Frequency Measurement; Period Measurement; Totallizing (Event Counting); External Gate (Back Of Mainframe) - Hameg Instruments HM 8021-4 Manuel

of the HM 8021-4 unit reaches up to 1 GHz, this
module offers also an input (C) for frequency
measurements from 100 MHz up to 1 GHz. It is
also provided as a BNC socket and has an
impedance of 50 Ω.
Caution!
Particular care should be taken, when applying
signal voltages to the 1 GHz input of the HM
8021-4 unit. A maximum voltage of 5V
(DC+AC ) may be applied to the input C
peak
(see "Specifications").
exceeding this value will destroy the input
stage of the frequency counter!

Frequency measurement

Counters are used for both, frequency and time
interval measurements. However, frequency and
time interval measurements have contradictory
requirements in respect of correct triggering. For
frequency measurements, too high a sensitivity
means that the counter is too sensitive to noise.
Therefore do not use higher sensitivity than
needed for correct triggering. Signals which are
superimposed on a DC voltage, must be separated
via an input coupling capacitor (i.e. AC-coupling,
DC pushbutton released). The advantages of AC
coupling are: no DC-drift and good protection
against DC overload. AC-coupling however, gives
a drop in sensitivity for very low frequencies. The
signal frequency to be measured is applied to one
of the inputs, and the corresponding function is
selected. The trigger point is adjusted by use of
the TRIGGER knob (9, so that a stable value is
displayed. This stability is obtained, when the
trigger signal display LED flashes (see "Input
triggering"). Now the test frequency can be read
on the 8-digit display. The obtained resolution
depends on the gate time and can be selected in
3 steps with the GATE TIME pushbutton switch
[3]. When the measurement range is exceeded,
the OVERFLOW LED [1] is light up. A reliable
indication is no longer ensured under these
circumstances. The maximum resolution of 0.1
Hz is obtained with a gate time of 10sec.

Period measurement

For measurement of the period duration, the
reciprocal value of the frequency T=1/f is measured
in seconds. The signal is applied as for frequency
measurement.
Subject to change without notice
Any input voltage
Time interval measurement (Pulsewidth)
In TI mode, the time (e.g. number of 100ns
clock pulses) is measured between the positive
slope and the negative slope of an event at
channel A. (Corresponding for negative pulses in
TI mode). In single source time measurements
(e.g.Pulse width ) the resolution of the
measurement is 1clock pulse (100ns).By using
the time interval average technique, which means
multiple measurements of a repetitive signal, the
measuring accuracy and resolution are greatly im
proved.Compared to single time interval
measurements, the basic 100ns resolution is
improved by a factor of √N, where N is the
number of time intervals being averaged during
the measuring time. Note that the input signal
must be repetitive and must not have a phase
relation with the reference frequency. For time
interval measurements, too low a sensitivity
means that different signal slopes at the positive
and negative edge cause different delays between
the trigger level crossing and the trigger point,
resulting in incorrect measurements. The highest
possible sensitivity which does not overload the
input stage, is the ideal. DC-coupling, attenuation
and a continuously variable setting of the trigger
level is necessary for setting the trigger level at
any required point of the input signal, indepen-
dent of waveform and duty factor. Autotriggering
requiring AC-coupling is also possible. The display
resolution changes with the number of measure-
ments taken from the signal. At single pulse
measurements the resolution is 100ns, whereas
the resolution may be as small as 10ps, depending
directly on the measurement time set with the
gate switch [3] and the repetition rate of the input
signal.

Totallizing (Event counting)

The signal is applied as for frequency measure-
ment.

External gate (back of mainframe)

The external gate function allows full control of
the start and stop of the measurement. When
Ext. (gate) is selected [3] and the control input
signal is low, the counter makes all necessary
preparations for a measurement. With the high
level of the gate signal, measurement starts when
the input signal triggers after a synchronization
delay. Measurement stops on the first trigger
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