The SR620 Time Interval Counter can do a variety
of time interval and frequency measurements. The
instrument's high single-shot timing resolution,
low jitter, and reciprocal counting architecture
allow rapid, high resolution measurements.
Modes of Operation
Time Intervals between the A and B inputs may
be measured with 4 ps LSD, 25 ps rms resolution,
100 ps relative accuracy, and 1ns absolute
accuracy. Time intervals from -1ns to 1000 s or +-
1000 s may be measured.
Pulse Widths of either input may be measured.
The start and stop thresholds are set separately.
The resolution, jitter, and accuracy are the same
as for Time interval measurements.
Rise and Fall Times of either input may be
measured. The start and stop thresholds may be
set with 10 mV resolution. The 350 MHz
bandwidth of the inputs allows measurements of
rise and fall times down to 1 ns.
Frequencies from 0.001 Hz to 1.3 GHz may be
measured. The SR620 will provide 11 digits of
resolution when a one second gate is used.
Frequencies above 300 MHz may be measured on
either input using the UHF prescalers. NanoHertz
resolution is available in the x1000 display mode.
Periods may be measured with femtosecond
resolution. Period measurements are done the
same way as frequency measurements, except
the reciprocal of frequency is reported to the
The Phase between the signals on the A and B
input may be measured with 0.001° resolution.
The phase shift between signals from 0.001 Hz to
100MHz may be measured.
The Count mode is used to count input
transistions during a gate. Count rates up to 300
MHz will be tallied.
Arming and Gating
Each of these modes are supported with powerful
arming and gating modes. Time arming modes
include: +Time, +Time External, +Time External
with Stop Holdoff, +-Time, and +-Time External.
Frequency gating modes include fixed gates of
one period, 0.01 s, 0.1 s, 1 s, Externally triggered
fixed gates, External gates, Externally triggered
adjustable gates from 1 us to 10 ms. Gates which
are externally triggered may be delayed and
scanned by 1 to 50,000 gate widths to allow
transient frequency measurements.
The SR620 will compute and display statistics for
sample sizes of one to one million . The mean,
standard deviation or Allan variance, minimum
and maximum deviations may be displayed.
Statistics are available for all modes of operation.
Displayed values may be offset by the REL for
measurements relative to a previous mean value.
Scope Displays and Hardcopy
The SR620 can display histograms and strip
charts on any xy scope. Histograms show the
distribution of values within a group of
measurements. Strip charts of the previous 250
mean values or deviations show data trends.
Hardcopy of scope displays may be made to
printers or plotters via rear panel Centronics,
RS232 or GPIB ports.
The front panel REF OUT provides a precision
1KHZ square wave at TTL or ECL levels. This
source may be used for calibration, and is a
DVM's and DAC Outputs
Two rear panel DVM inputs allow dc voltage
measurements with 0.3% accuracy on 2 or 20 V
full scale ranges. The inputs may be displayed on
the front panel or read via the RS232 or GPIB
Two DAC outputs default to output voltages
proportional to the mean and jitter readings to
drive analog strip chart recorders. The DAC output
voltages may also be set or scanned from the front
panel of through one of the computer interfaces.
Both GPIB and RS232 interfaces allow complete
control of the instrument. A fast binary dump
mode allows up to 1500 measurements per
second to be taken and transfered to a computer.