Frequency & Time - Calibration Services

Ordering Calibrations Services

The Frequency and Time Group is responsible for Canada's standards of time and length. The SI second and metre are defined and maintained, and calibrations are perfomed relative to these standards. NRC, through activities of this Group, produces the official time for Canada and is one of the many international organizations contributing to the formation of Coordinated Universal Time (UTC), the international time scale produced by the Bureau Internationale des Poids et Mesures (BIPM). Canada's SI time standards are coordinated with the UTC. The metre is realized in accordance with the guidelines published by the BIPM - "Mise en Pratique 1992" - which specify the construction and operating conditions for sources of radiation at a variety of recommended wavelengths. The uncertainty for the published wavelengths depends on the source and ranges from 6x10-12 for the helium-neon lasers stabilized on a specific absorption line of methane (an infrared wavelength), to 2x10-8 for discharge lamps filled with cadmium-114. Calibrations services are available for frequency, time, and laser frequency for defining length in terms of wavelength.

 Uncertainties
 Facilities
 Laboratory Services
 Remote Services
 Fees for Service

Contact: Dr. Jean-Simon Boulanger
Tel. (613) 993-5698

Uncertainties

The uncertainties quoted here are expanded uncertainties representing a confidence level of approximately 95%. They were obtained assuming a normal distribution and multiplying the standard uncertainty (one standard deviation) by a coverage factor of k = 2.

Facilities

The Group operates an atomic clock ensemble consisting of three primary cesium beam time standards and two commercial cesium clocks. These clocks operate on a continuous basis and produce the NRC time scale. In addition to these cesium clocks, the laboratory operates atomic hydrogen masers whose stable output frequencies are used in the evaluation of various standards.

The Group maintains three 633 nm (visible red wavelength helium-neon lasers stabilized on the 11-5 R(127) component of iodine-127. The fractional uncertainty of the frequency of these lasers relative to the primary cesium standard is 5x10-11. These constitute the primary length standards for Canada.

Laboratory Services

The Group performs in-house calibrations on a variety of instruments such as commercial cesium atomic frequency standards, rubidium frequency standards, quartz oscillators, signal generators, synthesizers, and electronic counters and timers. The frequency drift and frequency stability of a frequency standard can also be measured. The uncertainty of the calibration is usually limited only by the quality of the instrument submitted. The basic reference for the measurements is the primary cesium standard, which has an uncertainty as good as 1 x 10-13 relative to the SI second. Its frequency stability over one day is 10-14. Hydrogen masers provide a reference that has a stability as low as 10-15 over 1000 seconds. The indicated time of clocks brought to the Council can be related to time scales in other countries, usually with an uncertainty of less than 100 ns.

Facilities for calibrating frequency-stable helium-neon lasers used in length metrology and scientific research are maintained. The absolute values of wavelengths of lasers are determined by comparing the laser frequencies against the primary standard laser frequencies. An ongoing research program in the development of new optical frequency standards provides many accurately known infrared laser frequencies that can be used as standards for laser frequency/wavelength calibrations. This service is available only by special arrangement and on an experimental basis.

Remote Services

The Group assists clients in making traceable time and frequency comparisons with NRC. The comparisons are made on equipment at the client's site and can have uncertainties in frequency as low as 10-13. Clients can arrange service by contacting the laboratory. Comparisons are made via television signals within the Ottawa area, by LORAN-C signals within range of the Great Lakes LORAN-C chain, or from GPS (Global Positioning Service) satellites across Canada. NRC can also assist in comparing the frequency of a client's standard with the frequency of the time scales of other laboratories such as BIPM (Bureau International des Poids et Mesures), PTB (Physikalisch Technische Bundesanstalt), and NIST (National Institute of Standards and Technology).

Users can make frequency calibrations and obtain time of day information from a variety of time signals disseminated across Canada by NRC. Short wave radio station CHU broadcasts time signals at three frequencies: 3.33 MHz, 7.335 MHz, and 14.67 MHz, with a frequency uncertainty of 5 x 10-12 as transmitted. The time of day is available from a telephone signal provided by NRC to the CBC AM radio network and retransmitted daily at 13:00 Eastern Time in English and 12:00 Eastern Time in French. The time of day can also be obtained by dialling (613) 745-1576 for English, (613) 745-9426 for French, or (613) 745-3900 for computer readable code. These numbers are not toll free.

Fees for Service

Ordering Calibrations Services NEW procedures effective March 23, 2006.

 Time Measurements
 Time Interval & Frequency Measurements
 Frequency Stability
 Laser Frequency/Wavelength
 Authenticated NTP Service

Time Interval and Frequency Measurements

(A33-07-02-01 to A33-07-02-06)

The uncertainty quoted in each of the following descriptions is for the specified measurement period under normal laboratory conditions only. Investigations of the effects of ambient temperature, other environmental factors, or instrumental parameters are not included. The overall uncertainty depends on the stability of the standard under test both during the test and during transit to and from NRC.

Repeated measurements can be taken upon request. Additional fees are charged only to cover the added time required for the test and are generally significantly lower than for the original test. The calibration of equipment which cannot be interfaced electronically with the measuring system, for example, stop-watches or oscillators with non-standard output, will generally cost more and produce much higher uncertainty than that shown below.

Frequency Stability

(A33-07-03-01 to A33-07-03-02)

For each service described below, the frequency stability is measured over the specified period and under normal laboratory conditions. It is preferable that the unit be operating on battery power when it is delivered to NRC. If this is not possible, a warm-up period should be specified indicating the length of time to wait after the unit is switched on at NRC before measurements can begin.

Laser Frequency/Wavelength

(A33-07-05-00 to A33-07-05-02)

Calibration of Helium-Neon Lasers at 633 nm

The Optical Frequency Standards (OFS) project can offer routine frequency and vacuum wavelength calibration of client helium-neon lasers at 633 nm with an uncertainty of less than 1x10-10, normally limited by the reproducibility and stability of the client laser.
The calibration method involves comparing the frequency of the client's laser with that of the National Standard (a known frequency) and measuring the difference frequency. This is done by overlapping the output beams of the two lasers so that the combined beams illuminate a fast-response photodiode. A beat frequency equal to the relatively small difference (typically less than a few hundred megahertz) between the two laser frequencies is generated at the photodiode and this signal is measured with a calibrated frequency counter.

Frequency measurements are performed with the NRC laser stabilized on a series of four hyperfine lines in the R(127) line of the 11-5 band of the B-X 127I2 (iodine) transition to obtain an unambiguous determination of the client's laser frequency. During a typical calibration, the client's laser frequency is checked on over five different occasions over a period of at least three days in order to determine the overall stability and frequency reproducibility. Estimates of the client's laser warm-up period and sensitivity to optical feedback are also provided.

In most requested calibrations, the client's 633-nm helium-neon laser system employs a frequency stabilization method that is inferior to locking on an iodine resonance. For example, polarization stabilization, Lamb-dip stabilization, Zeeman stabilization, etc. are used. For these types of lasers, the frequency is calibrated to an uncertainty commensurate with its stability: generally, the uncertainty will not be worse than 5 parts in 10^9. This is more than sufficient for most industrial applications.

Client helium-neon lasers that are iodine-stabilized can be calibrated to uncertainties approaching the limits of the NRC laser which has been calibrated through comparison with a laser at the Bureau International des Poids et Mesures (BIPM) and directly through the NRC optical frequency comb. Under optimal operating conditions, the NRC laser has an uncertainty of less than 2 10-11. More precautions and additional measurements must be taken to realize this level of accuracy and the fee is accordingly higher.

Calibration of Lasers at 1511 to 1552 nm

These calibrations use one of two similar NRC built laser systems which are frequency stabilized on saturated absorption overtone lines in 12C2H2 and 13C2H2 (acetylene). Our acetylenestabilized lasers have been calibrated at over one hundred different lines with traceability to the SI second by means of the NRC optical frequency comb and through frequency difference measurements. These lasers are calibrated periodically with the NRC optical frequency comb. The large number of absorption lines between 1511 nm and 1552 nm permits client lasers to be calibrated over much of this region through heterodyne beat measurements. The calibration procedure is similar to that described previously for helium-neon lasers at 633 nm.

Custom Calibration of Lasers at 550 to 1150 nm and 1530 to 1560 nm

Custom calibrations of laser frequency/wavelength with traceability to the SI second through the NRC optical frequency comb are offered for lasers in the ranges 550 nm to 1150 nm and 1530 nm to 1560 nm.. Laser frequency is determined by measuring the heterodyne beat between the client laser and a single element of the optical comb. The frequencies of the comb elements are fixed by locking both the comb's repetition frequency and its offset to a signal from a calibrated hydrogen maser. In this way, an uncertainty of less than 10 Hz is achievable from 193 to 550 THz. In practice, the uncertainty is determined by the reproducibility and stability of the client laser.

Contact:
Dr. John Bernard
Phone: 1-613-993-2181
Email: john.bernard@nrc-cnrc.gc.ca

Authenticated NTP Services

(A33-07-06-01 to A33-07-06-03)

NRC offers NTP (Network Time Protocol) servers with optional authentication procedures. Using authentication a client's server can have assurance that the Internet data packets containing the NTP time stamp comes from NRC. Authentication is obtained by encrypting the data in MD5 ( Message Digest 5) format. MD5 is restricted for use in Canada and U.S.A. only.

At present there is no fee for unauthenticated NTP time service. To receive authenticated NTP service, for a one-time fee, a client will receive a key code and a password on an NTP server at NRC. Authentication is available on our stratum-1 and stratum-2 servers.

The client must specify how many servers they will synchronize to, and whether each is stratum-1 or stratum-2. The client will specify how the keyID and password will initialy be sent. They can be sent by telephone, fax, email or courier.