Kenwood VT-183, Руководство по обслуживанию, Страница: 5 / 20

General
This AC voltmeter is combined with Meter unit and Control
unit. Meter unit switch to different range according to the
remote control signal and display the result to the meter.
Control unit will output the remote control signal according to
the output of the Meter unit.
Description of Functional Circuits
Meter Unit
1) First Attenuator
It is the attenuator based on the resistance dividing method,
and its two-staged attenuation volume-one is 0dB(the range
between 10µV and 300mV),and the other is –60dB is con-
verted by a relay.
2) Impedance Conversion Circuit
It is the circuit to convert the signals from the first-stage
attenuator into a fully low impedance in order to send it to
the second-stage attenuator (1mV–300V) .
3) Second Attenuator
A resistance divider act as a attenuator. The amount of
attenuation is switch in two steps by relay contacts:0dB and
–30dB.
4) Third Attenuator
A resistance divider network acts as an attenuator. The
amount of attenuation is switched in four steps by a FET
switch:0dB, –10dB, –20dB and –30dB.
5) Main Amplifier
A wideband, non-inverting differential amplifier acts as a
main amplifier, which has high input impedance, Iow output
impedance and 20-fold gain. This output signal level is
20mVrms for the full scale read on the Meter .
6) Output Amplifier
A widehand, non-inverting differential amplifier acts as an
output amplifier, which has 50-fold gain and 600
Ω
output
impedance. The output signal level is 1Vrms for full-scale
read on the Meter, and works stable even for cpacitive
loads.
7) Absolute-Mean Valve Detector
An absolute-mean value detector comprised of a high
through-rate and high gain amplifier. Which has a very good
linearity by negative feedback from the current flowing
through the Meter load. In switching, this provides a suffi-
ciently wide frequency band so that the high frequency
phase compensation circuit is reset.
8) Attenuator Control
A logic control circuit comprised of a diode matrix and output
buffer transistors. This encodes a 12-bit signal from the
Decoder on the control board to a 6-bit signals, which con-
trol the First, Second and Third Attenuators. The remote
control connector is connected to this circuit.
9) Power Supply
The power source circuit supply
±
5V DC from the AC input,
which contain a silicon diode bridge for full-wave rectifica-
tion, high-capacitance electrolytic capacitors for smoothing,
and an IC regulator stabilization.
Control Unit
1) Pre-Amplifier
A wideband, non-inverting differential amplifier act as a pre-
amplifier. Which has 50-fold gain and the purpose is to
buffer the signal from meter unit and then driving the two
rectifier circuit.
2) Rectifier
Two transistors to from a full wave rectifier.
3) DC Output Circuit
A non-inverting operational amplifier act as a DC output dri-
ver with 1V full scale voltage. The output impedance is
600
Ω
.
4) Peak Hold Regulation Circuit
Two transistors to from a full wave rectifier, and the peak
voltage is held by a smoothing capacitor.
5) Discharge Circuit
The peak voltage mention above will be discharge by a tran-
sistor frequently with a constant period.
VT-183
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CIRCUIT DESCRIPTION
In studying the operation of each circuit in voltmeter please refer to "BLOCK DIAGRAM".
VT-183(K) internet 98.6.8 9:37 AM y [ W 10