Stanford Research Systems SR620 Datasheet

Frequency Counters

SR620  Universal time interval and frequency counter

· 25 ps single-shot time resolution

· 1.3 GHz frequency range

· 11-digit frequency resolution (1 s)

· 0.001° phase resolution

· Statistical analysis & Allan variance

· Graphical output to X-Y scopes

· Hardcopy to printers and plotters

· GPIB and RS-232 interfaces

· Optional ovenized timebase

· SR620 ... $4950

(U.S. list)

The SR620 Time Interval Counter performs virtually all of the
time and frequency measurements required in a laboratory or
ATE environment. The instrument's single-shot timing
resolution and low jitter make it the counter of choice for
almost any application.

SR620 Measurements

The SR620 measures time interval, frequency, pulse-width,
rise and fall time, period, phase and events. Time intervals are
measured with 25 ps rms resolution, making the SR620 one of
the highest resolution counters available. Frequency is
measured from 0.001 Hz to 1.3 GHz, and a choice of gates
ranging from 1 period to 500 seconds is provided. The SR620
delivers up to 11 digits of frequency resolution in one second,
making it suitable for measurement applications ranging from
short-term phase locked loop jitter, to the long-term drift of
atomic clocks. All measurement modes are supported by a
wide variety of flexible arming and triggering options.

Histograms and Strip Charts

Unlike conventional counters that only have numeric displays,
the SR620 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.

SR620 Time Interval & Frequency Counter

www.thinkSRS.com

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Both histograms and strip charts can be displayed on any
oscilloscope with an X-axis input (see pictures), 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 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 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 they 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 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. 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 debugging, the last 256
characters transmitted over the interfaces can be viewed on
the front panel.

SR620 Time Interval/Frequency Counter

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Histogram display

Allan variance plot

SR620 rear panel