Kenwood VT-176 User manual

2 CHANNELAC VOLTMETER
VT-176
VT-177
INSTRUCTIONMANUAL
KENWOODCORPORATION
©PRINTED INJ,,N
KENWOOD

CONTENTS
1. GENERAL3
2. FEATURES3
3. SPECIFICATIONS4
4. FUNCTIONALCONTROLS6
5. OPERATION••8
6. APPLICATIONS10
7. MAINTENANCE 13
8. ALIGNMENT 14
9. CAUTIONSFORUSE16
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1. GENERAL
2. FEATURES
KENWOOD'S Model VT-176, and VT-177 aredual-
channel electronicvoltmeter sets havingtwoindepen-
dentACvoltmetersina singlecabinet.Two-pointer
meterallows easy dualmeasurementsandinter-channel
comparisons.
VT-176, and VT-177 alsoarewideband,highsensitive
voltmeterforuseanywherevoltagemeasurementsare
made, with a remotecontrolunit.Theeasy-to-use
voltmeterprovidesfrequencyresponseaswideas5 Hz
to1 MHz,measurablerange from 0.3mVto100V,
and input impedanceof10MI2.Theoptionalremote
controlfeatureisconvenientformeasurementin
productionlines.
The Model VT-177 issameas VT-176 typeindesign
andspecifications.Rangeindicatorlampisprepared
onthetopsideofdualpointermeterandremote
controlofrangeswitchingisavailabetocheckthe
input range.
VT-177 ismeasuringrangecanberemotelycontrolled
by RT-62. (VT-176 : RT-61)
a. Twopowersourcecircuits,positiveandnegative,
are providedforverystableDCbiasandrecover
from anyoverloadina veryshorttime.
b.Small-sizedcompactconstructionis easy tocarry
andlarge-sizedtwo-pointermeteris easy toread.
c. Four-scaledialplateandredandblackpointers
allowquick,andaccuratevoltagereading.
d. Numderofadjustingtrimmersareminimized with
amplifiersthatarepreciselycalculatedinopen
loop gainsandarenegativefeedbacked through
metal-filmresistorsasaccurateas1%.
Amplifiercharacteristicsthereforearefree from
secular change.
e. Inputimpedanceisashighas10MOonallranges
anditsparallelcapacitance less than45pF
f.IndirectattenuatorswitchingbyrelayandFET
(field-effect-transistor)switchprovidehigher
reliability,signal-to-noiseratio,andinter-channel
crosstalk thanmostpreviousdirectmethodof
rotaryswitch.
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g. Remoterangeselectionispossibleina simpleway
that optional remote control unit " RT-62" canbe
connectedto VT-177, sinceisattachedremote
function.(VT-176: RT-61)
h.Twochannelrangesettingcanbemadeeither
individuallyortogether(ininterlockedmanner).
i.A ground modeselectormay float measuringcircuit
aboveground.
3. SPECIFICATIONS
[Meter Section]
Measurablevoltages: 0.3mV-100Vin12ranges:
0.3mV,1mV,3mV,10mV,
30mV,100mV,0.3V,1V,3V,
10V, 30Vand100V full scales.
dB : -90~+40dB(0dB=1V).
dBm: -90~+42dBm
(0dBm=1mW,60012).
Error : Within ±3%of full scale at
1kHz.
Frequency response: ±10%at5Hz~1MHz,
±5% at10Hz~500kHzand
±3% at20Hz~200kHzas
±2% at30Hz~100kHz
referencedto1kHzresponse.
Input impedance: 10MO±5%, with less than
45pF parallelcapacitance.
Durable input voltage: 500V(DC+ACpeak)
1V—100V range
100V (DC+ACpeak)
0.3mV~300mVrange
Stability: Within ±0.5%of full scale for
±10% linevoltagefluctuation.
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Residual voltage: Less than 30A/ V with
inputshortedon0.3mVrange.
Crosstalk, Individual: Less than-80dBwithother
inputterminatedwith 60012.
Interlock: Less than-50dBwithother
inputterminatedwith 60012.
[AmplifierSection]
Gain : Approx. 70dB.
Outputvoltage: 1Vrms(full scale) ±20%.
Outputimpedance: 600O±20%.
Distortion: Less than1%at full scale.
(Rated bysignal-to-noiseratio
in0.3mV,1mVand1V ranges.)
Signal-to-noise ratio: Over40dBat full scale.
(Over 30dBat0.3mVrange)
Frequency response: Within±3dBat5Hz~500kHz.
[Environmental]
Coefficient : ±0.08%/°C
Tempe rature
(withinspecification):10~40°C
(fulloperation):0~50°C
Relative humidity: Less than80%
[Power SupplySection]
Line voltage: 100,120,220VAC±10%,
216-250V AC,50/60Hz
Power consumption: Approx.7W
[Dimensions] 128(138) Wxl90(212)Hx238(268)Dmm.
Values in( ) include
protrusions.
[Netweight]Approx.3kg.
[Accessories]
Power cable: 1 pc.
Inputcable: BNCcord, 2pcs.
Replacement fuse: 0.3A 2pcs.
0.5A 2pcs.
Instructionmanual: 1 copy.

4.FUNCTIONALCONTROLS FrontPanel(seeFigure1)
Figure 1 - Fron*PanelView
-6™
REFER-
ENCENo.
IDENTIFICA-
TION
DESCRIPTION
® Power-onindicator
(LED)
-j-- ON/JBLOFF
Power on-off switch
®
RANGE-CH 1/2
Channel 1 and2 atten-
uatorrangeselector
©
CH1 INPUT
Channel 1 input
connector
©
CH2SELECTOR
Individual-interlock
rangesettingselector
©
CH2 INPUT
Channel 2 input
connector
©
RANGE-CH 2
Channel 2 attenuator
rangeselector
®
GND MODE
.OPEN/mGND
Negative input float
switch
© Dual-pointermeter
® Meterzero-adjust
trimmer
CHI(left), CH2(right)

Rear Pane! (seeFigure2)
REFERE-
NCE No.
IDENTIFICA-
TION
DESCRIPTION
© GND
Casing grounding
post
@
OUTPUT-2
Channel 2 monitor
output connector
@
Power cableconnector
@
Power cableconnector
© OUTPUT-1
Channel 1 monitor
output connector
©
CONT-INPUT
VT-176 type:
Remote control
mountinghole
VT-177 type: Connectc
for' remotecontrol
VT-177typeOnly
Figure 1 - Rear PanelView
©
Range indicatorlamp
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5BOPERATION
•Set-up
(1) Press the ON/OFF pushswitch© in.ThePower-
onindicator©,a light-emitting diode,will light, (5)
indicatingthatpowerhasbeen applied.
(2) Plugthesignalcalbes into theCH1andCH2
INPUT connectors® and©.
(3) CH2SELECTOR©, with theswitchreleased(m),
takes individualmodeinwhichrangesCH1and
CH2 arechangedoverusing RANGE selectorCH1/
2®andCH2®,respectively.
WiththeswitchpressedtheCH2 SELECTOR (6)
takes interlockmodeinwhich both rangesCH1U)
andCH2aresimultaneouslychangedoverusing
RANGE selectorCH1/2®.Intheinterlookmode,
RANGE selectorCH2© isnolongeroperableto(8)
select a range.
Select eitherindividualorinterlookmodeaccording
toyourparticularmeasurement.
(4) Setthe RANGE-CH1/2 selector© andthe RANGE-
CH2 selector© to100V.TomeasureanAC
voltagesuperimposedona DCvoltage,besureto
set theselectorstothepositionsbeforeconnecting
thecablestopointstobemeasured.Otherwise,
theDCvoltage causes a highsurge,whichcould
burnvoltmeter.
GND MODE© iseffected with theswitch
released {ML), inwhich both CH1andCH2are
connectedtothegroundingterminalofthecasing,
takingGNDstate, with theswitchpressed (-**-),
thegroundingofCH1andCH2isfloatedto
OPEN stateinwhichyoumovetheearth point
tothesignalsourceside.Normallyusethe
device intheGNDstate.
Connect thecablestopointstobemeasure.
Turn the RANGE selectors® and© forproper
ranges until eachMeterpointerswingsoverone
third ofthefullscale.
OUTPUTS CH2® andCH1@ provide output
signals byamplifying input signalsinsucha
degreeasthesignalamplitudeofa meterfull-
scale becomes1 Vrmsnomatterwhichrangeis
set. Outputinpedanceof60012.
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(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"0.3V"
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 of0.3mVto100Vis110dBattenuation.
Assume a referencevoltagelevelonthe scale @ be
1V with the RANGE selectorat"1V,"a givenvoltage
can bereadaslowas-70dB(0.3mV)by turning the
selectordownward.Further,asthe scale ® allows
readingto-20dB(0.03mV),youcancontinuously
measure thevoltage ratio as high as-90dB(0.03mV
to1V).Thereadof-90dBmea»~~a signal-to-noise
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ratio ofaround10dB.Also,thedB scale allows
continuousmeasuringupto+40dB(1to100V)by
turning theselectorupward.
(3) dBm Scale
Ingeneral,voltmetershavea referenceleveldivision
ofOdBmequalto0.775V(1mWpower)inducedacross
a 600Oresistanceload.Therefore,thedBm scale is
available tomeasurea powerlevelreferencedto0
dBm, with theimpedanceofthegivenpowercircuit
being600Opureresistance.Wheremeasuredacross
specific resistanceloads,forexample,10kO,other
thanthe600Oload,thelevelsaresometimes
expressed indBs.
Figure 3 - Meter Scale Graduation

•HowtoUseRemoteControlFunction 6.APPLICATIONS
This equipmentischaracterizedbyanoptionalremote
controlfunction.
For the VT-177, inserttheconnectorplugattheend
ofthecord from the RT-62 (option) into theconnector
onitsrearpanelforremotecontrolofrange
selection.
The VT-176allowsremotecontrolbyusingthe RT-61.
Remove theblankboard from therearpanelofthe
VT-176.
Connect theaccompanyingreceptacletothe RT-61.
Connect. theconnectorconnectedtothereceptacleto
theoneontheprintedcircuitboardofthe VT-176.
For details,refertotheinstructionmanualforRT-61
or RT-62.
The basicuseofyourvoltmeteristomeasuresinusoidal
wave voltagesasanACvoltmeter.Inaddition,it
providesa widevarietyofapplicationsasdescribed
below.
AmplifierGainMeasurement
Voltmeteriscapableofmeasuringanamplifiergain,
whichisa signalmagnification from point A toB in
Figure 4 with a signalgeneratorconnectedtotheamplifier
input. IfthemeasuredsignallevelsatpointsA andB
are a andb dB,respectively,thenthegain is(b-a) dB.
Figure 4 - AmplifierGainMeasurement
Also themethodisapplicableformeasuringanopen
loop gainofeachamplifiercircuit with thenegative-
feedbacksignal leaves applied.Further,themethodcan
beusedformear^ngthefrequencyresponsesofgiven
-10-
SIGNAL.
GENERATOR

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+10dBrangeofthechannel2.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 vaIue/root-mean-squarevalue)areknown; thenthe
root-mean-squarevalueandpeakvaluecanbecalculated
as follows.
Assume theMeterreadx.
2V?
•Absolute-meanvalue=x = 0.9x
71
•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).
•Aboslute-meanvalue=— x = 0.9x
71
•Root-mean-squarevalue=0.9x.
• Peak value=0.9x.
For sawtooth waves, their form factoris2/>/3andthe
crest factorv^3»
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(1) Frequencyresponse
STEREO AMP
Ways ToBetterDual-ChannelVoltmeterOperation
The two input channelsandtwometerpointersarranged
specifically inVoltmeteraremostusefulformeasuring
an electronicequipmenthavingtwosignalsources.
For example,Voltmeterisfarmoreconvenientfor
measuringstereo left and right channelcharacteristics
thanusingtwounitsunitsofusualsingle-channel
voltmeter.
CH2 SELECTOR switchtopressed(interlockposition)
as moststereoamplifiersarenotdeviatedvertuallyin
the left and right channellevels.
Set theGNDMODEswitchto"GND."Ifthegivenstereo
amplifier output hasnoconnectorcommontothe left
and right channels,then turn theswitchto" OPEN " and
connecttheGNDpostontherearpanelofvoltmeterto
thatofthestereoamplifier.
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2A/2
•Absolute-meanvalue=x = 0.9x.
71
2V2 2
•Root-mean-squarevalue= x —-—x=
71 <s/3
4A/2
—x = 1.04x
7U\/o
4V2 ^ AV2
• Peak value=-xv
/3x=x ^ 1.8x.
71 V 3 71
Figure 6 - StereoAmplitierFrequency
Response Measurement

(2) Crosstalkcharacteristic
7. MAINTENANCE
Crosstalk measurementisneededifthereisa large
differencebetweenthe left and right channel output
levels. CH2 SELECTOR pushbutton torelease(individual
position).Setthe RANGE-CH 1/2selectorand RANGE-
CH 2 selectortoproperpositionsfor ease ofread.Set
theGNDMODEswitchfornoadverseeffectbyhumas
explainedinaboveExample (1), the"Frequencyresponse."
Replacing thefuse(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.
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STEREO AMP
SHORT
Figure 7 - StereoAmplifierCrosstalk
.•.Measurement;

8.ALIGNMENT
F Say re8 - Replacingthefuse
Voltmeterwaspresicelyalignedatthefactory.However
itcanbealigned through theadjustholeslocatedonthe
side with leavingishousedinthecasing,ifrequired.In
realignment,firstadjustthelinetotheratedvoltage,use
a preciselycalibratedmeasuringinstruments,andproceed
as follows.
Preset ControlsonSidePanel(see Figure9)
The following controls,placedontheMainPCboard,
(X65-1210-02), aretobepresetontheright-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 (right forchannel1 and left
forchannel2)onthe front panel until thepointers
correctlyindie"01
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2. SettheCH2 SELECTOR pushbattonto release
(individualposition).
3. Connecta voltmetercalibrator1kHz(or400Hz)
output tothe INPUT connector©.
4. Setthe RANGE-CH 1/2selector©onyourvoltmeter
tothe"30mVrangeandsetthevoltmetercalibrator
output voltageto30mV[50mV].
5. Adjust VR102 until thepointerswingstothefullscale,
6. Inturn,setthe RANGE-CH1/2 selector®tothe "10 V
range andsetthevoltmetercalibrator output voltage
to10V.
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.
12. AdjustTC101 until thepointerswingstothe full
scale.
13, Repeat Steps 3 through10.
14 Forchannel2 alignment,similaryproceedwith
Steps 3 through13.
CH 1
CH2
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Figyre 9 - Pre" ControlsonSidePanel

9.CAUTIONSFORUSE
1. Yourvoltmeterwillworkjustwhenthe ON/OFF
switch ispressedin.Foraccuratemeasurements,
waitaroundfiveminutesforwarm-up.
2. Avoidplacingyourvoltmeterwheremagneticfield
and electricfieldaretoostrong.
3. Theinputsignalcableotherthansuppliedshouldbe
low-capacitance shieldedcable,orcoaxialcable.For
measurements athigherthanaudiofrequencies,
terminatetheinputconnectorswith5011or600O,
resistor.
4. Thecontinuousmaximuminputvoltageallowablefor
yourvoltmeteris100V (DC+ACpeak) withthe
RANGE selectorat "-70dB" to "-10dB\
Full careshouldbeobservedinmeasuringhigh
voltages.
5. Becarefulofa linenoiseandsimilarsmallnoisesas
yourvoltmeterisa highlysensitivevoltmeter.
6. Donotleaveyourvoltmeteratanyofhigh
temperatureandhumidityplacesfora longperiod
oftime.
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.
Aproductof
KENWOOD CORPORATION
17-5, 2-chome, Sh.buya, Shibuya-ku, Tokyo150,Japan
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