Table of Contents
Advertisement
three digits of the frequency or output amplitude can be incremented or
decremented by the up/down keys located beneath each digit.
The lower
two digits can also be controlled by a rotary encoder.
Frequency ranges
are automatically switched when the numeral on the digital frequency
indicator passes through each cross point
(concerned with 1599 or 16).
The current range can be known by reading the range indicator
(LEDs)
and
the decimal point on display.
The indicator displays frequencies or
output amplitudes, whichever selected to be controlled.
The display can
be switched manually, however,
the setting reverts to the previous one
in the following up or down
keystroke .
1.3
Distortion Meter
Distortion meter section of the VP-7721A contains a tracking rejection
filter which is tuned to the oscillator frequency.
A multi-stage
filter circuit achieves a wide and steep frequency response,
permitting signals with some frequency shift to be measured and a dis¬
tortion factor of down to 0.001% to be displayed.
The meter measures
total harmonic distortion from 0.003% full scale to 100% full scale in
ten ranges that can be switched automatically.
Since the distortion meter utilizes the Ratio Calculating Method*, the
operator is released from the tedious set-level procedure.
The ampli¬
tude of the input signal is monitored on the other meter.
If the
anplitude deviates from the range suitable for measuring the distortion
factor,
an annunciator lights.
The distortion meter can be adapted for
automatic range switching,
in which the appropriate range is automati¬
cally selected.
Figure 1-2 shows a conceptional block diagram of the
VP-7721A.
4
rg
o
04
O
1-2
* A conventional distortion meter determines distortion factors by
dividing the
(amplitude of the signal which excludes the fundamental
component)
by the
(total signal amplitude)-
It requires that the total signal amplitude be set to a reference
value
(set-level)
before the distortion factor can be read directly
from the amplitude of the signal which excludes the fundamental
component.
However,
direct reading of the calculated ratio between
these two types of signals eliminates the need of the set-level proce¬
dure.
It was developed by Matsushita and has been used in the VP-7702
series and later.
Advertisement
Table of Contents
