comparative • Referent velocity pressure

43. Calibration of Heat Stress Monitors • Chamber – cold/hot • NIST traceable Instrulab platinum resistance thermometer

44. 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.

45. Calibration of Sound Level Meters & Noise Dosimeters • ANSI Standards. • Accuracy of dB measurements, response time and frequency. • Anechoic Chamber

46. 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.

47. Calibration of Mass Concentration Meters • Arizona Road Dust Standard. • Laminar flow chamber. • Comparative Standard – R&P 1400A

48. 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.

49. Calibration of Optical Particle Counters • ASTM Standard • Spherical Latex Particles • Aerosol Generator • Mini-Chamber • Classifier. • Bi-polar ion generator. • Referent CNC / OPC.

50. 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.