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