Keithley 615 User manual

CONTENTS
02738

SPECIFICATIONS
SPECIFICATIONS
MODEL 615
AS A VOLTMETER:
RANGE: 100 millivolts full scale (100 microvolts. least sig
nificant digit) to 100 volts in four decade ranires.
ACCURACY: +0.290 of reading +1 digit on all ranges exclu.
sive of noise and drift.
ZERO DRIFT: Less than 1 millivolt in the first hour or subse-
quent 24.hour periods after l.hour warmup. Less than
150 mliCrOYOlt*pm “C.
NOISE: * 1 digit with input shorted on most sensitive range.
INPUT IMPEDANCE: Greater the” 10” phms shunted by
35 picofarads. Input resistance may aIs0 be selected in
decade steps from 10 to 10” ohms.
NMRR: Greater than 60 d8 on the most sensitive range de.
creasing to 40 dB on the lOOwIt range at line frequency.
AS AN AMMETER:
RANGE: lo-‘2 ampere full scale (1O-L5 ampere, least sig.
nificant digit) to 0.1 ampere in 12 decade ranges.
ACCURACY: b-0.5% of reading, -tl digit on 0.1 to l@’
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 1O-Loto lo.‘1 ampere
ranges exclusive of noise and zer0 drift.
NOISE: f-4 digits with input open and shielded on most
sewitive range.
OFFSET CURRENT: Less than 5 x IO-l5 ampere
AS AN OHMMETER:
RANGE: 10,000 ohms full scale (10 ohms. least significant
digit) to 10” ohms in eleven decade ranges.
ACCURACY: &0.5% of reading. hl digit on 10’ to lOa ohm
ranges using optimum sensitivity control setting; *4% of
reading + 1 digit from 109 to 10’” ohms exclusive pf noise
and zero drift.
AS A COULOMEMETER:
RANGE: 10.” coulomb full sca1e (lo-” coulomb. least
significant digit) to 10’5coulomb in seven decade ranges.
ACCURACY: +5% of reading 3~2 digits on all ranges. Drift
due ta offset c”rrent does not exceed 5 x lO-‘I coulambs,
secpnd.
GENERAL:
DISPLAY: 4 digits from 0000 to 1999 on 0.1, 1.0, and 10.0
sensftlwty settings; from 0000 to 999 on the 100.0 sensi-
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 100 volts with respect to chassis ground.
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 microamperes or fess.
1 mA: fl milliampere at up to 1 volt for full scale input,
100% overrange capability except on 100.0 sensitivity
setting.
1 V: *l volt at up to 0.1 microampere for full scale input.
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 19” wide Y 10” deep
(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.
ii
0372R

MODEL 615 ELECTROMETEX
SECTION 1. GENERAL DESCRIPTION
l-l. GENERAL.
a. The Keittlley Model 615 Digital Eleceromeeer is a
fast, accurate and sensitive Electrometer with digital
display. It is a versatile, comp’letely solid-state
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 re-
sult of extensive instrument development with high in-
put 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 am-
pere, 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 dif-
ferential amplifier and complimentary outpue stage.
A large amount of negative feedback is used for sta-
biliey 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-
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 re-
corders 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 in-
tearaeing 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 pro-
vides BCD outputs far significant digits, range, pol-
arity, 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
TABLE 2.
Model 615 Front Panel Controls and Terminals (Figures 1 & 3).
contra1 F”“ctio”*l Description Par.
SENSITIVITY Switch Selects full-ecsle voltage sensitivity; slso used to mulriply 2-2,2-3
current, resietance and charge ranges on the Range Switch.
Automatically eelecrs the proper decimal point position.
RANGESwitch Selects the mode which ia to be measured: voltage, current, Z-2,2-3
resistance or cherge.
FEEDBACKSwitch Selects either NORMALor FAST modes of operation. 2-2,2-4,2-5
POWERSwitch Controls e-c line power to instrument (an/off). 2-2
DISPLAY RATE Control Determines number of analog-to-digital conversions per second. 2-3
ZERO caner01 Provides fine zero control adJuseme”e. 2-2
ZERO CHECK Switch Provides zero offset check without disturbing the source circuit. 2-2
INPUT Receptacle Connefts wurce to input. ~ecepeacle is a Teflon insulneed 2-l
triaxia1 connector.
LO TERMINAL
*Display Lights
Numerical Readout
Provides connection to input low.
Indicates polarity of input signal.
Indicates magnitude of input signal.
2-l
2-3
2-3
TABLE 3.
Control
COARSEZERO Switch
Model 615 Rear Panel Controls end Terminals (Figure 2).
Functional Description
Provides extended adfustment cepabflity of the front panel
ZERO Control.
Psr.
2-2
1 MA OuTPuT Receptacle
PRINTER/CONTROL
CO”“eCtOC
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.
2-9
2-10
SPARE Receptacle Blank hole with cover plate for mounting edditional 50 pi”
CO”“BCtOC. __-
Xl OUTPm and
G”m.tl Terminals
CASE GROUNDTerminal
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.
2-9
2-6
LO Terminal
1 VOLT OWPIPI
Line Cord
F”M
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.
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

MODEL615 ELECTROMETER GENERAL DESCRIPTION
SENSITIVITY Switch
(S1203) RANGESwitch ZERO CHECK
(51201) (S1202)
POWER DISFLAY ZERO FEEDBACK LD INPUI
Switch PATE CONTROL Switch (S1204) BINDING RECEPTACLE
(S102) CONTROL (R1222) POST (51209)
(R1201) (51202)
FIGURE 1. Model 615 Front Panel Controls and Terminals.
1 VOLT ODTPW (9102)
Transistor Transformer
COARSEZERO
switcn (S1205)
Xl ouepur
(51203)
FIGURE 2. Model 615 Rear Panel Controls and Terminals.
0570
3

OPERATION MODEL 615 ELECTROMETER
SECTION 2.
2-l. INPLPI CONNECTIONS.
8. The INPUT Receptacle of the,Model 615 is a Tef-
lon insulated triaxial connector. The center termi-
nal is the high impedance terminal: the inner shield
is the low impedance terminal; the outer shield is
case ground. (See Figure 3).
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.
INPUT
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.
TABLE 4.
Color Coding of Alligator Clips for Model 6011 Input
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
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. Unless the shielding is thorough, pickup
may cause definite readout disturbances.
e. “se high resistance, low-loss materials - such
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. “se a law-noise type cable which
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 precau-
tions may be necessary to isolate the instrument and
the connecting cable from the vibration.
NOTE
Clean, dry connections and cables are very
important to maintain the value of all in-
sulation materials. Eve” the best insula-
tion 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 clean-
ing agent.
g.
The accessories described in Section 7 are de-
signed 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 sensi-
tive ~“rrent range with the FEEDBACK Switch at FAST,
same insulators - such as Teflon - may produce ran-
dom signals which show up as erratic readout deflec-
tions. Insulation used in the Model 615 is carefully
selected to minimize these spurious signals.
j. It is advantageous to connect the Model 615 in-
put to the source only when a reading is to be made.
“se a high impedance transfer switch and well shield-
ed chamber if available.
4
04728

MODEL615 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 en-
ables 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 off-
ground when using the Adapter. The instru-
ment 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.
a. Check the 117-234V Switch for the proper AC line
voltage.
b. Check for proper rated fuse.
C. See the front panel controls as follows:
ZERO CHECK Button
RANGESwitch
SF.NSItI”ITY Switch wise- Position
FEEDBACK Switch NORMAL
POWERSwitch OFF
d. Connect the power cord. Place POWERSwitch to
ON position. After one-half hour warm-up, adjust the
ZERO Conerol if necessary. Zero is indicated by con-
tinuously flashing * polaricy lights.
NOTK
The rear panel COARSEZERO Control may be
adjusted if a large zero offset is indicated.
e. After a few moments increase the voltage sensi-
tivity by advancing the Switch to one position CLIUIIC-
erclockwiae. Continua zeroing with the FINE ZERO
Control.
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 used, but should
decrease to below the specified amo”nt
after one or two hours of “se. This is an
inherent characteristic of the input tran-
sistors; 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 Electrome-
ter 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 READOUTOPERATION.
a. Valtmecer Digital Readout.
1. When the RANGESwitch is placed in the VOLTS
position, ehe Electrometer digital readout desig-
nates the actual voltage measured using four numer-
ical digit readouts.
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 SENSITIVITY Switch
position is shown in Table 5.
TABLE 5.
SENSITIVITY Switch Decimal Point
Position msi.cion
I -~-
II
0.1 Positicm 1 (full”
counterclockwise)counterclockwise) .xXxX
11 PositionPosition 22 x.xXxx.xXx
1010 PositionPosition 33 xX.xXxX.xX
100100 PosFtFonPosFtFon 44 (fully(fully xXx.xxXx.x
clockwise)clockwise)
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 read-
outs will blank (none of the digital readout tubes
will be lighted). The polarity (*) display indica-
0570 5

OPERATION
MODEL 615 ELECTROMETER
tars remain lighted during an overload condition
indicating the correct polarity. Thus the Electrom-
eter display will indicate correctly within specifi-
cations 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 RANGESwitch is placed in the AMMETER
position, the Electrometer digital readout desig-
nates the voltage across an accurately known self-
contained resistor. The RANGESwitch 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 re-
sismr.
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.
Full Scale RANGE SENSITIVITY I
Switch
C. Ohmmeter Readout.
1. When the RANGESwitch is placed in the OHMS
position, the Electromerer digital readout desig-
nates the actual voltage across the unknown resis-
tor as an accurately known current (internal to the
Electrometer) is applied to the unknown.
2. The RANGESwitch selects the current for Olw
lll~ClS”C~lU~“t~. The current is the reciprocal value
of the OHMSrange 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 RANGESwitch 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
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 RANGESwitch setting times the digital
readout display.
e. DISPLAY RATE Control. (This control is a con-
tinuously 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 in-
pllt 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 ex-
treme clockwise position. The front panel DISPLAY
SATE Control applies to the digital circuitry only.
2-4. VOLTAGEMEASUREMENTS.
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).
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 meaaure-
ments 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
RANGESwitch 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 VOLTS
SENSITIVITY Switch 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 con-
nected.
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 automat-
ically 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 VOLTS Fully Clockwise
FEEDBACK Switch FAST
NOTE
To make off ground measurements. refer to
Paragraph 2-6.
0470

OPERATION MODEL 615 ELECTROMETER
2. Model 6103A Divider Probe for measurements up
to 30 kilovolts. This probe permits meas”rements
with overall accuracy of Cg%.
1012
Input r**i*t**c* is
ohms maximum. The actual voltage is obtained
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. In the Normal Mode - used on
eny renge - the cwrent is determined by measuring
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
below 10-S ampere range - a self contained resistor
is connected between the electrometer amplifier in-
put 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 capac-
itance.
C. Normal Mode Current Measurements.
1. Set the front panel controls as follows:
ZERO CHECK nutron LOCK
RANGESwitch 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 RANGESwitch setting. The best accuracy
for current meas”rements is obtained by “sing a
TABLE 7.
Typical Effects of External Inp”t Capacitance on Response Speed and Noise Performance in C”rre,,t Measurements
with the Model 615.
i-l**** Rise Time (seconds) Output
Noise (Peak-Co-Peak)
No C
$;to -
2eE 5000pF No C
- x 5000pF
2.0 2.0 2.0 6 x lo-l5 1.5 x 10-14 7 x 10-13
$" .07.45 .45.07 8.5 x 10-14
10-S
.45'.07
,015 ,015 ,015 ;.i ;,m;l3 ;.":
$5; i.2 ;,!p;"
10-7 ,003 .003 ,003
10-6
s’x 10-11
2 x 10-10
.003 ,003 ,003 3.3
x 10-10
s

MODEL 615 ELECTROMETER
OPERATION
SENSITIVITY Switch seeting which permits the use of
the smallest value rage resistor. The rsnge resis-
tor value is equivalent CO the reciprocal of the
RANGESwitch setting. The input voltage drop across
the shunt resistor is indicated directly on the
Electrometer digital display.
NOTE
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
E ohms) used have a volt-
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. ‘rherefore ie is reconrmended t” select
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
4. Adjust the RANGESwitch 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 RANGESwitch 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 cesis-
t”r value is equivalent to the reciprocal of the
RANGESwitch settine. The input voltane drop, across
ehe shunt resistor Is indicated directly on the
EiectromeLer digital display.
NOTE
the smallest input drop possible to minimize
voltage coefficient errors.
d. Fast mde Current Weasurements (for current be-
low 10-5 amperes).
1. Set the front panel controls es follows:
ZERO CHECK Button
RANGESwitch
LOCK
10-6 AMPERES
SENSITIVITY Switch
FEEDBACKSwitch
Fully Councerclock-
wise
FAST
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 af-
fected. The range resistor is the recip-
rocal of the AMPERES range in ohms.
NOTE
TO make aff graund measurements refer ta
Psragraph 2-6.
2. Connect the Model 6011 Triaxial 1”put Cable
for measuring an unknow” current ae in 2-5, c-2.
3. unlock the ZERO CHECK Sutton t” make e mee-
surement
CAUTION
Foe measurement of capacitor leakage cur-
rents using the Pest Mode, a very stable
voltage supply must be used. With a ~a-
pacitor connected across the input, the
electrometer is exCrem*ly sensitive to
voltage transients with a resultant in-
crease in readout noise.
I I I I
I ‘f I
I I
I-
a-7 : ME)WJ&NG I
I 1 readout
I 1 I X _____
I SOURCE I I
AMMETER
I
L--------l L------------l
1= ’ readout R+Ri” R
FIGURE 4.
Error Due to Ammeter Resistsnce.
0470 9

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 GROUNDMEASUREMENTS.
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 be-
tween 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.
10
b. Normal Mode Measurements. D‘sconnect the short-
ing 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 Alec-
trometer 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 Alec-
trometer 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.
0470

MODEL 615 ELECTROMETER
OPERATION
3. Set the front panel controis as fallows:
ZERO CHECK SULLO” LOCK
RANGE Switch 1011 OHMS
SENSITI”ITY Switch Fully Counterclock-
wxse
FEEDBACK switch NORMAL
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
OHMSranges; 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 multi-
plying the digital display times the RANGEtwitch
setting. “se the smallest RANGESwiech 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
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.
2. set the front panel controls as follows:
ZERO CHECK Button LOCK
RANGESwitch 1011 OHMS
SENSITI”ICY SWFtch Fully Counterclock-
wise
FEEDBACKSwitch FAST
3. connect the unknown resistance between the
Electrometer input high and GUARDTerminal 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 RANGEswitch
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 GUARDTerminals
“n the rear panel. This allows the CASE GROUNDur
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 GUARDTerminal.
d. Volt-Ammeter Resistance Measurement (to 10’6
ohms).
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
FIGURE 6. Volt-Ameter Resistance ,.,easuremenc.
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 uo-
known 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 instruc-
tions 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 per-
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 RANGESwitch
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 Eq. 1
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.
a. Charge measurement or current integration can be
accomplished using the Model 615 in the coulombmeter
mode, The electrometer indicates the voltage across a
very accurate self-contained capacitor. The Electrom-
eter output is 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 Volt-
meter es a Current Integrating or Charge
Meas”ring I”sCr”ment.”
12
b. Set the front panel controls as follows:
ZERO CHECK Button
KANCE Switch
SENSITIVITY Switch
LOCK
10-7 COULOMBS
Fully Counterclock.
wise
FEEDS.4CK switch FAST
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 mulci-
plying the digital display times the RANGESwitch
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. Dis-
charge capacitor for at lease 20 seconds on the IO-’
COULOMBrange before making another measurement.
2-9,
RECORDEROUTPUTS.
The Modal 615 provides several outputs for
~~.
1toring an a”al”g or dIgital signal. me “ario”
outputs are summarized as follows.
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 COULDMBSmode for Static
Charge meesuremeots since the Electrometer
is very sensitive to charge trensients.
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. This output provides a I vole
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 ELec-
trometer output to exceed 0.1 microamperes. This
output is also used for calibration of the analag-
to-digital converter.
a. General
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.
1. The Model 615 has provision for the installa-
tion of output buffer printed circuit boards co ob-
tein Sinary Coded Decimal (RCD) outputs. Two !+!a-
pin card-edge connectors are installed and complece-
ly wired on the main PC board.
4. DIGITAL OuTPLm. refer to Paragraph 2-10 for
a complete description of the PRINTER/CONTROL con-
nector and external controls.
2. A factory-wired 50-pin PRINTER/CONTROL cannec-
tar is also provided on the rear panel. Thik con-
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.
b. Use of the Xl Output (Unity Gain)
1. normal “ode ?.,eaeureme,,ts.
a) Connect the Electrometer to the unknown volc-
age source as described in Paragraph 2-4, d for
normal Mode voltage measuremeots.
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
b) Connect an *ccuraLe voltmeter such as a a) Model 4401 Printer Output Cards. include two
0.01% differeneial voltmeter between the X1 Output buffer output cards and a mating Amphenol connec-
and the GUARDTerminal as shown in Figure 7. tor.
c) Adjust the Model 615 ZERO Control to obtain
a null reading on the differential voltmeter with
the ZERO CHECK Switch in LOCK position.
b) A fifty line cable for hook-up to external
devices (printers, computers, etc.) is avaiLable.
Specify part number SC-51 and length desired.
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.
1. me PRINTER/CONTROLoutputs are i3inary Coded
Oecimsl (SCO) signals with l-2-4-8 Standard code.
b) Connect a recorder or oscilloscope between
the x1 Output and the GUARDTerminal. In the FAST
Mode, the XI Output Terminal is connected to input
low. The GUARDTerminal provides an output for
recording purposes.
2. The Standard signsl levels are as follows:
Logic “0” < co.4 volt
Logic “1” > *lO volts at up to 1 milliampere.
-
FIcUwi 7. Use of xl Output for Measurement from a High Resistance Source.
0470 I 3

OPERATION MODEL615 ELECTROMETER
.n NO.
TABLE 8.
PRINTER/CONTROL Connector Pin Identification. (Refer also to Figure 8).
omput Function I Pi” NO. *UtD”t F”“Cei”n
1 1 x 100
2 x 100 oata
2 “ata .... ... ..‘.” ......................:.I...? ....................“.“..r.”.......
27 8 x 10 oata
,........................................................ . ........*................
3 1 x 101
2 x 101 “ata 28 4 x 101 OBCB
4 mea
,................................................................................... ........ .2 ......................8..x.!.? ....................D.2.” ......
5 1 x 102
2 x 102 oaca 30 4 x 102
8 x 102 oata
6 oata 31 oata
,................................ *............................e.....................II ............................................................m......... ....
7 1 x 103 oata 32 COlll!llO” ___
8 COllllllO” __- 33 8 x 103 Overload
.................................................................................... ................*...................... *..................................
9 1 x 100 Range 34 4x 100
10 2 x 100 Range
Range 35 8 x 100 Range
.................................................................................... ............................................................,............,
11 1 x 101 Range
COlllUlO” ---
!.f ................................................................................ .........i.:. ....................~~~.! ...................... :.I .......,
13 1 x 100 m*arity 38 COUXllO” ___
14 ___
........................T!.?Y...................................................... .........3: ..... ................t!” ......................... :.:.-. ......,
15 1 x 100
2 x 100 sensitivity 40 common -_-
16 Se”Siti”ity 41 COllllllO” -__
,................................................................................... ...... ....................................................................
17 t15v __- 42 -15v ---
18 +3.6V --- 43 cammon ___
,................................................................................... ..........................................................................
19 Blank ___ 44 Grounded Hold i/l
20 Blank _-_ 45 Grounded “old $2
................................................................................... ...................e......................................................
21 Blank 46 Grounded
22 Blank ‘Trigger
___ 47 Blank ---
........... ......*............-.................................................... ........................................................... ..............I
23 114” Pulse Print Command 48 Blank -__
.........................................*..............*........................... ............................ ............................................. .
24 +BV Hi Reference 49 Blank --_
25 +2v LOWReference 50 Blank ___
d
FIGURE 8.
PRINTER/CONTROL Connector Terminal Identification
14 0470

MODEL 615 ELECTROMETER OPERATION
C. output Information.
TABLE 9.
Model 4401 minter outpue Cards.
Model 4401 Printer Output Cards: Provide BC,, out-
put and external Control of Model 615; may be
purchased installed or separately for field in-
stallation (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-
8. “0” < co.4 volt; “1” z 110 volts at up to
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 conver-
sion 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.
NOTE
The term “Closure to Ground” or “Grounded
control line” means a shore to common di-
rectly or through a saturated NPN eransis-
tar (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 cor-
responding RCD outputs as show” in Table 10.
TABLE 10.
3 1 x 101 O,l
4 2 x 101
2,3
28 4 x 101 4,5x6,7
29 8 x 101 8.9
5 1 x 102 0.1
6 2 x 102 2,3
30 4 Y 102 4>5,6,7
31 8 x 102 829
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 3332 87 OverloadC”olm””Comma” 1 x 103 (2(4(8 xxx 103)103)103) O,l 008
3. mlarity IndicaLio”. The poiaricy is indicat-
ed automatically by the Polarity Iadicator Lighfs
and corresponding BCD output as show” in Table i?.
TABLE 12
OUtoUt oecima1 Digits
Generated I
I 3814 13 39 +15vcommon Polarity +15v (2(8 (4xx (1 x100)100) x W) 100) 0,1 028 I
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
OutpUt Decimal Digits
Generated I
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 RANGESwitch 88 show” in Table 14.
0470 15

MODEL 615 ELECTROMETER
OPERATION
TABLE 14
I Connector Decimal Digits
Pin NO. Output Generated I
9
10
34
35
11
12
36
37
1 x 100
100 Exponent 021 2 v Exponent 223
4 x 100
100 Exponent
495,637
8 x 101 Exponent 899
1 x Exponent 031
COUSIIO”
COUSUO”
Common
The print-out of the RANGEswitch 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 (am-
peres, coulombs, or ohms).
b) “HOLD 2”. This control inhibits A ta D con-
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.
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.
d) “PRINT COMMAND”. This control provides a
positi”* going pulse of 14 volts after a complete
A to D conversion is made end all data line out-
puts are final readings.
7. Examples of e typical printer output for vari-
ous 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 to 9. In this case, eight
columns ere needed to print all date.
4. Power Supply Voltages. The PRINTER/CONTROL
Connector also provides p”we= supply u”ltaSes of
+15, -15, and ~3.6 valta as shown in Table 16.
d. External Control. TABLE 16
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 in-
stalled provides several printer control commands for
the purpose of synchronizing external equipment to
schieva maximum conversion rates.
I Maximum
VOltaRe ‘aed Current Pin
No. I
+3.6V
r
+15v
-15V
+50 In4 18
Cl0 mA 14,17,39
-10 IsA 42 I
2. Several alternate approaches may be used in de-
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.
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.
Front Panel
Diaital Readout
+0.275
+1.347
-086.4
-(blank)
+(hla”kj
+oo.oo
-.1632
+19.99
b) A” external device ca” also be used for
mester control such 8s a high speed printer.
c) A completely independent “master clack” can
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.
TABLE 15.
Range Switch Significant ;
setting Polarity E Digit 6. Overlosd I i Renge
Msg. i sells. i mp. I”t*CpC*t~tiLW
1O-5 AMPERES + i 0 ! !
109 OHMS 275 1 05 +.2?5 x 10-5 + i 1 i 347 1 09 +1.347 x lo9 ampohms
VOLTS 0 1
lo-l1 AMPERES F 864 i 3 I 00 -R6.4 volts : 000 - . 11 averlaad10-7 COULOMBS .i : negstive+ ! : 000 ; - 07 positive overload
VOLTS + 0 i
: 000 1 2 I 00 +oo.oo volts
VOLTS 1 632 0 00 -. 1632 volts
10-7 AMPF,RBS i + 1 f 999 j 2 E 07 +19.99 x 10-7 amp
I
0470
16

MODEL615 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 grear-
er then +10 voles into a resistance load of 10 kil-
ohms or greater.
b) The “OFF” stete is defined a9 en outPut less
than co.4 volts.
TABLE 17.
Decimal
Number 4 bit 3 bit 2 bit
1 bit
0 0 0 0 0
1 0 0 0 1
? 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 I 1 0
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
L
c) Refer to Figure 19 for e circuit diagram of
the Model 4401 Standard Printer Output buffer
stage.
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 read-
ings 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’vari-
able control to provide a conversion rate from
24 readings per second to 2 readings per minute.
3. ‘71OI.D2” With TRIGGER Control. With the
“HOLD 2” command grounded, a closure to~ground of
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 conver-
sion rate uslng.an external trigger is 24 read-
ings 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. Refer fo Timing Diagram Figure
9. P
1. integrator Zero Period (ZERO). When a
trigger pulse initiates a new conversion cycle,
the Integrator circuit is zeroed for e period
not to exceed 8.33 miilisecands for 60 SC oper-
ation. (The Integrator Zero Period is 10.00
milliseconds for 50 Hz operation).
2. Integrator Sampling Period (INTEGIUTE).
The Integrator Sampling Period follows automac-
ically the Integrator Zero Period and lasts for
a duration of 16.67 milliseconds for 60 HZ op-
eration. The Integrator Sampling Period Lasts
for a duration of 20.00 milliseconds for 50 ilz
0pa 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.
4. PRINT COMMAND. The PRINT COMMANDsignal
is used to trigger external printers or paper
tape punches. The PRINT COMMANDsignal is de-
layed 10 microseconds to allow the storage leg-
isters to settle. The PRINT COMMANDpulse 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 con-
trols are changed, the Sensitivity or Range
SCD output may be effected.
2-11. 117-234V LINE POWEROPERATION. 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
:-I-- l
41.67 ms bi
INTEGRATE COUNT ei
16.67 mS
16.67 Ins
SUFFER
STORE
PULSE
PRINT
COMMAND
CLOCK PULSES
.^
2000 3000 5000 (~OOU) 2000
FIGURE 9.
Timing Diagram for Model 615.
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 removing
the fuse holder cap on the rear panel. Refer to Table
3 for proper type of fuse require*.
Z-12. 50 HZ LINE
POWERFREQUENCYOPERATION. The Model
615 is shipped for use with 60 Hz line power frequency
unless ordered for 50 Hz operation. The Model 615 will
operate at either 50 or 60 Hz but line frequency noise
reJection will be degraded. Field conversion from 60
Hz eo 50 Hz is not recommended since the A to D con-
verter would require recalibration. TO co”“erc the
line frequency operation. replace the oscillator ccys-
tal Y501 as shown in Table 18.
18 0470