Time & Frequency (TF) Metrology
National standard
NMISA currently maintains four cesium atomic clocks, with one of the clocks being designated as the master clock for South Africa. Development work is in progress to design a steered frequency source so that the master clock for South Africa will become the average of all clocks in the ensamble.
Services offered
The TF laboratory offers time distribution, calibration and consultation services. Time is distributed through the Telephone Time Service (TTS), the Network Time Protocol or satelite common view (GPS and GLONASS). More information is available on the SA Time page in the main menu. The information, together with more time related information, is also available in a monthly bulletin.
The TF laboratory is accredited for the work performed for customers on a regular basis. Below are descriptions of common calibration services
- Frequency measurements
The frequency of the full range of clocks and oscillators can be calibrated, from crystal oscillators with drift rates of parts in 108 to cesium devices with drift rates of parts in 1014. A variety of techniques are used and uncertainties quoted depend on the period of observation, the unit under test and the technique used. The accredited uncertainty for certain fixed frequencies are 1 part in 1013
The frequency output of a frequency source or generator can be measured from 1 mHz to 40 GHz where the best uncertainty is 2 parts in 1010.
The laboratory is accredited to measure the frequency of optical frequency sources (e.g. a laser). The accuracy of the measurement is directly traceable to the master clock. The accredited best measurement uncertainty is 4 parts in 1011.
- Time Interval
Time interval measurements can be performed from 1 ns to 100 000 s with a best uncertainty of 2 parts in 1011.
- Pulse characteristics (Rise- & falltime and waveform aberrations)
Calibration for the characterisation of pulses and the step response of oscilloscopes is provided by the use of a reference pulse generator traceable to an international laboratory. The best measurement uncertainty is 6 ps.
- Phase angle measurements
The national standard for phase angle is generated by a phase standard capable of generating phase angle with a resolution of 0,001° at a frequency range from 1 Hz to 100 kHz for voltage output of 50 mV to 125 V (RMS). The best measurement uncertainty is a function of frequency and voltage and is available on our accreditation scope.
- Phase noise
The phase noise of generaters and clocks can be measured for carrier frequencies up to 1,8 GHz. The laboratory has traceability for measurements from 5 MHz to 640 MHz with the best measurement uncertainty being 2,4 dB for a noise floor down to -165 dBc.
Technology Advisory Forum Meetings (TAF)
TAFs are used as a vehicle by the NMISA to invite industry participation into its strategic planning process with specific regard to technical support for industry. These TAFs focus on measurement activities in industry and what calibration and measurement support you, our industry partner, require to successfully execute your daily activities and how the NMISA can assist in breaking down technical barriers that might exist for global competitiveness. For a schedule of upcomming events,go to the TAF page, or go to the TF TAF page for a list of previous meetings.
Contact information
For enquiries regarding time and frequency related queries, please contact Chris Matthee on telephone number +27 12 8412245.