HP 5328A User Manual

Model 5328A
Operation
time base in the measurement of a 10 MHz signal
is 1 x 10-6 x 10' = 10 Hz. Similarly, for the
measurement of a 100 msec period, the error would be
1 x 10-6 x 10-I = 1 x or 100 nsec.
3-43. Trigger Error
3-44.
Noise on the input signal will cause uncertainties in the point at which theschmitttrigger
switches. Provided the noise
is not large enough to cause false triggering (i.e., cross both limits of
the hysteresis band which would produce more pulses out of theschmitt trigger than input cycles
to it) no significant error is introduced in a frequency measurement.
3-45.
For period measurements, however, this uncertainty produces like error in the time the
gate
is open since it is this signal that controls the gate. It can be shown that with essentially low
frequency noise and a signal to noise ratio of 4OdB, the resultant worst case trigger error
is .32%of
the period. Thus, the trigger error in the measurement of the period of a 1 kHzsignal
is 3.2~ 10-3x
10-3
= 3.2 psec worst case. For 60 dB S/N, worst case error is .032%whilefor a 20dBS/N signal it is
3.2%.
3-46.
For an arbitrary waveshape (but constant slew rate through the hysteresis band), the
trigger error takes on a different expression. In Figure 3-7, it
is shown that for this case, the trigger
eiiOr iS
k2 x peak noise voltage
signal slew rate
For a 40 dB S/N, this translates to
f.0025 psec
signal slew rate (V/psec)
3-47. For time interval measurements, trigger error is generally negligible when compared to
the systematic error introduced by the uncertainty in the setting of trigger levels. For an
uncertainty in trigger level of flOmV and a peak noisevoltage of 1 mV, trigger error is a factor of
5
less than the error caused by trigger level uncertainty, regardlessof signal slew rate. For example,
trigger level uncertainty of ?I0 mV on a 100 mV/ns signal introduces an error in the time interval
measurement of
fO.l ns. The tiigger error for such a signal, with 1 mV peak noise, is less than LO2
ns, a factor of five less. Averaging reduces the trigger error still further (but not the trigger level
uncertainty error). The error
is reduced by 6for time intervals averaging and by N for period
averaging.
I
Figure 3-7. Trigger Error
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HP 5328A Specifications

General

Brand	HP
Model	5328A
Category	Cash Counter
Language	English