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.
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.
fast wnrm UD is an inherent characteristic ok
b.
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.
‘the ,“O-hour life ai rhe batteries enables us-
d.
age in long-term experiments xiehauc interruptions
<or replacement. Baeeery life is maintained even wiwn
the i-milliampere recorder output is used. Fur rilrther convenience. battery condition is readily check-
ed on the panel meter.
zero offset due to
FIGURE 1.
1
Fro”,. Panel cantro13.
GENERA‘ DESCRIPTION
MODEL 6008
TABLE l-l.
Front Panel Canerols
MULTIPLIER Switch
(SlOS)
METER Switch
(5106)
ZERO Control
FINE (R133)
ZERO CHECK Switch
(5102)
FEEDBACK SWFtCh
(5103)
INPUT(.JlOZ)
Functional oescripeian
Sets the paramet~~r to be measured:
VOLTS, AMPERES,
?&S or COULOMBS.
sees rix? full-scale meter sensitivity.
When used with AMPERES, OHMS or COULOMBS
the setting should be multiplied by ehe
RANGE setring.
Controls parer co instrument. Also selects
the meter polarity and center scale.
TABLE 1-2.
Rear Panel Controls and Terminals
Paraeraph
2-2
2-2
2-2
2-2
2-2
2-2
2-2
ZERO Control
COARSE (slo::
lV-lMA CAl Canerol
Adjusement for recorder output.
(R179)
Barrier strip cunnecrion (J104)
Xl
OHMS GUARD
Unity gain output.
output low Con".?cflo*.
A Connect link to OHMS GUARD when using 1V o"QmF.
B
Output high connection.
GND Chassis ground (input low).
2-7
2-S
2-7
2-7
2-7
2-7
MODEL 6000 ELECTROMETER
OPEKATION
SWTION 2.
2-1.
INPUT CONNECTIONS. The Model 6008 INPUT Recep-
cacle is a Teflon-insulated UHF connector. A shield
cap is provided. The ground posr, below ehe Recep-
tacle, is conneceed co chassis ground.
a. The accessories described in Sectton 5 are designed co increase rhe accuracy and convenience of
input connecfions. Use them eo gain rhe maximum c=pability of rhe Model 6008.
c. Use hixh resisronce. low-loss marerials - such
as ‘Teflon , recommended,, polpe~hylene or oolpsqrene
- for insulation. Insuinci”” leakage resiseance of
test fixtures and Leads shouid be several orders of
magnitude higher than rhe internal resistance of the
SOUrCe.
reading irom nigh imoedance sources.
used should be II io” noise type whici, employ a graph-
ite or ocher conducrive coacinq berrreen the dieiectric
used and a binding post adapeer may be used. however,
keep the leads short.
f. When the Model 6008 is used on the most sensi-
tive current range with the FEEDBACK Switch =e FAST,
Borne insulators
dom signals which show up as erratic meter deflections.
InsulaCion used in the Model 6008 is carefully seiec-
ted LO minimize these spurious signals.
g. If a well shielded chamber and a well made high
impedance transfer switch is
ous CO connect ehe Model 6008 to the circuit only when
a reading is being made.
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-
may be no decoy of the terminal voltage when ehe Elrc-
trometer is left connected across the copacicor’s fer-
“i”8iS.
Keep the shield cao on the INPUT aeceofocle
when the ~leccromerer is nof in use.
3-2.
PRELMINARY PROCEDURES.
8. Check battery condition by holding the llETER
Swirch tn the S,,TTER,’ CHECK position. Turn the ilulciplier Switch eo 10, 3 end I pOsitiOns =nd observe
one meter readings. The meter shoutd read one-haii
of fllll ‘.-.!e or more in ench Nuleiplier switch ?“Si
tion.
Table f.
POSiCi”“. Ii rhe reading for any baccery is below
one-i,alf full scale, replace the indicated baetery.
- 4uch as Teflon - may produce ran-
available
it
is advantage-
In ~“me cases, rhe offsee
smoere, there
XOTE
show the batferies checked by each
Clean, dry connecrions and cables are very imporcaoc to maincain the value oi 311 insularion
materials.
Even the besr insulation will be com-
promised by d”SC. cirrc. so,oer Tl”X, LilrnS of
oil or water vapor. A good cleaning agent is
methyl =lcohoi. which disolves most common dirr
wirhour chemic=lly acr=cking the insulation.
:,ir dry the cables or ~onnecei”“s after uashing
vith alcohoi or “se dry nirrogen if available.
Or, if available, Freon is an excellent cleaning
agent.
d. When working with a high impedance source any
change in shunt cnpaci~once of the input circuit will
cnuse disturbances in the reading.
Nake the messuring
sefup as rigid as possible, nnd eie down connecting
cables to prevent their ,!?A~iL%iii.. ;\ i~il.illY”Ub “LYLA-
tion may appear 8~ the outpur as a sinusoidal signnl,
=nd orher precaurions may Le necessary co isolace rhe,
insrrumenc and connecting cnble from the “ibra+zton.
e. For low impedsnce meesuremencs - below LOS
ohms or above LO-8 ampere - unshielded leads may be
0872R
TABLE 4.
Nultiolier Switch Positions far Checking Conditions
of SatCaries.
SaeCeev Checked
10 BA103 di DA104
3
1 Ml05
SAlOl 6. k4102
b. Set the controls as follows:
ZERO CHECK nutcon
Range Swirch
EUICI~L~~~ Switch
FEEDBACK Switch
METER Switch
Turn the METER Switch to CENTER ZERO. Within
.c.
LOCK
VOLTS
1
NORMAL
POWER OFF.
ten seconds, ehe meter needle should come co the ce”-
3
OPERATION
HODEL 6OOS ELECTROMETER
ter zero pasit.ion.
1f not. adjust the meter zero
with the front panel ZERO Control. Normally, there
is no need co “se the COARSE ZERO Switch.
d. After a
few moments increase
the voltage sensitivity by advancing the Multiplier Switch to .3, .1,
etc.
Continue zeroing with the ZERO Control.
e. After long periods of starage or after an over-
load, the Model 6008 nay drift excessively. The in-
put cransistars are insensitive to mechantcal shock;
however. B severe inpa overload may cause a zero
offset. This is corrected with the Zero Controls.
Drifting, though. can occur foe several hours.
f.
Although the offset current of the Electrom-
eter is much below that found in conventianal valt-
meters. it can be observed on the meter.
The c”rrent
charges ehe input caoacitance. and the Electrometer
appears to drift uhen the input is open.
Use the
ZERO CHECK S”tr~n co discharge the charge build-up.
Depressing the ZERO CHECK Button removes all signal
from the amolifier.
2-3.
“OLTXE \E‘\SUREEENTS.
a. The liodel 6~3011’s high input impedance allaws
circuit measurements wi’chaut causing circuit loading.
FOC law resistance in-circuit tests, the input resis-
tance can be lowerr<, 1,, -v,..:,.: ,,:, ‘k-t&p ~,i~c,b:,e,,is.
Range Switch to lo-’ AMPERES range.
Set the full-
scale voltage range with the ~“lci~lier Switch. Operaeing 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.
6OOB’s
range to 100 volts; averall accuracy is *&%
and Input resistance is 1010 ohms.
extends the Model 6008’s range to 10 kilovolts’ overall accuracy is r6% and input resistance is 10
The Model 6102A extends the Model
The Node1 6103
12
ohms,
Follow the same Operating procedures with the dividers as in subparagraph b. The riall-scale voltage
range is the divider ratio times the MultipLier Switch
setting.
2-4.
CURRENT MEASUREMENTS.
a. The Model 6008 can measure currents three ways.
1. In the normal method - used on any range the current is determined by measuring the voltage
drop across a resistor shunring che’amplifier input. This method is useful when lower noise is more
important than faster response speeds or if some
damping is needed.
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
speed. Also, the inpue voltage drop is reduced to
less than One millivolt on any range.
3. For galvanometric current measurements, the
Model 6006 acts as B null indicator between a very
cccurate current source and the “nknawn current
SO”CCe.
Make all voltage meas”rement~ with the FEED-
BACK Switch & in the NORMAL posieion.
b. High Impedance Eleasurements ( LO14 ohms, ‘0
picofarads), Follow the instr”ctions of paragraph
Set the concrois as foliows:
2-2.
ZERO CHECK Sutton
LOCK
Range Switch VOLTS
multiplier Switch
FEEDBACK Switch
METER Switch
connece the ““know” source co the INPUT Recepeacle
LO
NORMAL
CENTER ZERO
and unlock the ZERO CHECK Buteon. Set the METER
Switch to + or -, as necessary. Increase the sensitivity with the Multiplier Switch. Recheck the zero
setting after increasing the sensitivity.
Low Impedance Measurements. TO decrease the
in;& resistance frnm
nh”w +Pe *II,- nnn.y CWifCh
1OL4
to one of the AMPERES ranges. The input resistance
is now the reciprocal of the current range. For instance, to obtain an inpur resistance of 10’ ohms -
which is normal for convantional “T”Ms - set the
4
b. Rise time varies primarily with the current
range, the input capacity and the method used. With
ehe FEEDBACK Switch in ehe FAST oosition. the rise
time on ehe ?ast sensitive range is less than 2.5
seconds and on the lo-6 ampere range is less than 3
milliseconds. Given a choice. it is beteer ta place
the Electrometer near to the current source than to
the data reading instrument. Transmitting the input
signal through long caaxial cables slightly decreases
the respanse speed and significantly increases noise
due to the cable capacitance.
c. Normal Methad (0.3 to lo-l3 ampere ranges)
1. hollow rhe instructions
of
paragraph 2-2
Set the controls as follows:
ZERO CHECK Sutton
Range Switch
Multiplier Switch
FEEDBACK Switch
METER Switch
LOCK
10-l AMPERES
1
NORMAL
CENTER ZERO.
Connece the unknown source to ehe INPUT Receptacle
and unlock the ZERO CHECK Sutton. Set the METER
Switch to + or -, as necessary. Increase the sen-
0872B
MODEL 6000 ELECTROMETER OPERATION
FIGURE 4.
Error Due to hmeter Reeisfmce.
resistance (a).
the current with the ammeter short circuited is I = E/R.
Current SOUPCSS may be considered a voltage (E) in series with 3
!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
Svitcn.
31, not set c.i:e !luitiplier jwiwh higher
than 3 for Lange Switch settings LO-3 and above.
Check zero xieh the ZERO CHECK Sutton.
2.
The full-scale current range is the Range
Switch setting times the ~lultiplier jwirch secti”g.
When selecting ehe ?luleiplier Switch setting, re-
member mail seer,ings permit lwer currene 'iour'ce
Switch setting times ~i:e !iulriplier Switch setting.
use the smallese >lulti=lier Switch setting possible
to obeain the best accuracy.
The input resistor
varies with the Range Switch setting. from 10 ohms
at 10-l .u!PERES CO iUi! ohms for lo-11 AHPERES.
3. !$ich the fast method, the input drop is re-
duced and the response speed is
100 times. iiowever,
follow rhese cautions:
increased
at ieasc
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 than .I ai the value oi
::mT.
ihe Lardmck resistor wing "sea.
Otherwise,
full feedbacK voltage cannot be developed at the
On the iaw current ranges, baiance out ihe
oifset current vitb the Zero Controls or
suberacr ehe value from the reading. To
input, and zero instability results.
resistor value is the reciprocal of the AMPERES
range of the Range Switch.
The feedback
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
Fallow the inseructions of paragraph Z-1.
1.
2-8).
see the conerois as follows:
the fast mechod to meas-
A very stable voltage
Connecting a capacitor fo
ZERO CHECK Sutton
Range Switch
,Hultiplier Switch
FEEDBACK Switch
METER Switch
LOCK
lo-” AXPERES
1
FAST
CENTER ZERO.
Use,‘with caution,
C)
ure capacitor leakages.
supply must
the inpue
be used.
changes the circuit to a differenciacor,
resulting in extreme sensitivity to very small
voltage transients and a” increase in meter noise.
~iir
Connect the unknown source to the
INPUT
Receptacle
and ““lock the ZE:.’ ?LF.Y p:,?+-- =.- tL* ‘!--‘”
Switch to t or -, as necessary.
increase the se”sitivity with chc I;ar,ge Sw,,ci~ a”- ~lir kurLIpiier
Switch.
ERRS or higher.
Button.
remove the
DO not set the Range Switch to 1O-5 AHP-
Check zero with the ZERO
Da nor short the input because this will
feedback
from the circuit.
“LlhSR
CHECK
e.
Galvanometric Method.
1.
Operate the Model 6008 as a picaammeter in
the tast method.
use an accurare reference current
source s,,ch as the Keithley Model 261 to buck out
the unknown current source.
connect as shown Fn
Figure 5.
5
OPERATION
MODEL 6008 ELECTROMETER
2. Set the METER Switch to CENTER ZERO and “se
the higher current rangas. Adjust the buckout current to indicate null on the Model 6006.
Increase
the Electrometer sensitivity as needed. When the
Node1 6008 is as close to null aa possible, the unknown current is equal to the algebraic sum of the
H.adel 261 setting and the Model 6008 current read-
ine
Method. Cse an Llccur3te reference currene source CO
buck 0”~ ehe unknown c”rrenf s~“rce. The Eladel 6008,
on its current ranges. ierves as a null detector.
“se a UHF-tee ittlng at the Xodel 6008 input,
connect the Elecz:Jmeter to the two s~“rces with CO.%ial cable. Select cable carefully for very low currents (see parngrapil ‘-1).
2-5.
KLSISTANCE XEASUFGXZNTS.
The Xodel 6000 can meas”re resistance by tw
II.
merhads.
1. In the constant current methad, the Electrometer measures the voltage drop across the unknown
sample as a knno;.r.,
The voltage drop is proportional to the resis-
it.
tance Of the snmple.
_^__._...
_“...,-..... i..Zi’i;lCi L:u”,r &‘“ugiL
In this method the Model 6008
can be used in one af ~0 different modes: normal
or fast.
a) The normal wj:r is trcommended for “se from
1 kilohm to 1011 ohms.
NOTE
Discharge any capacitor completely befare
removing it from the circuit.
Depressing
the ZERO CHECK Sutton shorts the input
through a IO-megohm resistor, providing a
discharge path.
b. Xormal constant Current Method (recommended f,ar
“se from 1 kilahm to 1011 ohms).
1. Set the controls as follows:
ZERO CHECK Butfo”
Range Switch
Multiplier Switch
FEEDBACK Switch
LOCK
1011 OHMS
1
NORMAL
XZTER Switch
Unlock the ZERO CHECK Button.
Check zero only wit!:
the ZERO CHECK Button.
NOTE
Do not open circuit the Electrameter 0” the
OHMS ranges; the input will develao “o f~
10 volts due to its consrant current characteristic. Keep the input shorted or the
ZERO CHECK Sutfon Locked.
2. The full-scale ohms range is the Hultiplier
Switch setting times the Range Switch setting.
the smallest Range Switch se:cing possible to obtain the best accuracy.
3. Before making a final :eading, manipulate ti:e
X~ltiplier and Range Switches. so the sample is
tested at a number of test potentials.
The applier.
test voltage is the percentage ai full scale that
the meter reads times the-X”iti?lier Switch seccin;.
4. When the test current is applied, the high
terminal of the INPUT Receptacle is positive.
test current is the reciprocal of the OHMS Range
setting.
NOTE
II s c
The
b) Above lOi
ohms the fast method is prefer-
red. It results in faster respanse speed and
also nullifies leakage across the Electrometer
input, since the pacential acr‘oss the input ter-
minal is small.
In the preceding merhod, the voltage across
2.
the sample cannot be arbritrarily see. I” some
cases. as in measuring capacieor leakage, this results in excessively long testing time.
In the
voltmeter-anrmerer method the Moiri COGa is “sad as
a picoammeter. The unknown resistance sample is
connected to an external known voltaee 80”rce and
ehe current through the sample is measured.
Either the normal or fast method may be used. The resistance is calculated from the readings.
Shield the inpue if the resistance sample
exceeds lOa ohms.
c. Fast Canstant C”rrent(C”ardedi Method (recom-
mended for “se from 1011 to 1013 ohms).
1. Follow the instructions of paragraph 2-2
set the controls as fallows:
ZERO CHECK Button LOCK
Range Switch
Multiplier Switch
1012 OHMS
1
FEEDBACK Switch ?AST
METER Switch
c
Connect the high impedance side of the resistance
sample to the INPUT Receptacle and the low impedance
side t” the OHMS GUARD Terminal.
CHECK
Button.
Unlock the ZERO
MODEL 6008 ELF.CTRO”ETER
OPERATION
2.
Read the resistance as in subparagraph b2
above.
d. voltmeter-amecer Method (to 1016 ohms).
1.
Turn
the ZERO CHECK Switch to LOCK. Connect
sample between INPUT receptacle and pawer supply.
(see Figure 6). Put a switch in the high voltage
line to ground low impedance end af the sample when
it is disconnected from the potential.
Set the FEEDBACK Switch to NORHAL.
2.
lJeilallp
this method is best, since inStabilities can arise
for resistance samples less than 0.1 the value of
the feedback resistor.
3. TO make e meaetiremenc. scare with switch S
3s shown in Figure 6 and make sure the ZERO CHECK
Sutton is set to LOCK. set switch S to apply e patential t~cross the samoie far a known period of
rime. ~!:en uniock rhe ZERO CHECK Gutcon and take
the reading.
$9~ eke !<a,ge Switch ea 10-l A:NPE?.ES
and increase sensitivity until .I reading is obtained.
If the current is read by the face method,
7.
the input drop Is so slight that it need not be in-
cluded in the calculation.
If the capacity shunted
acreee the sample is large, such as encountered in
capacitor leakage measurements. the faster methad
increases response speed and thFs cannectian is recannended. Xate. however. Lhat power supply transiente will be magnified.
2-6. CHARGE KSASUREMENTS
a. Follaw ehe instructiww of paragraph 2-2. see
the controls as follows:
ZERO CHECK Button
Range Switch
>lultFolier Switch
FEEDBACK sviech
XETER Switch
LOCK
10-7 CO”LOPBS
.Ol
FAST
CENTER ZERO
I!: the ?oce”ri;il mp1ieu is less than 100
U.
rimes the inmr droo. the resistance is equal to
rhe difference between the aoplied potential and
the input drop, 211 :I,, -~’ ‘,., ,.a ..,.,. :
FICUIW b.
,‘mmecer Xethod.
:!easuring ~es~srnnce oy tne VoLcmecer-
;s:>:::;; rrc:: : I::.:::: “I:‘--? “,
is applied to the unknown resistance sample, I<,. The
Xodel 6008
wi,ich the resistance is calculated.
measures
the current through R,. from
Switch S connects
the low end of R, ea ground when na potential is
appiied.
For recording with the Node1 6008, use the
b.
Xeiehley ?lodel 370 Recorder for ease. economy, versa-
eility and performance. The Model 370 is a pen recorder with LO chart speeds and 1% linearity. Inter-
face pnblems ofren encountered between a measuring
inscrumenc and a recorder ore avoided using the Node1
~> 7n
\‘- preempiifier is needed.
:;0 special wiring
is required. when using the Node1 370 make sure the
Recorder’s sensitivity conrrol is set t0 maximum
(completely clackwise).
oR72R
7
OPERATION
MODEL 6008 ELECTROMETER
WARNING
The Model 6008 may be used with the FEEDBACK
Switch in FAST position with other instru-
merits.
terminal (output lo”) is floating with respect
to chassis ground.
c.
the OHMS GUARD Terminal and Terminal A.
cilloecopes and pen recorder amplifiers to the OHMS
GUARD
EO”*W.TtOC.
scale recorder deflection to correspond with fullscale meter deflection. Output is *l volt.
nal resistance is 1000 ohms.
The METER Switch does not reverse the output polarity
Output polarity is opposite input polarity.
I-Volt
Terminal and Terminal S on the barrier strip
However, make sure that the OHMS GUARD
output.
Adjust the lv - LMA CAL Control for full-
Place the shorting link between
connect os-
Inter-
d. l-Milliampere Output: Connect l-milliampere
instruments to the OHMS GUARD Terminal and Terminal
B on the Barrier Strip Connector and remove the sharting link. The output is approximately 1 milliampere
for full-scale meter deflection on any range.
exact output, adjust the meter on the .Ol volt range
with the ZERO Control for full-scale deflection.
adjust the 1V - 1MA CAL Control until the recorder
reads full scale.
and repeat adjustment if necessary.
e.
approximately 1000 ohms total es show” in Figure 7.
I” this application the
G’JARD and terminal ‘A” should be disconnected. The
value of the divider resistor should be one ohm for
every 1 m” OUtput.
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,
For servo rebalance recorders, use a divider of
f. When the FEEDBACK Switch is in the NORMAL pasi-
elan, the GUARD terminal
nector is connected to the instrument case.
fore. no difficulty will be experienced using oscilloscopes and recorders with the Node1 6008 set for
normal operation.
Check the recorder and meter zero
shorting
In FAST position. however, Che
link between OHMS
of the Rarrier Strip Con-
Fo=
mere-
The”
FIGURE 7.
for Driving 50 and LUU-millivolt Recorders.
resisrors in rhe dividers. The value of resistor R
is one ohm far every 1mV of output.
Divider Clrc”its Acrosr Modri hnna “wv”“’
use 5%
2-S.
UNITY
can be used as a” impedance matching device to minimize circuit loading errors
a.
wi,thin 7.5 ppm when the load reeietance is 100 kilohms
or greater. By placing the Model 6008 between a IOn
V,, and e 0.01% voltmeter to obtain high accuracy without causing circuit loading.
The Model 6008 is used between
MODEL 6008 ELECTROMETER
OPS~TION, CIRCUIT DESCRIPTION
1. Connece the voltmeter co ehe xl and OHMS
GUARD Terminals as shown in Figure 8. The OHMS
GUARD Terminal is at ground with the FEEDBACK Switch
in NORMAL. laxnwm output amplitude is 10 volts
peak-to-peak?
2.
Adjust the Model 6008 zero Controls co obtain
a zero-voltage reading on rhe exrernal voltmeter.
Make cure the latter’s sensitivity is high enough
SECTION 3.
CIRCUIT DESCRIPTION
far a precise zero adjustment.
b. When the FEEDBACK Switch is in FAST position,
the unity-gain terminals permit more convenient con-
nections to oscilloscopes with a load resistance of
greeter than 100 kilohms without special precautions.
In this mode, the Xl Terminal is grounded and ehe
OHMS GUARD Terminal delivers en output equal co the
input signel.
3-l. CESEUL.
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
10L4
ohms shunted by 20 ?icoiarads.
p.nel controls, shunt m~istors and capacitors are selected to make meesuremencs over a total ot 61 YOLC-
age, currene, fes~scance: .2nA *nl*lnmh -1”Z-E
and resiseance dre measured using precision resistance
stanaards, irom 10 ohm wirewound resistors to 1011 ohm
glass sealed, deposited carbon resistors. coulombs
are measured using close tolerance polystyrene film
capacitor standards.
b. Batteries furnish the neceesarv amolifier oower.
3-2.
“OLTHETER OPERATI(IN.
a. The Model 6008 empioys matched insulated-gare,
field-effect transistors fallowed by a eransisror differential amplifier with a high-voltage comvlementary
oueput stage. Figure 9 shows the block diagram for
the voltmeter made of operation.
b. Voltmeter operation of the Model 6008 is as
fallows:
The amplifier is always in a unity-gain, input
1.
voltage co output current converter contigurarxm.
The internal circuitry is arranged such that a full
scale input voltage (ei) results in exactly a 1 mil-
liampere outout curreoc through the divider string
composed
of the circuit is determined by the ratio of R177 to
h.
of
Rm. R177, end the meter. Voltage gain
Output is taken across R177.
By using the frone
r?~~~,mt
2. The voleage drop across the amplifier is
where & is the amplifier loop gain, greater t!lan
5 I 10’ on all ranges.
c. ‘ihe complementary oufpot sK.ege, 4109 and 4110,
drives the amplifier ground at the same potential as
ehe input signal. ‘Thus the input impedance is maintained for any value input voltage and the need for
input dividers is eliminated. ‘The amplifier *round
is not chassis ground, hue it is connected directly
to the unity gain output.
NOTE
Refer to Schematic Diagram 22BOSE for circuit designations.
3-3. “OLTELETER CIRCUIT.
a. The amplifier input staSe is a pair of insulated
gate,
differential configuration.
turned to amplifier common, the unity gain output.
the gate of the active insulated gate devices at zero
p”LSLLLldl.
ferential amplifier. composed of QlOlA-QlOS. Q106 and
Q107 make up the output gain stage, which is utilized
in e gain multiplier configureciao. This stage pro-
vides the remainder of the high gain required by the
field-effect transiecars, Qlll and Qll5, in a
The gate of Qlll is re-
b. Depressing the ZERO CHECK Sutton, S102, places
c. The input stage is fallowed by a transistor dif-
r%“L”D
9
CIRCUIT DESCRIZ’TION
MODEL 6008 ELECTROMETER
UHF INPUT
amplifier.
ALSO, this stage prevents fold-over and
lock-up with ?ositi”e input overloads.
>i
OiOdR DlO1,
beeween base and emitter of QIOB, prevents fold-over
and lack-up under negative inpue overloads.
frequency compensation networks provide a I-W-
d.
trolled frequency characteristic to insuee stability
under all conditions ai caps:iLivr iuading on input
and o”ep”t while an any =ange.
fed back to the am<lifier inp”t through a feedback
resistor seleceed with the Range Switch.
~loaring ground is connected to the law imped-
10).
(See Figure
ance side of the input, and the output ground is
flOaCi”g.
~hls method increases the response speed
by minimizing the effects of inp”t capacity; it also
reduces the input drop to less than 1 millivolt.
3-5.
OHMMETER OPERATION.
e. ‘rhe recorder o”cp”c is derived from the c”==ent
flow from 4109 and QllO through the divider, Km, R177,
and the mete=. With the shorting link between the
OHMS GIRD Tenninal and Terminal h (paragraph 2-7~)
21 vale fo= full scale deflection is obtained a= the
mtpuf by ~1.1 milliamperes flawing through the divider.
3-4. AMMETER OPERATION.
a. Normal Method. In the normal method of c”==enC
measurements (FEEDBACK Switch in NORMAL position),
one of the Range Switch resistors, R136 through R146,
shunts the input.
(See Figure 10). The Model 6008
then meas”=es the voltage drop acrbss the resistor.
The meter is calibraird io ‘ea..i i&e ~“arni in ampexs
for the appropriate range.
b. Fast Method.
In the fast method of c”==ent mea-
S”=aments (FEEDBACK Switch in FAST position), the MO-
de1 6008 functions 88 an attnwEe= with negative feedback. The differenelal amplifier output is divided
by the Multiplter Switch resistors, R168 to R174, and
10
a. No=mal Nerhod. I,, the normal method of r‘esis-
eance meas”=emenEs (FEEDBACK Switch in NORMAL posi-
eionj,
the Model 6008 uses a constant-c”==ent, voltage.
drop ci=c”It. Refer to Figure 11. Rx is the unknown
resistor. A voltage source, E, applies a potenfial
acroes Rx.
The source is obtained f=om the batteries
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
range resistor. !+ is one of the resistors, R136
through R146. I is equal to E/R., =egardless of the
value of R,, as long as the voltage drop across Rx
does not exceed the Multiplier switch setting. This
circuit provides a t=“e source regardless of the in-
The Model 6008 can then meas”=e the voltage drop
put.
across R~ and indicate ehe =esisfance value on its
;zlib=n:ed mete=.
-.*-“4 Method.
L
_____-
1x1 the guarded method af =esis-
tance meas”=emen=s (FEEDSACK Switch.i” FAST position
and the sample resistsnce connected between the INPUT
~erroinal, 5102, and the GUARD Terminal), feedback is
applied through the sample. Refer tO Fig”=e 11. The
circuit is similar to the normal method, except far
0872rl
MODEL 6008
CIRCUIT DESCRIPTION
the feedback. This reduces the slowing effect of the
instrument’s input capacity.
Leakage error is also
reduced since the potential ac.ro~~ the INPW Terminal
is small. In this mode. floating ground is connected
Co the low impedance side of the input and the output
ground is floating.
The GUARD Terminal is at output
ground potential.
3-6.
COULOMBMETER OPERATION. The Model 6008 circuit
far measuring charge is similar to that used for an
ameter with the fast method. A negative feedback is
applied around a shunt capacitor, cl10 to ~113, se-
lected with the Range Switch. The shunt capacitor replaces Rs in Figure 10.
The stored charge is propor-
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.
4-1.
GENEPAL.
troubleshooting procedures for the Model 6008 Electrom-
eter. Follow these procedures as closely es possible
to maintain the performance of the instrument.
4-2.
SERVICING SCHEDULE.
dition of the batteries, using the convenie::t battery
check as described in paragraph 2-i. Exceot Ear baetery replacement, the Model 6008 requires no periodic
maintenance beyond the normal care required of highquality electronic equipment. The value of the highmegohm resistors, Rl44, R145 and R146 should be checked
approximately every 6 months for specified accuracy.
4-3.
PARTS KKPUCEMENT .
a. The Keplaceable Parts List in Section 7 describes the elecrricoi comoonents of the Elecrrometer.
Replace components only 8s necessary. Use only reliable replacements which ma-r rh- 4ycifications.
b. The XOS FET input c-i-=i?rnr=, Qll5 and ‘>lll,
are specislly selected nod matched; order only as a
plug-in
unit, part number 23735
strnmenes, 1°C.
4-4. TRO”BLESHOOTING.
8. The procedures which follow give instructions
section 4
contains the maintenance and
Periodically check the con-
, from Keithley In-
SERVICING
for repairing troubles which might occur in the Model
6008.
ified replacement perts.
ommended for troubleshooting.
be readily located or repaired, coneect Keithley Instrumenes, Inc.,
might occur. If the repairs indicated in the table
do not clear up the trouble, find the difficulty
through a circuit-by-circuit check such as given in
paragraph 4-5. Refer to the circuit description in
Section 3 to find the more critical components and to
determine their function in the circuit. The complete
circuit schematic, 22808E, is in Section 7.
condition of the batteries (paragraph 2-2). Then make
sure the shorting link is connected between the UIIMS
GUARD and A Terminals on the Barrier Strip Connector.
terminal voltages referenced to either iloacing ground
or output ground: e properly operating Electrometer
will have these values -lo%, if operating from fresh
Use the procedures outlined and use only spec-
Table 5 lists equipment rec-
If the trouble cannot
or its representatives.
b. Table 6 contains the more common troubles which
If the instrument will not operate, check the
a.
The schematic diagram indicates all transistor
b.
uipment Recommended for xodel 6008 Calibration and Troubleshooting.
CENERAI..
me iunction a,i the C3libratio" Section is to
il.
orovide a :nethad of checking the XZI
;ure Ch"C ic cperalLes ?roperiy and within the speci:icarions given in 1clbla L '2" page ii.
xiel 600" to make
once a year or when componenes are replaced.
,i
Check etle ?,lodel no09 accurac\ (paragraph 5-11)
once a year, after the other adjusments, or if impcuper operaeian is suspected.
5-2. C‘\LIBRATION SCHEDULE.
check offset current (paragraph 5-8) 8f regular
n.
intervals to make sure the input transistoes are functioning correctly.
b. Verify the value oi the high-megahm resistors
(paragraph 5-10) approximately every six months.
C. Calibrate the meter zero (paragraph 5-4) about
14
08728
MODEL 600B ELECTROMETER
CALIBRATION
b. Check the meeer O-10 scale for no more ehan 1%
(l/Z division) tracking error going from zero to tull
scale in one-tenth oi full scale voltage steps.
a. Zero check the !,odel 6008 and set the inscrumenr
to the 10 volt range. Connect the Node1 241 Voltage
supply eo rhe Xodel 000~ ISPLT receptacle and to the
Yodel 662 oiifereneinl '!'aImeeer iligh teminal. Cannect the Electrometer 'I Terminal to the LOW rerminal
of ehe XodeL 662. set ehe ?,odeL 662 dial co 0 and the
Xuil Switch La ! aillivalt.
clicnte al: or near zero.
The Node, 662 shouid in-
SOTE
Burro”.
should be less than 2 x IO-l4 ampere.
than 20% of full scale).
the battery condition and the input tran~i~eor, ~115.
If the insrrumene has not been used for a long rime,
allow it to run 7 hours before checking ehe offset
C"rT*"C.
5-9. DRIFT CHECK. The unit mutt be oii at !euse one
ihour prior ea a drift run.
a. see the front pvnei controls to:
The offset current indicated on the meter
If this is exceeded, check
ZERO C,iECK sutean
Multiplier Switch
Range Switch
FEEDBACK Witch
NETER Switch
(This is less
LOCK
.Ol
'VOLTS
SORMAl
2. iepeac :.:e rese or iubparagraph 1 above usin*
-10 "OiCS.
j-7. YOISE CiECS.
connecr ehe OUTOUC ea a Hevierc-Packard XodeI 34OOA
ms "alemerer.
a. See the !ETER Switch co CENTER ZERO and zero
the Node1 6008 on the LO millivolt range.
b. *he oucpuc noise must be less than 10 millivolrs
rms an the 10 millivoit through 10 volt ranges.
5-8. OFFSET CURF\ENT CHECK. Check offset c"rrent
whenever excessive noise or drift is suspected. TO
read the offset current of the Model 6008, set the
front panel conero1s to:
Zero check the Electrometer and
VOTE
If new lmtreries ihave been instailed, :he
Model 6OOB zero drift will be exceeded far
a? 1easr 24 ho"rS.
hours co enable rhe barter? ccminni ,;o‘cages to stabilize.
5-10. HIGH-bEGOHM RESISTOR "ERIFICWIOI
a. About every six months ie is necessary co check
the value of the high-megohm resistors, R144 to 13146
on the Range Switch. The instrument should be within
its rated accuracy far two or three years from the
time it leaves the factory. After Chis. some of the
resistors may drift sue of tolerance and should be,
_( .",
..:,. _..L.
the accuracies of mea~uremenc~ far ehe 10T9 Co 10mll
HW'LKES and the 108 to 1012 OHMS ~eteing~ of the Lange
switch.
?sdif high-megohm fe~i~for~ will affect
.\ge rhe unir isr 1'
Cap the INPUr Receptacle and unlock the ZERO CHECK
0872B
b. To check Cheae re~i~tora, it is necessary ro use
a bridge capable of better than 1% accuracy UP to 1O1l
15
CALIBRATION MODEL 6008 ELECTROMETER
ohms such as the Keithleg Instr”ments Model 515 Xegohm
aridge.
1f such equipment is not available, two pro-
cedures are recomended to check out the resistors:
Return rhe complete instrument to the factory
1.
for resistor calibration.
Replace the high-megahm resistors periodically
2.
with a certiiied set from Keithley Instruments to
assure &moiute calibrntion accurncy.
Checking tile accuracy is the q”ickest way to
a.
spot f3ulty i’lodel 6OOB operation.
Perform the check
*bout once n ycac, if components are repiaced, or ii
tither adjustments ilre made.
If accuracy is verified
I)Yer sill ron~es, the Xodel 6008 should be nble to meet
311 spetific~ci,v~.s.
[I the accuracy must be checked
.,iten, check tijc stabiiif,v.
(FEEDBACK Switch in NORMAL). Check the 3 x lo8 thro”gh
oh,,, ranges for on accuracy of t5% of full scale
Id3
by employing the resistance measurement method .os described in paragraph 2-6~ (FEEDBACK Switch in FAST).
e. Chaege.
To check the accuracy oi the Modei
6008 as a charge amplifier, set the FEEDBACK Switch to
FAST. Apply 10 volts from the Model 241 Voltage Supply through a Model 5155 10L1 ohm Standard to the Nod-
et 6008 input. Set the Multiplier and Range Switches
to the settings given in Table 8. Use a stop watch or
B Tektronix Model 561A Oscilloscope to time the rise
to full peek deflection. Check each setting to *5?..
TABLE 8.
Charge Ranges Accuracy Check. The Table gives the
xultiplier Switch setting, the Coulomb Range Switch
setting and the rise time for each coulomb range.
Rise ‘Time. %*=a
Range Switch
to Full Scnle
Setting, COULOMBS
5-12. FREQIIENCY RESPONSE C!LECK.
C. B: Connect the Xodel 6008 to the Xcdel
161 and monitor the oucpuc with the ?lodel 163 WM.
Check tl,c iull-acnle rrccurncy of all the c”rren~,posi-
tions on the I(an,~e Switch
ror the 10-o f” LO“’ :,>i-
PEP.? settings of the Range Switch, set the FEEDBACK
svitch to F;1ST .md the xultiplier Switch to 1.
‘The
jlodel 602 should indicacr GLS iIlrw. -~r‘;:lz : ~1. u,Y
iull scale to the 10ml” *m ere range; 15% of full scale
irom the 3 !i io-il to 10-
15
ampere ranges.
For the
ranges above IO-’ ,mpere, constr”ct B current sauce
WhoYe cl”tp”t is zo.25::. jet the Model 6008 FEEDBACK
svitck co SOprL4L 2nd the Yultiplier Switch to .O1 when
cniibracing these rnnges.
40TE
For 10-l mlpere t!lro”gil 10-5 ampere rnnges,
a Inrper ?hltipliec Switch setting will re-
sult in inaecurac~rs due co loading of the
current source: hence the .Ol Multiplier
Switch setting must be used. The appro-
priate current source is two decades less
than range setting; that is, on the 10-l
ampere range we IO-3 ampere source, etc.
Resistance. Connect the high side of a Keithley
d.
Model 5155 Resistor to the Electrometer TNPUI’ kecepLb-
cle and the low side to the OHMS GUARD Terminal. Check
full ,scale acrx~t.. : ?C
“.?I. +- yeib’.?“o nn ,h. I)il”$rp,
switch by measuring the voltage drop of the known cur-
rent across the known sample with the Model 6008. Test
current applied is the reciprocal of the OHMS Range
Stti”*.
Check the 103 through log ohm ranges for an
accueacy of +4% of full scale by using the resistance
meaa”rement method as described in paragraph 2-6b
8. Zero check the unit.
Connect a Wavetek >iodeI
102 Function venerator through a iOU:l divider to the
!lodeI 600” input nnd connect the Electrometer output
to a Hewlett-Packard Model 400 AC VTW. Set the
Electrometer FEEDBACK Switch to NOR&U..
NOTE
If other than a constant amplitude signal
generator (wavetek) is used. it will be
necessary to monitor the o”tput ui the
signai generator with another VTVN in
order to maintain the same signal level
at various frequencies specified.
b. Zero the Model 6008 on the 10 millivolt range.
set the signal ccneracor to 20 Hz at minimm
1.
um.put.
Release the Electrometer LCRO CHECK autfon
and increase the Generator wfput to obtain 0.7 volt
cm nt the Model 6006 output.
2. Set the Generator to L kHz. The Electrometer
o”tp”t voltage m”st be within ~3 da of the 20 ,Lz
0.7 volt rms output.
Zero the Model 6008 on the 3-volt range and
c.
.:hange the divider to IO:i.
Set the Generator to 100 Hz for minimum output.
1.
Release me Electrometer ZERO CHECK Button and increase the ~eneeator o”tp”t to obtain .07 volt rum
at the Nodel 6008 output.
2. Set the venerator to 20 kHa. The Electrometer
output must be within t3 dB of the 100 HZ .07 vole
cm output.
08728
MODEL 6008 &LECTROMETER
CALIBRATION
FIGORB 12.
of X-189.
1069
ComponenE Layout of
Model 6008 Chassis. Front panel faces
left.
see Figure 13 far component layout
17
CALIBRATION
MODEL 6GOE ELECTROMETER
PIGIRE 13. component Layout for PC-189.
For other Model 6008
Components, see Figure 12.
1069
MODEL 6008
ACCESSORIES
SECTION 6.
6-1. GENERAL. The follawiq Keithley accessories
can be used with the Model 6008 to provide additional
convenience and versatility.
Model 6101A Shielded Probe
Oescriprion:
The Model 6lOW is a shielded cable with a needle-point
probe and 30 inches of low noise cable terminated by a
UHF connectar.
Model 61018 Shielded Probe
Description:
The Model 61018 is a shielded cable with a “gripping
type” probe and 30 inches oi low noise cable terminated
by a UHF co”nector.
ACCESSORIES
OPERATING INSTRUCTIONS. A separate Instruction
6-2.
Manual is supplied with each accassary giving complete
operating Fnformarian.
I
\r
-..
Yodei 6103A Divider ?robe
Description:
The Nodei 6103A is a sbieided cable irirh a needle-point
pmbe and 30 incnes ai !O” n0is.e cable eerminaeed by a
LHF connector.
divider with a 101*2 input resistance. Accuracy is
+% at 30 kilovolts.
The orooe includes a iOOO:1 voltage
Hode1 6102.4 Divider Probe
19
ACCESSORIES
MODEL 6008
Modbl 6106 Electrometer Connection Kit
Description:
The Model 6106 contains a group of the most useful
leeds and adapters for low cu==ent meeao=ement~. A11
eo,,,ponents are housed in B rugged carrying case with
i”di”idU.41 compartments.
Models 2501, 2503 Static Detector Probes
Description:
Parts List:
oescription
Cable, 30”, UHF to clips
Cable, 24”. UHF to UHF
connector, UHF to UHF
Adaptor, UHP to BNC
Adaptor, UHF to BNC
Adaptor Tee, UHF to UHF
Adapto=, Binding Post
Item
NO.
1
2 la265c
3 CS-5
4
5
6
7
Keithley
Part No.
19072C
cs-115
CS-172
cs-171
190718
The two cables (Items 1 and 2) are coaxial shielded
leads useful for connections where low noise is essentie1.
The 24” cable (Item 2) ten be used to intercannect two in~teument~ having UHF receptacles. The 30”
cable (Item 1) c8n be used to connect Co the circuit
under test through the use of clip leads. A binding
post adapter gives easy access to the elecerometer
“high” terminal. TWO unz fernal couplers (Item 3)
permit cables to be connected together. The UHF “tee”
connector simplifies galvanometric current meesu=ementE
when using a current source and electrometer or picoammeter. Adapters (Items 4 and 5) are useful fo= conversion from UHF to BNC terminations.
The Models 2501 and 2503 are specially designed detectors used to me.wure static charge on pla
Either probe mwt be used with an electrometer such as
the 6008.
Model 2501:
.1---1 ^_ 119L
The 2501 is useful fur ,,,sorr.-r-..:A .Jf
surfaces.
The static heed is 3 inches in diameter.
_ .._ _ b-
_..
Recommended spacing is 318” from the surface far
10,OOO:l divider ratio.
The 2501 is calFb=eted such
that a 1 volt deflection on the electrometer co==e-
spo,,ds
to 10 kilovolts of static charge.
Hodel 2403:
The 2503 consists of a rigid probe 112 inches m ol-
ameter.
Operation is similar to the use of the 2501
probe.
Model 6107 pH Electrode
The Model 6107 is a test fixture which simplifies con-
nections to the electrometer when making pH measuremerits.
The adapter c-n be wed wi.Ch elw.rrndes “an”faotured by Leeds & Northrup, Coleman and Beckman.
The 6107 can be used for guarded measu=ements BS shown
in the diagmm.
A voltage-to-pa conve=‘slo” chart 1s
supplied with the 6107.
Adepter
---we
Xi
0877.R
MODEL 6008
the Model 6104 is
or three-terminal
teflon insulated.
ACCESSORIES
Model 6104 Test Shield
56
57
EXT
TO 6008 GUARD
JS
INPUT
HIGH O-+-C BNC
32
Jl
GND
53
“1
Appiicaeians:
1. Two Terminal Connections. nrsisww. IW**U~*mencs can be made conveniently using the INPUT and
GROUND terminals on the Test BOX. Connect the eiec-
tromecec eo the SNC output.
NORI.,@.,. mode for ohms measurement.
2.
Three Terminal Connecfions. The GUARD o"fput
on the Model 6008 electrometer can be used for re-
sistance measuremenes where the effects of cable capacieance may be significant.
INPUT and EXT terminals.
the WARD output on ehe eiecteometer.
erometer in FAST mode ior ohms measurement.
34
J5
Use the electrometer in
~m,necc the unknown between
Connect ehe EXT terminal to
CASE
"se the elec-
Description:
The ModeL 6105 is a guarded test fixture far meQsu=ement of surface and volume resistivieies.
is designed in accordance with ASTH Standard Method of
Test for Electrical Resistance of Insulating Materials,
0257-66.
elecerm,,eter and voltage supply.
Applications:
Reststivity can be determined by measuring the current
through a sample with a known voltage impressed. The
measurement can be made most canveniently when a set
of electrodes ore used which can be
of surface or volume resistiviry. The Keithley Model
6105 Resistivity Adapter has been designed for use with
a Keithlay electrome~r and an optional high voltage
supply such ae the Model 240A.
The 6105 can be used in canjuncti~on with en
calibrated in eerm~
The chamber
REPLACEABLE PARTS
MODEL 6008 ELKCTROMSTER
SECTION 7.
7-I.
REPUCEASLE PARTS LIST.
List describes componenc.s Of the Model 6008. me LiSC
gives rhe circuir. designation, the pare description,
a suggested manufaceurer, the manuiaccurer’s part numher and the Keiehley Parr xumller. The last calunn in-
dicates the figure picturing the part. The name and
address of rhe xanufactu~ers lismd in the ‘Wg. Code”
me Replaceable Parts
REPLACEABLE PARTS
column are in Table 11.
and serial number, the Keithley Part Number, the circuit designation and a description of the part.
structural parts and eho~e parts coded for Keithley
manufnccure (80164) must be ordered through Keithley
I”stP”*e”ts, 1°C. or it5 representatives. I” ordering
All
a part noe listed in the Replaceable Pans List, cornpletely describe the part. its function an* its location.