Time standard – synchronisation made easy

Stanford Research Systems 620

Precise time/frequency measurement is essential for telecommunications, broadcasting, navigation and the military. Synchronising instrumentation is crucial for the accurate measurement of laboratory and other test equipment.

Frequency standards are used for calibration and master clock synchronisation of communications devices and test and measurement systems.

Time and frequency standards

Atomic clocks are the most accurate time and frequency standards. The two most widely used atomic clocks are the caesium standard and the rubidium standard. The latter is the more compact, portable and cost-effective, and is used to control the frequencies of:

  • television stations
  • mobile phone base stations
  • test equipment, and
  • a satellite navigation systems such as GPS (extremely accurate timing is needed for the triangulation involved in GPS).


Acal BFi supply rubidium standards and distribution amplifiers to synchronise multiple devices. We supply counters and time interval analysers such as the highly accurate SR620 time and frequency counter from Stanford Research Systems. The SR620 measures time interval, frequency, pulse width, rise and fall time, period, phase and events.

The SR620’s ability to perform statistical calculations (mean, minimum, maximum, standard deviation and Allan variance), plus its single-shot timing resolution and low jitter, makes it applicable to almost any frequency- or time-related system.

With time intervals measured with 25ps RMS resolution, the SR620 is one of the highest resolution counters available. Frequency is measured from 0.001Hz to 1.3GHz, with a choice of gates ranging from 1 period to 500 seconds. The SR620 delivers up to 11 digits of frequency resolution in one second, making it suitable for measurement applications from short-term phase-locked loop jitter to the long-term drift of atomic clocks.

The SR620 makes measurements on a single-shot basis or calculates the statistics of a set of measurements. For sample sizes from one to one million, the SR620 will automatically calculate the mean, standard deviation or Allan variance, minimum and maximum for each set of measurements. 


  • Live graphical displays in three formats (conventional counters only have numeric displays).
  • Built-in auto calibration.
  • Rear panel allows external connection of any 5MHz or 10MHz source as a timebase.
  • 0.001° phase resolution.
  • Outputs up to 1,400 measurements per second to a computer.
  • Can be remotely controlled via standard GPIB and RS-232 interfaces – all instrument functions and configuration menu settings are accessible via these interfaces.

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