National Institute of Standards and Technology
100 Bureau Drive, Stop 8393
Gaithersburg, MD 20899-8393
Please contact the technical staff before shipping instruments or standards to the address listed below.
Fees are subject to change without notice.
NIST provides calibration of many types of ozone measuring instruments. The calibrations are done by comparison against the NIST Standard Reference Photometer (SRP) which serves as the reference standard for the United States and is traceable to the International Bureau of Weights and Measures (BIPM).
Maximum Calibration Range: 0 nmol/mol (ppbv) to 1000 nmol/mol
A single calibration run is performed over the customer specified concentration range consisting of ten independent concentration points, and a zero ozone concentration point at the beginning and end of each calibration run.
Calibrations of most commercial ozone instruments are done using an automated control system which reads the analog signal, or RS-232 (serial) port of the instrument under calibration. Calibrations can also be performed manually by entering the values from the instrument under calibration into the SRP control system. In general, the source for the ozone sample and reference air (if necessary) is provided by NIST instrumentation. If requested, the ozone sample can come from a commercial ozone instrument.
Calibration runs utilizing analog or serial communication are generally performed overnight and consists of 5-10 independent calibration runs. Manual calibrations will consist of only one independent calibration run.
Independent special tests (37515S) require additional costs.
Delivery and return shipment of the instrument under calibration must be handled by the instrument owner.
The NIST Standard Reference Photometer (NIST SRP), developed by NIST and the U.S. Environmental Protection Agency, is a photometric instrument for the assay of up to 1000 nmol/mol of ozone in calibration atmospheres. The measurement is based on the application of the Beer-Lambert Law using an absorption cross-section of 1147 x 10-20 cm2/molecule. The NIST SRP design consists of a dual cell system where each cell alternates between sample and reference during a variable length instrument cycle. This minimizes affects of lamp drift, and absorption cell or detector biases. The NIST SRP has served as the reference standard for all ozone measurements at NIST since 1983, and has recently been adopted as the Bureau International des Poids et Mesures (BIPM) reference standard for international ozone traceability. More than 25 years of NIST SRP inter-comparisons show agreement within 1.0 percent over the 0 nmol/mol to 1000 nmol/mol concentration range against NIST SRP 2, most agree to better than 0.3 %. The spread in the agreement of all NIST SRPs is 0.7%. Recent bias improvement upgrades are showing an improved agreement spread between all SRPs. The uncertainty estimate for a NIST SRP is located in Appendix I.
The current NIST SRP Network consists of 42 instruments located worldwide in the following countries: Australia (1), Austria (1), Canada (2), China (1), Czech Republic (1), Finland (1), France (7), Germany (2), Hong Kong S.A.R., China (1), Japan (1), Mexico (1), Portugal (1), Russia (1), Spain (1), Switzerland (4), Sweden (1), Taiwan R.O.C. (1), United Kingdom (1), and the United States (13).
General Comment: Each request for construction of an instrument will be considered individually and customers, especially other National Laboratories and Metrology Institutes, are encouraged to enter into a research collaboration with NIST establish worldwide traceability for ozone measurements.
Power Requirements: 115 VAC, 50/60 Hertz. A power transformer (if necessary) will be adequate. The control computer (not included) can operate on an independent power service separate from the NIST SRP.
Laboratory Requirements: A laboratory with reasonably stable temperature, pressure, and humidity control. Large temperature drifts and cyclical changes can affect instrument stability. Humidity levels above 50 % have been shown to cause SRP detector drift. The whole SRP system will fit on a normal desktop or laboratory bench top.
Physical Dimensions: Electronics Module: 18.75 x 12.75 x 7.5 inches, (47.6 x 32.4 x 19.1 cm).
The SRP system can be set up on a laboratory bench top with the optical bench setting on a stand and the electronics and pneumatics modules situated underneath. The required bench top space is 46.0 x 17.0 inches (116.8 cm x 43.1 cm) with a necessary clearance height of approximately 27 inches (68.6 cm). Additional space is then required for the control computer, which will need to be located near the instrument, and another lab bench will be necessary for setting up guest instruments to be calibrated.
Shipping Dimensions and Weight Included with a NIST SRP purchase are two customs shipping containers.
Container 1: Instrument Modules and associated cables and interface components.
Container 2: Optical Bench Module
All shipment costs including customs fees, duty, and taxes must be handled by the customer.
Air Supply: Minimum input pressure of 15 psig (34.7 psia, 239.2 kPa) of clean, dry air.
An SRP draws 2 SLPM into each cell (4 SLPM total), plus some excess is required in the sample and reference manifolds, and additional flow requirements for instruments under calibration.
General Items needed in the Laboratory for SRP operation and Maintenance
- Zero air supply - specifications stated above under Air Supply.
SRP control system: allows for fully automated calibration of commercial ozone instruments. Details on the Control software are below:
This new software requires a newer computer to operate. The computer requirements are:
Included with the NIST SRP Instrument:
- Control circuit cards and inter-connection cables
- Customs Charges, Taxes, or Duty on the instrument
Appendix 1 - SRP Uncertainty Budget Summary
The effective number of degrees of freedom for all components is large therefore, the conventional 95% coverage factor of 2 is appropriate.
The uncertainty budget above is summarized in one equation describing the uncertainty as a function of ozone mole fraction:
Removing the absorption cross-section uncertainty, the equation becomes:
This summarizes the above uncertainty budget for an SRP without the absorption cross-section uncertainty or the temperature probe heating bias included. Without the temperature probe bias, the 95% level of confidence expanded uncertainty is:
U95 = x ± 2 × u(x) nmol/mol
With the temperature probe bias, the 95% level of confidence expanded uncertainty is:
U+95 = 2 × u(x) nmol/mol, U–95 = (-2 × u(x) - 0.001 × x) nmol/mol
NIST provides ozone reference standard instruments called Standard Reference Photometers (NIST SRP) to government laboratories around the World. It is recommended that the NIST SRP be validated bi-annually. This validation service is provided by NIST for any existing NIST SRP instrument.
An official SRP validation consists of multiple inter-comparison runs over multiple days to look at within day, and between day variations. The data is summarized and provided in a report.
Independent special tests require additional costs.
Delivery and return shipment of the NIST SRP to be validated must be handled by the owner.Calibrations Phone: 301-975-2200, Fax: 301-975-2950 NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363