compared to the frequency at the B input, and the ratio of A/B is
displayed. This can be accomplished for 1, 10, 100, or L000
cycles at the B input (as deternined by the selection of the
white pushbuttons), displaying the ratio with resolutions out to
the third decinal place. Either the rising or falling edge can
be selected for both the A and B inputs. fnput frequencies can
range from DCto 10 MHz into the A input, and DCto 2 NlHz
into
the B input.
(5) TruE
The fourth gray pushbutton selects the Tine Interval mode of
operation. The amount of tine that elapses between a signal edge
that occurs at the A input and an edge at the B input is
measured, and displayed in microseconds. In essence, the signal
at A starts the timer, and the signal at B stops it. Either the
rising or falling edge can be selected for both the A and B
inputs, and the display can be the average of the result of
either Lt 10, L00, or L000 A-to-B events (as determined by the
selection of the white pushbuttons). It is inportant to note,
however, that whereas the resolution will increase when more
cycles are averaged, the accuracy of the reading does not. This
is due to the inherent +/- 1 count uncertainty, coupled with the
fact that the instrument actually takes an entirely new
measurement for every A-to-B transition. There is therefore a
+/- 1, +/- 10, +/- L00, or +/- l-000 count uncertainty for the 1-,
10, l-00, and 1000 cycle averages, and absolute reading accuracy
does not change. The Time fnterval mode is functional over a
200ns to L0 second range.
(6
) conMr
The fifth gray pushbutton selects the Event Counter mode of
operation. The instrument will display the number of rising or
falling signal edges (deternined by the setting of the SLOPE
switch) that occur at the A input. The rate can be up to 10 MHz,
and the maximum count displayed before counter overflow is
99,999,999. In the Event Counter rnode, the white pushbuttons
perforrn the following functions:
(71 RUN. The first white pushbutton, when
pressed in, will allow the 500L to display, in
real tine, the number of events that have been
counted. If the RESBT button had been
pressed, the display will be cleared, with
only the rightmost decirnal point lit, when RUN
is selected. If the HOLD button had been
pressed in, selecting RUNwill update the
display from the frozen count to the present
count and allow real-time display of the count
to continue.
(8) HOLD. The second white pushbutton provides
a ttdisplay holdtr function. When selected, the
instrument will freeze the count on the
display, but the running count will continue
to accumulate. When the RUNbutton is pressed
