VT-185_VT-186_VT-187_1.pdf

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2CH AC VOLTMETER
VT-185/VT-186/VT-187
SERVICE MANUAL
KENWOOD TMI CORPORATION
© 1998-8/B51-1134-00 (K/K)
VT-187 only
HANDLE
: (K01-0564-08)
HANDLE COVER : (B09-0410-08)
FRONT PANEL
VT-185: (A63-0303-08)
VT-186: (A63-0304-08)
VT-187: (A63-0305-08)
PUSH KNOB
(K24-3015-08)
ROTARY KNOB
(K21-0960-08)
SIDE PANEL
(A13-2254-08)
RUBBER FOOT
(J02-0543-08)
VT-185/VT-186/VT-187
WARNING
The following instructions are for use by qualified personnel only. To avoid electric shock,
do not perform any servicing other than contained in the operating instructions unless you
are qualified to do so.
CONTENTS
SPECIFICATIONS ..........................................................................................................3
SAFETY ..........................................................................................................................4
CIRCUIT DESCRIPTION ................................................................................................5
BLOCK DIAGRAM ..........................................................................................................6
ADJUSTMENT ................................................................................................................7
PARTS LIST (UNIT)......................................................................................................10
PARTS LIST (ELECTRICAL) ........................................................................................11
SCHEMATIC DIAGRAM ...............................................................................................16
P.C. BOARD .................................................................................................................26
2
VT-185/VT-186/VT-187
SPECIFICATIONS
ITEMS
VT-185
1mV to 300mV in ranges:
1, 3, 10, 30, 100, 300mV,
1 , 3, 10, 30, 100, 300V
full scal.
-80 to +50dB (0dB=1V)
-80 to +52dBm
(0dBm=1mW at 600Ω)
VT-186
VT-187
Meter Section
Measurable voltage
0.3mV to 100mV in 12 ranges :
0.3, 1, 3, 10, 30, 100, 300mV,
1, 3, 10, 30, 100V full scale.
dB
dBm
Error
Frequency response
Input impedance
Max. input voltage
Stability
Residual Voltage
Crosstalk Individual
Crosstolk Interlock
-90 to +40dB (0dB=1V)
-90 to +42dBm
(0dBm=1mW at 600Ω)
Within
±3%
of full scale at 1kHz
±10%
at 5Hz to 1MHz,
±5%
at 10Hz to 500kHz,
±3%
at 20Hz to 200kHz and
±2%
at 30Hz to 100kHz
as response to 1KHz response.
10MΩ
±5%,
with less than 45pF parallel capacitance.
500V(DC +AC peak)
500V(DC +AC peak) 1V to 100V range
1V to 300V range
100V(DC +AC peak) 0.3mV to 300mV range
100V(DC +AC peak)
1mV to 300mV range
Within
±0.5%
of full scale for
±10%
line voltage fluctuation
Less than 20
µV
with input
Less than 30
µV
with input shorted on 0.3mV range
shorted on 1mV range
Less than -80dB with other input terminated with 600Ω
Less than -50dB with other input terminated with 600Ω
Approx. 60dB
Approx. 70dB
1Vrms (full scale)
±20%
600Ω
±20%
at 1kHz
Amplifier Section
Gain
Output voltage
Output resistance
Distortion
Signal to noise ratio
Frequency response
Less than 1% at full scale
Less than 1% at full scale
(Rated by signal to noise ratio
(Rated by signal noise ratio in 1mV and 1V ranges)
in 0.3mV, 1mV and 1V range).
Over 40dB at full scale. (Over 30dB at 0.3mV range)
Within
±
3dB at 5Hz to 500kHz
±:
0.08%/°C
Within specifications : 10 to 40°C
Full operation
: 0 to 50°C
Less than 80%
2000m
¿
2
100/120/220/230 Vac
±10%
50/60Hz
Max. 11W
128 (128) X 190 (210) X 239 (269)
Value in ( ) include protrusions
Approx. 3.1 kg
1 pc.
CA-41p 2 pcs.
1 pc.
1 copy
1 pc.
EN55011 (1991) CLASS B
IEC801-2 (1991) 8kVAD
IEC801-3 (1984) 3V/M
IEC801-4 (1988)
Approx. 3.2 kg
Environmental
Coefficient
Temperature
Relative humidity
Maximum altitude
Overvoltage Category
Pollution Degree
Power Supply Section
Line voltage
Power consumption
Dimensions
W X H X D (mm)
Net Weight
Accessories
Power cable
Input cable
Replacement fuse
Instruction manual
Adjust driver
Regulatory Information (VT-186 only)
EMI
Immunity
7
The above specifications are subject to charge without noise.
3
VT-185/VT-186/VT-187
SAFETY
SAFETY
Before connecting the instrument to a power source, care-
fully read the following information, then verify that the
proper power cord is used and the proper line fuse is
installed for power source. The specified voltage is shown
on the rear panel. If the power cord is not applied for
specified voltage, there is always a certain amount of dan-
ger of electric shock.
Line fuse
The fuse holder is located on the rear panel and contains
the line fuse. Verify that the proper fuse is installed by
replacing the line fuse.
Voltage conversion
This instrument can be operated from 100 to 230V,
50/60Hz power source.
Use the following procedure to change from 100 to 230V
operation or vice versa.
1. Remove the fuse holder.
2. Replace fuse F1 with a fuse of appropriate value.
3. Reinsert it for appropriate voltage range.
4. When performing the reinsertion of fuse holder for the
voltage conversion, the appropriate power cord should
be used. (See fig.1)
Line voltage
This instrument operates using ac-power input voltages
that 100/120/220/230 V at frequencies from 50 Hz to
60Hz.
Power cord
The ground wire of the 3-wire AC power plug places the
chassis and housing of the instrument at earth ground. Do
not attempt to defeat the ground wire connection or float
the instrument ; to do so may pose a great safety hazard.
The appropriate power cord is supplied as an option that
is specified when the instrument is ordered.
The optional power cords are shown as follows in Fig.1
Plug configuration
power cord and plug type
North American
120 volt/60 Hz
Rated 15 amp
(12 amp max ; NEC)
Universal Europe
230 volt/50 Hz
Rated 16 amp
U.K.
230 volt/50 Hz
Rated 5 amp
Australian
240 volt/50 Hz
Rated 10 amp
North American
240 volt/60 Hz
Rated 15 amp
(12 amp max ; NEC)
Switzerland
230 volt/50Hz
Rated 10 amp
Factory installed
instrument fuse
0.2A, 250V
slow blow
5x20mm
0.1A, 250V
slow blow
5x20 mm
0.1A, 250V
slow blow
5x20 mm
0.1A, 250V
slow blow
5x20 mm
0.2A, 250V
slow blow
5x20mm
0.3A, 250V
slow blow
5x20 mm
Line cord
plug fuse
None
Parts No. for
power cord
E30-1983-08
None
E30-1982-08
5A
Type C
E30-1985-08
None
E30-1986-08
None
–
None
–
Fig.1 Power Input Voltage Configuration
4
VT-185/VT-186/VT-187
CIRCUIT DESCRIPTION
The voltage or sentence in parenthes is applicable in case of the "VT-185".
In studying the operation of each circuit in voltmeter please refer to "BLOCK DIAGRAM".
General
A Signal voltage to be measured, which is input from the
INPUT connector, is passed through the First Attenuator
and is converted to a low impedance by the Impedance
Convertor. The impedance-converted signal is normalized,
or further attenuated in proportion to 1mVrms fullscale value
through the Second and Third Attenuator. The normalized
signal is magnified 20-fold by the Main Amplifier and is fed
to the Output Amplifier and the Absolute-Mean Value Detec-
tor.
The Output Amplifier magnifies the signal 50-fold and feeds
to the OUTPUT connector. The Absolute-Mean Value
Detector converts the signal from the Main Amplifier to DC
current in proportion to the absolute mean value. The con-
verted signal activates the Meter.
The Attenuator Control encodes the signal led from the
RANGE selector to generate an Attenuator Control signal.
This signal controls the First, Second and Third Attenuator
to set the sensitivity corresponding to each range.
The Power Supply feeds to the functional circuit ±5V DC
voltages stabilized by its IC regulator.
6) Output Amplifier
A wideband, non-inverting differential amplifier acts as an
output amplifier, which has 50-fold gain and 600Ω output
impedance. The output signal level is 1Vrms for fullscale
read on the Meter, and works stable even for capacitive
loads.
7) Absolute-Mean Value Detector
An absolute-mean value detector comprised of a high
through-rate and high gain amplifier, which has 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
RANGE selector switch to 6-bit signals, which control the
First, Second and Third Attenuator. The remote control con-
nector 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.
Description of Functional Circuit
1) First Attenuator
A potential divider acts as an attenuator. The amount of
attenuation is switched in two steps by relay contacts:0dB
and -60dB.
10) CH1/CH2 Rotary Switch
A 12-contact rotary switch for setting a desired channel 1
and 2 measurable voltage range. This feeds a signal corre-
sponding to the range into the Attenuator Control.
2) Impedance Converter
A FET differential input Amplifier acts as an impedance con-
verter with 0dB(10dB) gain, which converts the First Attenu-
ator output signal to a sufficiently low impedance and feeds
of the Second Attenuator.
11) CH2 Rotary Switch
A 12-contact rotary switch for setting a desired channel 2
measurable voltage range. This feeds a signal correspond-
ing to the range into the Attenuator Control.
3) Second Attenuator
A resistance divider acts as an attenuator. The amount of
attenuation is switch in two steps by relay contacts:0dB and
-30dB.
12) CH2 Selector Switch
A Selector which is used to select either individual or inter-
locked range setting of channels 1 and 2.
4) Third Attenuator
A resistance divider network acts as an attenuator. The
amount of attenuation is switched in four steps by FET
switch:0dB, -10dB, -20dB, and -30dB.
13) CH1/CH2 Select Circuit
The range setting individual or interlocked selection circuit
are control by IC.
14) GND MODE Switch
A switch is used to disconnect the input negative circuits
from the casing ground.
5) Main Amplifier
A wideband, non-inverting differential amplifier acts as a
main amplifier, which has high input impedance, low output
impedance and 20-fold gain. This output signal level is
20mVrms for the fullscale read on the Meter.
15) Power ON/OFF
The power switch is designed to act on the secondary side
of the power transformer.
5

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