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Idiomas disponibles
Idiomas disponibles
O p e r a t i o n a l c h e c k
Input Triggering
As the input signal can have very different wave-
forms, it is necessary to shape the signals so
that the counting circuits can handle the signals.
The HM8021-4 offers a variaty of signal shaping
The HM8021-4 offers a variaty of signal shaping
possibilities to improve triggering, such as AC/
possibilities to improve triggering, such as AC/
DC coupling and two trigger level ranges (–2... 2V,
DC coupling and two trigger level ranges (–2...
–40...+40V). The trigger level can be set in one of
2 V, –40...+40 V). The trigger level can be set in
two ways: either by Autotrigger or with the trigger
one of two ways: either by Autotrigger or with the
trigger level potentiometer. In Autotrigger mode
level potentiometer. In Autotrigger mode the
the counter automatically sets the triggering to
counter automatically sets the triggering to the
the 50% level of the input signal. When this mode
50% level of the input signal. When this mode is
is selected AC coupling is necessary. When the
selected AC coupling is necessary. When the
trigger level control has been set in the manual
trigger level control has been set in the manual
trigger mode, the functioning of the trigger circuit
trigger mode, the functioning of the trigger circuit
can easily be checked on the trigger indicator. The
can easily be checked on the trigger indicator.
LED shows the state of triggering.
The LED shows the state of triggering.
LED on: the signal is above the trigger level
LED on:
the signal is above the trigger level
LED off: the signal is below the trigger level
LED off:
the signal is below the trigger level
LED
LED blinking: the signal is crossing the hysteresis
blinking: the signal is crossing the hysteresis
band, correct triggering.
band, correct triggering.
For reliable triggering the trigger level should, in
For reliable triggering the trigger level should,
always most cases, be at 50% of the signal's
in always most cases, be at 50% of the signal's
peak-to-peak voltage.
peak-to-peak voltage.
Selecting the correct attenuation is important to
Selecting the correct attenuation is important to
obtain the best results from your instrument. If
obtain the best results from your instrument. If
the attenuation is too high, the measurement will
the attenuation is too high, the measurement will
be affected by the noise of the input comparator.
be affected by the noise of the input comparator.
This results in an unstable display. With an input
This results in an unstable display. With an input
signal too great, the input stage may saturate
signal too great, the input stage may saturate and
and thus producing overshoots which result in a
thus producing overshoots which result in a display
display which is twice too high e.g. at frequency
which is twice too high e.g. at frequency
measurements. Always try to set the control to
measurements. Always try to set the control to
AC-coupling and use as much attenuation as pos-
AC-coupling and use as much attenuation as
sible for frequency measurements and DC-coup-
possible for frequency measurements and DC-
ling with no attenuation for time measurements.
coupling with no attenuation for time measure-
In many cases it is vital to have a good impedance
ments. In many cases it is vital to have a good
matching to avoid reflections which might make
impedance matching to avoid reflections which
the trigger level setting very difficult. Always use
might make the trigger level setting very difficult.
a 50 Ω termination in 50 Ω systems. The C-input
Always use a 50 Ω termination in 50 Ω systems.
The C-input facilitates no input conditioning
22
Subject to change without notice
controls and needs no trigger level setting. The
facilitates no input conditioning controls and
needs no trigger level setting. The input signal is
triggered from 50 mV up to the maximum input
voltage of 5V. The input frequency for the C-input
must always be in the range from 100 MHz to
100 MHz to 1000 MHz. For frequencies lower
1000 MHz. For frequencies lower than 100 MHz the
than 100MHz the measurement result may be
measurement result may be incorrect.
erroneous.
Measuring time and resolution
Measuring time and resolution
The measuring time can be varied in 3 steps
between 100ms and 10sec. The gate time may
The measuring time can be varied in 3 steps
be modified during a measurement. In the reci-
between 100ms and 10sec. The gate time may be
procal mode (at all frequencies with HM8021-4),
modified during a measurement. In the reciprocal
the counter totalizes the input cycles until the set
mode (atall frequencies with HM8021-4), the
measuring time has elapsed and the synchroniza-
counter totalizes the input cycles until the set
tion conditions are met. Hence, the effective mea-
measuring time has elapsed and the syn-
suring time (also called gate time) is longer than
chronization conditions are met. Hence, the
the set measurement time. The measurement in
effective measuring time (also called gate time) is
the HM8021-4 is always synchronized to the input
longer than the set measurement time.The
signal. This is called the input synchronized or
measurement in the HM8021-4 is always
reciprocal method.
synchronized to the input signal. This is called the
input synchronized or reciprocal method.
In this mode, both the opening and closing of the
main gate are synchronized with the input signal,
In this mode, both the opening and closing of the
so that only completed input cycles are counted.
main gate are synchronized with the input signal,
This means that a ±1 input cycle error is avoided.
so that only completed input cycles are counted.
During the gate time, the counter totalizes the
This means that a ±1 input cycle error is avoided.
number of clock cycles. When the preselected
During the gate time, the counter totalizes the
gate time is over, the counter waits for the next ac-
number of clock cycles. When the preselected
tive transition of the input signal to stop counting.
gate time is over, the counter waits for the next
If the recurrence of this signal is low, e.g. with long
active transition of the input signal to stop counting.
period times, the stop synchronization time may
If the recurrence of this signal is low, e.g. with
be long compared to the preset gate time. In that
long period times, the stop synchronization time
case the effective gate time may be very different
may be long compared to the preset gate time. In
from the preset value (if the signal was removed
that case the effective gate time may be very
during measurement, this time becomes infinite
different from the preset value (if the signal was
and the measurement finishes never). The reso-
removed during measurement, this time becomes
lution in the input synchronized mode is caused
by trunctation of the clock pulses, which results
infinite and the measurement finishes never).
in +1clock pulse error (100ns). The resolution
The resolution in the input synchronized mode is
of the measurement thus only depends on the
caused by trunctation of the clock pulses, which
measurement time. For example, the resolution
results in +1clock pulse error (100ns).
for 1s measuring time is 10
resolution of the measurement thus only depends
frequency. In conventional counters the gate time
on the measurement time. For example, the
is synchronized with the clock signal. The first
resolution for 1s measuring time is 10
and last input cycle can therefore be truncated,
dent of input frequency. In conventional counters
causing a ±1 cycle error. This resuits in a good
the gate time is synchronized with the clock
resolution for high frequency measurements,
signal. The first and last input cycle can therefore
but a poor resolution for low frequency measure-
be truncated, causing a ±1 cycle error. This resuits
ments (±1: frequency, for 1sec. measuring time).
in a good resolution for high frequency measure-
ments, but a poor resolution for low frequency
measurements (±1: frequency, for 1sec.
measuring time).
Signal inputs
The
-7
, independent of input
-7
, indepen-
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