Tektronix DC504 5-digit 80MHz Digital Counter

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List of Options
Detailed Specifications
Operating Instructions
Misc. Part Numbers

Samples of e-Bay Prices
Tektronix Catalog CostLow BidHigh Bidaverage
$425 (1977)
$600 (1982)
$52.00 7/24/01 #1618029810 aplussurplus
$27.00 9/6/01 #1633228337 rrkotowski
$25.00 9/11/01 #1635819480 jbarkley
$21.50 9/24/01 #1639731537 reliableendmill
$45.00 9/24/01 #1639559156 jds8 (latch missing, w/opt 1)
$39.99 9/25/01 #1639989833 sales
no bids (asked $29.99) 10/3/01 #1643078280 sales@astglobal
$57.00 10/23/01 #1651216670 sales(astglobal)
$15.50 10/27/01 #1653828433 madsciguy (no side panels)
$20.50 11/9/01 #1658356079 judinkes
$24.99 11/15/01 #1659779947 lyntec
$43.22 7/12/02 #1747465238 atysonrh
$26.66 2/1/03 #3308507575 riatia (guarantee) (6 bids $10 start)
$21.50 3/24/06 #7601349646 playerservices (5 bids $0.99 start) (powers up & counts)
$10.50 4/14/06 #7608083524 electronicscafe (2 bids $9.99 start) (untested - cosmetically good)
$45.78 (free ship) 5/20/09 #290320355087 idc-comm (10 bids $20 start) (tested-10 MHz, 80 MHz displays shown)
$26.99 (+$7.99 ship) 11/29/10 #190471562342 gliderpilot2002 (5 bids $0.99 start) ("working"-no details)

  • 0.1Hz to at least 80 MHz
  • 1 Ás to 999.99 s at a maximum rate of 80MHz.
  • 5 Digit LED Display
  • Period Measurement for Resolution at Low Frequency
  • Rpm Counting
    Option 1 = More Stable Time Base -


    The DC 504 Counter Timer measures frequency from 0 Hz (with 0.1 Hz resolution) to 80 MHz, period from 1 microsecond to 999.99 seconds, and totalizes events from 0 to 99,999 at a maximum rate of at least 80 MHz. A resolution of 0.1 Hz can be obtained by allowing the more significant figures of the counter to overflow. Five 7 segment light-emitting diodes (LED's) provide a visual numeric display. The decimal point is automatically positioned and leading zeros (to the left of the most significant digit or decimal point) are blanked. Digit overflow is indicated by a front panel LED. Signals to be counted timed can be applied to either a front panel BNC connector or to the rear interface connector.
    Internal switches select frequency or rpm operation, internal time base or external standard, and override display storage.



    CharacteristicsPerformance RequirementsSupplemental Information
    Frequency Range or (Revolutions Per Minute, RPM)

    DC Coupled

    0 Hz to at least 80 MHz

    Coupling selected with an internal switch
    AC Coupled
    10 Hz to at least 80 MHzCoupling selected with an internal switch
    Sensitivity 20 mV rms (56.6mV p-p) below 15 MHz
    35 mV rms (99 mV p-p) at or below 50 MHz derating to typically < 175 mV rms (495 mV p-p) at 80 MHz
    Sine wave used for measurement
    Impedance1 MΩ paralleled by approximately 20 pF
    Maximum Safe Voltage250 V (DC + peak AC) at 500 kHz or less
    Trigger Level RangeNominally -1.5 V to +1.5 V
    Triggering Error<=0.5% of one cycle at minimum trigger sensitivity
    Signal SourceInternal (rear connector interface) or external (front panel BNC)Selected by front panel SOURCE switch
    Slope Plus for all functions

    CharacteristicsPerformance RequirementsSupplemental Information
    Display Accuracy± 1 count ±time-base accuracy
    ±trigger error
    Maximum Resolutions
    kHz Positions

    0.1 Hz, 1 Hz, and 10 Hz
    (1 RPM, 10 RPM,, and 100 RPM)*

    Seven digit resolution possible in overflowed kHz position
    MHz Positions
    0.1 kHz, and 1 kHz
    (1000 RPM and 10k RPM)*
    Nine digit resolution possible in overflow kHz position
    1Events being totalized must be positive-going pulses at least 6.25 ns in width. The repeatable of the pulse must be at least 6.25 ns apart (i.e., 80 MHz square-wave). The pulse amplitude must meet 80 MHz input sensitivity requirements. Less input amplitude will be required for wider pulses.
    mSEC Positions

    1 μs, and 10 μs

    A random error of up to 5 counts may occur in the 10 μSEC period position when measuring the periods of less than 2.0 mSEC. Such short periods should be measured in the 1 μs period position to obtain higher resolution.
    SEC Positions
    10 ms, 1 ms, and 0.1 ms
    Display Time Variable from about 0.1 s to about 10 s. Detent position of DISPLAY TIME knob provides a HOLD mode.

    Crystal Frequency
    StandardOption 1
    1 MHz5 MHz
    Stability (0°C) after 1/2 Hour Warm-UpWithin 1 part in 105Within 5 parts in 107
    Long-Term Drift1 part or less in 105 per month1 part or less in 107 per month
    AccuracyAdjustable to within 1 part in 107Adjustable to within 5 parts in 109
    *Assuming transducer output is one pulse per revolution.

    above excerpts from 1977 TM 500 brochure and DC 504 COUNTER / TIMER Instruction Manual



    To measure and display the frequeny of a signal up to 80 MHz, set the FUNCTION switch to the appropriate FREQUENCY position. Set the DISPLAY TIME control fully ccw, connect the signal to the INPUT connector, and set the SOURCE switch to EXT (front-panel BNC connector). You will note that higher resolution measurements take more counting time, e.g. a 1 kHz resolution measurement on the MHz scale requires 1 ms while a 0.1 Hz resolution measurement on the kHz scale takes 10 s.

    Final selection of FREQUENCY position of the FUNCTION switch depends on the frequency being measured, desired resolution, and willingness of the operator to wait for a measurement. Using the FREQUENCY MHz position, higher frequencies may be measured, but at the expense of the greater resolution capabilities of the longer FREQUENCY kHz position.

    OVERFLOW. Through intentional use of "overflow" displays, it is possible to improve the resolution of the counter. Choose the FUNCTION switch position which displays the most significant number of the measurement as far to the left as possible. Note the numbers displayed to the right of the decimal. Move the decimal point to the left by choosing a higher resolution FUNCTION position, if possible. The OVERFLOW LED will light when the most significant number overflows the last storage register. Note that the increased resolution does not change the accuracy of the measurement. Jitter in the input signal will become more apparent as the resolution increases.


    Once a stable measurement is obtained, the rate at which measurements are made can be controlled by the DISPLAY TIME control. Turning the control cw holds off the counting and stores the display for a longer time before a new measurement is made and displayed. DISPLAY TIME and COUNTING time together complete a measurement-display cycle.

    The DISPLAY TIME control is uncalibrated and variable from about 0.1 s at the ccw end to about 10 s at the cw end. At the cw end, there is a detent position called HOLD. In HOLD, the last count taken will be stored and displayed for an indefinite time. A new count and display may be initiated by pushing the RESET button, by turning the DISPLAY TIME control ccw, or changing the FUNCTION switch to any other position.

    The internal RPM switch, when set to its RPM position, allows the DC 504 to be used as an RPM counter in the FREQUENCY positions of the FUNCTION switch. By moving the RPM switch to RPM, the gate times of the DC 504 are lengthened by a factor of six, so that the longest gate time becomes 1 minute, giving a "counts per minute" or RPM function. The decimal point is erased from the display in the RPM measurements to indicate that RPM rather than FREQUENCY is the selected function and to facilitate the use of transducers with other than 1 pulse per revolution. The table below should be used to interpret the DC 504 front-panel markings and the RPM display readings.

    Gate Time
    Read display
    number as
    MHz1 kHz6 ms10,000RPM x 10,000
    MHz0.1 kHz60 ms1,000RPM x 1,000
    kHz10 Hz0.6 s100RPM x 100
    kHz1 Hz6 s or 0.1 m10RPM x 10
    kHz0.1 Hz60 s or 1 m1RPM x 1



    In the TOTLIZE EVENTS mode, signal events applied to the INPUT are counted and the accumulated total is displayed until the reset button is pushed or the FUNCTION switch is changed to another position. This mode is a manual analog of the frequency mode. Its main application is to accumulate a count of relatively slow and irregular events.


    Apply the signal to the INPUT connector and set the trigger controls the same as for frequency measurement.

    STARTING THE COUNT. Adjust the TRIGGER LEVEL control until the displayed total begins to increment. The accumulated count is displayed in whole numbers in the TOTALIZE EVENTS mode, only the TRIGGER LEVEL control and the RESET button affect the display.

    STOPPING THE COUNT. If pin 28B at the rear interface connector is pulled to ground, the TOTALIZE mode operation will be stopped (no more incoming events will be added to the total). This is the most reliable method to stop the count. A discrete transistor or open-collector logic should be used to pull pin 28B on the interface connector low, e.g., pin 28B must not be forced high. Rotating the TRIGGER LEVEL control until the DC 504 no longer reacts to the input signal will also stop the totalize count. An extra count may be added to the total by rotating the TRIGGER LEVEL control counterclockwise through the 0 level.

    RESTARTING AND RESETTING. When pin 28B at the rear interface connector is allowed to go high, or when the TRIGGER LEVEL control is again adjusted to trigger the DC 504 on the input signal, incoming events will advance the displayed total. (If the TRIGGER LEVEL control is rotated through the threshold point (0 level for zero volts dc in) in a ccw direction, the displayed total will advance by one.) Resetting the count to zero can be done at any time by pressing the RESET button or by moving the FUNCTION switch to some other position, then back to TOTALIZE events.



    Period measurement is provided in counter/timers primarily to overcome a basic limitation of counters, i..e., the long time required to make a high-resolution, high-accuracy measurement of low-frequency signals. For example, a 1 kHz signal requires 1,000 seconds of counting time to accumulate a million counts. However, in only one second, a 1 kHz signal can gate one million clock pulses from a 1 MHz clock into the counter.

    Simply stated, the PERIOD mode reverses the functions of signal and clock as compared to the frequency mode. In frequency mode, signal events are counted for some number of clock pulses, then displayed. In PERIOD, clock pulses are counted for some number of signal events then displayed.


    Period measurements of signals below 10 Hz, and particularly in the lowest decade from 0.1 Hz to 1.0 Hz, become rather sensitive to wave shape and amplitude. Since it is desirable for the signal to pass through the trigger hysteresis abruptly, square-wave inputs are preferred. Sine and triangle waves can be measured accurately at the very low end if the input amplitude is kepy somewhat above minimum specification so that the trigger input is driven hard.

    Be especially wary of high frequency ringing or noise on the input signal which can cause false triggering in the PERIOD mode.

    above excerpt from DC 504 COUNTER / TIMER Instruction Manual

    1-4366-1170-01Knob: Gray, 4 Sided (Function)
    1-3366-1031-05Knob: Red (Display Time/Hold)
    1-2366-0494-00Knob: Gray (Trigger Level)
    1-5366-1257-30Push Button : Gray -- RESET
    R190311-1342-00Res.,Var,Nonwir: 500K Ohm, 10%, 0.5W (Clarostat CM39425NP) (Display Time)
    R125311-0091-00Res, Var, Nonwir: 1K OHM, 10%, 0.5W (A-B W3083E) (Trigger Level)
    1-40260-1421-00Switch: Push (RESET)