600B(Model60B).pdf part of Keithley 600B(Model60B) 600B(Model60B).pdf, Keithley 600B 600B(Model60B).pdf text manual preview

Text preview for : 600B(Model60B).pdf part of Keithley 600B(Model60B) Keithley 600B 600B(Model60B).pdf

Back to : 600B(Model60B).pdf | Home

CONTENTS
SPECIFICATIONS MODEL
600B

SPECIFICATIONS
7

CONNECTORS: Input: Teflon4nrulared UHF Type. Out-
puo: &wrier srrip.

BATTERIES: Four 2N6 (or 246. VS305. NEDA 1602,; one
RM.IW. 700waur lxmerv life
DIMENSIONS. WEIGHT: 10~1/4" high x S-112" wide x
6-l/2" deep: net weight. 7.114 poundo.
ACCESSORIES SUPPLIED: Mating input connector.

0872R
MODEL 6008 ELECTROMETER GENERAL DESCRIPTION

SECTION 1. GENERAL DESCRIPTION

uremenfs with a minimum of adjustment. Zero drift with
rime is less than 2 m" per day. zero offset due to
temperature change is less than 200 microwits per %.
after a ,O-minute warm-up. This offset, however. can
easily be compensated for with the front-panel zero
controls.

b. fast wnrm UD is an inherent characteristic ok
this Electrometer. It can be used well wiehin 30
minutes of a cold scare on the mose sensitive range
and nlmosc immediately on less sensitive ranges.

d. `the ,"O-hour life ai rhe batteries enables us-
age in long-term experiments xiehauc interruptions
the i-milliampere recorder output is used. Fur rilr-
ther convenience. battery condition is readily check-
ed on the panel meter.

1

FIGURE 1. Fro",. Panel cantro13.
GENERA` DESCRIPTION MODEL 6008

TABLE l-l.
Front Panel Canerols

Functional oescripeian Paraeraph
Sets the paramet~~r to be measured: 2-2
VOLTS, AMPERES, ?&S or COULOMBS.

MULTIPLIER Switch sees rix? full-scale meter sensitivity. 2-2
(SlOS) When used with AMPERES, OHMS or COULOMBS
the setting should be multiplied by ehe
RANGE setring.

METER Switch Controls parer co instrument. Also selects 2-2
(5106) the meter polarity and center scale.

ZERO Control 2-2
FINE (R133)

ZERO CHECK Switch 2-2
(5102)

FEEDBACK SWFtCh 2-2
(5103)

INPUT(.JlOZ) 2-2

TABLE 1-2.
Rear Panel Controls and Terminals

ZERO Control
COARSE (slo::

lV-lMA CAl Canerol Adjusement for recorder output. 2-7
(R179)

Barrier strip cunnecrion (J104)
Xl Unity gain output. 2-S
OHMS GUARD output low Con".?cflo*. 2-7
A Connect link to OHMS GUARD when using 1V o"QmF. 2-7
B Output high connection. 2-7
GND Chassis ground (input low). 2-7
MODEL 6000 ELECTROMETER OPEKATION

SWTION 2. OPERATION

2-1. INPUT CONNECTIONS. The Model 6008 INPUT Recep- used and a binding post adapeer may be used. however,
cacle is a Teflon-insulated UHF connector. A shield keep the leads short.
cap is provided. The ground posr, below ehe Recep-
tacle, is conneceed co chassis ground. f. When the Model 6008 is used on the most sensi-
tive current range with the FEEDBACK Switch =e FAST,
a. The accessories described in Sectton 5 are de- Borne insulators - 4uch as Teflon - may produce ran-
signed co increase rhe accuracy and convenience of dom signals which show up as erratic meter deflections.
input connecfions. Use them eo gain rhe maximum c=p- InsulaCion used in the Model 6008 is carefully seiec-
ability of rhe Model 6008. ted LO minimize these spurious signals.

g. If a well shielded chamber and a well made high
impedance transfer switch is available it is advantage-
ous CO connect ehe Model 6008 to the circuit only when
a reading is being made. In ~"me cases, rhe offsee
current can charge the external CASE circuifry. ilne
e::ample of this occurs when measuring a capacitor'5
leakage resistance by observing the decay of the ter-
minal voltage. If rhe leakage c~rre":~is less than
the offset current (Less thnn 2 :< LO- smoere, there
may be no decoy of the terminal voltage when ehe Elrc-
trometer is left connected across the copacicor's fer-
"i"8iS.

c. Use hixh resisronce. low-loss marerials - such XOTE
as `Teflon , recommended,, polpe~hylene or oolpsqrene
- for insulation. Insuinci"" leakage resiseance of Keep the shield cao on the INPUT aeceofocle
test fixtures and Leads shouid be several orders of when the ~leccromerer is nof in use.
magnitude higher than rhe internal resistance of the
SOUrCe. Excessive Leakage reduces the accuracy "i 3-2. PRELMINARY PROCEDURES.
reading irom nigh imoedance sources. coaxi cabies
used should be II io" noise type whici, employ a graph- 8. Check battery condition by holding the llETER
ite or ocher conducrive coacinq berrreen the dieiectric Swirch tn the S,,TTER,' CHECK position. Turn the ilul-
.Ind ehe surrounding shield or=id, An+2nol-Sorg Elec- ciplier Switch eo 10, 3 end I pOsitiOns =nd observe
tronics core., ?,icr"do~, I:::. , _.." "_...r.-.. ..LL5 aLIu one meter readings. The meter shoutd read one-haii
lz-lble co. make socisixcory types. of fllll `.-.!e or more in ench Nuleiplier switch ?"Si
tion. Table f. show the batferies checked by each
POSiCi"". Ii rhe reading for any baccery is below
NOTE one-i,alf full scale, replace the indicated baetery.

Clean, dry connecrions and cables are very im- TABLE 4.
porcaoc to maincain the value oi 311 insularion
materials. Even the besr insulation will be com- Nultiolier Switch Positions far Checking Conditions
promised by d"SC. cirrc. so,oer Tl"X, LilrnS of of SatCaries.
oil or water vapor. A good cleaning agent is
methyl =lcohoi. which disolves most common dirr SaeCeev Checked
wirhour chemic=lly acr=cking the insulation.
:,ir dry the cables or ~onnecei""s after uashing 10 BA103 di DA104
vith alcohoi or "se dry nirrogen if available. 3 SAlOl 6. k4102
Or, if available, Freon is an excellent cleaning 1 Ml05
agent.

d. When working with a high impedance source any b. Set the controls as follows:
change in shunt cnpaci~once of the input circuit will
cnuse disturbances in the reading. Nake the messuring ZERO CHECK nutcon LOCK
sefup as rigid as possible, nnd eie down connecting Range Swirch VOLTS
cables to prevent their ,!?A~iL%iii.. ;\ i~il.illY"Ub "LYLA- EUICI~L~~~ Switch 1
tion may appear 8~ the outpur as a sinusoidal signnl, FEEDBACK Switch NORMAL
=nd orher precaurions may Le necessary co isolace rhe, METER Switch POWEROFF.
insrrumenc and connecting cnble from the "ibra+zton.
.c. Turn the METER Switch to CENTER ZERO. Within
e. For low impedsnce meesuremencs - below LOS ten seconds, ehe meter needle should come co the ce"-
ohms or above LO-8 ampere - unshielded leads may be

0872R 3
OPERATION HODEL 6OOS ELECTROMETER

ter zero pasit.ion. 1f not. adjust the meter zero Range Switch to lo-' AMPERES range. Set the full-
with the front panel ZERO Control. Normally, there scale voltage range with the ~"lci~lier Switch. Op-
is no need co "se the COARSE ZERO Switch. eraeing procedures are the same as subparagraph b
above.

d. To measure ~~"rces more than 10 volts, "se the
Model 6102A 1O:l Divider Probe or the 6103.4 1OOO:l
Divider Probe. The Model 6102A extends the Model
6OOB's range to 100 volts; averall accuracy is *&%
d. After a few moments increase the voltage sensi- and Input resistance is 1010 ohms. The Node1 6103
tivity by advancing the Multiplier Switch to .3, .1, extends the Model 6008's range to 10 kilovolts' over-
etc. Continue zeroing with the ZERO Control. all accuracy is r6% and input resistance is 10 12 ohms,
Follow the same Operating procedures with the divid-
e. After long periods of starage or after an over- ers as in subparagraph b. The riall-scale voltage
load, the Model 6008 nay drift excessively. The in- range is the divider ratio times the MultipLier Switch
put cransistars are insensitive to mechantcal shock; setting.
however. B severe inpa overload may cause a zero
offset. This is corrected with the Zero Controls. 2-4. CURRENT MEASUREMENTS.
Drifting, though. can occur foe several hours.
a. The Model 6008 can measure currents three ways.
f. Although the offset current of the Electrom-
eter is much below that found in conventianal valt- 1. In the normal method - used on any range -
meters. it can be observed on the meter. The c"rrent the current is determined by measuring the voltage
charges ehe input caoacitance. and the Electrometer drop across a resistor shunring che'amplifier in-
appears to drift uhen the input is open. Use the put. This method is useful when lower noise is more
ZERO CHECK S"tr~n co discharge the charge build-up. important than faster response speeds or if some
Depressing the ZERO CHECK Button removes all signal damping is needed.
from the amolifier.
2. In the fasr method - far "se anly below the
10-Z ampere range - the shunt resistor is between.
the amplifier ""ep"t and input in the feedback loop.
This circuit largely neutralizes the effect af in-
pue capaciey and greatly increases the response
2-3. "OLTXE \E`\SUREEENTS. speed. Also, the inpue voltage drop is reduced to
less than One millivolt on any range.
a. The liodel 6~3011's high input impedance allaws
circuit measurements wi'chaut causing circuit loading. 3. For galvanometric current measurements, the
FOC law resistance in-circuit tests, the input resis- Model 6006 acts as B null indicator between a very
tance can be lowerr<, 1,, -v,..:,.: ,,:, `k-t&p ~,i~c,b:,e,,is. cccurate current source and the "nknawn current
SO"CCe.

b. Rise time varies primarily with the current
Make all voltage meas"rement~ with the FEED- range, the input capacity and the method used. With
BACK Switch & in the NORMAL posieion. ehe FEEDBACK Switch in ehe FAST oosition. the rise
time on ehe ?ast sensitive range is less than 2.5
b. High Impedance Eleasurements ( LO14 ohms, `0 seconds and on the lo-6 ampere range is less than 3
picofarads), Follow the instr"ctions of paragraph milliseconds. Given a choice. it is beteer ta place
2-2. Set the concrois as foliows: the Electrometer near to the current source than to
the data reading instrument. Transmitting the input
ZERO CHECK Sutton LOCK signal through long caaxial cables slightly decreases
Range Switch VOLTS the respanse speed and significantly increases noise
multiplier Switch LO due to the cable capacitance.
FEEDBACK Switch NORMAL
METER Switch CENTER ZERO c. Normal Methad (0.3 to lo-l3 ampere ranges)

connece the ""know" source co the INPUT Recepeacle 1. hollow rhe instructions of paragraph 2-2
and unlock the ZERO CHECK Buteon. Set the METER Set the controls as follows:
Switch to + or -, as necessary. Increase the sensi-
tivity with the Multiplier Switch. Recheck the zero ZERO CHECK Sutton LOCK
setting after increasing the sensitivity. Range Switch 10-l AMPERES
Multiplier Switch 1
Low Impedance Measurements. TO decrease the FEEDBACK Switch NORMAL
in;& resistance frnm 1OL4 nh"w +Pe *II,- nnn.y CWifCh METER Switch CENTER ZERO.
to one of the AMPERES ranges. The input resistance
is now the reciprocal of the current range. For in- Connece the unknown source to ehe INPUT Receptacle
stance, to obtain an inpur resistance of 10' ohms - and unlock the ZERO CHECK Sutton. Set the METER
which is normal for convantional "T"Ms - set the Switch to + or -, as necessary. Increase the sen-

4 0872B
MODEL 6000 ELECTROMETER OPERATION

FIGURE 4. Error Due to hmeter Reeisfmce. Current SOUPCSS may be considered a voltage (E) in series with 3
resistance (a). the current with the ammeter short circuited is I = E/R. !4ith the short circuit removed, the
effective ineue resisrance of the ammeter (Ri") is in series with the source resistance (R). The current in
the complete circuit is reduced and Imere= = E/(R i Ri"). If the effective srmneter input resistance is small
camparea to 2. :,,ter ,., I a"d the error introduced by circuir loading is negligible.

sensicivic:: k.ith the d.inge sw~cch and the Wiclpiier 2. The full-scale current range is the Range
Svitcn. 31, not set c.i:e !luitiplier jwiwh higher Switch setting times the ~lultiplier jwirch secti"g.
than 3 for Lange Switch settings LO-3 and above. When selecting ehe ?luleiplier Switch setting, re-
Check zero xieh the ZERO CHECK Sutton. member mail seer,ings permit lwer currene 'iour'ce
resistance. 2nd Larger settings improve insceumene
1. The rull-scale curre"c range is the Range zero seabiliev.
Switch setting times ~i:e !iulriplier Switch setting.
use the smallese >lulti=lier Switch setting possible
to obeain the best accuracy. The input resistor 3. !$ich the fast method, the input drop is re-
varies with the Range Switch setting. from 10 ohms duced and the response speed is increased at ieasc
at 10-l .u!PERES CO iUi! ohms for lo-11 AHPERES. 100 times. iiowever, follow rhese cautions:
The input voltage drop is the Meyer reading times
the Multiplier Switch serFin!. a\ The internal impedance ai the unknown cur-
rent should not be less the value oi
than .I ai
::mT. ihe Lardmck resistor wing "sea. Otherwise, ~iir
full feedbacK voltage cannot be developed at the
On the iaw current ranges, baiance out ihe input, and zero instability results. The feedback
oifset current vitb the Zero Controls or resistor value is the reciprocal of the AMPERES
suberacr ehe value from the reading. To range of the Range Switch.
find the amount of offset current, cap the
INPUT Receptacle and read the meter. b) The OHMS GUARD Terminal of the Barrier Strip
Cmnector is "a longer connected to case ground.
d. Fast Eleehod (ranges below 10-j ampere). Therefore. do "at use a grounded recorder. .is an
alternate. use the unity-gain output (paragraph
1. Fallow the inseructions of paragraph Z-1. 2-8).
see the conerois as follows:
C) Use,`with caution, the fast mechod to meas-
ZERO CHECK Sutton LOCK ure capacitor leakages. A very stable voltage
Range Switch lo-" AXPERES supply must be used. Connecting a capacitor fo
,Hultiplier Switch 1 the inpue changes the circuit to a differenciacor,
FEEDBACK Switch FAST resulting in extreme sensitivity to very small
METER Switch CENTER ZERO. voltage transients and a" increase in meter noise.

Connect the unknown source to the INPUT Receptacle e. Galvanometric Method.
and ""lock the ZE:.' ?LF.Y p:,?+-- =.- tL* `!--`"
Switch to t or -, as necessary. increase the se"- 1. Operate the Model 6008 as a picaammeter in
sitivity with chc I;ar,ge Sw,,ci~ a"- ~lir kurLIpiier the tast method. use an accurare reference current
Switch. DO not set the Range Switch to 1O-5 AHP- source s,,ch as the Keithley Model 261 to buck out
ERRS or higher. Check zero with the ZERO CHECK the unknown current source. connect as shown Fn
Button. Da nor short the input because this will Figure 5.
remove the feedback from the circuit.

"LlhSR 5
OPERATION MODEL 6008 ELECTROMETER

2. Set the METER Switch to CENTER ZERO and "se NOTE
the higher current rangas. Adjust the buckout cur-
rent to indicate null on the Model 6006. Increase Discharge any capacitor completely befare
the Electrometer sensitivity as needed. When the removing it from the circuit. Depressing
Node1 6008 is as close to null aa possible, the un- the ZERO CHECK Sutton shorts the input
known current is equal to the algebraic sum of the through a IO-megohm resistor, providing a
H.adel 261 setting and the Model 6008 current read- discharge path.
ine
b. Xormal constant Current Method (recommended f,ar
"se from 1 kilahm to 1011 ohms).

1. Set the controls as follows:

ZERO CHECK Butfo" LOCK
Range Switch 1011 OHMS
Multiplier Switch 1
FEEDBACK Switch NORMAL
XZTER Switch

Unlock the ZERO CHECK Button. Check zero only wit!:
the ZERO CHECK Button.

NOTE
Method. Cse an Llccur3te reference currene source CO
buck 0"~ ehe unknown c"rrenf s~"rce. The Eladel 6008, Do not open circuit the Electrameter 0" the
on its current ranges. ierves as a null detector. OHMS ranges; the input will develao "o f~
"se a UHF-tee ittlng at the Xodel 6008 input, con- 10 volts due to its consrant current charac-
nect the Elecz:Jmeter to the two s~"rces with CO.%- teristic. Keep the input shorted or the
ial cable. Select cable carefully for very low cur- ZERO CHECK Sutfon Locked.
rents (see parngrapil `-1).
2. The full-scale ohms range is the Hultiplier
Switch setting times the Range Switch setting. II s c
2-5. KLSISTANCE XEASUFGXZNTS. the smallest Range Switch se:cing possible to ob-
tain the best accuracy.
II. The Xodel 6000 can meas"re resistance by tw
merhads. 3. Before making a final :eading, manipulate ti:e
X~ltiplier and Range Switches. so the sample is
1. In the constant current methad, the Electrom- tested at a number of test potentials. The applier.
eter measures the voltage drop across the unknown test voltage is the percentage ai full scale that
_^__._...
sample as a knno;.r., _"...,-..... i..Zi'i;lCi L:u",r &`"ugiL the meter reads times the-X"iti?lier Switch seccin;.
it. The voltage drop is proportional to the resis-
tance Of the snmple. In this method the Model 6008 4. When the test current is applied, the high
can be used in one af ~0 different modes: normal terminal of the INPUT Receptacle is positive. The
or fast. test current is the reciprocal of the OHMS Range
setting.
a) The normal wj:r is trcommended for "se from
1 kilohm to 1011 ohms. NOTE

b) Above lOi ohms the fast method is prefer- Shield the inpue if the resistance sample
red. It results in faster respanse speed and exceeds lOa ohms.
also nullifies leakage across the Electrometer
input, since the pacential acr`oss the input ter- c. Fast Canstant C"rrent(C"ardedi Method (recom-
minal is small. mended for "se from 1011 to 1013 ohms).

2. In the preceding merhod, the voltage across 1. Follow the instructions of paragraph 2-2
the sample cannot be arbritrarily see. I" some set the controls as fallows:
cases. as in measuring capacieor leakage, this re-
sults in excessively long testing time. In the ZERO CHECK Button LOCK
voltmeter-anrmerer method the Moiri COGa is "sad as Range Switch 1012 OHMS
a picoammeter. The unknown resistance sample is Multiplier Switch 1
connected to an external known voltaee 80"rce and FEEDBACK Switch ?AST
ehe current through the sample is measured. Eith- METER Switch c
er the normal or fast method may be used. The re-
sistance is calculated from the readings. Connect the high impedance side of the resistance
sample to the INPUT Receptacle and the low impedance
side t" the OHMS GUARD Terminal. Unlock the ZERO
CHECK Button.
MODEL 6008 ELF.CTRO"ETER OPERATION

2. Read the resistance as in subparagraph b2 7. If the current is read by the face method,
above. the input drop Is so slight that it need not be in-
cluded in the calculation. If the capacity shunted
d. voltmeter-amecer Method (to 1016 ohms). acreee the sample is large, such as encountered in
capacitor leakage measurements. the faster methad
1. Turn the ZERO CHECK Switch to LOCK. Connect increases response speed and thFs cannectian is rec-
sample between INPUT receptacle and pawer supply. annended. Xate. however. Lhat power supply transi-
(see Figure 6). Put a switch in the high voltage ente will be magnified.
line to ground low impedance end af the sample when
it is disconnected from the potential. 2-6. CHARGE KSASUREMENTS

2. Set the FEEDBACK Switch to NORHAL. lJeilallp a. Follaw ehe instructiww of paragraph 2-2. see
this method is best, since inStabilities can arise the controls as follows:
for resistance samples less than 0.1 the value of
the feedback resistor. ZERO CHECK Button LOCK
Range Switch 10-7 CO"LOPBS
3. TO make e meaetiremenc. scare with switch S >lultFolier Switch .Ol
3s shown in Figure 6 and make sure the ZERO CHECK FEEDBACK sviech FAST
Sutton is set to LOCK. set switch S to apply e pa- XETER Switch CENTER ZERO
tential t~cross the samoie far a known period of
rime. ~!:en uniock rhe ZERO CHECK Gutcon and take
the reading. $9~ eke ! and increase sensitivity until .I reading is obtained.

U. I!: the ?oce"ri;il mp1ieu is less than 100
rimes the inmr droo. the resistance is equal to
rhe difference between the aoplied potential and
the input drop, 211 :I,, -~' `,., ,.a ..,.,. :

b. For recording with the Node1 6008, use the
Xeiehley ?lodel 370 Recorder for ease. economy, versa-
eility and performance. The Model 370 is a pen re-
corder with LO chart speeds and 1% linearity. Inter-
face pnblems ofren encountered between a measuring
FICUIW b. :!easuring ~es~srnnce oy tne VoLcmecer- inscrumenc and a recorder ore avoided using the Node1
,`mmecer Xethod. ;s:>:::;; rrc:: : I::.:::: "I:`--? ", ~>7n \`- preempiifier is needed. :;0 special wiring
is applied to the unknown resistance sample, I<,. The is required. when using the Node1 370 make sure the
Xodel 6008 measures the current through R,. from Recorder's sensitivity conrrol is set t0 maximum
wi,ich the resistance is calculated. Switch S connects (completely clackwise).
the low end of R, ea ground when na potential is
appiied.

oR72R 7
OPERATION MODEL 6008 ELECTROMETER

WARNING d. l-Milliampere Output: Connect l-milliampere
instruments to the OHMS GUARD Terminal and Terminal
The Model 6008 may be used with the FEEDBACK B on the Barrier Strip Connector and remove the shart-
Switch in FAST position with other instru- ing link. The output is approximately 1 milliampere
merits. However, make sure that the OHMS GUARD for full-scale meter deflection on any range. Fo=
terminal (output lo") is floating with respect exact output, adjust the meter on the .Ol volt range
to chassis ground. with the ZERO Control for full-scale deflection. The"
adjust the 1V - 1MA CAL Control until the recorder
c. I-Volt output. Place the shorting link between reads full scale. Check the recorder and meter zero
the OHMS GUARD Terminal and Terminal A. connect os- and repeat adjustment if necessary.
cilloecopes and pen recorder amplifiers to the OHMS
GUARD Terminal and Terminal S on the barrier strip
EO"*W.TtOC. Adjust the lv - LMA CAL Control for full-
scale recorder deflection to correspond with full- e. For servo rebalance recorders, use a divider of
scale meter deflection. Output is *l volt. Inter- approximately 1000 ohms total es show" in Figure 7.
nal resistance is 1000 ohms. I" this application the shorting link between OHMS
G'JARD and terminal `A" should be disconnected. The
value of the divider resistor should be one ohm for
every 1 m" OUtput.

f. When the FEEDBACK Switch is in the NORMAL pasi-
The METER Switch does not reverse the output polarity elan, the GUARD terminal of the Rarrier Strip Con-
Output polarity is opposite input polarity. nector is connected to the instrument case. mere-
fore. no difficulty will be experienced using oscil-
loscopes and recorders with the Node1 6008 set for
normal operation. In FAST position. however, Che
OHMS GUARD terminal is floating with respect to
chassis ground. Therefore the recordine instrumenr
must be capable of floating such es witi rhe Keithley
Model 370 Recorder,

2-S. UNITY GAIN OUTPUT. The unity-gain amplifier
can be used as a" impedance matching device to mini-
mize circuit loading errors

a. The unity-gain output is equal to the input
wi,thin 7.5 ppm when the load reeietance is 100 kilohms
or greater. By placing the Model 6008 between a IOn
FIGURE 7. Divider Clrc"its Acrosr Modri hnna "wv""' ohm source, For example, and J. 0.01% voltmeter with 1
for Driving 50 and LUU-millivolt Recorders. use 5% i-megohm input resisrance, overall accuracy better
resisrors in rhe dividers. The value of resistor R the" 0.025% ce" be achieved.
is one ohm far every 1mV of output.

I
FIGURE 8. bleanuring Pore"l~?l -6 !J?$ !.:---:I:.:.. c----L "I.;. ;.c;;i. Accuracy. The Model 6008 is used between
a high-resistance source. V,, and e 0.01% voltmeter to obtain high accuracy without causing circuit loading.
MODEL 6008 ELECTROMETER OPS~TION, CIRCUIT DESCRIPTION

1. Connece the voltmeter co ehe xl and OHMS far a precise zero adjustment.
GUARD Terminals as shown in Figure 8. The OHMS
GUARD Terminal is at ground with the FEEDBACK Switch b. When the FEEDBACK Switch is in FAST position,
in NORMAL. laxnwm output amplitude is 10 volts the unity-gain terminals permit more convenient con-
peak-to-peak? nections to oscilloscopes with a load resistance of
greeter than 100 kilohms without special precautions.
2. Adjust the Model 6008 zero Controls co obtain In this mode, the Xl Terminal is grounded and ehe
a zero-voltage reading on rhe exrernal voltmeter. OHMS GUARD Terminal delivers en output equal co the
Make cure the latter's sensitivity is high enough input signel.

SECTION 3. CIRCUIT DESCRIPTION

3-l. CESEUL. 2. The voleage drop across the amplifier is

a. The Keirhley Yodel bOOR is basically an eutreme-
ly stable and iinear dc ~volcmeter with a fuil-scale
sensitivity oi 10 millivoits and an input impedance of where & is the amplifier loop gain, greater t!lan
10L4 ohms shunted by 20 ?icoiarads. By using the frone 5 I 10' on all ranges.
p.nel controls, shunt m~istors and capacitors are se-
lected to make meesuremencs over a total ot 61 YOLC- c. `ihe complementary oufpot sK.ege, 4109 and 4110,
age, currene, fes~scance: .2nA *nl*lnmh -1"Z-E r?~~~,mt drives the amplifier ground at the same potential as
and resiseance dre measured using precision resistance ehe input signal. `Thus the input impedance is main-
stanaards, irom 10 ohm wirewound resistors to 1011 ohm tained for any value input voltage and the need for
glass sealed, deposited carbon resistors. coulombs input dividers is eliminated. `The amplifier *round
are measured using close tolerance polystyrene film is not chassis ground, hue it is connected directly
capacitor standards. to the unity gain output.

b. Batteries furnish the neceesarv amolifier oower. NOTE

3-2. "OLTHETER OPERATI(IN. Refer to Schematic Diagram 22BOSE for cir-
cuit designations.
a. The Model 6008 empioys matched insulated-gare,
field-effect transistors fallowed by a eransisror dif- 3-3. "OLTELETER CIRCUIT.
ferential amplifier with a high-voltage comvlementary
oueput stage. Figure 9 shows the block diagram for a. The amplifier input staSe is a pair of insulated
the voltmeter made of operation. gate, field-effect transiecars, Qlll and Qll5, in a
differential configuration. The gate of Qlll is re-
b. Voltmeter operation of the Model 6008 is as turned to amplifier common, the unity gain output.
fallows:
b. Depressing the ZERO CHECK Sutton, S102, places
1. The amplifier is always in a unity-gain, input the gate of the active insulated gate devices at zero
voltage co output current converter contigurarxm. p"LSLLLldl.
The internal circuitry is arranged such that a full
scale input voltage (ei) results in exactly a 1 mil- c. The input stage is fallowed by a transistor dif-
liampere outout curreoc through the divider string ferential amplifier. composed of QlOlA-QlOS. Q106 and
composed of Rm. R177, end the meter. Voltage gain Q107 make up the output gain stage, which is utilized
of the circuit is determined by the ratio of R177 to in e gain multiplier configureciao. This stage pro-
h. Output is taken across R177. vides the remainder of the high gain required by the

r%"L"D 9
CIRCUIT DESCRIZ'TION MODEL 6008 ELECTROMETER

UHF INPUT >i

amplifier. ALSO, this stage prevents fold-over and fed back to the amlock-up with ?ositi"e input overloads. OiOdR DlO1, resistor seleceed with the Range Switch. (See Figure
beeween base and emitter of QIOB, prevents fold-over 10). ~loaring ground is connected to the law imped-
and lack-up under negative inpue overloads. ance side of the input, and the output ground is
flOaCi"g. ~hls method increases the response speed
d. frequency compensation networks provide a I-W- by minimizing the effects of inp"t capacity; it also
trolled frequency characteristic to insuee stability reduces the input drop to less than 1 millivolt.
under all conditions ai caps:iLivr iuading on input
and o"ep"t while an any =ange. 3-5. OHMMETEROPERATION.

e. `rhe recorder o"cp"c is derived from the c"==ent a. No=mal Nerhod. I,, the normal method of r`esis-
flow from 4109 and QllO through the divider, Km, R177, eance meas"=emenEs (FEEDBACK Switch in NORMAL posi-
and the mete=. With the shorting link between the eionj, the Model 6008 uses a constant-c"==ent, voltage.
OHMS GIRD Tenninal and Terminal h (paragraph 2-7~) drop ci=c"It. Refer to Figure 11. Rx is the unknown
21 vale fo= full scale deflection is obtained a= the resistor. A voltage source, E, applies a potenfial
mtpuf by ~1.1 milliamperes flawing through the di- acroes Rx. The source is obtained f=om the batteries
vider. through the resisrar divider nerwork, R128 through
R130. E varies depending upon ehe OHMS range used.
The voltage source is connected beeween floating
ground and the input gaee of Q115 through R,, the
3-4. AMMETER OPERATION. range resistor. !+ is one of the resistors, R136
through R146. I is equal to E/R., =egardless of the
a. Normal Method. In the normal method of c"==enC value of R,, as long as the voltage drop across Rx
measurements (FEEDBACK Switch in NORMAL position), does not exceed the Multiplier switch setting. This
one of the Range Switch resistors, R136 through R146, circuit provides a t="e source regardless of the in-
shunts the input. (See Figure 10). The Model 6008 put. The Model 6008 can then meas"=e the voltage drop
then meas"=es the voltage drop acrbss the resistor. across R~ and indicate ehe =esisfance value on its
The meter is calibraird io `ea..i i&e ~"arni in ampexs ;zlib=n:ed mete=.
for the appropriate range.
L -.*-"4
_____- Method. 1x1 the guarded method af =esis-
b. Fast Method. In the fast method of c"==ent mea- tance meas"=emen=s (FEEDSACK Switch.i" FAST position
S"=aments (FEEDBACK Switch in FAST position), the MO- and the sample resistsnce connected between the INPUT
de1 6008 functions 88 an attnwEe= with negative feed- ~erroinal, 5102, and the GUARD Terminal), feedback is
back. The differenelal amplifier output is divided applied through the sample. Refer tO Fig"=e 11. The
by the Multiplter Switch resistors, R168 to R174, and circuit is similar to the normal method, except far

10 0872rl
MODEL 6008 CIRCUIT DESCRIPTION

the feedback. This reduces the slowing effect of the 3-6. COULOMBMETER OPERATION. The Model 6008 circuit
instrument's input capacity. Leakage error is also far measuring charge is similar to that used for an
reduced since the potential ac.ro~~ the INPW Terminal ameter with the fast method. A negative feedback is
is small. In this mode. floating ground is connected applied around a shunt capacitor, cl10 to ~113, se-
Co the low impedance side of the input and the output lected with the Range Switch. The shunt capacitor re-
ground is floating. The GUARD Terminal is at output places Rs in Figure 10. The stored charge is propor-
ground potential. tional to the voltage across the capacitor, which is
measured by the Model 6008 voltmeter circuits.

FIGURE 10. Slack Diagram of Fast Mode Picoamecer.
SERVICING MODEL 6008 ELECTROMETER

SECTION 4. SERVICING

4-1. GENEPAL. section 4 contains the maintenance and for repairing troubles which might occur in the Model
troubleshooting procedures for the Model 6008 Electrom- 6008. Use the procedures outlined and use only spec-
eter. Follow these procedures as closely es possible ified replacement perts. Table 5 lists equipment rec-
to maintain the performance of the instrument. ommended for troubleshooting. If the trouble cannot
be readily located or repaired, coneect Keithley In-
4-2. SERVICING SCHEDULE. Periodically check the con- strumenes, Inc., or its representatives.
dition of the batteries, using the convenie::t battery
check as described in paragraph 2-i. Exceot Ear bae- b. Table 6 contains the more common troubles which
tery replacement, the Model 6008 requires no periodic might occur. If the repairs indicated in the table
maintenance beyond the normal care required of high- do not clear up the trouble, find the difficulty
quality electronic equipment. The value of the high- through a circuit-by-circuit check such as given in
megohm resistors, Rl44, R145 and R146 should be checked paragraph 4-5. Refer to the circuit description in
approximately every 6 months for specified accuracy. Section 3 to find the more critical components and to
determine their function in the circuit. The complete
4-3. PARTS KKPUCEMENT. circuit schematic, 22808E, is in Section 7.

a. The Keplaceable Parts List in Section 7 de-
scribes the elecrricoi comoonents of the Elecrrometer.
Replace components only 8s necessary. Use only reli- a. If the instrument will not operate, check the
able replacements which ma-r rh- 4ycifications. condition of the batteries (paragraph 2-2). Then make
sure the shorting link is connected between the UIIMS
b. The XOS FET input c-i-=i?rnr=, Qll5 and `>lll, GUARD and A Terminals on the Barrier Strip Connector.
are specislly selected nod matched; order only as a
plug-in unit, part number 23735 , from Keithley In-
strnmenes, 1