AC VOLTMETER
VT-181/VT-181E
SERVICE MANUAL
KENWOOD TMI CORPORATION
© 1998-4/B51-1132-00 (K/K)
HANDLE : (K01-0564-08)
HANDLE COVER : (B09-0410-08)
FRONT PANEL
VT-181 : (A63-0301-08)
VT-181E : (A63-0316-08)
SIDE FRAME (A13-2254-08)
PUSH KNOB |
KNOB |
(K24-3015-08) |
(K21-0959-08) |
RORARY KNOB (K21-0961-08)
RUBBER FOOT (J02-0543-08)
VT-181/VT-181E
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.
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CONTENTS |
SPECIFICATIONS .......................................................................................................... |
3 |
SAFETY .......................................................................................................................... |
4 |
CIRCUIT DESCRIPTION ................................................................................................ |
5 |
BLOCK DIAGRAM .......................................................................................................... |
6 |
ADJUSTMENT ................................................................................................................ |
7 |
PARTS LIST.................................................................................................................... |
9 |
PARTS LIST (ELECTRICAL) ........................................................................................ |
10 |
SCHEMATIC DIAGRAM ............................................................................................... |
15 |
P.C. BOARD ................................................................................................................. |
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VT-181/VT-181E |
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SPECIFICATIONS |
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Item |
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VT-181 |
VT-181E |
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Meter Section |
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Measurable Voltage |
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1mV to 300mV in 12 ranges:1,3, |
0.3mV to 100mV in 12 ranges:0.3, |
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10,30,100,300mV,1,3,10,30, |
1,3,10,30,100,300mV,1,3,10, |
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100,300V full scale. |
30,100V full scale. |
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dB |
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-80 to +50dB(0dB=1V) |
-90 to +40dB(0dB=1V) |
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dBm |
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-80 to +52dBm(0dBm=1mW at 600Ω ) |
-90 to +42dBm(0dBm=1mW at 600Ω ) |
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Error |
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Within ±3% of full scale at 1kHz |
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Frequency response |
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±10% at 5Hz to 1Mhz, ±5% at 10Hz to 500kHz and |
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±2% at 20Hz to 100kHz as reference to 1kHz response. |
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Input impedance |
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10MΩ ±5%, with less than 50pF parallel capacitance. |
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Durable input voltage |
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500V (DC +AC peak) 1V to 300V range |
500V (DC +AC peak) 1V to 300mV range |
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100V (DC +AC peak) 1mV to 300mV range |
100V (DC +AC peak) 0.3mV to 300mV range |
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Stability |
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Within ±0.5% of full scale for ±10 line voltage fluctuation |
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Residual voltage |
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Less than 20uV with input shorted on 1mV range |
Less than 30uV with input shorted on 0.3mV |
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range |
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Amplifier Section |
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60dB ±1dB(Approx.70dB) |
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Gain |
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Output voltage |
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1Vrms ±20% |
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Output resistance |
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600Ω ±20% at 1kHz |
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Frequency response |
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Within±3dB at 5Hz to 500kHz |
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Distortion |
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Less than 1% at full scale (Rated by signal-noise |
Less than 1% at full scale (Rated by signal- |
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ratio in 1mV and 1V range) |
noise ratio in 0.3mV,1mV and 1V ranges) |
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Signal to noise ratio |
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Over 40dB at full scale |
Over 30dB at 0.3mV range |
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Environmental |
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Within specifications |
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10 to 40˚C / 80% RH or less |
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temp./ hum.range |
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Full operation temp./ |
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0 to 50˚C / 80% RH or less |
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hum.range |
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Indoor Use Only Altitude up to 2000m OVERVOLTAGE CATEGORY¿ POLLUTION DEGREE2 |
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Power Supply Section |
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Line voltage |
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100/120/220/230/ Vac ±10% 50/60Hz |
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Power consumption |
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Max.6.9W |
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Dimensions |
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128(128)X190(210)X239(259) |
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WXHXD(mm) |
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Value in ( ) include protrusions |
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Net Weight |
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2.8kg |
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Accessories |
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Power cable |
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1pc |
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Input cable |
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CA-41p 1pc |
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Replacement fuse |
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1pc |
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Instruction manual |
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1copy |
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Adjust driver |
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1pc |
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3
VT-181/VT-181E
SAFETY
SAFETY
Before connecting the instrument to a power source, carefully 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 danger from electric shock.
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 by an option that is specified when the instrument is ordered.
The optional power cords are shown as follows in Fig.1
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 may be operated from either a 100 to 230V, 50/60Hz power source.
Use the following procedure to change from 100 to 230V operation or vice verse.
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)
Plug configuration |
power cord and plug type |
Factory installed |
Line cord |
Parts No. for |
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instrument fuse |
plug fuse |
power cord |
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North American |
0.2A, 250V |
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120 volt/60 Hz |
slow blow |
None |
E30-1983-08 |
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Rated 15 amp |
5x20mm |
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(12 amp max ; NEC) |
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Universal Europe |
0.1A, 250V |
None |
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230 volt/50 Hz |
slow blow |
E30-1982-08 |
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Rated 16 amp |
5x20 mm |
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U.K. |
0.1A, 250V |
5A |
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230 volt/50 Hz |
slow blow |
E30-1985-08 |
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Type C |
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Rated 5 amp |
5x20 mm |
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Australian |
0.1A, 250V |
None |
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240 volt/50 Hz |
slow blow |
E30-1986-08 |
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Rated 10 amp |
5x20 mm |
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North American |
0.2A, 250V |
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240 volt/60 Hz |
slow blow |
None |
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Rated 15 amp |
5x20mm |
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(12 amp max ; NEC) |
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Switzerland |
0.3A, 250V |
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230 volt/50Hz |
slow blow |
None |
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Rated 10 amp |
5x20 mm |
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Fig.1 Power Input Voltage Configuration
4
VT-181/VT-181E
CIRCUIT DESCRIPTION
The voltage or sentence in parenthes is applicable in case of the "VT-181E".
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 Detector.
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 converted 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.
Description of Functional Circuit
1) First Attenuator
A potential divider act as a attenuator. The amount of attenuation is switched in tow steps by relay contacts:0dB and - 60dB.
2) Impedance Converter
A FET differential input Amplifier act as a impedance converter with 0dB(10dB) gain. Which converts the First Attenuator output signal to a sufficiently low impedance and feeds of the Second Attenuator.
5) Main Amplifier
A wideband,non-inverting differential amplifier act as the 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.
6) Output Amplifier
A wideband,non-inverting differential amplifier act as a 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 a very good linearity by negative feedback from the current flowing through the Meter load. In switching, this provides a sufficiently 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 connector is connected to this circuit.
9) Rotary Switch
A 12 contacts rotary switch which design the operation range. For different range,different attenuation ratio are activated.
10) Gain Control
To using the dB scale to measure relative voltage, you may get a reference reading by change the gain control. (relative ref.) Which capable to vary 0 to 10dB.
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 act as a attenuator. The amount of attenuation is switched in four steps by FET switch:0dB,-10dB,-20dB,and -30dB.
11) 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.
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INPUT |
CH1. PC BOARD |
OUTPUT-1 |
1st ATT |
IMPEDANCE |
3rd ATT |
MAIN AMP |
OUTPUT AMP |
2nd ATT |
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CONVERTER |
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GAIN
CONTROL
ATT
ROTARY SW 
RELATIVE REF CONTROL
METER
ABSOLUTE
MEAN
VALUE DET
AC 100V/120V/220V/230V 50/60Hz
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DC5V |
POWER |
GND |
POWER SUPPLY |
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TRANSFORMER |
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DC-5V |
POWER ON/OFF |
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BLOCK |
181E-181/VT-VT |
DIAGRAM |
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VT-181/VT-181E
ADJUSTMENT
To obtain the best performance, periodically calibrate the unit. Sometimes, only one mode need be calibrated, while at other times, all modes should be calibrated. When one mode is calibrated, it must be noted that the other modes may be affected. When calibrating all modes, perform the calibration in the specified sequence.
The following calibration required an accurate measuring instrument and an insulated adjusting flat blade screwdriver. If they are not available, contact your dealer. For optimum adjustment, turn the power on and warm up the scope sufficiently (more than 30 minutes) before starting.
Before calibrating the unit, check the power supply voltage.
TEST EQUIPMENT REQUIRED
The following instrument or their equivalent should be used for making adjustment.
Test Equipment |
Model |
Maker |
Digital Multimeter |
DL-712 |
KENWOOD |
Frequency Counter |
FC-756 |
KENWOOD |
Oscilloscope |
CS-6010 |
KENWOOD |
Test Equipment |
Model |
Maker |
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Calibrator |
5100B |
FLUKE |
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CR Oscillator |
AG-203 |
KENWOOD |
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Attenuator |
RA-920 |
KENWOOD |
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Q-Meter |
4343B |
YHP |
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Distortion Meter |
885 |
Shibasoku |
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Insulation Meter |
SM-5 |
TOA |
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50Ω Termination |
TA-57 |
KENWOOD |
PREPARATION FOR ADJUSTMENT
Control Settings
The control settings listed below must be used for each adjustment procedure.
Exceptions to these settings will be noted as they occur. After completing a adjustment, return the controls to the following settings.
NAME OF KNOBS |
POSITION |
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RANGE |
VT-181 : 300V |
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VT-181E : 100V |
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RELATIVE REF |
CAL |
ITEM |
ADJUSTMENT POINT |
PROCEDURE |
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300mV range |
VR102 |
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Main unit |
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Oscillator or calibrator |
Oscilloscope |
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OUT |
OUT |
CAL |
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IN |
OUT |
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Oscillator |
Calibrator |
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50Ω oscillator |
(Unless otherwise specified, the above connection should be used as to the following items.)
RANGE: 300 mV
1)Input a 1 kHz (or 400 Hz), 300 mVrms sine wave, and set the pointer to 3.0 of the 0-3 scale. Check that the variable range is less than 98% and more than 102% with respect to 3.0 (full-scale).
2)Waveforms shown on the oscilloscope shall not be deformed.
OK |
NG |
NG |
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