Time Interval and Frequency Counter

2 Instrument OverviewIntroductionThe SR620 Time Interval Counter can do a varietyof time interval and frequency measurements. Theinstrument's high single-shot timing resolution,low jitter, and reciprocal counting architectureallow rapid, high resolution measurements.Modes of OperationTime Intervals between the A and B inputs maybe measured with 4 ps LSD, 25 ps rms resolution,100 ps relative accuracy, and 1ns absoluteaccuracy. 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 sameas for Time interval measurements.Rise and Fall Times of either input may bemeasured. The start and stop thresholds may beset with 10 mV resolution. The 350 MHzbandwidth of the inputs allows measurements ofrise and fall times down to 1 ns.Frequencies from 0.001 Hz to 1.3 GHz may bemeasured. The SR620 will provide 11 digits ofresolution when a one second gate is used.Frequencies above 300 MHz may be measured oneither input using the UHF prescalers. NanoHertzresolution is available in the x1000 display mode.Periods may be measured with femtosecondresolution. Period measurements are done thesame way as frequency measurements, exceptthe reciprocal of frequency is reported to thedisplay.The Phase between the signals on the A and Binput may be measured with 0.001° resolution.The phase shift between signals from 0.001 Hz to100MHz may be measured.The Count mode is used to count inputtransistions during a gate. Count rates up to 300MHz will be tallied.Arming and GatingEach of these modes are supported with powerfularming and gating modes. Time arming modesinclude: +Time, +Time External, +Time Externalwith Stop Holdoff, +-Time, and +-Time External.Frequency gating modes include fixed gates ofone period, 0.01 s, 0.1 s, 1 s, Externally triggeredfixed gates, External gates, Externally triggeredadjustable gates from 1 us to 10 ms. Gates whichare externally triggered may be delayed andscanned by 1 to 50,000 gate widths to allowtransient frequency measurements.StatisticsThe SR620 will compute and display statistics forsample sizes of one to one million . The mean,standard deviation or Allan variance, minimumand maximum deviations may be displayed.Statistics are available for all modes of operation.Displayed values may be offset by the REL formeasurements relative to a previous mean value.Scope Displays and HardcopyThe SR620 can display histograms and stripcharts on any xy scope. Histograms show thedistribution of values within a group ofmeasurements. Strip charts of the previous 250mean values or deviations show data trends.Hardcopy of scope displays may be made toprinters or plotters via rear panel Centronics,RS232 or GPIB ports.Reference OutputThe front panel REF OUT provides a precision1KHZ square wave at TTL or ECL levels. Thissource may be used for calibration, and is aconvienent trigger for many types ofmeasurements.DVM's and DAC OutputsTwo rear panel DVM inputs allow dc voltagemeasurements with 0.3% accuracy on 2 or 20 Vfull scale ranges. The inputs may be displayed onthe front panel or read via the RS232 or GPIBinterfaces.Two DAC outputs default to output voltagesproportional to the mean and jitter readings todrive analog strip chart recorders. The DAC outputvoltages may also be set or scanned from the frontpanel of through one of the computer interfaces.Computer InterfacesBoth GPIB and RS232 interfaces allow completecontrol of the instrument. A fast binary dumpmode allows up to 1500 measurements persecond to be taken and transfered to a computer.SR620 Universal Time Interval Counter