Figure 3-4.
Electronic counter totalizing method, block diagram
Figure 3-5.
Electronic counter frequency measurement, block diagram
b. Frequency measurements.
The input signal is first applied to a signal
shaper that changes the input signal to uniform pulses. The output of the shaper
is then applied to the decade counting assemblies, often passing through a gate
which is controlled by the time base of the counter, as shown in Figure 3-5.
c. The number of pulses for the desired period of time, totalized in the
decade-counting assemblies, represents the frequency of the input signal.
The
counted frequency is shown on a numerical readout with a positioned decimal point.
This reading is held until a new sample is taken. The sample rate control decides
the display time of the frequency measurement being performed.
The sample rate
control also starts counter reset and the next measurement cycle.
The time base
selector switch determines the gating interval, positions the decimal point, and
selects the proper measurement units.
d. The electronic counter makes periodic measurements with its function
arranged (fig 3-6). An unknown input signal controls the gate time. The time base
frequency is counted in the decade-counting assemblies. The input shaping circuit
uses the positive-going zero axis crossing of successive cycles as triggers for
opening and closing the gate.
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