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INSTRUCTION MANUAL
MODEL 604
DIFFERENTIAL ELECTROMETER AMPLIFIER
KEITHLEY INSTRUMENTS, INC.
PRINTED JANUARY 1977, CLEVELAND, OHIO U.S.A.
CONTENTS MODEL 604
CONTENTS
Section Page
SPECIFICATIONS ................................. iv
1. GENERALDISCRIPTION. ............................ 1
2. OPERATION.................................. 3
3. CIRCUIT DESCRIPTION. ............................ 11
4. MAINTENANCE.................................1 3
5. ACCESSORIES. ................................ 25
6. REPLACEABLEPARTS. ............................. 27
SCHEMATICS...................................3 6
ii 0177
MODEL 604 ILLUSTRATIONS
ILLUSTRATIONS
Fig. No. Title Page
1 Model604FrontPanelControls .................... 3
2 Model 604 Rear Panel Controls .................... 3
3 Model 6041 Front Panel. ....................... 4
4 TypicalExperiment .......................... 5
5 Error Due to Ammeter Resistance ................... 8
6 Internal View of Model 301 Amplifier. ................ 9
7 Model 604 Block Diagram ....................... 11
Ripple Obtained for the 26 Volt Supply. ............... 14
: Ripple Obtained for the 15 Volt Supply. ............... 15
10 Ripple Obtained for the 21 Volt Supply. ............... 15
11 Location of Voltage Supplies Test Points. .............. 15
12 Null Obtained with the Signal Generator at 5H.z. ........... 17
13 Null Obtained with the Signal Generator at 1kHz ........... 17
14 Top View Model 604. ......................... 21
15 Bottom View Model 604 ........................ 22
16 Component Layout of PC-165. ..................... 23
17 Resistor Locations on PC-165. .................... 24
18 Top Cover Assembly. ......................... 35
19 Bottom Cover Assembly ........................ 35
0177 iii
SPECIFICATIONS MODEL 604
SPECIFICATIONS
iv 0177
SECTION 1. GENERAL DESCRIPTION
Another outstanding feature of the Keitbler
Mo%l 604 is its zero stability. signals can be
monitored over weeks without constant rezeroing.
Zero drift of the Amplifier is leas than 4 milli-
volts per week; zero offset due to temperature chan-
ges is less than 300 microvolts per OC. Zero shift
due to mechanical shock or vibration is negligible.
h. Overloads up to +4OO volts will not damage
the 604 Amplifier, and recovery is almost immediate.
h. When used in conjunction with the Model 6041 A unique circuit provides protection while main-
Differential Current Shmt the Model 604 hecome* a taining the favorable features of the MOS PET input.
single-ended or differential picoameter. Single-
endp and differential current measurement* from AS another convenience feature, the Model 604
lo- to 10-14 ampere can be made with this setup. &ides a very stable tl volt suppression on any
Also, high megohm resistors may be installed within range. variations a5 small as 1 millivolt in a
the Model 604 to allow shunt picoammeter operation. l-volt signal can be displayed full scale.
j. Variations in line valtagee from 105 to 125
volts cauee no apparent change even on the most sen-
a. AS an amplifier, the Model 604 will operate sitive range. Line frequency noise is practically
over a bandwidth from dc to 50 km or greater with eliminated from the Model 604 output.
six select&l* 3-dB points from 30 kHz to 100 Hz.
Thus, the signal-to-noise ratio may-be optimized for l-3. MODEL 6041. The Model 6041 Differential cur-
a particular application. The amplifier output fur- ent Shunt is an accessory specifically designed to
nishes 210 volts at 5 milliamperes single-ended. convert the Model 504 Amplifier into a single-ended
or differential multi-range picometer.
b. The Electrometer Amplifier has an input re-
sistance of greater than lOI4 ohms shunted by less a. The driven guard enables the Model 604 Ampli-
than 5 picofarads in the unguarded position, that fier and the Model 6041 Shunt combination to obtain
allows high impedance measurement to be made easily. fast response in c*rrent measurexnente. Input capac-
When in the guarded position the input impedance is itance at the end of a IO-foot cable is maintained
shunted by less than 1 picofarad. at 1 picofarad in the guarded mode. As a result,
risaltimes of 0.5 millisecond are possible with
LOW OffSet Current - 1855 than 2 x m-14 ampere lo- ampere input signals. Guarding is maintained
- tkimiaes zero offset with high source resistance through the Model 6041 by the use of triaxial input
and permits maximum resolution when measuring cur- conneotors and total auardina within the Shunt
rent. itself.
d. A choice of outputs which can he used simul- h. For those applicarions where maximum signal-
taneously or *ingly is available. Each input of to-noise ratio is more desirable than fast response,
the Model 604 has' a unity gain output, which has the Model 604 can be used in its unguarded mode.
*so omn acc"rac". This alloWS the Model 604 to be Noise will be as low as 2 x 10-15 anumre usins a
used-& a prea&ifier with differential or digital lOI ohm resistor. Hcwever, rise t&es are m&h
voltmeters for precise measurements. Also, these longer than when the Model 604 is in its guarded
outputs can he fed into an X-Y recorder for recording mode. Regardless of mode, the high frequency cut-
data from high impedance sources. When desired, the off can be used to reduce noise at the higher fre-
unity-gain outputs can be monitored for absolute quencies .
values while recordings are made from the amplifier
output. C. For those cases where a limited current span
is to he monitored, a pair of high megohm resis-
e. All outputs are short-circuit proof, and out- tors, available as the Model 6033, can be mounted
put noise referred to the input is nearly constant internally within the Model 604. Although this
regardless of the gain. method limits the current span to only four decades,
it does slightly improve both the noise and the
f. The guarding capability of the Model 604 al- rise time characteristics over that obtainabLe with
lows fast masurements from high resistance sources, the multi-range Model 6041 Current Shunt. The cam-
by eliminating the effects of cable capacitance and promise between noise and rise time still must be
leakaoe. TO convenientlv facilitate these measure- made by choosing the guarded or unguarded mode.
ments, the Model 6301 Gu&ded Probe can be used to
connect the eonroe to the Model 604 in the guarded d. Low offset cn~lent minimizes zem offset with
mode. the guard feature is switch seleotable. high source resistance, permitting maximum resolu-
tion when measuring current.
0373
Varies the high frequency rolloff of the Model 604 and
selects the maximum bandwidth to be measured. When the
Switch is in the OFF Position the full handwidth of the
Model 604 is available.
Turns instrument off and on; disconnects meter; selects 2-2
meter polarity: sets instrument for center zero operation.
Indicates instrument is on. 2-8
2-6
shunts respective INPUT Receptacle. Locking either one 2-2
allows single ended use. Locking both zeroes the meter.
Opening both allows differential measurements,
2-2
t+, and c-, INPUT connect inputs to sources. May be wed either singularly 2-l
Receptacles. or conjointly for single ended or differential measure-
ments respectively. Receptacles are Teflon-insulated
triaxia1 COnrLectOTs.
Control Functional Description Paragraph
UNITY GAIN O"TP"l3: For use as an extremely linear preamplifier. Outputs 2-11
FROM c-j TNP"Ti FROM (+I are equal to respective inputs within *0.005% at dc,
INPUT exclusive of offset, noise and drift.
Post
GROUND Connected to ground of all the outp"ts and the ground ---
wire of the power cord.
I
FUSE 3x slow Blow. 117 volt operation: -l/8 ampere. 2-8
I 234 ""It nnaration: -,~/I~6 amnerc.
Functional Description Paragraph
switches shunt resistor at input of the amplifier 2-2
for the Model 604 +INPUT Receptacle, thus determining
full scale current range Model 604 is to measure.
Switches shunt resistor at input of the amplifier 2-2
for the Model 604 -INPUT Receptacle, thus determining
full scale current range Model 604 is to measure.
~0th switches are used in differential current measure-
INPUT : + and - Connects Model 6041 inputs to BOUTCBS. May be used either 2-2
singularly or conjointly for single-ended or differential
measurements respectively. Receptacles are Teflon-
insulated triaxial connectors.
lo 604 INPUTS: Connects Model 6041 to respective Model 604 Input Recep- 2-2
+ and - tac1es.
GND connected to ground of Models 604 and 6041
2 0373
SECTION 2. OPERATION
2-l. INPUT CONNECTIONS. The Model 604 has two in- d. When working with a high impedance source
put connectors, the +1NFUT receptacle and the -IN- carefully shield the input connection and the source
PUT Receptacle, for use either single-endedly or since any variation in the electrostatic field near
for measuring the difference between two input the input may cause definite meter disturbances.
signals.
Use high resistance, low-loss materials --
a. The Model 604 INPUT Receptacles are Teflon- s":h as Teflon (recommended,, polyethylene or poly-
insulated triaxial connectors. The center terminal styrene -- for insulation. The insulation leakage
is the high impedance terminal; the inner shield is resistance of test fixtures and leads should be
either guard or ground; the outer shield is ground. several orders of magnitude higher than the inter-
The inner shield of the INPUT Receptacle may he nal resistance of the source. Excessive leakage
used as a driven guard with the GUARD-OFF Switch in reduces the accuracy of reading from high impedance
the GUARD Position. sources. Triaxial or coaxial cables used should be
a low noise type which employs a graphite or other
h. There arc Keithley Accessories available which conductive coating between the dielectric and the
are designed to lnclease accuracy and co""e"ie"ce surrounding shield braid. Amphenol-Borg Electronics
of input connections. Corporation, Microdot, Inc., and Simplex Wire and
Cable Company make satisfactory types. use of the
Model 6011 Input Cable insures good input connec-
C. The Model 6011 Input Cable facilitates input tions.
connections. Table 5 indicates the color coding
of the alligator clips. The center terminal is NOTI?
shielded by the inner braid of the triaxial cable up
to the miniature alligator clip. If the unshielded Clean, dry connections and cables are very
clip causes pickup from nearby electric fields, re- important to maintain the value of all in-
move it and connect the shielded lead directly to sulation materials. Even the best insulation
the source. will be compromised by dust, dirt, solder
flux, films of oil 01 water vapor. A good
cleaning agent is methyl alcohol, which dis-
solves most commm dirt without chemically
attacking the insulation. Air dry the cables
I Lead circuit Terminal I or connections
use dry nitrogen
after washing with alcohol
if available. Or, if it
or
heavy wire with center is available, Freon is an excellent cleaning
red clip cover high agent.
thin wire with Inner Shield
black clip cover guard f. With the GUARD-OFF Switch in GUARD Position
thin wire with Outer Shield the Model 604 may have at least ten feet of triaxial
"7%-P" rlin rn.lP? cable on its input without adding capacitance to the
FI
0373 3
input (input capacitance is specified at 1 pF).
Note, hwever, that guarding can only eliminate in-
put cable capacitance effects. Except in one spec-
ial case, see subparagraph S-Ii, guarding cannot be
used to eliminate effects due to source capacitance.
--__-not connect the guard circuit
DO __--.~ to the source.
NOTE
For a complete discussion on guarding with
the Model 604 refer to paragraphs 2-3 and
2-4.
4. When working with a high impedance source any
change in the shunt capacitance of the input cir-
cuit will cause disturbances in the reading. Make
the measuring setup as rigid as possible, and tie
down connecting cables to prevent their movement.
A continuous vibration may appear at the output as
a sinusoidal signal, and other precautions may be
necessary to isolate the instrument and the connec-
ting cable from the vibration.
h. For low impedance measuremen~s~-- measurements
that are above 10-8 ampere -- ""shielded leads may
ae usea.
The Model 6012 Triaxial-to-Coaxial Adapter
enkles using coaxial cables and accessories with L
the Model 604 by adapting the triaxiol INPUT ~ecep- F:LG"Rr! 3. Model 6041 Front Panel Controls and
tacles to the UHF coaxial type.
1. The Adapter connects the Model 604 inner
shield to ground defeating the guard capability d. For differential measurements unlock both ZERO
that the triaxial receptacles make possible. EX- CHECK Buttons and apply one signal to one of the In-
cept for the special case spelled out in the fol- put Receptacles and the other sianal to the other
lowing subparagraph 2, the GUARD-OFF Switch must Kecepta&. It does not matter ;hich Receptacle
be in the OFF position for the instrument to func- accepts the high or low signal. If the signal to
tion the -INPUT Receptacle is positive with respect to
the signal to the +INPUT Receptacle, then the output,
2. If the Model 6012 Adapter is used with the and the meter, will read negative. If the signal
Model 6041 Shunt in front of the Model 604 and to the +IINPUT Receptacle is positive with respect
the current souroe can be floated off ground, then to the signal to the -INPUT Receptacle, then the
a feedback picoameter connection is possible. output will be positive.
In this situation the coaxial shield is guard
with the GUARD-OFF Switch in the GUARD position. The Model 6041 'is a Differential Current Shunt
TO make possible a guarded circuit, connect guard, whpch, when used in conjunction with the Model 604,
the coaxial shield, to the low of the current enables the Model 604 to become either a single-
SOUlCe. Remember, however, if the current source ended or differential shunt ammeter. The INPUT ne-
low is grounded, the GUARD-OFF Switch must be in ceptacles on the Model 6041 are nominally labeled.
the OFF position for the instrument to operate, That is, it is not essential that, single-endedly,
and no guarded circuit is possible this way. a positive signal be applied to the C+) Receptacle
and a negative to the (-) Receptacle or, differen-
tially, the high signal to the (+I and the low to
the (-).
a. The Model 604 + INPUT Receptacle is the input
to the non-inverting amplifier. This means that 1. The Model 6041 outputs (labeled: TO 604
for a single-ended positive input to this Receptacle INPUTS; + and -,, which connect the Model 6041 to
the output is positive and for a negative input the the Model 604, are directly tied to their corres-
output is negative. The polarity can also be inter- pending Input Receptacle. That is, a signal to
preted with the METER Switch and displayed on the the +INPUT Receptacle will be accepted at the +
meter. output and a signal to the -TNPUT Receptacle will
be accepted at the - output.
b. The Model 604 - INPUT Receptacle is the input
to the inverting amplifier. Thus for a single- 2. Though it is not absolutely necessary, it
ended positive input signal to this Receptacle the is recommended that upon connecting the Model
output is negative and for a negative input the 6041 to the Model 604, the corresponding output
output is positive. receptacle of the Model 6041 be connected to the
corresponding Input Receptacle on the Model 604.
C. For single-ended measurements just lock the Otherwise, the user may become utterly confused
ZERO CHECK Button for the Input Receptacle that you at what the polarity at the Model 604 output
do not intend to me, and apply the signal to the corresponds to.
other Receptacle. When locked, the ZERO CHECK But-
ton will connect its Input Receptacle to ground pre- 3. Note that the +INPUT Switch on the Model
senting an open circuit to the respective amplifier. 6041 applies to the Model 6041 +INPUT Receptacle
The Model 604 always measures the signal differen- only and the -INPUT switch applies to the -INPUT
tially. In the single-ended mode it measures the Receptacle only, regardless of the relative or
difference between the applied signal and the ref- absolute polarities of the signals at the inputs.
erence signal (ground).
4 0373
2-3. GUARDING. f3dB = .16 = 1.6 iiz
10~~10+90) (10-l')
a. There are several factors which contribute to
the bandwidth of an experiment. So, in this example, connecting the source to the
amplifier with a 3 foot cable, withcut guarding,
1. The amplifier bandwidth; would cause a IO:1 reduction in bandwidth.
2. The so"rce resistance and capacitance;
3. The capacitance of the cable connecting The Model 604 is designed to eliminate (guard)
amplifier to the source. thz'cable capacitance when used in the guard mode.
The Model 604 will reduce the apparent capacity at
the end of an up to 10 foot long triaxial cable to
approximately 1 picofarad by driving the inner
shield of the cable.
Model 604
The capacity from the center conductor of a
triaxial cable to the inner shield is about
30 picofarads per foot. From the inner shield
to the outer shield it is about 70 picofarads
per foot, The signal source, however, only
sees the capacity from the center conductor
to the inner shield. The guard circuit,
though, drives the entire capacity, about
100 picofarads per foot. The yodel 604 guard
circuit effectively drives up to 1000 pico-
farads; th"s the 10 foot cable limitation.
1. In the above example, then, the guard fea-
ture of the Model 604 allows the user to achieve
almost the entire bandwidth of the so"rce circuit.
f 3dB = .16 = 14.1 LIZ.
lo~(lo+l) (lolr)
2. Notice that, in the above case, guarding
GLw.E 4. Figure Depicts a Typical Experiment Show- does not increase the bandwidth of the so"rce, but
g the Amplifier, Cable and Source. In the figure $xf.y;ically eliminates the effect of cable cap-
is the capacitance due to the connecting cable,
is the source capacitance, KS is the source re-
stance and ES is the source voltage. d. The guard feature does, however, have several
limitations.
b. In the typical setup shown in Figure 4, if a 1. It is effective driving only up to 1000
perfect amplifier were placed at the source,the 3 dD picofarads. Thus, no more than 1000 picofarads
frequency of the so"rce would be should be guarded from either input for optimum
response.
f3dB = &I$ cs = .M& cs equation 1.
2. The guard voltage swing is limited by the
where f3du is the 3dB bandwidth of the source in HZ: common mode voltage swing (tll volts dc to 1 kliz
R, is the ~o"rce resistance in ohms. and approximately 22 volts at 5 !a~).
and Cs is the so"rce capacitance in farads.
3. The guard feature is not effective beyond
1. If, to take an example, Rs is equal to lo9 5 kllz because of internal phase shifts. These
ohms and Cs is equal to 10 picofarads, then shifts cause peaking to occur above 5 kHz, but
the system still remains stable.
e. Note that each input of the Model 604 has its
own separate guard circuit which is completely in-
2. NOW, if a cable is used to connect the so"rce dependent of the other. Note, also, that guard and
to the amplifier, a new bandwidth is encountered the unity-gain 0"tp"ts are electronically identical
because of the addition of the cable capacitance (see schematic diagram 228201: in Section5 ).
and equation 1 becomes
2-4. GUARD-OFF SWITCH.
f3dB = .16 equation 2
Rs (c,+c,) a. This Switch when in the GUARD Position reduces
the effect of input cable capacity and provides
where $$B is the 3d0 bandwidth of the system in high speed measurements from high resistance so"rces
at the end of a cable by driving the cable capaci-
R,'is the source resistance in ohms; tance and the inner shield of the INPUT Rece~ta-
Cs is the source capacitance in farads; cle(s) (refer to paragraph 2-3). h guarded ckuit
=*d Cc is the cable CaDacitance in farads. is possible in this way.
An average cable adds approximately 30 picofarads b. With the Switch in the GUARD Position input
per foot to the circuit. Th"s, a 3-foot cable capacity is decreased (to approximately 1 pi even
would add 90 picofarads and with "p to 10 feet of cable on the input) and rise
time is decreased. Note, however, that the noise
is increased.
0373 5
C. With the GUARD-OFF switch in the OFF position 4. Set the VOLTS Switch to a more sensitive
the input capaoity is increased to 5 pF with no range and readjust for zero, if necessary.
cable the input and 100 pF with 3 feet of cable
on the input. The speed of response and the noise
are decreased.
a. A good differential amplifier is character-
ized by Its common mode rejection and also its
common mode voltage range. The Model 604 rates re1-
When using the Model 6041 with the GUARD- atively well in both these areas.
OFF Switch in the GUARD position the total
system is guarded. Also, less than 3 pF b. The specifications in Table 1 read greater
will be present at the Madel,~ input than 90 dB from dc to 120 HZ decreasing to 80 dB
with 3 feet of cable on the Input: at 1 kHz. Actually, the comm mode rejection is
greater than this. The specification is based on
d. Therefore, although guarding increases speed, the nonlinear distortion caused by swinging the
it also increases noise as well and a oompromise amplifier between i-11 volts comon mode. The fun-
between speed and noise will have to be made. damental is almost completely removed and all that
appears at the output is predominately second bar-
manic of the cornon mode input signal. This dist-
ortion inoreases with frequency and the specifica-
a. This Switch allows the user to select the most tion is degraded acoordinyly. At lower ~mnmn
amenable bandwidth to achieve optimum rise time and mode levels, lets say 2 volts peak-to-peak, it is
noise The amplifier ro+ off at 6 dB/octave and practically impossible to see any output change
the S&itch determines fhe meGured bandwidth of the due to the common mode signal up to 1 kHz at any
amplifier and cuts off higher f&quenc~ea a+ the 3 gain setting on the Model 604.
dEi point. For example, if the Switch is set to 1
kHz the~bahdwidth~of the Model 604 is 1 ~HZ and all
higher frequencies are cut off. Setting the Switch
to OFF gives the rated frequency response. a. Check the Fuse and the LINE VOLTAGE Switch
for the proper line voltage. Connect the power
b. The user oan use the HIGH CUT HZ Switch to cord to the power source.
select the optimum bandwidth for his measurement by
cutting off higher frequency noise components, ring-
ing and overshoot. Note, however, the lower the
bandwidth the longer the rise time. So the "ser
will have to use the reguirements of his experiment
and the method of trial and error to select the
proper setting of the Switch for optimum achieve-
ment.
GUARD-OFF Switch OFF
2-6. SUPPRESS CONTROLS. METER Switch POWER OFF.
There are three SUPPRESS Controls: Fnm ALU., C. Turn the METER Switch to CENTER ZERO. The
ME,";,ld and COARSE. The COARSE and MEDIUM SUPPRESS Meter Pilot Light should turn an. Within a few
Controls are eight position switches. The MEDIUM seconds the meter needle should come to the center
control interpolates between the setting of the position. If not, adjust the meter zero with the
COARSE Control. The FINE ADJ. Control is a ten- FINE AN. and MEDIUM SUPPRESS Controls. Normall".
turn potentiometer that interpolates between the there is no need to use the COARSE Control. .
settings of the MEDIUM Control. These controls may
either be used for suppression or for zeroing the NOTE
Model 604.
Using the center zero scales decreases accu-
b. The zero suppress circuit cancels any constant raoy because the scale span is reduced.
dc voltage in order to use a more sensitive range to
observe a superimposed signal. There is up to 11 d. After a few moments increase the voltage sen-
volt available for zero suppression. This means sitivity by advancing the VOLTS Switch to .3, .1,
that on the most sensitive ranges up to 1000 times etc. Continue zeroing with the FINE ADJ Control.
full scale may be suppressed. For example, the Model
604 can measure changes of 1 millivolt full scale in e. After long periods of storage or after an
a 1 volt steady signal on its .OO1 wit range. overload, the Model 604 may drift excessively. The
input transistors are insensitive to mechanical
C. operation. shock; however, a severe input overload may cause
a zero offset. This is corrected with the SUPPRESS
1. Adjust the VOLTS Switch to the range that Controls. Drifting, though, can occur far several
c,:,;~ the closest to a full scale meter deflec- ho"rS
2-Y. VOLTAGE MEASUREMENTS.
2. Turn the SUPPRESS Controls completely in
the direotion opposite meter deflection (counter- The Model 604 can be used to measure voltages
clookwise for positive deflections and clockwise tW:'WayS. Both ways may be used in either the
for negative deflections). guarded or the unguarded mode (refer to ,,aragraphs
2-3 and 2-4).
3. turn the COARSE Control setting until the
meter needle passes through zero. Turn the MED- 1. In the single-ended method the unknown volt-
IUM Control until the needle passes back through age is connected to one of the Input Receptacles.
zero and then adjust the FINE ADJ. Control for The other Receptacle is locked in Zero Check Po-
zero deflection. sition Irefer to paragraph 2-2).
6 0373
NOTE ""lock both ZERO CAECK Buttons. set the rnTER
Switch to + or -, as necessary. Increase sensi-
The ZERO CHECK Buttons are tr"e transfer tivity with the VOLTS Switch until the greatest
type switches. When they are depressed, o" scale meter deflection is obtained. Recheck
the input will be briefly connected to 7.ero settina after increasinil sensitivitv. me
lo9 ohms to ground. Then as the L3uttons difference Gig"& is equal to the perce";age of
are further depressed toward LOCK posi- full scale that the mete* reads times the VOYPS
tion the input is open circuited and will switch setting. (Refer to paragraph 2-2 also).
remain so until the B"tto" is released.
I" the LOCK position the Model 504 input 3. For guarded, fast IneasureInents, set the
is internally connected to ground. Please GUARD-OFF Switch to GUARD. (Refer to paragraphs
note that for certain very high impedance 2-3 and 2-4).
sources it may be necessary t" "ever con-
nect the i"p"t to ground, eve" through 4. Set the HIGA CUT HZ switch to the desired
109 ohms. 1f this is the case, depress position to obtain "ptimum response. (Refer to
and release the ZERO CHECK Button as paragraph 2-5)
fast as possible and the source will see
109 ohms for only a few milliseconds. d. TO tneaS"re sollrces greater than 1 Volt, use
one of two divider probes. The Model 6102A 10:1
2. In the differential method one ""know" "olt- Divider Pr*be extends the Model 604's range to 10
age is connected to one of the Input Receptacles volts' overall accuracy is i48 and input resistance
and the other voltage is connected to the other is 1Oio ohms. The Model 6103. 1OOO:l Divider Probe
Input Receptacle. I" this mode both ZERO CHECK extends the ?.,odel 604's range to 1 kilovolt; over-
ButtonS are unlocked. (Refer to paragraph Z-2). all accuracy is 26% and input resistance is 1012
ohms. Follow the same operating procedures with
3. ACC~SSCX-y probes extend the Model 604's the dividers as in subparagraph b. The Model 6012
range to 10 kilovolts. (Use either single-endedly Triaxial-to-coaxial Adapter must be used with the
or differentially only with the GUARD-OFF Switch ~"dels 6102A and 6103A Divider Probes. Note, how-
in the OFF position). ever, "sing the Adapter connects the inner shield
to ground, defeating the g"ardi"g capability of
b. Single-Ended Method Voltage Measurements. the Model 604. Th*r*fOre, the GUARD-OFF Switch
This method should be used when an unknown voltage rnu~t be in the OFF position for the instrument to
from a single source is to be measured. (Refer to operate. The full-scale voltage range is the di-
paragraph 2-2 also). vider ratio times the VOLTS Switch setting.
1. set the Model 604 front pane1 Controls as NOTE
follo"s:
If the Models 6102~ and 6103A Divider Probes
are used with the Model 604 in the differen-
tial mode, the comm"" mode rejection is lim-
ited by the probe matching and typically weld
be about 30 dU. Thus, 30 Volts of common
mode voltage would cause a full scale indica
tion.
2. connect the unknown voltage to one of the Z-10. CURRENT MEASURl?MENTS. The Model 604 becomes
Input Receptacles. Zero the meter (paragraph 2-6, an ammeter when used in conjunction with the Model
and ""lock the ZERO CHECK Button pertaining to 6041 Differential C"rre"t Shunt or when resistors
tile used Input Receptacle. Keep the other ZERO are installed within the cases of the Model 301 (see
CHECK Button in the LOCK position. Set the METER Figure 61. When using the Model 6041, resistors
witch to + or -, as necessary. Increase sensi- are switched across the inputs of the Model 301
tivity with the VOLTS switch until the greatest Amplifiers in the Model 604 with the + and - INPUT
on-scale meter deflection is obtained. Recheck Switches on the Model 6041. The full scale current
zero setting after increasing sensitivity. CR*- range is equal to reciprocal of the INPUT Switch
fer to paragraph 2-2 also). setting on the Model 6041 times the setting of the
VOLTS Switch on the Model 604. For example, if
3. For guarded, fast r"easure,"e"ts, set the the INPUT Switch is set to lOa and the VOLTS switch
GUARD-OFF Switch to GUARD. This method reduces is set to .Ol, the" the full scale cwrent range
the effects of input cable capacity with very is equal to l/108 x .Ol = 10-B x .Ol = 10-10 amp-
high impedance sources and allouis guarded voltage eres.
measurements (Refer to paragraphs 2-3 and Z-4).
4. set the HIGH CUT HZ Switch to the desired
position to obtain optimun response. (Refer to The Model 301 Instruction Manual, SUpplied
paragraph Z-5). with the Model 604, gives complete informa-
tion on Model 301 operation, circuit descrip-
Differential Method Voltage Measurements. tion, troubleshooting, calibration, parts
T.;, method should be used to ",eas"re the difference lists and schematic diagrams. There are
between two ""know" voltages "either of which has two Model 301 Operational Amplifiers used
to be at ground potential, and either of which may as plug-i" ""its in the Model 604.
be as much as 211 volts off ground. (Refer to para-
graph 2-Z). a. the Model 604 can measure curlent~ several
ways. each of which may be used either in the guard-
1. Set the Model 604 front panel controls as ed or ""guarded mode.
show" in subparagraph bl above.
1. I" the single-ended method the ""know" cur-
2. connect one unknown voltage to one Of the rent is connected to one of the 1"p"t Receptacles
input receptacles and the &her "oltage to the 03 the Model 6041. The other I"p"t Receptacle on
other 1npLlt Receptacle. zero the meter and the" the Model 6041 is locked in Zero Check position
7
0373
by its corresponding ZERO CllECK Button on the range, the input capacity and the method used
Model 604 front panel. (Refer to paragraph 2-2). (guarded or unguarded). See specifications, Table
1, page ii. On all ranges, the rise time in the
2. I" the differential method one unknown cur- guarded method is less than one second with the spe-
rent is connected to one of the Input Receptacles cified capacity across the input. Even with much
on the Model 6041 and the other current is con- larger capacities on the input the negative feedback
nected to the other Input Receptacle. In this maintains a relatively short rise time. Given a
mode both ZERO CHECK Buttons are ""locked. CR*- choice, it is better to place the Model 6041 nearer
fer to paragraph Z-2). to the CUrrent source than to the data readinq in-
strulnent. Transmitting the input signal through
3. With the shunt resistors mounted inside the long cables decreases the responses speed and in-
cases of the Model 301 Amplifiers in the Model 604 creases noise.
the Model 604 may be used as an anuneter either
single-endedly or differentially. This method, Single-Ended Method Current Measurements with
however, limits versatility and gives only four MC&l 6041. This method is used to measure an "n-
decades of response. The same input considera- known current from a single source (Refer to para-
tions apply with this method as spelled out in graph 2-2).
,,aragraph 2-2.
1. Connect the Model 6041 Outputs, labeled TO
CAUTION 604 INPUT + and -, to the corresponding Input
Receptacles on the Model 604 with the supplied
When resistors are mounted internally, the mating cable. Set the Model 604 and 6041 front
input is open circuited when in zer" check. pane1 controls as follows:
This presents a" open circuit to the cur-
rent source, stopping CUrrent flow. I"
some cases this could be harmful to the
current source and possibly to the Model
604 itself when high complicance voltages
are encountered.
when making measurements from high impedance
sources or low current sources usinq the 2. Connect the unknown current to one of the
guarding feature, it may be desireable to input Receptacles on the Model 6041. zero the
set the HIGH CUT HZ Switch to the lowest meter and unlock the ZERO CHECK Button that CDT-
setting, 100 HZ, to limit the noise band- responds to the Input Receptacle being used. Set
width in some ca6es'. The noise increase. the METER switch to + or -, as necessary. In-
when guarding, increases linearity with create sensitivity with the VOLTS Switch and the
the bandwidth increase and the noise may Input Switch that corresponds to the Input Recep-
eventually overload the amplifier. This tacle beinq used until the qreatest on-scale
would cause a" error in a meter reading, meter deflection is obtained. Recheck zero set-
but the error would go undetected ""less ting after increasing sensitivity. (Refer to
the o"tp"t was monitored o" an oscilloscope. paragraph 2-2 also).
b. Rise time varies primarily with the c"rre"t 3. The full-scale c"rrent range is the VOLTS
measuring point
LB------------
`70error in reading due to circuit loading = -100 it!,
it Rin (< R, I a I meter and 9b error E 0
FIGURE 5. Error due to Ammeter Resistance. Current sources may be considered a voltage (E) in series with
a resistance (R). The current with the ammeter short circuited is I = E/R. With the Short circuit removed,
the effective i"p"t resistance of the ammeter (Ri") is in series with the source resistance (R). The cur-
rent of the complete circ"it is reduced and Imeter = E/(R+Ri"). If the effective ammeter input resistance
is small compared to R, Imeter N I and the error introduced by circuit loading is negligible.
8 0373
Switch setting times the reciprocal of the In- ing cable. set the Models 604 and 6041 front pan-
put Switch setting. use the Smallest VOLTS el COntrOlS as follows:
Switch setting possible to minimize input volt-
age drop and thus obtain the best accuracy. The
full scale input voltage drop is equal to the
VOLTS Switch setting.
(Far example: If a currenf2sourae has a
300 Volt compliance and 10 ohms OutpUt
resistance, then I = 300/101z = 3 x 10m10
ampere. Using a lo9 ohms shunt resistor
and a 300 millivolt full scale voltage
range would display this current full
scale. The loading error would he only
O.l%, which is 40 times less than the
accuracy of the system. The signal-to-
noise ratio would be 100 times better
than if a 107 ohms shunt resistor and
a 3 millivolt full scale range were
used, .
d. Differential. Method Current Measurements with
the Model 6041. This meth*d is used to measure the
difference between two unknown currents neither of
Which has to he at ground. (Refer to paragraph 2-2 Each Mode: 34 Input Receptacle is connected
also). toe, Model 301 c rational Amplifier hooked up in
single-ended COI pration. The Amplifier corres-
1. Connect the Model 6041 outputs, labe?lad TO panding to the XJT Receptacle is in a non-in-
604 DWJTS + and -, to the respective Input R&- verting mode ant ne Amplifier corresponding to the
ceptacles on the Model 604 with the supplied mat- -INPUT Receptac: is in an inverting mode. If so
IGURE 6. internal View of Model
01 Amplifier Showing Location
31 Installing Internal Resistor.
or complete and comprehensive
nfomation on the Model 301. re-
?I? to the supplied Model 3oi
nstruction Manual.
9
0373
TWLE 6. Typical Rise Times and Noise of the Model 604 As A" Ammeter W◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo