Keithley 615 Service manual
CONTENTS
02738
SPECIFICATIONS
MODEL 615
SPECIFICATIONS
AS A VOLTMETER:
RANGE:
ACCURACY: +0.290 of reading +1 digit on all ranges exclu.
ZERO DRIFT: Less than 1 millivolt in the first hour or subse-
NOISE: * 1 digit with input shorted on most sensitive range.
INPUT IMPEDANCE: Greater the” 10” phms shunted by
NMRR: Greater than 60 d8 on the most sensitive range de.
AS AN AMMETER:
RANGE: lo-‘2 ampere full scale (1O-L5 ampere, least sig.
ACCURACY: b-0.5% of reading,
NOISE: f-4 digits with input open and shielded on most
OFFSET CURRENT: Less than 5 x IO-l5 ampere
AS AN OHMMETER:
RANGE:
ACCURACY: &0.5% of reading.
AS A COULOMEMETER:
RANGE:
ACCURACY: +5% of reading 3~2 digits on all ranges. Drift
100
nificant digit) to 100 volts in four decade ranires.
sive of noise and drift.
quent 24.hour periods
150 mliCrOYOlt* pm “C.
35 picofarads. Input resistance may aIs0 be selected in
decade steps from 10 to 10” ohms.
creasing to 40 dB on the
nificant digit) to 0.1 ampere in 12 decade ranges.
ampere ranges using optimum sensitivity control setting;
*2% of reading *I digit 0n l@a and lo-3 ampere ranges
and 14% of reading *1 digit on
ranges exclusive of noise and zer0 drift.
sewitive range.
digit) to
ranges using optimum sensitivity control setting; *4% of
reading + 1 digit from
and zero drift.
millivolts full scale
10,000
ohms full scale
10” ohms
in
eleven
109 to 10’”
(100
microvolts.
least sig
after l.hour warmup. Less than
lOOwIt range at
-tl
line frequency.
digit
on 0.1 to l@’
1O-Lo to lo.‘1 ampere
(10
ohms. least significant
decade ranges.
hl
digit on
ohms exclusive pf noise
10’ to lOa ohm
10.” coulomb full sca1e (lo-” coulomb. least
significant digit) to 10’5coulomb in seven decade ranges.
due ta offset c”rrent does not exceed 5 x lO-‘I coulambs,
secpnd.
GENERAL:
DISPLAY: 4
sensftlwty
tivity setting.
POLARfTV SELECTION & OVERLOAD INDICATION: Auto-
matic.
OVERRANGING: lOO%overrangingon all ranges exceptwhen
“Sing Se”sltl”lty setting of 100.0.
DISPLAY RATE: 24 readings per second maximum (20 per
second on 50 Hz models); adjustable to tw, readings
per minute.
PRfNTER OUTPUTS AND OUTPUT CONTROLS: Model 4401
accessory provides BCD output and external cpntmls.
ISOLATION: Circuit ground to chassis ground: Greater than
IO6 ohms Shunted by 0.2 microfarad. Circuit ground may
be floated up to
CMRR: For high open-circuit CMRR. residual unshielded
capmtance between input high and chassis ground is less
than 0.1 picofarad.
ANALOG OUTPUTS:
Unity gain: At dc. Output is equal to input within 100 ppm.
exclusive of noise and zero drift. for Output currents of
100
1 mA: fl milliampere at up to 1 volt for full scale input,
100%
setting.
1 V: *l volt at
100% pverfange capability except M 100.0 sensitivity
setting.
CONNECTORS: Input: Tefkxvinsulated triaxial. Analog wt.
puts: Unity Gain: Binding Ppsts. 1 mA; Switchcraft Nl13B.
1V; Amphenol 80 PC 2F. Printer output &controls: 50.pin
Amphenol Micro-Ribbon.
DIMENSIONS, WEIGHT: 5%” high x
(132 x 433 x 280 mm); net weight. 20 pounds (9.1 kg).
POWER: 105.125 or 210.250 volts (switch selected), 60 HZ:
50 Hz models available. 35 watts.
ACCESSORIES SUPPLIED:
Made1 6011 Input Cable: 30” triaxiel cable with triaxial
connector and 3 alligator clips.
digits from 0000 to
settings; from 0000
100 volts
microamperes or fess.
overrange capability except on
up to 0.1 microampere for full scale input.
1999 on 0.1, 1.0,
to 999 on the 100.0 sensi-
with respect to chassis ground.
100.0
19”
wide Y 10” deep
and 10.0
sensitivity
ii
0372R
MODEL 615 ELECTROMETEX
SECTION 1.
l-l.
GENERAL.
a. The Keittlley Model 615 Digital Eleceromeeer is a
fast, accurate and sensitive Electrometer with digital
display.
instrument which measures a wide range of d-c voltage,
current, resistance and charge. Thy4Electrometer’s
input resistance of greater than 10 ohms is the result of extensive instrument development with high input impedance transistors. The Model 615 has all the
capabilities of conventional VTVMs, but it can also
make many more measurements without circuit loading.
b. The Electrometer has four decade voltage ranges
from 0.100 volt full scale to 100 volts, 12-decade
CUrrent ranges from 10-12 ampere full scale tcl 0.1 ampere, 11 decade linear resistance ranges from lo4 ohms
full scale to 1OL4 ohms, and seven decade charge rang-
es from lo-11 coulomb full scale to 1O-5 coulomb.
C. The Model 615 employs matched insulated-gate
field-effect ~ransiseors followed by a transistor differential amplifier and complimentary outpue stage.
A large amount of negative feedback is used for stabiliey and accuracy.
1-2. FEATURES.
a. Unique input circuit provides overload profec-
tion up eo 500 volts on most ranges without damage.
b. Time stability is better than 1 millivolt/day
after l-hour warmup. Less than 150 microvolts per ‘=C
zero drift with temperature.
C. Offset current less than 5 x 1O-L5 amperes min-
It is a versatile, comp’letely solid-state
GENERAL DESCRIPTION
imizes zero offset with high source resistance.
d. A front panel ZERO CHECK Switch permits check-
ing zero-offset without disturbing the tneasurement
CiX”iC.
e. Operarion up to *lOO voles above case ground is
possible without affecting the reading. Isolatio”~
from csrcuit low to case ground is greaeec than 106
ohms shunted by 0.2 microfarad.
f. Analog output provided for 1 mA full scale recorders such as the Keiehley Model 370 Recorder or
other floating instrument.
g. Digital display enables voltage’measurements to
l O.Z% of reading *I digit.
h. Polarity is automatically indicated on the dis-
Pk+,
i. Display rate 1s adjustable from 24 readings per
second to two readings per minute LO acconmadate the
mode of data retrieval.
j. Analog-to-digital converter is a dual slope intearaeing type circuit to pro”ide inaounity to line
power frequency pickup.
k. Model 4401 Printer Output.Cards are available
for factory or user installation. This option provides BCD outputs far significant digits, range, polarity, sensitivity and overrange. Various remaee
control lines are also provided. The Output Buffer
cards are easily inserted into prewired, premouneed
card-edge connectors an the Model 615 chassis.
04728
OPERATION
WDEL 615 ELECTROMETER
Model 615 Front Panel Controls and Terminals (Figures 1 & 3).
TABLE 2.
contra1 F”“ctio”*l Description
SENSITIVITY Switch
Selects full-ecsle voltage sensitivity; slso used to mulriply
current, resietance and charge ranges on the Range Switch.
Automatically eelecrs the proper decimal point position.
RANGE Switch
Selects the mode which ia to be measured: voltage, current,
resistance or cherge.
FEEDBACK Switch
POWER Switch
Selects either NORMAL or FAST modes of operation.
Controls e-c line power to instrument (an/off).
DISPLAY RATE Control Determines number of analog-to-digital conversions per second.
ZERO caner01 Provides fine zero control adJuseme”e.
ZERO CHECK Switch Provides zero offset check without disturbing the source circuit.
INPUT Receptacle
Connefts wurce to input. ~ecepeacle is a Teflon insulneed
triaxia1 connector.
LO
TERMINAL
*Display Lights
Numerical Readout
Provides connection to input low.
Indicates polarity of input signal.
Indicates magnitude of input signal.
Par.
2-2,2-3
Z-2,2-3
2-2,2-4,2-5
2-2
2-3
2-2
2-2
2-l
2-l
2-3
2-3
Control
COARSE ZERO Switch
1 MA OuTPuT Receptacle
PRINTER/CONTROL
CO”“eCtOC
SPARE Receptacle
Xl OUTPm and
G”m.tl Terminals
CASE
GROUND Terminal
LO Terminal
1 VOLT OWPIPI
Line Cord
F”M
Model 615 Rear Panel Controls end Terminals (Figure 2).
TABLE 3.
Functional Description
Provides extended adfustment cepabflity of the front panel
ZERO Control.
Connect[i analog output to monitoring device.
50 pin connector for BCII digital output: provldea printer
control and remote control when Model 4401 printer ootput
cards ere installed.
Blank hole with cover plate for mounting edditional 50 pi”
CO”“BCtOC.
Provides extremely linear unity gsi” operation. Also used
for guerded reeFstance a.easureme”te.
Connected to Model 615 cabinet and outside shell of input
Connector.
Pravidea connection to input low end front panel LO connection.
Provides l’volt output for calibration purposes.
connecta line power to inatroment.
3
AD
Slow Blov.
117 volt - 314 A.
234 volt - 3/g A.
Psr.
2-2
2-9
2-10
__-
2-9
2-6
2-6
2-9
2-2
2-2
117-234V Switch Sets lnatrument for either 117 or 234 volt a-c power operation.
2-2
2 0470
MODEL 615 ELECTROMETER
GENERAL DESCRIPTION
SENSITIVITY Switch
POWER DISFLAY
ZERO
Switch PATE CONTROL
(S102)
CONTROL (R1222)
(R1201)
FIGURE 1. Model 615 Front Panel Controls and Terminals.
(S1203)
FEEDBACK LD
Switch (S1204)
RANGE Switch
(51201)
BINDING
POST
(51202)
ZERO CHECK
(S1202)
INPUI
RECEPTACLE
(51209)
COARSE ZERO
switcn (S1205)
Xl ouepur
(51203)
1 VOLT ODTPW
Transistor
FIGURE 2. Model 615 Rear Panel Controls and Terminals.
(9102)
Transformer
0570
3
OPERATION
MODEL 615 ELECTROMETER
SECTION 2.
2-l.
INPLPI CONNECTIONS.
8. The INPUT Receptacle of the,Model 615 is a Teflon insulated triaxial connector. The center terminal is the high impedance terminal: the inner shield
is the low impedance terminal; the outer shield is
case ground.
b. The front panel LO Terminal is connected to
the inner shield or low impedance terminal. The LO
Terminal is connected to the rear panel LO Terminal.
When the shorting link o” the rear panel is connected,
the LO is connected to case ground.
(See Figure 3).
INPUT
OPERATION
d. Carefully shield the input connection and the
source being meaaured, since power line frequencies
are well within the pass band of the Electrometer o”
a11 ranges.
may cause definite readout
“se high resistance, low-loss materials - such
e.
as polyethylene, polystyrene or Teflon - for insula-
tion. The insulation resistance of test leads and
fixtures should be several orders of magnitude higher
than the source resistance. Excessive leakage will
reduce accuracy.
employs a graphite coating between the dielectric and
the surrounding shield braid.
f. Any change in the capacitance of the measuring
circuit to ground will cause disturbances in the read-
ing, especially on the more sensitive ranges. fake
the measuring setup a.s rigid as possible, and tie
down connecting cables to prevent their movement. If
a continuous vibration is present, it 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.
Unless the shielding is thorough, pickup
disturbances.
“se a law-noise type cable which
NOTE
FIGIRE 3. Model 615 Triaxial Input Receptacle.
c. The Model 6011 Input Cable (provided) is a 30”
triaxial cable with triaxial connector and 3 alligator
clips. See Table 4 far color coding of the alligator
clips.
The high impedance terminal is shielded by the
inner braid of the eriaxfal cable up to the miniature
alligator clip.
Color Coding of Alligator Clips for Model 6011 Input
TABLE 4.
Cable.
Lead
heavy wire with
Input
high
C*llt*r
red clip cover
thin wire with
Input low
Inner Shield
black clip cover
thin wire with Case Ground
Outer Shield
green clip cO”er
Clean, dry connections and cables are very
important to maintain the value of all insulation materials. Eve” the best insulation will be compromised by dirt, dust,
solder flux, films of ail or water vapor.
A good cleaning agent is methyl alcohol,
which dissolves most common dirvwithout
chemically attacking the insulation.
D=Y
the cables or connections after washing
with alcohol or dry nitrogen if available.
If available, Freon is a” excellent cleaning agent.
The
g.
accessories described in Section 7 are designed to increase the accuracy and convenience of
input connections. “se them to gain maximum
capabil-
ity of the Model 615.
h. Far low impedance measurements - below lo*
ohms or above 10-S ampere - unshielded leads may be
used.
i. When the Model 615 is used on the most sensitive ~“rrent range with the FEEDBACK Switch at FAST,
same insulators - such as Teflon - may produce random signals which show up as erratic readout deflec-
tions. Insulation used in the Model 615 is carefully
selected to minimize these spurious signals.
It is advantageous to connect the Model 615 in-
j.
put to the source only when a reading is to
be made.
“se a high impedance transfer switch and well shielded chamber if available.
4
04728
MODEL 615 ELECTROMETER
OPERATION
NOTE
In some cases, the offset current can charge
the external test circuitry. One example of
this occurs when measuring a capacitor’s
leakage resistance by observing the decay of
the Germinal voltage. If the leakage current
is less than the offset c”rrent (less than 5
x lo-l5 ampere), there may be no decay of the
terminal voltage when the Electrometer is
left connected across the capacitor’s termi-
nals.
k. The Model 6012 Triaxial-to-Coaxial Adapter enables using coaxial cables and accessories with the
Model 615 by adapting the triaxial INPUT connector to
the UHF coaxial type,
CAUTION
The Adapter connect? circuit law to case
ground. The Model 615 cannot be used offground when using the Adapter. The instrument cabinet will be at the same potential
as the input law.
NOTE
Keep the shield cap (provided) on the INPUT
Receptacle when the Electrometer is not in
use co prevent overloads due to external
noise pickup.
2-2.
PKECMINARY
OPERATING
PROCEDURES.
f. The Model 615 may have excessive drift or zero
offset after long periods of storage or after an over-
load. This my be corrected with the zero controls
although drifting may continue for several hours.
NOTE
If the Model 615 has been stared for a long
time, the offset current may exceed the
specification when first
decrease to below the specified amo”nt
after one or two hours of “se.
inherent characteristic of the input transistors; the instrument is not faulty.
g. Although the offset current of the Electrometer
is much below that found in conventional voltmeters,
it cm be observed on the readout since the offset
currene charges the input capacitance, the Electrometer appears to drift when the input is open. Use the
ZERO CHECK Button to discharge the charge build-up,
h.
Follow the particular procedures in paragraphs
2-3 co 2-7 for measuring voltage, current, resistance,
and charge.
2-3. DIGITAL READOUT OPERATION.
a. Valtmecer Digital Readout.
1. When the RANGE Switch is placed in the VOLTS
position, ehe Electrometer digital readout designates the actual voltage measured using four numerical digit readouts.
used,
but should
This is an
a. Check the 117-234V Switch for the proper AC line
voltage.
b. Check for proper rated fuse.
See the front panel controls as follows:
C.
ZERO CHECK Button
RANGE Switch
SF.NSItI”ITY Switch
FEEDBACK Switch NORMAL
POWER Switch OFF
d. Connect the power cord. Place POWER Switch to
ON position.
ZERO Conerol if necessary. Zero is indicated by continuously flashing * polaricy lights.
The rear panel COARSE ZERO Control may be
adjusted if a large zero offset is indicated.
e. After a few moments increase the voltage sensitivity by advancing the Switch to one position CLIUIICerclockwiae.
Control.
After one-half hour warm-up, adjust the
NOTK
Continua zeroing with the FINE ZERO
wise- Position
2. The SENSITIVITY Switch has four positions
which control the lighted decimal point location
and therefore the full scale voltage range. The
full scale voltage range far each
position is shown in Table 5.
TABLE 5.
SENSITIVITY Switch
Position
I -~-
0.1 Positicm 1 (full”
1 1 Position Position
10 10 Position Position
100 100 PosFtFon PosFtFon
I I
3. The fourth (left most digit) readout permits
a.* averrange display. The largest reading that can
be displayed “sing all four digit readouts is 1999.
If there is’an overload condition, then all readouts will blank (none of the digital readout tubes
will be lighted).
counterclockwise) counterclockwise)
2 2 x.xXx x.xXx
3 3 xX.xX xX.xX
4 4 (fully (fully xXx.x xXx.x
clockwise) clockwise)
The polarity (*) display indica-
SENSITIVITY
Decimal Point
msi.cion
.xXxX
Switch
0570
5
OPERATION
MODEL 615 ELECTROMETER
tars remain lighted during an overload condition
indicating the correct polarity. Thus the Electrometer display will indicate correctly within specifications with no ambFguous overload display.
4. To remove the overload condition, change the
SENSITIVITY Switch setting or decrease the input
signal magnitude.
b. Ammeter Digital Readout
1. When the RANGE Switch is placed in the AMMETER
position, the Electrometer digital readout desig-
nates the voltage across an accurately known selfcontained resistor. The RANGE Switch selects the
calibrated range resistor for current measurements
from 10-l to lo-11 amperes. The range resistor is
the reciprocal value of the Range setting. The
readout indicates the voltage across the Range resismr.
2. The full scale current range is determined by
multiplying the Range setting times the digital
readout display.
The SENSITIVITY Switch operates
in the same fashion aa for voltmeter measurements.
(Refer to preceding paragraph 2-3, a).
3. The full scale current range far various front
panel control settings is shown in Table 6.
TABLE 6.
ac~rately knovn capacitor since the Electrometer
is sensitive to the integral of the current applied
from the external unknown source.
2. The coulomb measurement is determined by mul-
tiplying the RANGE Switch setting times the digital
readout display.
e. DISPLAY RATE Control. (This control is a continuously variable control that permits the user to
select the rate of analog-to-digital conversion).
That is, the control determines the number of times
a new reading will be recomputed per unit of time.
Thts is useful for sampling a continuously varying inpllt current as well as for controlling slower external
devices such as paper tape punches and printers. With
the DISPIAY Control in the MAX Position the display
rate is 24 times per second (20 for 50 HZ models).
When the control is varied clockwise, the rate de-
creases to a minimum of about 2 per minute in the extreme clockwise position. The front panel DISPLAY
SATE Control applies to the digital circuitry only.
VOLTAGE MEASUREMENTS.
2-4.
a. The Model 615 can meas,,re an unknown voltage
when the low impedance terminal is up to 100 volts
off case ground. Safe operation of the Electrometer
is insured by grounding the case. To use the Model
615 for off ground voltage measurements, disconnect
the shorting link between LO and CASE GND Terminals
on rhe rear panel. (Refer t.3 Figure 2).
Full Scale RANGE SENSITIVITY I
Switch
C. Ohmmeter Readout.
1. When the RANGE Switch is placed in the OHMS
position, the Electromerer digital readout designates the actual voltage across the unknown resistor as an accurately known current (internal to the
Electrometer) is applied to the unknown.
2. The RANGE Switch selects the current for Olw
lll~ClS”C~lU~“t~.
The current is the reciprocal value
of the OHMS range setting from 105 to lo12 ohms.
The SENSITIVITY Switch operates in the same fashion
aa for voltmeter measurements.
3, The actual resistance measurement is deter-
mined by multiplying the RANGE Switch setting tFmes
the digital readout display.
d. Coulombmeter Readout.
1. When the RANGE Switch is placed in the CO”LO”BS position, the Electrometer digital readout
designates the actual voltage across a self-contained
CAUTION
Operating the Model 615 at more than 100
volts off ground may permanently damage
the instrument. The isolation between
circuit low and ground could break dawn
making the instrument unusable far safe
off ground measurements.
Refer to Paragraph 2-6 far complete instructions for
making off ground measurements.
b. The Model 615 has been designed to meas”re valt-
ages up to 100 volts from very high resistance sources.
However, the Model 615 can also be used for meaaurements from low sr,urce resistance and voltages up to 30
kilovolts with high voltage divider probe.
1, The input resistance can be decreased in or-
der to reduce the effects of stray pickup with low
sou*ce resistances.
Refer to Paragraph 2-4, f for
complete instructions.
2. ear measurements of voltage up to 30 kilovolts
refer to Paragraph 2-4, g which describes various
divider probes available from Keithley.
c. The Model 615 can measure voltages in two modes:
Normal Mode and Fast Mode.
1. Normal Mode.
In the Normal Mode - FEEDBACK
Switch at NOWAL - the unknown voltage is connected
to the INPW Receptacle. Input impedance with th
RANGE Switch in VOLTS position is greater than 10
84
ohms shunted by 35 picofarsds,
0570
2. Fast Mode.
1" the fast Mude - FEEDBACK
Switch at FAST - the effects of inp"t cable capaci-
tance may be reduced for measurements fcum very high
source resistances. Guarded valtage measuremenr~
may aiso be made.
d. normal lode voltage Measurements
ZERO CHECK ButtOn LOCK
RANGE Switch
SENSITIVITY Switch
VOLTS
Fully Cluckwise
FEEDBACK Switch NORMAL
TO make aff graund measureme"zs, refer 'CO
Paragraph 2-6.
2. connect the Modei 6011 Trianial Input Cable
eo the unknown voltage as fallows:
a) the heavy wire with red clip cover should
be connected to the source high potential.
c) The thin wire wirhgrceaclip cover should
not be connecred when the shorting link between
LO end CASE Terminals on the rear panel is connected.
NOTE
To make off ground measurements. refer to
Paragraph 2-6.
3. ""lock the ZERO CHECK Button eo make a mea-
surement
4. Adjusr the SENSITIVITY Switch c~unrercL~ckwie.e
LO increase the Model 615 sensitivity. Readjust rhe
ZERO control as necessary after each change in sen-
sitivity.
5. The voltage measured is indicated directly 0"
the digital display with the decimal poinr automatically indicated. The poiarity is auLomatical,y
indicated corresponding CO Lhe potential of the
Electr~merer input high with respect to input low.
NOTE
The Model 615 has 100% overranging on all
ranges except for rhe 100 volt full range
sensitivity. An overload on any range is
indicated by a blanked digital display, a
feature which averts erroneous readings
when 200% of full range Is exceeded. The
digital display is Lighted when the over-
load is removed.
e. ~aat Mode voltage Measurements
1. set the frant panel controls as follows:
ZERO CHECK Butfc'n LOCK
RANGE Switch
SENSITIVITY SWitCh
FEEDBACK Switch
VOLTS
Fully Clockwise
FAST
0470
OPERATION
2.
Model 6103A Divider Probe for measurements up
to 30
kilovolts. This probe permits meas”rements
with overall accuracy of Cg%.
1012
ohms maximum. The actual voltage is obtained
Input r**i*t**c* is
by multiplying the Electrometer digital display
times the divider ratio.
NOTE
The Model 6012 Triaxial-to-Coaxial Adapter
must be
used
with Models 6102A and 6103A
sF”ce tile probes are termFnated with a LW
connector. When using the Model 6012, the
case ground is connected to inp”t law so
that the Electrometer may not be used for
off ground measurements. -
2-5. CURRENT
MEASUREMENTS.
a. The Model 615 can measure an unknown current
when the low impedance terminal is up to 100 volts off
case ground. Safe operation of the Electrometer is
insured by grounding the case. To “se the Model 615
far off ground current measurements, disconnect the
shorting link between LO and CASE GND Terminals on the
rear panel. (Refer co Figure 2).
CAUTION
Operating the Model 615 at more than 100
volts off ground may permanently damage
the instrument. The isolation between
circuit low and ground could break down
making the instrument unusable for safe
off ground meawrements.
Refer to Paragraph 2-6 for complete instructions for
making off ground meas”eements.
b. The Model 615 can meas”re currents in two modes:
Normal Mode and Fat Mode.
1. Normal Mode.
eny renge
- the cwrent is determined by measuring
In the Normal Mode - used on
the voltage drop across a self-contained reeistor
shunting the electrometer amplifier input. This
method permits a minimum noise m~as”rement when re-
sponse speed is not.critical.
2. Fwt Mode.
I” the F.ast Mode - for “se only
MODEL 615 ELECTROMETER
below 10-S ampere range - a self contained resistor
is connected between the electrometer amplifier input and output (in the feedback loop). This method
permits faster response speed since the effect of
input capacitance is minimized. The input volcsge
drop is reduced to less than 100 microvolts on any
range. Refer to Table 7 for typical Response and
Noise performance for various values of input capacitance.
C. Normal Mode Current Measurements.
1. Set the front panel controls as follows:
ZERO CHECK nutron
LOCK
RANGE Switch 10-l AMPERES
SENSITIVITY Switch Fully Counterclock-
wise
FEEDBACK Switch NORMAL
NOTE
To
make off
ground measurements, refer to
Paragraph 2-6.
2. Connect the
Model 6011 Triaxial Input Cable
for meeauring s,, unknown current as follows.
a) The heavy wire with red clip cover should
be connected to the source high potential.
b) The thin wire with black clip cover should
be connected so as to place the Electrometer in
series with the c”rrent to be measured.
c) The thin wire with green
clip cover should
not be connected when the shorting link between
LO and CASE GND Terminals an the rear panel is
connected.
3.
Unlock the ZERO CHECK Button to make B mea-
surement.
4. Adjust the RANGE Switch to increase the Slec-
emmeter sa”siti”ity for CUrrent measurements.
5. The full range c”rrent for the Electrometer
is determined by multiplying the digital display
times the RANGE Switch setting. The best accuracy
for current meas”rements is obtained by “sing a
Typical Effects of External Inp”t Capacitance on Response Speed and Noise Performance in C”rre,,t Measurements
TABLE 7.
with the Model 615.
i-l****
$;to -
$"
10-S
10-7
10-6
s
Rise Time (seconds)
No C
2.0 2.0
.07 .45 .45 .07
,015 ,015
,003 .003
.003 ,003
2eE
5000pF
2.0 6 x lo-l5 1.5 x 10-14
.45' .07
,015 ;.i ;,m;l3 ;.":
,003
,003 3.3
No C
- x
8.5 x 10-14
Output
Noise
(Peak-Co-Peak)
$5;
s’x 10-11
x 10-10
5000pF
7 x 10-13
i.2 ;,!p;"
2
x 10-10
MODEL 615
SENSITIVITY Switch seeting which permits the use of
the smallest value rage resistor. The rsnge resistor value is equivalent CO the reciprocal of the
RANGE Switch setting. The input voltage drop across
the shunt resistor is indicated directly on the
Electrometer digital display.
ELECTROMETER
NOTE
OPERATION
The ZEN, CHECK Sutt~” provides a short
across the feedback of the Electrometer
Amplifier to enable zero adjustment.
Do not apply a short circuit ecross the
Electrometer input terminals since this
will creete ““stable amplifier operation
The SENSITIVITY Switch settings permit sn
input voltage drop af O.i, 1, 10, and 100
volts for current measuremenfs in the
mrmsl Mode. on the LO-9 to 10-l’ AMPERES
settings of the RAN E Switch, the resistors
(109, 1010, and 101
age coefficient uf .O*% per vale (naminal).
1f the SENSITIVITY Switch is adjusted far a
100 v”lt input drop, then a” additional
error of 2% occurs for the current messure-
lS**t.
the smallest input drop possible to minimize
voltage coefficient errors.
d.
low 10-5 amperes).
1. Set the front panel controls es follows:
ZERO CHECK Button
RANGE Switch
SENSITIVITY Switch
FEEDBACK Switch
TO make aff graund measurements refer ta
Psragraph 2-6.
2.
for measuring an unknow” current ae in 2-5, c-2.
3. unlock the ZERO CHECK Sutton t” make e mee-
surement
‘rherefore ie is reconrmended t” select
Fast mde Current Weasurements (for current be-
Connect the Model 6011 Triaxial 1”put Cable
E
ohms) used have a volt-
LOCK
10-6 AMPERES
Fully Councerclock-
wise
FAST
NOTE
4. Adjust the RANGE Switch to increase the Slec-
tr”meCer seneitivity for current measurements.
5. The full range current for the Electrometer
is determined by multiplying the digital readout
times the RANGE Switch setting. The best accuracy
for current measurements is Obtained by using a
SENSITIVITY switch setting which permits the use of
the smallest value range resistor. The range cesist”r value is equivalent to the reciprocal of the
RANGE Switch settine. The input voltane drop, across
ehe shunt resistor Is indicated directly on the
EiectromeLer digital display.
NOTE
The source resistance of the circuit eo be
measured should not be Less than 0.1 rimes
the range resistar used since adequate
feedback voltage cannot be developed at the
input and zero stability is adversely affected. The range resistor is the reciprocal of the AMPERES range in ohms.
CAUTION
Foe measurement of capacitor leakage cur-
rents using the Pest Mode, a very
voltage supply must
pacitor connected across the input, the
electrometer is exCrem*ly sensitive to
voltage transients with a resultant in-
crease in readout noise.
be
used. With a ~a-
stable
I
I
I-
a-7
I 1
I
SOURCE I
L--------l L------------l
FIGURE 4.
0470 9
I I
I
: ME)WJ&NG I
I
1 = ’ readout
‘f
X
R+Ri”
Error Due to Ammeter Resistsnce.
I
I
I
1 readout
__ _ _ _
I
R
AMMETER
I
I
OPERATION MODEL 615 ELECTROMETER
e. Galvanometric current Measurement Method.
I. operate the Electrometer in the Fast Mode as
described in Paragraph 2-5, d.
3. Adjust the Current Source co obtain a null on
the Electrometer digital readout. Increase the
Electrometer sensitivity as needed. The value of
the current which is suppressed is indicated o” the
current source setting.
NOTE
The connections for the Galvanometric Method
require the following accessories.
1 - Model 261 Current Source
1 - Model 6012 Adapter
1 - UHF tee fitting, Part No. cs-171
1 - Low noise coaxial cable, Model 2611
1 - Low noise coaxial cable, Part No. 19072C.
2-6.
OFF GROUND MEASUREMENTS.
a. ‘fhe Model 615
can be used for measurements when
the low impedance rerminal is up to IO0 volts off case
ground.
Safe operation of the Electrometer is insured
by grounding the case. To use the Model 615 for off
ground measurements, disconnect the shorting link between LO and CASE GNC Terminals a” the rear panel.
(Refer co Figure 2).
CAUTION
Operating the Model 615 at more than 100
volts off ground may permanently damage
the instrument. The isolation between
circuit low and ground could break down
making the instrument unusable for safe
off ground measurements.
b. Normal Mode Measurements. D‘sconnect the shorting link between LO and CASE GND Terminals on the rear
panel.
Connect the Model 615 case securely to earth
ground for maximum operator safety. Operate the Alectrometer 8s described in Paragraphs 2-4 or 2-5.
c. Fast Mode Measurements. Disconnect the shorting
link between LO and CASE CND Terminals on the rear
panel. Connect the Model 615 case securely eo earth
ground for maximum operator safety. Operate the Alectrometer as described in Paragraphs 2-4 or 2-5.
WARNING
The 1X4 analog outp”f can only be
used with
a recorder which will operate off ground
such as the Keithley Model 370.
NOTE
The
Model 615 ca”““t be operated off ground
if the Model 6012 Adapter is used since the
input Low and chassis ground are connected.
2-7. RESISTANCE MEASUREMENTS.
a. The Model 615 ca” be used to measure resistance
since the Electrometer permits accurate voltage or
current measurements from high resistance sources.
ResFstance can be
measured F” the following three ways.
1. Normal constant CurrenL Technique.
2.
Fast Constsne Current Technique.
3. Volt-Ammeter Method.
b. Normal Constant C”rre”t Resistance Measurement.
1. I” the constant current method, the Electrom-
eter meas”res the voltage drop across the unknown
resistance when a constant current is applied. The
voltage drop is the” proportional to the resistance
of the unknown.
2.
The Normal mode is recommended f r measure-
ments from 100 to 1O’l ohms. Above 10
Pl
ohms use
the Fast constant current technique.
10
0470
MODEL 615 ELECTROMETER
OPERATION
3. Set the front panel controis as fallows:
ZERO CHECK SULLO” LOCK
RANGE Switch
SENSITI”ITY Switch
FEEDBACK switch NORMAL
1011 OHMS
Fully Counterclock-
wxse
4. Connect the unknown resistance between the
electrometer input high and low as for normal Mode
Voltage Measurements.
5. Unlock the ZERO CHECK Hutton to make a mea-
S”Tellle”t.
NOTE
Do nae open circuir the Electromeeer on the
OHMS ranges; the input will de”elop a large
voltage due to its constant currene charac-
teristic. Keep the input shorted or the
ZERO CHECK Button locked.
6. the unknown resistance is determined by multiplying the digital display times the RANGE twitch
setting. “se the smallest RANGE Swiech setting for
beBe possible accuracy.
7. The applied test voltage is indicated directly
on the digital display in volts.
8. The test current is the reciprocal of the OHMS
Range setting.
NOTE
2. set the front panel controls as follows:
ZERO CHECK Button LOCK
RANGE Switch 1011 OHMS
SENSITI”ICY SWFtch Fully Counterclock-
wise
FEEDBACK Switch FAST
3. connect the unknown resistance between the
Electrometer input high and GUARD Terminal as for
Fast Mode Voltage Measurements.
4. ““Lock the ZERO CHECK Button to make a mea-
SuremenL.
5. the unknown rcsisrance is determined by multi-
plying the digital display times the RANGE switch
setting.
6. The low terminal of the INPUT Receptacle is
now a driven guard.
It may be used t” minimize the
effects of capacity berween hi&h end low and errors
due to leakage reSiSta”ce between big,, and low.
7. The Model 6oLl Input Cable. supplied with the
Model 615, provides a convenient means of making
guarded reeistance meesurements. connect the shart-
in&t link between the CASE GRO”ND and GUARD Terminals
“n the rear panel. This allows the CASE GROUND ur
blue test lead terminal to be connected CO the Luw
impedance side of the unknown resistance.
me inner
shield or the black test clip is the GUARD Terminal.
d.
Volt-Ammeter Resistance Measurement (to 10’6
ohms).
Shield the input if the resistance sample
exceeds 108 ohms.
Fast COnSLant current Resistance Measurement.
(&ommended for 10” to 1ol4 ohms measurements).
1. The Fast Mode permits faster response speed
when measuring very high resistances.
FIGURE 6. Volt-Ameter Resistance ,.,easuremenc.
1.
In the Volt-Ammeter method the voltage applied
to the sample is arbitrarily set at any cO”“enir”t
uoltage. The current through the resistance sa,“ple
is measured by the Electrometer. ‘rhe resistance of
the unknown is calculated in terms of the known
voltage impressed and the resultant measured current
2. This method requires the use of the folluwing
0470
11
OPEP.ATION
MODEL 615 ELECTROMETER
instr”me”ts and *cc***0ri**.
1 - Voltage Source, such as Keithley Models
240A or 241.
1 - Shielded switch, such as Keithley Models
6104, 3011 or 4194.
1 - Test Cable, such as Model 6108
1 - Model 6012, “XF to Triax Adapter.
3. Connect the voltage source, switch, and uoknown resistance as shown in Figure 6. since the
~lecrrometer is used for the measuremene of current,
refer to Paragraph 2-5 for complete instructions.
NOTE
Refer to Paragraph 2-6 for complete instructions for meking off ground measurements.
4.
To make a eesistame measurement, place Switch
s in the “OFF” position 8s shown in Figure 6. Ad-
,,st the voltage source for a predetermined voltage.
Place Switch S in the “ON” position to
apply the
voltage ecross the unknown resistance. Allow a
iod of time for the current through the unknown re-
sistance to stabilize.
Unlock the ZERO CHECK Sutton
to take a current reading. Adjust the RANGE Switch
and SENSITIVITY Switch to obtain a satisfactory
reading.
5. After a reading is made. place the ZERO CHECK
Sutton to LOCK poeition and place Switch s to “OFF”
pOSiti”“.
Rem”“* the unknown resista”Ce and replace
with a second sample if necessary.
NOTE
If the voltage applied to the sample is not
100 times the Electrometer input drop, the”
the unknown resistance ia calculated es
follows:
R x = Vsource
- “Input oroe
lMeeasured
where Rx = ““known resistance,
VSource - Applied voltage,
“Input Drop
= Electrometer input voltage
drop
and l”easured = Current measured by Electrom-
eter.
2-8. CHARGE mASuP.EMmTS.
per-
Eq. 1
b. Set the front
ZERO CHECK Button
KANCE Switch
SENSITIVITY Switch
FEEDS.4CK switch
panel controls as
LOCK
10-7 COULOMBS
Fully Counterclock.
wise
FAST
follows:
c. Connect the Electrometer to the current eource
to be measured as described in Paragraph 2-5.
d. Unlock the ZERO CHECK Sutton to make B measure-
ment. Adjust the SENSITIVITY Switch to obtain a see-
isfactory reading.
changing the SENSITIVITY Switch
setting doea not affect the transfer of charge from
the source to Electrometer.
e. The coulombmeter reading is determined by mulciplying the digital display times the RANGE Switch
CO”LOMBS setting.
If the RANGE Switch must be changed
to obtain a satisfactory reading, repeat steps b, c.
and d above.
NOTE
The input offset current of the Electrometer
contributes a charge of 5 x IO-l5 coulomb
per second and should be subtracted from the
actual reading.
f. After a coulombmeter reading is made, discharge
the integrating capacitor in the Electrometer by
placing tile ZERO CHECK BUteon to I.OCK position.
Discharge capacitor for at lease 20 seconds on the IO-’
COULOMB range before making another measurement.
NOTE
For informeti”” concerning Static Charge
measurements, request the Product Note
entitled “Electrometer Stetic Charge
Measurements”. The Model 615 should be
used with Keithley Models 2501 end 2503
Static detector Probes for
Static
Charge
Meas”rements. 0” not sttempe to use the
Model 615 in the COULDMBS mode for Static
Charge meesuremeots since the Electrometer
is very sensitive to charge trensients.
2-9,
RECORDER OUTPUTS.
The Modal 615 provides several outputs for
1toring an a”al”g or dIgital signal. me “ario”
outputs are
summarized as follows.
~~.
a. Charge measurement or current integration can be
accomplished using the Model 615 in the coulombmeter
mode,
very accurate self-contained
eter output is
The electrometer indicates the voltage across a
capacitor. The Electrom-
therefore a voltage which is
propor-
tional to the integral of the applied curreot.
NOTE
For a more complete discussion of current
integration, request the Keithley Product
Note entitled “Using the Electrometer Voltmeter es a Current Integrating or Charge
Meas”ring I”sCr”ment.”
12
1. 1MA OUTPUT. This ““tpot provides a 1 milli-
ampere analog outpoe corresponding to a full range
itlP”C .
NOTE
The Keithley Model.370 may be conveniently
used to obtain a chart record with 1% Ii”earity. The Model 370 haa 10 speeds, re-
quires no preamp, and permits operation up
to *lOO volts off ground when used with
the Model 615.
A special
phone plug such
as Switchcraft S-290 must be used with the
Model 615.
0470
OPERATION
2. 1 VOLT OlJTPLn.
analog output corresponding to a full range input.
The 1 VOLT OOTPW is useful for monitoring by oscil-
loscopes or voltmeters which will not load the ELectrometer output to exceed 0.1 microamperes. This
output is also used for calibration of the analag-
to-digital converter.
3. X1 OUTPUT (unity Cain). This output provides
a unity gain signal for applications requiring very
accurate measurements from high impedance sources.
The output is equal to input within 100 ppm at dc,
exclusive of noise and zero drift, for output cur--
rents of 100 microamperes or lees.
4. DIGITAL OuTPLm.
a complete description of the PRINTER/CONTROL connector and external controls.
b. Use of the Xl Output (Unity Gain)
1. normal “ode ?.,eaeureme,,ts.
a) Connect the Electrometer to the unknown volcage source as described in Paragraph 2-4, d for
normal Mode voltage measuremeots.
b) Connect an *ccuraLe voltmeter such as a
0.01% differeneial voltmeter between the X1 Output buffer output cards and a mating Amphenol connecand the GUARD Terminal as shown in Figure 7.
This output provides a I vole
refer to Paragraph 2-10 for
a. General
1. The Model 615 has provision for the installation of output buffer printed circuit boards co obtein Sinary Coded Decimal (RCD) outputs. Two !+!apin card-edge connectors are installed and complecely wired on the main PC board.
2. A factory-wired 50-pin PRINTER/CONTROL cannectar is also provided on the rear panel.
nector is wired to provide signals as described in
Table 8. This Amphenol (RLue Ribbon Series) connec-
tar can be ordered with special wiring configure-
tions.
3. Output buffer cards available from Keithley
as Model 4401 Printer Output Cards. may be ordered
factory installed or ordered at a later date for
user installation, since no soldering or rewiring
is required. These Output Cards are available with
other codes (Standard Code is l-2-4-8) on a CIISC~I
design basis.
4. Accessories
a) Model 4401 Printer Output Cards. include two
tor.
Thik con-
c) Adjust the Model 615 ZERO Control to obtain
a null reading on the differential voltmeter with
the ZERO CHECK Switch in LOCK position.
2. Fast Mode MeasuremenLs b. Output Codes and Levels.
a) Connecr the Electrometer to the unknown volt-
age source ee described in Paragraph 2-4, e for
Fast Mode voltage measucements.
b) Connect a recorder or oscilloscope between
the x1 Output and the GUARD Terminal. In the FAST
Mode, the XI Output Terminal is connected to input
low. The GUARD Terminal provides an output for
recording purposes.
b) A fifty line cable for hook-up to external
devices (printers, computers, etc.) is avaiLable.
Specify part number SC-51 and length desired.
1. me PRINTER/CONTROL outputs are i3inary Coded
Oecimsl (SCO) signals with l-2-4-8 Standard code.
2. The Standard signsl levels are as follows:
Logic “0” < co.4 volt
Logic “1” > *lO volts at up to 1 milliampere.
-
0470
FIcUwi 7. Use of xl Output for Measurement from a High Resistance Source.
I 3
OPERATION
MODEL 615 ELECTROMETER
PRINTER/CONTROL Connector Pin Identification.
.n NO.
1
2
,........................................................ . . . . . . . . . * . . . . . . . . . . . . . . . .
3
4
,...................................................................................
5 1 x
6
,................................ * . . . . . . . . . . . . . . . . . . . . . . . . . . . . e . . . . . . . . . . . . . . . . . . . . . II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . m . . . . . . . . . . . . .
7
8
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
10 2 x 100
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11 1 x 101
!.f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
14
. . . . . . . . . . . . . . . . . . . . . . . . T!.?Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
16
, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
18 +3.6V
, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19 Blank
20 Blank
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21 Blank
22
. . . . . . . . . . . . . . . ..*............-....................................................
23 114” Pulse
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . . . ..*...........................
24 +BV
25 +2v
omput Function
1 x 100
2 x 100
1 x 101
2 x 101
102
2 x 102
1 x 103
COllllllO”
1 x 100
oata
“ata
“ata 28 4 x 101
mea
oaca 30
oata
oata
__-
Range 34
Range 35 8 x 100
Range
COlllUlO”
1 x 100
1 x 100
2 x 100
t15v
---
m*arity 38
___
sensitivity
Se”Siti”ity 41
__-
--___
_-_
Blank
___
Print Command
Hi Reference
LOW Reference 50
I
. . . . . . . . . ‘.” . . . . . . . . . . . . . . . . . . . . . . :.I...? . . . . . . . . . . . . . . . . . . . . “.“..r.” . . . . . . .
. . . . . . . . . 2 . . . . . . . . . . . . . . . . . . . . . .8..x.!.? . . . . . . . . . . . . . . . . . . . . D.2.” . . . . . .
. . . . . . . . . . . . . . ..*...................... * . . . . . . . . . . . . . . . . . . . . . . . . ..........
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . ..,
. . . . . . . . . i.:. . . . . . . . . . . . . . . . . . . ..~~~.! . . . . . . . . . . . . . . . . ...... :.I .......,
. . . . . . . . . 3: . . . . . . . . . . . . . . . . . . . . . t!” . . . . . . . . . . . . . . . . ......... :.:.-. ......,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . e . . . . . . . . . . . . . . . . . . . . . .................................
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... .
(Refer also to Figure 8).
Pi” NO. *UtD”t F”“Cei”n
27
8 x 10 oata
OBCB
4 x 102
31
32
8 x 102
COlll!llO”
33 8 x 103
4x 100
oata
oata
___
Overload
Range
Range
COUXllO”
40
common
COllllllO”
42
-15v
43 cammon
44 Grounded
45 Grounded
46 Grounded
47
Blank
48 Blank
49
Blank
Blank
d
___
-_-
-__
--___
Hold i/l
“old $2
‘Trigger
---
-__
--_
___
TABLE 8.
14
FIGURE 8.
PRINTER/CONTROL Connector
Terminal
Identification
0470
MODEL 615 ELECTROMETER
OPERATION
C. output Information.
TABLE 9.
Model 4401 minter outpue Cards.
Model 4401 Printer Output Cards:
Provide BC,, output and external Control of Model 615; may be
purchased installed or separately for field installation (no wiring required).
minter outputs: BC” positive output represents
each of the four digits, exponene, sensieivity,
polarity and overrange. Standard code is l-2-4-
“0” < co.4 volt; “1” z 110 volts at up to
8.
one milliampere: o=oooo.
Print Commnd: Positive pulse of 14 volts from
a zzoo-ohm source with 1 volt per microsecond
rise time, 100 microseconds minimum pulse width.
print co,,ms”d give” after each A LO D conversion.
Renwte Controls:
Hold iii: Closure to ground inhibits A to D co”version, ac that instant.
Hold ,12: Closure to ground inhibits A to D co”version after reading has bee” completed.
trigger: Closure to ground initiates one conversion when in Hold 02. Integraeion period stares
8.3 ms (10 ma on 50-Hz models) after “Trigger”
or release of Hold 82.
connector: 50-p<* Amphenol Micro-Ribbon mou”Led
an Model 615. O”fp”t macing connector supplied
with 4401.
2. Overrange Indication.
The fourth (from the
right) Numerical Readout Indicatar represmts the
overrange or m”se significant digit. A” overload
candieia” is shown by a blanked readout with “nly
the polarity indicared. The Model 615 uses one RCD
line to identify ehe overrange digit and overload
condicio” as sham in Table 11.
‘TABLE 11
I
33 32
8 7
Overload C”olm”” Comma”
1 x 103
(2 (4 (8 x x x 103) 103) 103)
O,l
0 0 8
3. mlarity IndicaLio”. The poiaricy is indicated automatically by the Polarity Iadicator Lighfs
and corresponding BCD output as show” in Table i?.
TABLE 12
OUtoUt
oecima1 Digits
Generated I
NOTE
The term “Closure to Ground” or “Grounded
control line” means a shore to common directly or through a saturated NPN eransistar (VcE < c0.N). Only the “COMMON” as
supplied at the PRINTER/CONTROL co”“ector
should be used for claaures to ground.
1. Full Scale Magnitude. The full scale magni-
tude for the ~“del 615 is indicated by three front
panel Numerical Readout indicamr lights with corresponding RCD outputs as show” in Table 10.
TABLE 10.
3 1 x 101
4 2 x 101
28 4 x 101
29 8 x 101
5 1 x 102
6 2 x 102
30 4 Y 102
31 8 x 102
O,l
2,3
4,5x6,7
8.9
0.1
2,3
4>5,6,7
829
I
38 14
13
39 +15v common
Polarity
+15v (2 (8 (4 x x
(1
x 100) 100) x W)
100) 0,1
0 2 8
Four pins may be used to obcai” BCD polarity codes
*or external printers, where 1010 = + and 1011 =
- printer characters.
4. 8ensiei”ity Indication (mcimal Point coca-
Lion). The
SENSITI”ITY
Switch has four positions
which automarically control the locaeio” of the
lighted Decimal Point Indicator. The decimal point
location is also represented by a BCD outpue as
sham i” Table 13.
TABLE 13
Decimal Digits
OutpUt
Position 1.2
Position 3,4
COIIEW”
C~lmM”
5. Range Indication (Exponent). The Model 615
provides BCD outputs corresponding LO ehe exponent
of the RANGE Switch 88 show” in Table 14.
Generated
I
I
0470
15
OPERATION
I
0470
TABLE 14
MODEL 615 ELECTROMETER
b) A” external device ca” also be used for
mester control such 8s a high speed printer.
Connector
Pin NO. Output
I
9
10
34
35
11
12
36
37
The print-out of the RANGE switch expanent uses 2
coluums to represent information far exponents from
00 thru 12. The exponent must be interpreted as
positive or negative depending on the parameter (amperes, coulombs, or ohms).
6. The ““de1 615 with Model 4401 Printer Output
Cards also provides ee,,wte control commanda for ex-
ternal devices. These commands are described fully
in Paragraph 2-10, d.
7. Examples of e typical printer output for various Model 615 readings are show” t” Table 15. In
the examples the p=<ntl”S davice 1s assumad to co”-
tain fonts of digits 0
columns ere needed to print all date.
1 x 100
2 v Exponent
4 x 100
8 x
1 x Exponent 031
COUSIIO”
COUSUO”
Common
Exponent 021
100
Exponent
100
Exponent 899
101
to
9.
Decimal Digits
Generated
223
495,637
In this case, eight
c) A completely independent “master clack” can
I
be used for system control for maximum flexibility.
3. Description Of external controls.
a) “HOLD 1”. This control inhibits A to D co”-
version at the instant a closure to Sraund is
made. The conversion cycle will =esume inmediate-
ly when the “HOLD 1” line is opened.
“HOLD 2”. This control inhibits A ta D con-
b)
version after a complete reading cycle. Further
conversions are inhibited as long as a closure to
ground is made. The c”“ve=slo” cycle will resume
immediately when the “HOLD 2” line is opened.
c) “TRIGGER”. This control initiates one com-
plete conversion when “HOLD 2” line is grounded.
Closure to ground may be momentsry or any longer
duration to initiate a conversion.
d)
“PRINT
positi”* going pulse of 14 volts after a complete
A to D conversion is made end all data line out-
puts are final readings.
Power Supply Voltages. The PRINTER/CONTROL
4.
Connector also provides p”we= supply u”ltaSes of
+15, -15, and ~3.6 valta as shown in Table 16.
COMMAND”. This control provides a
d. External Control.
1. To obtain optimum system performance, it is
often desirable to operate the Model 615 synchron““sly with other digital equipment, such a8 printers,
paper tape punches, computers and other data handling
devices. The Model 615 with 4401 Printer Cards installed provides several printer control commands for
the purpose of synchronizing external equipment to
schieva maximum conversion rates.
Several alternate approaches may be used in de-
2.
signing the overall system control scheme.
a) The Model 615 can be used to provide maste=
control of external devices so that the maximum
possible conversion rates ca” be obtained.
Front Panel
Diaital Readout
+0.275
+1.347
-086.4
-(blank)
+(hla”kj
+oo.oo
-.1632
+19.99
Range Switch
setting Polarity E Digit 6. Overlosd I
1O-5 AMPERES +
109 OHMS
VOLTS 0
lo-l1 AMPERES
VOLTS
VOLTS 1 632 0 00 -. 1632 volts
10-7 AMPF,RBS
+
+
+ 1
Significant ;
i
i
!
TABLE 16
Maximum
VOltaRe ‘aed Current
I
+3.6V
+15v
-15V
r
5. High and Low Reference. The PRINTER/CONTROL
Connector provides tw” Reference Voltages, High
(+SV) and Low (c2V). These levels may be used to
define the “HIGH” and “LOW” digital output states
for‘ external printing or computer devices.
TABLE 15.
Msg. i sells. i mp. I”t*CpC*t~tiLW
0 ! !
1 i 347 1 09 +1.347 x lo9 amp ohms
0
275 1 05 +.2?5 x 10-5
F 864
: 000 - . 11 averlaad 10-7 COULOMBS .i : negstive +
: 000
i
:
f
1
i
;
000 1 2
i
999 j 2 E 07 +19.99 x 10-7 amp
+50 In4
Cl0 mA 14,17,39
-10 IsA
i Renge
I
3
- 07
00 -R6.4 volts
positive overload
00 +oo.oo volts
I
Pin
18
42
No.
I
I
16
MODEL 615
ELECTROMETER
OPERATION
a. Summary of oigital Outputs and Controls.
1. Standard Output Codes and Levels.
The stend-
ard output code for Model 4401 Printer Output Cards
is 1-2-4-S binary Coded Decimsl (&Xl). A binary
coded decimal digit is represented by a four-bit
binary code as shown in Table 17.
a) The “ON” state is defined as en output grearer then +10 voles into a resistance load of 10 kilohms or greater.
b) The “OFF” stete is defined a9 en outPut less
than co.4 volts.
TABLE 17.
Decimal
Number 4 bit
0 0
1 0
? 0
3
4
5
6
7
8
9
0 0
0
0
0
0
1
1 0 0
3 bit 2 bit
0
0 0
0 1
0
1
1
1
I
1
0
0
0
1
1
0
1 bit
L
c) Refer to Figure 19 for e circuit diagram of
the Model 4401 Standard Printer Output buffer
stage.
the “TRIGGER” command inLtiac*s one complete
conversion cycle. A second conversion will fol-
law only if the TRIGGER cormwind is removed and
re-applied a second time. The maximum conversion rate uslng.an external trigger is 24 readings per second.
b) Conversion Cycle Timing. The Conversion
Cycle is composed of three timing periods, namely,
Integrator Zero, Integrator Sampling, and A-D
mounting period.
9.
P
1.
integrator Zero Period (ZERO). When a
Refer fo Timing Diagram Figure
trigger pulse initiates a new conversion cycle,
the Integrator circuit is zeroed for e period
not to exceed 8.33 miilisecands for 60 SC operation. (The Integrator Zero Period is 10.00
milliseconds for 50 Hz operation).
2. Integrator Sampling Period (INTEGIUTE).
0
1
0
1
0
1
0
1
0
1
The Integrator Sampling Period follows automac-
ically the Integrator Zero Period and lasts for
a duration of 16.67 milliseconds for 60 HZ operation. The Integrator Sampling Period Lasts
for a duration of 20.00 milliseconds for 50 ilz
0 pa L ;,ioyil.
*..
3. ‘A-D Counting Period (COUNT). The A-D
Counting Period is initiated immediately follow-
ing the Incegraeor Sampling Period. The actual
counting time duration will depend on the actual
integrator voltage up to a maximum of 2000 clock
pulses or 16.67 milliseconds.
Following the
counting period a Buffer/Storage command is
auromefically generated in order to store the
new reading in the output registers.
2. PRINTER/CONTROL Connector. The PRINTER/CONTROL
Connector used an the Model 615 provides for connec-
tions to 50 pins es Shown in
Table
8. The mating
connector supplied with Model 4401 is an Amphenol
Part Number 57-30500 or Keithley Part Number CS-220,
available on specie1 order.
3. Analog-to-Digital Conversion Cycle.
a) The analog-to-digital conversion cycle can
be initiated in any one of three ways.
1. DISPLAY RATE Control Set at MAX. With the
DISPLAY RATE Control set at MAX, cbe end of one
complete conversion triggers e second conversion
to obtain the maximum conversion rate of 24 readings per second.
2. DISPLAY RATE Control Set at Other Than MAX.
With the DISPLAY RATE Control set et some posi-
tion other than MAX, (uncalibrated control set-
ting) the end of one complete conversion triggers
a second conversion which is delayed by a speci-
fic time interval (DELAY). The time delay is a
function of the position of a continuously’variable control to provide a conversion rate from
24 readings per second to 2 readings per minute.
3.
‘71OI.D 2” With TRIGGER Control. With the
“HOLD 2” command grounded, a closure to~ground of
4. PRINT COMMAND. The PRINT COMMAND signal
is used to trigger external printers or paper
tape punches. The PRINT COMMAND signal is delayed 10 microseconds to allow the storage legisters to settle.
The PRINT COMMAND pulse width
is approximately 100 microseconds with e 1 voltl
microsecond rise time into a 1 kilohm load. The
pulse amplitude is approximated by the following
equation:
e, = 14~/(~+2200).
Eq. 2
where R ia the outpat load resistor.
The “OFF” state is less then +0.4 volt with ap-
proximately 1 milliampere sink current.
NOTE
The date stared in the Output Registers will
not change for et least 25 milliseconds for
60 HZ operation.
If the front panel controls are changed, the Sensitivity or Range
SCD output may be effected.
2-11. 117-234V LINE POWER OPERATION.
The Model 615
is shipped for use with 117” e-c line power unless
ordered for 234V operation. To convert eny instrument
for either 117” or 234V operation, use a screwdriver
to set the 117-234” Switch an the reer panel. The
0470
17
OPERATION
MODEL 615 ELECTROMETER
INTEGRATOR
ZERO
CROSSING
DETECTOR
SUFFER
STORE
PULSE
41.67 ms
INTEGRATE
16.67 mS
COUNT
16.67 Ins
:-I--
bi
ei
l
PRINT
COMMAND
CLOCK PULSES
slide switch is identified for either 117 or 234V co
avoid an incorrect sectinS. The proper fuse must be
used far 117 or 234V and can be changed by
the fuse holder cap on the rear panel. Refer to Table
3 for proper type of fuse require*.
Z-12.
615
unless ordered for 50 Hz operation. The Model 615 will
operate at either 50 or 60
reJection will be degraded. Field conversion from 60
Hz eo 50 Hz is not recommended since the A to D con-
50 HZ LINE
is shipped for use with 60 Hz line power frequency
POWER FREQUENCY OPERATION. The Model
2000
FIGURE
Hz but line frequency noise
3000
9.
Timing Diagram for Model 615.
removing
.^
5000 (~OOU)
verter would require recalibration. TO co”“erc the
line frequency operation. replace the oscillator ccystal Y501 as shown in Table 18.
2000
18
0470
XODEL 615 ELECTROMETER
CIRCUIT DESCRIPTION
SECTION 3.
3-l. GENE&U..
a. The Keithley Model 615 Digital Electrometer con-
SiSe.3 of t&m separate sections (except for the power
supplies) packaged rogeeber in one chassis for optimum
performance and convenience:
analog-to-digital converter.
b. The Electrometer is basically an extremely stable and linear DC voltmeter with a full-scale sensitir;‘y of 100 millivolts and an input impedance of
10 ohms shunted by 35 picafarads. sy using the
frone panel controls, shunr resiseors and capacitors
are selected to make measurements over a total of 120
voltage, current, resistance, and coulomb rariges.
Current and resistance are measured using precision
resistance standards, from 10 ohm wirewound resistors
to 1011 ohm glass-sealed, deposited carbon resistors.
Coulombs are measured using close tolerance polysty-
rene film capacitor standards.
the analog-to-digital converter is a dual slope
c.
integrating type converter with medium conversion
rate, cold cathode readout tubes, BCD outpue options
and external control.
3-2. ELECTF.omTER A!4PLIFIER OeEP.ATION.
a. The Model 615 electrometer amplifier employs
matched insulated-gate field-effect transistor8 fol-
lowed by a transis;or differential amplifier with a
high-voltage complementary output stage. Refer to
an Electrometer and an
CIRCUIT DESCRIPTION
Figure 10 which shows a block diagram of the Electrometer.
b. The Electrometer amplifier is connected as a
unity-gain, voltage-to-current converter configuration. Refer to Figure 11 for a simplified diagram of
the unity-gain amplifier in the Normal Mode. The
sensitivity selection circuitry is arranged such that
a full-scale input voltage (ei) results in a 1 rnilliampere output current through the Sensitivity resistor represented by Rs.
(es) is determined as follows:
The unity-gain voltage output
e, = ei .&
where K is the amplifier loop gain.
3-3. AMPLIFIER CIRCUIT
a. The amplifier input stage is a pair of insulatedgate field-effect rzr~nsistors (IGFET) designated 01201
and ~1202 connected in B differential configuration.
The “gate” terminal of transistor Q1202 is connected
eo the unity-gain output.
b. The input stage is followed by a Cransistor differential amplifier composed of transistors Q1203 and
Q1204. Transistors 01207 and 01212 make UP a bizh
&in stage which pre;ents “fold-we+ and ;‘lock-;p”
with positive input overloads. Diode D1214 between
0472R
19
CIRC”IT DESCRIPTION
INPUT- , 4x1
,
A
ei
(P-Q!
MODEL 615 ELECTROMETER
\
f
is
FIGURE II.
base and emitter of transistor Q1209 prevents “fold-
over”
and
“lock-up” under negative input overloada.
NOTE
Amplifier “fold-over” is defined 88 a co”-
dieion where the i”sfrumenL erroneously
Indicates an on scale reading with a large
overload.
an amplifier stage saturates.
c. Frequency compensation is provided by capacitors
Cl213 and C1214, resistors R1240 and R1241, and cepacieor c1215.
trolled frequency response characteristic to insure
stability under all condicians of input end output capncieance loading.
d. The complementary-output stage composed of transisters Q1210 and Ql211 is connected co the unity-gain
output to complete the unity-gain amplifier clrcult.
e. The power supplies which provide *120 volts dc
for the output transistor atsge are floating with respect to chassis ground. The *9v power auppliea for
the amplifier gain stages are referred to the unitygain output.
“Lock-up” is a condition where
The compensation networks provide a con-
""lty-Gain Amplifier
g. The analog output signal for recorder outputs is
derived from a resistor divider network represented by
resistor RD in Figure 10.
1. 1 VOLT OUTPUT (51207). This output is derived
from the 1 milliampere current (for full scale inputs) which flows through a,resistor network of
1010.1 ohms. This output has been designed co provide a reference voltage for the analog-to-digital
converter. The 1 VOLT OUTPUT Terminal may be used
for monitoring purpose where loading ca” be 0.1 mi-
croampere maximum.
2. 1 MA OUTPUT (51206). This output provides a
one milliampere dc current for a full scale input
voltage of 100 millivolts, 1 volt, 10 volts, or 100
volts depending on the SENSITIVITY Switch setting.
The output cannectar used is a Witchcraft N113S female phone jack which connects ehe output in series
with the reference voleege divider RD.
3. Xl OUTPUT (51203). This output is the unitygain output as shown in Figure 11. The ~1 Output
provides a voltage es which is equal to ehe input
according Co the following ratio.
f. The SENSITIVITY Switch S1203 selects a resistor
network (represented by resistor Rs) to provide full
scale input ranges from 100 millivolts to 100 “Olts in
four steps. The output voltage to current conve’rsio”
is determined as follows:
sq. 4
20
where K is the amplifier loop gain.
3-4. AMMETER OPERATION.
a. Normal Mode. With the FEEDBACK Switch in the
0470
CIRCUIT DESCRIPTION
NORMAL position, a* accurately known RANGE Swirch re~istor (CURRENT Range only) RI202 through R1212 is
connected in shunt across the Electrometer amplifier
input
Refer eo Figure 10 for a block diagram of the
Electrometer. The amplifier measures rhe voltage drop
across he Range resistor to determine the input current. The digital readout display and analog outputs
are calibrated to indicate the magnitude and polarity
of the voltage. The actual current is obtained by mul-
tiplying the readout times the current range selected.
b. Fast Node. With the FEEDBACK Switch in the
FAST position, an accurately known RANGE Switch resis-
tor (CURRENT Range only) R1202 through RI212 is con-
nected across the amplifier feedback Loop as shown in
Figure 12. The unity-gain output (Xl) is connected to
Input LO.
be used for monitoring purposes.
In this mode the GUARD and X1 Terminals may
The Fast Mode con-
ciguration minimizes the slowing effects Of input capacitance. The input voltage drop is maintained at
less than 100 micravalcs.
sistore are R1202 through F.1212.
c. Normal Mode Operation. When the FEEDBACK Switch
is in rhe NORMAL position, the unknown resistor is
connected between the INPUT high and low as described
in the OPERATTON section of this manual. The actual
resistance is determined by multiplying the digital
readour display times the OHMS Range selected.
The analog-to-digital converter circuit des-
cription can be found in paragraph 3-7.
This circuitry is separate from the analog
circuitry and is located on individual
printed circuit boards.
0470
CIRCUIT DESCRIPTION
1VOLT OUTPUT
INPUT ,
22
> I
I
C
+ ,,
I\
I
I
I
0
Y
m
0
+
::RO
<GUARD
vo
FIGURE 14. Coulombmeter Fast Made.
0470
MODEL 615 CIRCUIT DESCRIPTION
I
*II’1
. ! ! ! !
I I I I I I I
I I I I
I I I
I
0671
FIGURE 15.
Block Diagram ot
AID Converter.
23
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