Marker Outputs - HP 5326A Operating And Service Manual

Model 5326/27A
Operation
be a time lapse of 150 ns before Channel A can trigger.
Averaging of time intervals results in increased re¬
solutions and reduced inaccuracies. For a further
explanation of theory, refer to Paragraph 4-27.
3-17. Retio
3-1,8. The counter may be used to measure the ratio
of two signals in either the frequency or period mode.
By setting the rear-panel CSC I NT EXT switch to EXT,
the counter will accept an external signal (Fext) for
use as the internal oscillator. This frequency should
be 100 Hz to 10 MHz at 1 V rms minimum to 5 V peak
maximum. A second signal (Fa), applied to either
INPUT A or C jack, is used as the comparator signal.
The MULTIPLIER switch controls the resolution of
the display. For a ratio of frequencies, the Ratio =
fA _ DISPLAYED NUMBER
Fext MULTIPLIER SETTING'
(P), the Ratio =
For a ratio of periods
FA _ ?xt _ DISPLAYED NUMBER
P , Fa MULTIPLIER SETTING
ext A
3-19. Disregard the unite and decimal point; also,
ignore any zeros to the left of the most significant
digit. It makes no difference which signal is higher
in frequency, as long as the two frequencies are with¬
in the specifications of their respective channels.
3-20. MARKER OUTPUTS
3-21. Two marker output jacks are mounted on the
counter's rear panel. These outputs provide a
negative-going 2 ps pulse (approx.) at DTL levels each
time the input signal passes through the trigger point
of Channel A or B. The pulses may be used to trigger
other circuits or may be applied to the Z axis of an
HP 180 Oscilloscope. When using the pulses to
intensity modulate an oscilloscope, note that the
actual trigger point is the leading edge of the pulse.
The marker's pulse width determines the upper fre¬
quency limit of the input signal. The pulses overlap
on the oscilloscope trace when the period of the signal
is less than the pulse width.
3-22. HYSTERESIS
3-23. Each input channel has a small amount of
hysteresis (about 100 mV). If the SLOPE switch is set
to "+," the trigger pulse occurs at the top of the
hysteresis "window." If the SLOPE switch is set to
the pulse occurs on the bottom line of the window.
In other words, the signal must pass through the entire
hysteresis window before a trigger pulse is generated.
3-2
3-24. When measuring frequency or period, the
counter positions the hysteresis band around zero (see
Figure 3-1). This assumes a waveform with no de
component and the counter's LEVEL control is in the
PRESET position. The input amplifier then yields
maximum input sensitivity for both positions of the
SLOPE switch. The offset introduces no measure¬
ment error, since the trigger point is repetitive from
cycle to cycle. The trigger point is point A for +
slope and point B for - slope.
Figure 3-1. Hysteresis Offset
3-26. In the time interval modes only, both input
amplifiers have an automatic compensation network
that keeps the trigger level at the same potential when
switching from positive to negative slope (see Figure
3-2). In this example, the window shifts upward to
accomplish this. There is the possibility, therefore,
that if Point A is near the top of the signal, switching
to negative slope will place a portion of the window
outside the signal (C). In such case, there would be no
triggering. When switching from time interval to
frequency, or vice versa, the trigger point shifts by
half the hysteresis band.
Figure 3-2. Hysteresis Compensation
3-27. ACCURACY
3-28. FREQUENCY MEASUREMENTS. The basic
counter accuracy is determined by two factors. One
factor is the aging rate of the 10 MHz crystal standard
in the time base (less than 3 parts in 107 per month).
A second factor is the inherent error of ± 1 count of the