Kenwood VT-175 User manual

©PRINTED INPAN
KENWOOD
2 CHANNELACVOLTMETER
VT-175
INSTRUCTIONMANUAL
KENWOOD CORPORATION

CONTENTS
1. GENERAL3
2. FEATURES 3
3. SPECIFICATIONS 4
4. FUNCTIONAL CONTROLS6
5. OPERATION8
6.APPLICATIONS10
7. MAINTENANCE13
8.ALIGNMENT14
9.CAUTIONSFORUSE••16
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1. GENERAL
2. FEATURES
The Model VT-175 isdual-channelelectronicvoltmeter
sets havingtwoindependentACvoltmetersina single
cabinet.Two-pointermeterallows easy dualmeasurements
andinter-channelcomparisons.
MODEL VT-175 iswideband,highsensitivevoltmeterfor
use anywherevoltagemeasurementsaremade, with a
remotecontrol unit. Theeasy-to-usevoltmeterprovides
frequencyresponseaswideas5Hzto 1 MHz,measurable
range from 1mVto300V,and input impedanceof
10MO.
a. Twopowersourcecircuits,positiveandnegative,
are providedforverystableDCbiasandrecover
from anyoverloadina veryshorttime.
b.Small-sizedcompactconstructionis easy tocarry
andlarge-sizedtwo-pointermeteris easy toread.
c. Four-scaledialplateandredandblackpointers
allowquick,andaccuratevoltagereading.
d. Numberofadjustingtrimmersareminimized with
amplifiersthatarepreciselycalculatedinopen loop
gains andarenegativefeedbacked through metal-
film resistorsasaccurateas1%
Amplifiercharacteristicsthereforeare from secular
change.
e. Inputimpedanceisashighas10MOonallranges
anditsparallelcapacitance less than45pF
f.IndirectattenuatorswitchingbyrelayandFET
(field-effecttransistor)switchprovideshigher
reliability,signal-to-noiseratio,andinter-channel
crosstalk thanmostpreviousdirectmethodofrotary
switch.
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9- RangescanberemotelyselectedusingtheRT-61
(option).
h.Twochannelrange setting canbemadeeither
individually or together (ininterlockedmanner).
i.A ground mode selectormay float measuringcircuit
aboveground.
3.SPECIFICATIONS
[Meter Section]
Measurablevoltages: 1 mV-300Vin12ranges:
1 mV,3mV,10mV,30mVr100mV,
300mV,1V,3 V,10V,30V,100Vand
300V. full scales.
dB: -80~+50dB(0dB= 1V).
dBm: -80~+52dBm(0dBm= 1 mW,600n).
Error : Within ± 3%of full scaleat1kHz.
Frequencyresponse: ± 10%at5Hz— 1 MHz,
±5%at10Hz-500kHzand
±3%at20Hz-200kHzas
±2% at30Hz~100kHz
referencedto 1 kHzresponse.
Input impedance: 10MO±5%, with less than
45pF parallelcapacitance.
Durable input voltage:500V(DC+ACpeak)
at1V—300Vrange
100V(DC+AC peak)
at1mV~300mVrange
Stability: Within±0.5%of full scale fori 10%
linevoltage fluctuation.
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-5-
Residual voltage: Less than 20^V with input shorted
on 1 mVrange-
Crosstalk,Individual: Less than -80dB with other
input terminated with 600O
Inetrlock: Less than -50dB with other
input terminated with 600O.
[Amplifier Section]
Gain : Approx.60dB.
Output voltage: 1Vrms(Full scale) ±20%
Output impedance:600X1+20%
Distortion : Less than 1%at full scale. (Rated
bysignal-to-noise ratio in 1 mVand
1V ranges.)
Signal-to-noise ratio: Over40dBat full scale.
Frequencyresponse: Within ± 3dBat5 Hz—500kHz
[Environmental]
Coefficient:± 0.08%/°C
Temperature (within specification): 10~40°C
(full operation): 0~50°C
Relative humidity : Less than 80%
[PowerSupplySection]
Line voltage: 100,120,220VAC+ 10%,
216- 250VAC,50/60Hz
Powerconsumption:Approx.7W
[Dimensions]Wx190(212)Hx238(268)Dmm.
Values in( ) includeprotrusions.
[Net weight] 3 kg
[Accessories ]
Powercable: 1 pc.
Input cable: BNCcord,2pes.
Replacementfuse: 0.3A2pes.
0.5A 2pes.
Instruction manual: 1 copy.

4.FUNCTIONALCONTROLS FrontPanel(seeFigure1)
Figure 1 - FrontPanelView
REFER-
ENCED.
IDENTIFICA-
TION
DESCRIPTION
® Power-onindicator
(LED)
© ONOFF
on-off switch
©
RANGE-CH 1/2
Channel 1 and2 atten-
uatorselector
®
INPUT 1
Channel 1 input
connector
©
CH2 SELECTOR
Individual-interlock
rangesettingselector
©
CH2 INPUT
Channel 2 input
connector
©
RANGE-CH 2
Channel 2 attenuator
selector
©
GND MODE Negative
input floating
switch
© Dual-pointermeter
® Meterzero-adjust
trimmer
•CH1(left),CH2(right}
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RearPanel(seeFigure2)
Figure2 - RearPanelView
REFERE-
NCE No.
IDENTSFSCA-
.TION
DESCRIPTION
® GND
Casing grounding
post
@
CH2 OUTPUT Channel2
monitor
output connector
® Line
voltage selector
andfuse holder
® Power
Gable connector
©
CH1 OUTP' Channel1
monitor
output connector
©
CONT. INPUT Remote
control
mounting hole
_7_

5.OPERATION
•Set-up
(1) Press the ON/OFF Pushswitch©in.ThePower-on
indicator®,a light-emitting diode,will light, indicat-
ingthatpowerhasbeenapplied.
(2) Plugthesignalcalbes into theCH1 INPUT andCH2
INPUT connectors® and© .
(3) CH2SELECTOR©, with theswitch released(JH),
takes singlemodeinwhich Ranges CH 1 andCH2 are
changedoverugingAttenuatorsCH1/2©andCH2®,
respectively.' . ' •
Withtheswitchpressed (-—-), the SELECTOR takes
interlockmodeinwhich both Ranges CH 1 andCH2
are simultane-ouslychangedoverusingAttenuator
CH 1/2®.Intheinterlookmode,AttenuatorCH2®
is nolongeroperabletoselecta Range.
Select eithersingleorinterlookmodeaccordingto
yourparticularmeasurement.
(4) Setthe RANGE-CH 1/2selector©andthe RANGE-
CH2 selector® to"300V/TomeasureanACvoltage
superimposedona DCvoltage,besuretosetthe
selectors tothepositionsbeforeconnectingthecables
topointstobemeasured.rerwise,theDCvoltage
causes a highsurge,whichcouldburnvoltmeter.
(5) GNDMODE®iseffected with theswitchreleased
(•)r inwhich both CH 1 andCH2areconnectedto
thegroundingterminalofthecasing,takingGND
state, with theswitchpressed(-•».),thegroundingof
CH 1 andCH2isfloatedto OPEN stateinwhich
youmovetheearth point tothesignalsourceside.
NormallyusethedeviceintheGNDstate.
(6) Connectthecablestopointstobemeasure.
(7) Turntheselectors® and© forproperranges until
each Meterpointerswitngsoverone third ofthe
fullscale.
(8) OUTPUTS CH2@ andCH 1 @ provide output
signals byamplifying input signalsinsuch
a degreeasthesignalamplitudeofa meterfull-
scale becomes1 Vrmsnomatterwhichrangeisset.
(9) Read theMeter.
-8-

(1) Voltage Scales
See Figures
There aretwoblackvoltage scales : a scale ®
graduated0 to10anda scale © 0 to3.Whenthe
RANGE selector® isat"1V,forexample,the
division10onthe scale ® indicates1V.Atthe"300
mV"position,thedivision3 onthe scale ® indicates
300 mV.Similarly,theother RANGE selectorpositions
showtheir full scale values.
(2) dB Scale
Ingeneral,thedBvaluesareexpressedindBVwhich
is a unit referencedbyOdBequalto1 V.Thedivision
10 atthe scale ® correspondsto0 dBonthedB scale,
whichisa voltage ratio scale. Sincethe RANGE
selectorhas12rangepositionsinstepsof10dB,the
voltage ratio of1 mVto300Vis110dBattenuation.
Assume a referencevoltagelevelonthe scale ® be
1V with the RANGE selectorat"1V,"a givenvoltage
can bereadaslowas-60dB(1mV)by turning the
selectordownward.Further,asthe scale A allows
readingto—20dB(0.1mV),youcancontinuously
measure thevoltage ratio as high as-80dB(0.1mV
to1V).Thereadof-80dBmeansa signal-to-noise
ratio ofaround10dB.Also,thedB scale allows
continuousmeasuringupto+50dB(1to300V)by
turning theselectorupward.
(3) dBm Scale
Ingeneral,voltmetershavea referenceleveldivision
ofOdBmequalto0.775V(1mWpower)inducedacross
a 800Oresistanceload.Therefore,thedBm scale is
available tomeasurea powerlevelreferencedto0
dBm, with theimpedanceofthegivenpowercircuit
being60012pureresistance.Wheremeasuredacross
specific resistanceloads,forexample,10kO,other
thanthe600Oload,thelevelsaresometimes
expressed indBs.
Figure 3 - Meter Scale Graduation
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•HowtoUseRemoteControl 6.APPLICATIONS
The RT-61option,a remarkablefeatureofthe VT-175,
providesa remotecontrolcapability.Tousetheoption,
removethe case andtherear-panelblindplate,install
theconnectorsuppliedwiththe RT-61, thenplugthe
RT-61 into the16-pinconnectoronthe print circuit
board. Fordetails,refertotheRT-61Instruction
Manual.
The basic useofyourvoltmeteristomeasuresinusoidal
wave voltagesasanACvoltmeter.Inaddition,it
providesa widevarietyofapplicationsasdescribed
below.
AmplifierGainMeasurement
Voltmeteriscapableofmeasuringanamplifiergain,
whichisa signalmagnificationfrom point A toB in
Figure 4 witha signalgeneratorconnectedtotheamplifier
input.IfthemeasuredsignallevelsatpointsA andB
are a andb dB,respectively,thenthegainis(b-a)dB.
Figure 4 - AmplifierGainMeasurement
Also themethodisapplicableformeasuringanopen
loop gainofeachamplifiercircuitwiththenegative-
feedback signal leaves applied.Further,themethodc
beusedformeasi"thefrequencyresponsesofgiv
SIGNAL
GENERATOR
-10-

circuitsbychangingthesignalgeneratorfrequency.
Voltmeteriscapableofdirectlyreadinga gainbetween
twopointsashavingtwoindependentvoltmeters.Asan
example, letuscalculatetheopen loop gain(from point
A toB)ofthenegative-feedbackamplifiershowninFigure
5. Assumethatthemeasuredlevelat point A be+1.5dB
onthe-60dBrangeofthechannel1 andthatof point B
-4dB onthe-MOdBrangeofthechannel2.Thegain from
point A toB isthen
( + 10dB-4dB)-(-60dB+1.5dB) = 64.5dB.
SIGNAL
GENERATOR
Figure 5 - NegativeFeedbackAmplifier
Gain Measurement:
VoltageCalculationsofSomeSpecialWaveforms
Anvoltmeterofabsolute-meanvalueindicationtype,
reads root-mean-squarevaluesofsinusoidalwaveinputs.
Also itdeflectsthepointersin proportion totheabsolute-
mean valueofa given input wave.
Ifthe form factor(=root-mean-squarevalue/absolute-
mean value)ofthe input waveandthecrestfactor( =
peak value/root-mean-squarevalue)areknown; thenthe
root-mean-squarevalueandpeakvaluecanbecalculated
as follows.
Assume theMeterreadx.
•Absolute-meanvalue=x = 0.9x
•Root-mean-squarevalue= (Absolute-meanvalue)x
(Form factor).
• Peak value=(Root-mean-squarevalue)x (Crest factor).
For rectangular waves, their form factorandcrestfactor
are unity(1).
2x/2
•Aboslute-meanva!ue=• • x = 0.9x
n
•Root-mean-squarevalue= 0.9x.
• Peak value=0.9x.
For sawtooth waves, their form factoris 2/<\/3 andthe
crest factor\/l>.
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(1) Frequencyresponse
Ways ToBetterDual-ChannelVoltmeterOperation
The two input channelsandtwometerpointersarranged
specifically inVoltmeteraremostusefulformeasuring
an electronicequipmenthavingtwosignalsources.
For example,Voltmeterisfarmoreconvenientfor
measuringstereo left and right channelcharacteristics
thanusingtwounitsunitsofusualsingle-channel
voltmeter.
STEREO AMP
CH2SELECTOR swichtopressed(interlockposition)
as moststereoamplifiersarenotdeviated
vertuallyinthe left and right channellevels.Setthe
GND MODEswitchto"GND."Ifthegivenstereo
amplifier output hasnoconnectorcommontothe left
and right channels,then turnt heswitchto "OPEN "and
connecttheGNDpostontherearpanelofvoltmeterto
thatofthestereoamplifier.'
-12-
2«/2
•Absolute-meanvalue=• x = 0.9x.
it
2«/2 2
•Root-mean-squarevalue=——-x •——x =
7u v 3
4x/2
——x = 1.04x
TTVO
4<s/2 ^ 4V2
• Peak value=-xv3x = -~x = 1.8x.
TV v 3 71
Rch
Lch
Figure 6 - StereoAmplitierFrequency
Response Measurement

(2)Crosstalkcharacteristic 7.MAINTENANCE
Crosstalk measurementisneededifthereisa large
differencebetweenthe left and right channel output
levels. CH2 SELECTOR Pushbuttontorelease(individual
position).Setthe RANGE-CH 1/2selectorand RANGE-
CH2 selectortoproperposi-tionsfor ease ofread.Set
theGNDMODEswitchfornoadverseeffectbyhumas
explainedinaboveExample (1), the"Frequencyresponse."
Replacing the fuse (seeFigure8)
REPLACING FUSE
Whena fusegoesout,thedeviceisnolongeroperable.
Ifgoneout,checkfora trouble cause, remedyit,remove
thecapofthefuseholderontherearpanelusinga
minusscrewdriverandtakeitoutandreplacethefuse
with a newone.
Whenreplacingfuse,besuretocheckthecapacityofa
newfusefora specifiedvalueasfollows:
AC 100V,120V: 0.5A
AC 220V,240V: 0.3A
CHANGEOVER OF VOLTAGE IN SWITCHING
REGULATOR
Remove thefuseholderontherearsideofthedevice
set, usinga minussurewdriver,adjustyourpreferred
voltageindication with • markand plug theholderin.
For changing100Vor120Vto220Vor240V,changethe
fuse of0.5Ato that of0.3A.
-13-
STEREO AMPj
SHORT
Figure 7 - StereoAmplifierCrosstalk
Measurement

8.ALIGNMENT
Figure 8 - Replacingthefuse
Voltmeterwaspresicelyalignedatthefactory.However
itcanbealigned through theadjustholeslocatedonthe
side with leavingishousedinthe casing, ifrequired.In
realignment,firstadjustthelinetotheratedvoltage,use
a preciselycalibratedmeasuringinstruments,andproceed
as follows.
PresetControlsonSidePanel(seeFigure9)
The following controls,placedontheMainPCboard,are
tobepresetontheright-handsidepanel.
IDENTIFICA-
TION
DESCRIPTION
TC101
First Attenuatorpresettrimmer
capacitor
VR101
First Attenuatorpresetvariable
resistor
VR102
MeterAmplifiergainpreset
variableresistor
1. Before turning the ON/OFF switch"ON,"adjustthe
Meterzero-adjust screws (rightforchannel1 and left
forchannel2)onthe front panel until thepointers
correctlyindica"01
-14-

12. AdjustTC101 until thepointerswingstothefull-
scale.
13. Repeat Steps 3 through10.
14. Forchannel2 alignment,similaryproceedwith
Steps 3 through13.
CH 1
CH2
-15-
Flgure 9 - Pres ControlsonSidePanel
2. SettheCH2 SELECTOR pushbattonto release
(individualposition).
3. Connecta voltmetercalibrator1 kHz(or400Hz)
output tothe INPUT connector®.
4. Setthe RANGE-CH 1/2selector®onyour VT-165 to
the"30mV"rangeandsetthevoltmetercalibrator
output voltageto30mV.
5. Adjust VR102 until thepointerswingstothefullscale.
6. Inturn,setthe RANGE-CH1/2 selector®tothe"10V
range andsetthevoltmetercalibrator output
voltageto10V.
7. AdjustVR101 until thepointerswingstothefull-
scale.
8. Disconnectthevoltmetercalibratorandconnecta
widebandsignalgeneratortotheCH 1 INPUT con-
nector®.
9 Setthesignalgeneratorfrequencyto 1 kHzandset
the RANGE-CH 1/2selector@ onvoltmetertothe
"IV range.
10. Adjustthesignalgenerator output level until the
pointerswingstothefullscale.
11. Changethesignalgeneratorfrequencyfrom1 kHzto
50 kHz.

9.CAUTIONSFORUSE
1. Yourvoltmeterwillworkjustwhenthe ON/OFF
switch ispressedin.Foraccuratemeasurements,
waitaroundfiveminutesforwarm-up.
2. Avoidplacingyourvoltmeterwheremagneticfield
and electricfieldaretoostrong.
3. Theinputsignalcableotherthansuppliedshouldbe
low-capacitance shieldedcable,orcoaxialcable.For
measurements athigherthanaudiofrequencies,
terminatetheinputconnectorswith500or600O,
resistor.
4. Thecontinuousmaximuminputvoltageallowablefor
yourvoltmeteris100V (DC+ACpeak) withthe
RANGE selectorat "-60dB" to "-10dB".
Full careshouldbeobservedinmeasuringhigh
voltages.
5. Becarefulofa linenoiseandsimilarsmallnoisesas
yourvoltmeterisa highlysensitivevoltmeter.
6. Donotleaveyour VT-175 atanyofhightemperature
and humidityplacesfora longperiodoftime.
7. Ashavingtwochannelindependentvoltmeter,your
voltmeterisinvolvedinselectionofgrounding point
onsomeequipmentudnermeasurement.SettheGND
MODE switchto "OPEN" andconnecttheGNDpost
ofyourvoltmetertoa point wherenoiseeffectis
minimized.
8. The ON/OFF switchofthisunitisdesignedtoact
onthesecondarysideofthepowertransformer.
The primarysideofthetransformerremainsenergized
even ifthe ON/OFF switchissettoOFF.Therefore,
iftheunitistobeunusedfora longtime,thepower
cordshouldbeunpluggedfromthereceptacleoutlet.
KENWOOD CORPORATION
17-5, 2-chome, Shibuya, Shibuya-ku, Tokyo150,Japan
-16™