Keithley 415 User manual

Instruction Manual
Model 415
Micro-Microammeter
Keithley Instruments, Inc.
Instrument Division
Cleveland, Ohio, U.S.A.

WARRANTY
We warrant each of our products to be free
from defects in material and workmanship. Our
obligation under this warranty is to repair or
replace any instrument or part thereof (except
tubes and batteries) which, within a year after
shipment, proves defective upon examination.
To exercise this warranty, contact your Keithley
field engineering representative. You will be
given assistance and shipping instructions.
REPAIRS AND RECALIBRATION
Keithley Instruments and its internat.ional dis-
tributors maintain complete repair facilities.
To insure prompt repair or recalibration service,
please contact your Keithley field representative
before returning the instrument.
Estimates for repairs, normal recalibrations, and
calibrations traceable to the National Bureau of
Standards are available upon request.

INSTRUCTION MANUAL
MODEL 415
MICRO-MICROAMMETER

CONTENTS
INTRODUCTION
SPWZIFICATIONS
REXlgeS
Accuracy
Zero Drift
Grid Current
output
Rise Time
Current Suppress~ion
Zero Check
Tube Complement
Power
Accessories Supplied
Accessories Available
Dimensions
OPERATION
Operating Controls
Inout and Outpyt Connections
PrelimJ.nary Set Up
Makinp Measurements
Speed o.f Response
CIRCUIT DESCRIPTION
Circuit Block Diagram
Speed of Response
Detailed Circuj.t Description
MAINTENANCEAND CALIBRATION
General
Calibration
Trouble Shooting Procedure
Voltare Resistance Diagram
Circuit Schematic
Replaceable Parts List
SECTION
I
II
IV
v
415
ICE= mm, nio. cLEvEm, OHIO

SkCTION I - INTRODUCTION
The Model h15 Micro-microammeter incorporates advanced
high-speed circuitry developed by Keithley Instruments for rocket
and satellite experimentation -- where measurements of Lyman-
Alpha night slow, cosmic radiation, and upper air density re-
quire fast response,
The I~15 also provides zero suppression up to 100 full scales,
permitting full scale display of one per rant variatiors of a
signal, or suppression of a steady background signal.
Excelling other Keithley LOO Series Micro-microammeters in
speed of response, the Model hl5 is ideal for current measure-
ments in ion chambers, ionization pages, and photo-multipliers.
Other applications include uses with flame and Beta-ray
ionization detectors and in gas ChromatoKranhy, mass spectrometry.
Speed of respp? se of less than 600 milliseconds to 90% of
final value at lo- ampere is possible where external circui~t
capacity is less than 50 picofarads (uuf). Critical damping of
the circuit, with any input capacity, is maintained on all ranges
through one infrequent adjustment. There is no possibili.ty of
oscillation or poor transient response on any ranpe.
Accuracy is 22% of full scale o 10m3 -8 ampere
ranses; -+3$ of full scale on 3 x 10
-9
througQ210
throuph 10 ampere
ranples.
Other features i lude capability of detecting current of
approximately 1 x 10-YE ampere; zero stability of better than
2% per day and a one volt output at one milliampere; a 1%
mirror scale pane:1 meter.
415 I -1

SECTION II - SPECIFICATIONS
RANGES: lo-=, 3 x 10-12, lo-, 3 x lo-=, etc. to 10e3 ampere
full scale.
ACCURACY: Z 2% of full scale 10e3 ttiu lOWE ampere ranges;+ 3% of
full scale 3 x 10-9 thru lo-l2 ampere ranges.
Z!SO DRIFT: After 30-minute warmup, less than 2% of full scale per
2L hours on all ranges.
GRID CT:r'WNT: Less than 5 x 10-lL ampere.
~!ITPIIT: One volt for ful! scalp
3~i. up to 5 ma. Noise less than
20 m'llivolts.
RISE TIME: Typical value &ven in seconds to 90% of final value.
Range Gin-50 uuf
amps f.s. seconds Cin=150 uuf
seconds Cin=1500 uuf seconds
10-12
3 x 10-12
10-11
3&o-ll
3 x 10-10
10-9
3 x 10'9
and above
CURRENTSUPPRFSSION:
.600 .800 2.5
.200 .300 1.0
,060 .080 .250
.020 ,030 .lOO
.006 ,010 .030
,002 .003 .OlO
.OOl .OOl .003
.OOl .OOl .OOl
Up to 100 full scales; maximum buckout 10-5
ampere. One setting of bucking current serves
five adjacent ranges within above limits. FINE
adjustment allows precise control up to 100 times
suppression.
ZEROCHECK: Allows zeroing without disturbing the circuit.
TUBE COMPLEMENT: 2-5886, 2-6CB6, l-6Ch6, l-12BLA; 2-12AX7, l-OG3.
POAER: loo-130 v, 60 cps, 50 watts; 50 cps and 230 v units on
special order.
ACCESSORIESSUPPLIED1 Mating connectors for input, output; six
foot power cord.
ACCESSORIESAVAILABLE: Mating 6032 End Frames, mounting hardware,
rubber feet. Model L102 Input Assembly,
2-5886 electrometer tubes in a plug-in
can (replacement spare).
CABINET: 19" x 59 high x 10" deep. Net wei&ht 21 lbs.
415 II - 1

SECTION III - OPERATION
A. OPERATINGCONTROLS
-
The controls are discussed in order from left to right on the
front panel.
(1)
(2)
(3)
(Ii)
(5)
(6)
ZEROCHECK: Depressins this control effectively re-
moves all current from the amplifier input and allows
the meter to be set to zero with the ZEROADJUST con-
trol. After the button is depressed it may be locked
in position by turning the button one quarter turn as
indicated by the panel marking.
AMPERESFULL SCALE: The full scale meter sensitivity
is selected by this control. The use of zero suppres-
sion does not change the sensitivity.
CURRENTSUPPRESSI
(a) MULTIPLIER and AMPEHES: The combination of these
two dials set the amount of zero suppression. On
the OFF position of the AMPERESdial, the suppres-
sion circuit is disconnected.
(b) FINE8 The FINE control extrapolates between posi-
tions of the MULTIPLIER switch. For example when
the MULTIPLIER control is on aero, the FINE con-
trol has a ranpe of 0 to 1. If the control is on
1, the range of the FINE control is from 1 to 2 and
so forth.
METER: The METERswitch allows the choice of plus or
minus current polarity; using the meter for indica-
tion; or switching it off. In the METEROFF position,
the switch still permits choice of plus or minus cur-
rent polarity.
ON: This switch turns on power. The instrument is
ready to operate in about 60 seconds.
ZEROADJlJSTz This control is used with the ZEROCHECK
button depressed to adjust the micro-microammeter zero.
B. INPUT AND OUTPUTCONNECTIONS
-
(1) Input Connections: The input connections and the
current generator being measured must be carefully
shielded since power line frequencies are well within
the pass band of the amplifier on most ranges. Also,
unless the electrostatic shielding is thorough, any
alteration in electrostatic field in the neighborhood
will cause marked output disturbances. The insulation
415 III - 1

used in brinping the signal into the amplifier must
be either polyethylene, polystryene, teflan or similar
hish resistance, low-loss material. Any Coaxial cables
used must be of the low-noise type. This type of cable
employs a graphite coating between the dielectric and
the surrounding shield braid. Satisfactory types are
made by Amphenol, Microdot and Simplex. The use of
low-noise cable is mandatory due to the wide frequen-
cy response of the instrument. The Model hl5 is,
therefore, markedly more sensitive to external dis-
turbances than other Keithley Electrometers. Any
chance in the capacitance of the measuring circuit
to ground will, cause extraneous disturbances. It is,
therefore, recommended that the measuring set-up be
made as rigid as possible and any connecting cables
be tied down to prevent their movement. If continuous
vibration is present, itmay appear on the output as
a sinusoidal sJFna1 and some precautions may be nec-
essary to isolate the instrument and connectinS cable
from this vibration.
(2) Output Connections: The output of the instrument is
one volt for full scale meter deflection. up to 5 ma.
may be drawn from the output. The output is intended
primarily for driving oscilloscopes and pen recorders.
It may be divided down to drive 10 and 50 millivolt
recorders by placing: a suitable network across the
output. In general it will not satisfactorily drive
1 ma. Ester-line-Angus and Texas Instruments recorders
directly since the output voltage is too low for full
scale deflection or for providing the proper coil
dampin!?.
C. PRELIMINARY SET-UP
(1) Connect current source to input terminals per directions
in paragraph Bl above.
(2) Depress and lock ZEROCHECKbutton.
(3) Set CURRENTSUPPRESScontrols as follows:
(a) MULTIPLIER: Set to zero.
I”{ $W’BES: Set to OFF.
(Z, METEA: Turn to most counter-clockwise position. Turn to +position.
(b) Turn on power. After about 30 seconds meter should
indicate on scale.
(5) Set meter to zero with ZEROADJUST.
III - 2

D. MAKINGMEASUREMENTS
(1)
(2)
Current Measurements 'Without Zero Suppression? With
the current source attached and the AMPEREScontrol
on OFF, turn the AMPERESFULL SCALr; switch to the
most insensitive range and open the ZEROCHECKswitch.
Increase the instrument sensitivity until the largest
possible reading is obtained before full scale is ex-
ceeded, The reading is now %he actual current beinF
generated by the attached device,
Current Measurements With Zero Suppression: Proceed
as in paragraph (1) above. Then set the CURRENTSUP-
PRESSMULTIPLIER and AMPERESdials to correspond as
closely as their restilutlon permits to the current
reading obtained in para,sraph (1). This operation
should cause the meter needle to approach zero. Now
use the FINE control as necessary to set the meter ex-
actly to zero. Then
move AMPERESFULL SCALE switch to
the next more sensitive range and ad,just the FINE con-
trol as necessary. The input current is still the same.
Yowever , variations in current are beinp presented on
a scale three times as sensitive as before. Tf it is
desired to expand the scale further, the next more
sensitive range may be used. This nrocess may be re-
peated until one ner cent of the orifrinal scale is
presented as full scale. The sero suppression cir-
cuit is limited to this amount of suppression.
E. SPEEDOF RESPONSE
The specifications detail the possible speed of response with
various input capacities. It is evident from the data that
the less the input capacity, the better the speed of response.
Therefore, the Model hl5 should be located as closely as pos-
sible to the current source. The amount of capacity does not
affect the dampins. Under all conditions, tho response will
be aprroximately critically damped.
III - 3

SECTION IV - CIRCIJIT DESCRIPTION
A. CTRCIITTBLOCKDTACRAh~
I- O 0
Eln A Eo
0 v
+R- - +
X)BO
OUTPUT
FIG. 1
(1) The Electrometer: In block A Figure 1 is a high rain amp-
lifier with electrometer tube input. It can be assumed
with a high degree of accuracy that current neither enters
or leaves its input terminals, The amplifier is so arranged
that the output is the negative of the input. Therefore,
sjnce a feedback connection exisj.ts between e, and the innut,
any positive voltaae appearing at the i~nout of A, ~1~11 cause
a nepatjve voltage applied through R and B. Tf, for the
moment, we omit the box labeled B from the discussion, the
voltage e, will increase until it equals iR, the drop across
the resistor. This is necessary since this feedback connec-
tion results in a circuit designed to keep the input drop to
a minimum, Therefore, a8 a first approximation,
i = e,/R (1)
and a properly calibrated meter at the amplifier output will
read current directly.
(2) Current Suppression: In Figure 1, when an input current is
flowing, the output voltage is iR from (1). The output assumes
this voltage in order to balance out the input current so that
the input terminal remains at ground. Either the output must
supply this voltage, in which case the meter indicates a read-
ing; or a voltage may be inserted in series with the feedback
415 IV - 1