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 display. 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. Statistics 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. Reference Output 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 convienent trigger for many types of measurements. 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 interfaces. 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. 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.