Stanford SR620 Frequency Counter
Time interval and frequency counter (Distributed only in Germany.)
Histograms and Strip Charts
Unlike conventional counters that only have numeric displays, the SR620 Frequency Counter provides live, graphical displays of measurement results. Graphical data is available in three formats: a histogram showing the distribution of values within a set of measurements, a strip chart of mean values from successive measurements, or a strip-chart of jitter (standard deviation or Allan variance) values from successive measurements. Up to 250 strip chart points, or histogram bins, can be displayed.
Both histograms and strip charts can be displayed on any oscilloscope with an X-axis input (see the pictures above), or can be plotted on an HP-GL compatible plotter or dot-matrix printer. Convenient cursors allow you to read the value of any data point in the histogram or strip chart. Autoscale and zoom features make it simple to display all, or any portion, of the graphs.
Complete Statistical Calculations
The SR620 Time Interval / Frequency Counter can make measurements on a single-shot basis, or calculate the statistics of a set of measurements. Sample sizes from one to one million can be selected. The SR620 will automatically calculate the mean, standard deviation or Allan variance, minimum and maximum for each set of measurements.
Reference Output
A precision 50 % duty cycle square wave (1 kHz) is available at the front-panel REF output. The REF output can be used as a source of start or stop pulses for any of the SR620’s measurement modes. For instance, the length of a cable connected between REF and the B input can be precisely determined by measuring the time delay between REF and B.
Built-In DVMs and Analog Outputs
Two rear-panel DVM inputs make measurements of DC voltages with 0.3 % accuracy (±20 VDC range). These values may be read via the interfaces or displayed directly on the front panel.
Two rear-panel DAC outputs continuously provide voltages proportional to the mean and the jitter of the measurement sample. These 0 to 10 V outputs can drive strip chart recorders, or can be set to provide fixed or scanned output voltages.
Built-In Auto-Calibration
A sophisticated, built-in auto-calibration routine nulls insertion delays between start and stop channels, and compensates for the differential nonlinearites inherent in analog time-measurement circuitry. The auto-calibration routine takes about two minutes to perform, and should be run every 1000 hours of operation.
10 MHz Reference
The choice of timebase affects both the resolution and accuracy of measurements made with the SR620. SRS offers a choice of a standard timebase with an aging coefficient of 1 × 10-6/year, or an optional ovenized-oscillator timebase with only 5 × 10-10/day aging, and about an order of magnitude better short-term stability than the standard timebase. A rear-panel input lets you connect any external 5 MHz or 10 MHz source as a timebase.
Computer Interfaces
Standard GPIB (IEEE-488.2) and RS-232 interfaces allow remote control of the SR620 Frequency Counter. All instrument functions and configuration menu settings are accessible via the interfaces. A fast binary dump mode outputs up to 1400 measurements per second to a computer. A parallel printer port allows direct printing from the instrument. Standard IEEE-488.2 communications are supported, and plotter outputs are provided in HP-GL format. For convenient debugging, the last 256 characters transmitted over the interfaces can be viewed on the front panel.
