Presentation on theme: "Calibration of Industrial Hygiene Instruments David Silver, CIH."— Presentation transcript:
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 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 Calibration & metrology defined. Primary Standards. Uncertainty. How industrial hygiene instruments are calibrated.
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 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 Say what you do, do what you say. –Standard operating procedures (SOPs) –Calibration Procedures –Work instructions International Standards Organization (ISO) ANSI Z540
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 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 Electric constant Magnetic constant Speed of light in a vacuum Etc..
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 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) Seven base units: Lots of derived units: Area: m 2 Speed: m/s Force: 1 Newton = 1 kg·m/s 2 Voltage: 1 volt = 1 m 2 ·kg/s 3 ·A Frequency: 1 hertz = 1/s Power: 1 watt = 1 kg·m 2 /s 3 Electric Charge: 1 C = 1 A·s
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 One part per quadrillion accuracy!!! Accurate frequency gives accurate distance and time.
Artifact vs. quantum standards: 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 meter:
Mass - possible replacements Watt-balance Avogadro’s number 6.0221415 × 10 23 Goal: 10 parts per billion accuracy
Temperature: Kelvin, Celsius, and Fahrenheit 294 K 70 F21 C 273.15 K32 F0 C 77 K-321 F-196 C 4.2 K-452 F-269 C 0 K-459.67 F-273.15 C Water freezes Air liquefies Helium liquefies Room temperature Absolute zero
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 “The Congress shall have Power To… …fix the Standard of Weights and Measures;” From Article I, section 8 of the U.S Constitution: Most technologically advanced countries.
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.
Traceability Reference to SI units (National Primary Laboratory). Re-calibration at appropriate intervals to ensure accuracy of test instruments.
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 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 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 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 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. 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 Combined standard deviation = sq.rt. (0.6 2 + 10 2 + 2 2 ) = 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 Direct Differential Indirect Ratio Reciprocity Substitution Transfer
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 – 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 – 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 – 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 – 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 – 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 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 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.
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 ANSI Standards. Accuracy of dB measurements, response time and frequency. Anechoic Chamber
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 Arizona Road Dust Standard. Laminar flow chamber. Comparative Standard – 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 ASTM Standard Spherical Latex Particles Aerosol Generator Mini-Chamber Classifier. Bi-polar ion generator. Referent CNC / OPC.
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 “Canned Gas” – most common. Permeation gas – advantages: –Long shelf life. –Physical principals. –Repeatable.
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.