Keithley 414 User manual

INSTRUCTION MANUAL
MODEL 414, 414C
MICRO-MICROAMMETER

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, transistors, fuses, and batteries, which,
within a year after shipment to the orig-
inal buyer, proves defective on examination.
DAMAGE IN SHIPMENT
Be sure to include the instrument model num-
ber and serial number in all communications,
if the instrument is damaged when received,
or fails to operate properly, a claim should be
filed with the carrier. Upon receipt of the claim
agent’s report, we will inform you regarding
repair or replacement.
REPAIRS
When returning an instrument for repair or
recalibration, it should be securely packed
against shipping damage and sent to the fac-
tory, freight prepaid. A brief letter describing
the difficulty should accompany the instrument.

CONTENTS
INTRODUCTION
SPECIFICATIONS
Ranges
Accuracy
Input Drop
Grid Current
Zero Drift
Response Speed
Zero Check
Tube Complement
Power Requirements
Accessories Supplied
output
Noise
Connectors
Accessories Available
Cabinet
OPERATION
Operating Controls
Operation
CIRCUIT DESCRIPTION
Basic Theory
Circuit Description
MAINTEUANCE
Factory Adjustments
Trouble Shooting
Voltage Resistance Diagram
Circuit Schematic Diagram Model klh
Circuit Schematic Diagram Model LlhC
Replaceable Parts List
414
KEITHLEY INSTRUMENTS
SECTION
I
II
III
IV
V
CLEVELAND, OR10

SECTION I - INTRCDDCTION
Model klk
----
The Keithley Model lilh Micro-microammeter is a line operated
vacuum tube electrometer for measuring currents in the range
of 2 micro-microamperes to 10 milliamperes. Features include
a response speed of greater than 0.5 seconds on all ranges,
an input drop of less than 5 millivolts at full scale, a
zero drift of less than 2% per day on any range, good accu-
racy and calibration stability, negligible noise, and
simplicity of operation. For recording, an output signal
of five volts at 1 milliampere is available.
This model is identical to the klh except that a meter-relay
replaces the panel meter. An adjustable conta& pointer is
built into the meter-relay, When the indicating pointer
rises to the value set with the adjustable contact, the
contacts lock and actuate an internal relay. The relay's
SPDT s-ampere contacts are brought out through an AN con-
nector at the back of the chassis.
A manual reset button is supplied on the front panel. Reset
connections are also brought out through the AN connector for
rem&e resetting of the locked-up meter-relay.
414
I-l

SECTION II - SPECIFICATIONS
Ranges:
Accuracy:
Input Drop:
Grid Current!
Zero Drift:
Response
Speed:
Zero Check:
Tube
Complement:
Power
Requirements:
Accessories
Supplied:
output:
Noise :
Connectors:
Accessories
Available:
Cabinet:
17 ranges in overlapping 1 and 3 sequence, from 10
milliamperes to 0.1 milli-microamperes full scale.
Within 3% of full scale on all ranges from 10 milli-
amperes to 10 milli-microamperes, and within k% of
full scale from 3 milli-microamperes to 0.1 milli-
microamperes.
Less than five millivolts for full scale on any
range.
Negligible.
Less than 2% in any eight hour period after a five
minute warm-up if the source voltage is not less
than one volt.
Greater than 0.2 second for 67% of full scale on
any range with up to 5000 micro-microfarads of
input capacity.
Zero check switch allows zeroing of the instrument
without disturbing the test circuit.
1 5886, 1 613~8, 1 6CM6, 1 082.
100-130 or 200 to 260 volts SO-60 cps, 33 watts.
Mating connectors, two wire adapter for power cord.
Five volts at up to one milliampere is developed for
full scale deflection.
Noise at output and on indicating meter is less than
1% of full scale peak to peak on any range if the
source voltage is not less than one volt.
Input: teflon insulated UHF (Amphenol 83-798)
Output: binding posts on front panel, Amphenol SOPC2F
at rear.
Model 6031 end frames for bench mounting.
Dimensions 19" x 5i” high by 10" deep. Net weight
16 pounds.
414
II - 1

SECTION III - OPERATION
A. OPERATINGCONTROLS
1. Zero Check: This is a push-button located at the extreme left
of the panel. Its function is to allow the zero of
the instrument to be checked while the current source
is attached. To uss, depress and set the zero with
ZEROCONTROL. It is a feature of the instrument that
the external circuit is not disturbed during the test.
2. Range Switchr The RANGESWITCHis the dial next to and to the right
of the ZEROCHECKbutton. The range in use is always
at the top of the dial for convenient operation.
3. Power, Meter
Reverse Switch: The knob to the right of the RANGESWITCHis the
Ir. Zero I
B. OPERATION8
1.
2.
Precautions:
Operation:
power and meter polarity switch. This control per-
mits positive or negative meter readings. The out-
put voltage at the recorder terminals is not re-
versed by this switch.
This knob, next to the meter, is used in conjunction
with the ZEROCHECKswitch as described above to set
the instrument zero.
If the instrument is to be used at its extreme sen-
sitivity it is necessary to shield all input leads.
The lead-in cable should be polyethylene or teflon
insulated coaxial cable; and a low noise, graphits-
coated, dielectric cable such as Amphenol 21-537 is
recommended. At low sensitivities some of these
precautions may be disregarded.
(a) Connect to a power line of proper voltage. The
instrument is shipped for 117 volt SO-60 cps opera-
tion. For 230 volt operation see oircuit diagram
at the rear of the manual.
(b) Turn the RANGESWITCHto 10 milliamperes.
(c) Turn on power. After 30 seconds the instrument
is ready to operate.
(d) Depress ZEROCHECKbutton and set meter to zero.
CAUTION1 Do not use control to set meter to any
other point than zero.
(e) Instrument is now ready to operate. Attach
current source and turn RANGESWITCHto proper
range.
III - 1

3.
Special Instructions for Contact Meter Models:
(a) The operation of the instrument is identical to the non-
contact meter models with the exception that, on ttrn-on,
the meter pointer will strike the meter contact and lock.
Therefore, after the instrument is on for about one minute
press RESET button to release pointer and zero the meter.
At this point proceed as in Sections 1 and 2.
(b) Special Output Connection: The output connector at the
rear of the contact models is an AN connector which contains
the output terminals, the control relay contacts and the re-
setting circuit. It is necessary that ccntacts A and B in the
resetting circuit be shorted if the panel reset button is to
be operative. If remote resetting is desired terminals A and
B may be connected through a remote normally closed switch.
The wiring of thi~e connector is shown in detail in DR12&9C
AT THE REAR of the manual.
(c) The SPDT relay contacts are rated at 5 amperes at 110
volts AC or 2L volts DC.
IL. Recording:
The Model hlh is provided with binding posts at the front of
the instrument and a connector at the rear for connection to
a recorder. A mating plug is provided for the rear connector.
The wiring of the connector is shown in the schematics at the
rear of the manual and is different for the hlh and the UC.
The output is five volts and 1 milliampere for full scale
meter deflection. The terminals may be connected directly
to high impedance recording devices. A series resistor is
necessary when driving a milliampere recorder or a mirror
galvanometer. The exact value of resistance varies from
recorder to reccrder. For a one milliampere recorder, ap-
proximately 3.S kilohms is required. The exact sensitivity
may be set by means of a potentiometer in series with the
output if desired.
5. Speed of Response:
The speed of response of the instrument is specified as not slower
than 0.2 seconds for 67% of full scale with 5000 micro-microfarads
of input capacity. Capacities greater than 5000 micro-microfarads
may cause instability on some ranges. However, the above speci-
fications allows up to 500 feet of 10 mmf per foot coaxial cable.
III - 2
414

SECTION IV - CIRCUIT DESCRIP'TION
i in --
FIG. I
A. BASIC 'THEORY:
Figure 1 shows the basic circtiit. The input current 1 flows into
the input termj.nal. If we neglect Cl and C2 for the moment, the
current i flows throuph R the feedback resistor. Since A is an
amplifie? of gain k and the feedback is negative.
-
ein = co/k (1)
and since all the current must flow through R,
i q -e, + e, /k
--.-_,-~_ ~_--
R
(2)
now if &, the loop gain is large, the current flowing through
the input is e,/R and may be read from a properly calibrated
meter at the output. ei,, is the input drop of the ammeter.
The input resistance Rin is given by e-in/i and is,
Since in the Model hlh, the amplifier gain k is about 1000, the
input drop, ein will be about 5 millivolts for a five volt output
and the effective innut resistance Rin will be about l/1000 of
the range resistor being used.
IV - 1

If the capacities Cl and C2 are considered, the time constant
of the circuit is given by,
T = RCl/k + RC2
Thus the input time constant is reduced by a factor equal to
the loop gain. Capacitor C2 is placed across R to damp the
response and prevent ringing.
B. CIRCIJIT DiQXRIl'TION: Refer to DR127580 at the rear of the manual:
The input circuit consists of Vl, a type 5886 electrometer tube,
followed by a 6BH8 and a 6CM6 cathode-follower. This arrange-
ment provides a loop gain of about 1000. A high decree of zero
stability is assured by regulation of the filament supply of Vl
and B+ supply by Vlr the OA2 voltage regulator. The negative
bias supnly is regulated to the necessary degree by an NE81
neon lamp. The amplifier is a simple single ended direct-
coupled amplifier. Vl and V2 are directly coupled and the
coupling between V2 and V3 is by means of a NE81 neon lamp.
RlZh, the zero control, operates by varying the screen poten-
tial of Vl.
The current sensitivity is changed by either changing the
feedback resistor (RlOO through R113) or by changing the
feedback voltage by means of resistors Rll6 and R117. From
10 milliampers to 10 millimicroamperes a feedback voltage
of five volts is used and one resistor is used per range.
From 3 millimicroamperes to 0.1 millimicroamperes one resisLor
is used per decade and the feedback voltage is either one or
three volts depending on whether a 3x or 10x range is being
used.
The power supply consists of a conventional rectifier-filter
circuit for the positive and negative supplies.
IV - 2

SECTION V - MAINTENANCE
Except for occasional tube replacement very little maintenance is
required for the model hlh. Components are operated well below
rating, and high quality components have been used throughout.
1. FACTORYADJlJSTMENTS
Only one factory adjustment is made. This is Rl32, the meter
calibration potentiometer. This adjustment is only necessary
if the panel meter is changed. To calibrate set the instrument
on the 1 or 10 milliampere range anti set the meter to the cor-
rect reading with a calibration current sufficient to deflect
the panel meter to at least 75% of full scale.
2. TROUBLESHOOTING
Refer to DR12758-C and the voltage-resistance diagram at therear
of the manual.
Follow this general procedure in trouble shooting if the fault
is not apparent from the tabulated list below:
1. Check the B+ and J?- potentials: The E+ poten,tial can be
measured between the rectifier string and R201 and should
be about 320 volts. The ripple should not exceed 3 volts
rms. The B- potential may be measured between the negative
rectifier string (RFh,5) and R2O5 and should be about 2irO
volts. The ripple again should not exceed 3 volts RMS. If
either potential is no't correct the trouble is probably due
to a defective rectifier or filter component although in
some cases the transformer may be defective. Refer to the
schematic diagram to locate the defective component.
2. SPECIFIC FAULTS
a. Instrument will not balance: If no defect has been
foundT%x%zpection suggested in l., check the volt-
age at pin 1 or 5 of Vlr. This should be 150 volts. If the
voltage is not 15Ov, check R2O3, 202, and 201 for continuity
and check Vh. If the voltage is correct, check the voltage
at pin 3 of Vl (The red dot is next to lead 1) the reading
should be 3.2 volts. If the voltage at this point has risen
to 150 volts, the filament of Vl is open and this tube should
be replaced. If this voltage checks correctly, the following
procedure should be started: Short circuit the input to
ground with the range switch on 1 microampere full scale.
This removes the negative feedback and allows the operating
points of the individual tubes to be checked. It will usually
be found that the amplifier will become very sensitive and
difficult to balance, however it is only necessary that the
voltage swing through the correct operating value to confirm
that the circuit is operating correctly. Then with the input
V-l

shorted, measure the plate potential of Vl with a high impe-
dance VTVM (100 megs or better). This voltage should be
setable by means of the ZEROcontrol to 8 volts. If it is
not, either the electrometer tube is defective or the poten-
tial on the filament or screen is incorrect. We have already
measured the potential on lead 3 of Vl and found it correct.
Now measure the potential on lead L. This should be 2.2 volts.
If it is not check the value of R122, Rl23, R12h, R208 and
R2Ol4. Any of these could cause an incorrect voltage. The
screen voltage on lead 2 is derived from Rl& in the above
resistor string. It should be possible to vary the :screen
voltage from approximately 5.h to 10 volts. If this cannot
be done, but the voltages are correct, R12)1 is defective or
there is a short circuit to some other part of the printed
board or harness. Finally remove V2 from its socket. If it
is now possible to obtain the correct potential on the plate
of Vl, V2 is defective.
If it was possible to adjust the electrometer plate to 8 volts,
VI and its associated components are not at fault and it is
necessary to proceed to V2, the 6DH8. Check the voltage at
pin 2 of V2. This should be the same electrical point as
lead 1 of Vl and by moving the zero control it should be pos-
sible to vary the potential at V2 precisely as on lead 1 of
vl. If this is not possible, check for an open tape on the
printed circuit board from Vl to V2. If everything checks to
this point, measure the voltage on pin 9 of V2. The voltage
should pass through 38 volts by varying the ZEROcontrol. If
this does not occur, check the other potentials on V2; if
these are not correct look for a defective resistor or an
open connection on the board. Finally check for a defective
v2.
If no fault has shown up so far, proceed as follows: Check
the potential at pin 3, V3, this should be setable with ZERO
to about -8.3~. Tf this is not the case, check to see that
GLl, the NE 81 is lit. Then remove V3 from the socket and
check to see if now the correct potential can be obtained at
pin 3, V3 or the lamp lights. If the potential can now be
obtained with the zero control and the lamp lights, V3 may be
defective or there may be a short to ground or R- from the
cathode of V3. If the lamp does not now light, check R129
and if found good replace GL 1 with a new NE 81. If NE 81's
are not available, most NE 2's will work in the circuit.
If the circuit did operate to this point, check V3 as suggest-
ed above. Then, if necessary, check for continuity of R130
the cathod load resistor and check to see that the potential
at the bottom end of R129 is about -50 vol,ts. Finally, check
the potentials on the other elec.trodes of V3. If now it is
possible to swing the output signal through zero volts with
the ZEROcontrol, the instrument should operate properly with
the short to the input removed. If now this still is not
v-2

possible either the feedback connection is open or the circuit
is oscillating. To check the feedback connection, check to
see that lead 2 indicated on the circuit schematic is con-
nected from the output cathode as shown. If the circuit works
properly on some ranges but not on others, check to see if
R117 and Rll6 are defective.
Oscillation in the circuit with the input connector capped
(do not confuse with stray pickup) will be caused by a wrong
or changed value of Cl01 or ~126. Occasionally if a tube is
replaced and the replacement has an unusually high gm, oscil-
lation may occur. If this happens, try another tube or pad
Cl01 so as to double its value.
b. Oscillation:
immediately above. If oscillation occurs, see the paragraph
i;on V 1 on FACTORYADJUSTMENTS.
Inaccurate reading: For calibration procedure, see Sec-
If this adjustment is insuf-
ficient, be sure shielding of input is satisfactory before
proceeding. The only other causes of inaccuracy are either
insufficient loop gain or inaccurate feedback resistors. If
the feedback resistor is at fault, the inaccuracy will be
evident only on the range on which the resistor is being used.
(CAUTION: when calibrating, using a resistor and a voltage
source, the voltage should not be less than 0.1 volts.) The
inaccuracy would then involve one of the resistors RlOO to
R113 or ~116 and R117.
To check for low loop gain do the following: Turn the range
switch to the 1 millimicroampere scale and connect a voltage
source to the input whose impedance is not greater than 10K.
'The output will become relatively unstable, but with some care
it should be possible to determine the DC voltage necessary at
the input to cause a full scale meter deflection. If it re-
quires more than about 5 millivolts to achieve full scale
deflection, the loop gain is low. If no other symptons of
malfunction occur, this can be remedied by replacing tubes.
414 v-3

c2: ,150
cz-100
c31.-500
c31.-50
C3L-5
c52-20
C52-2
c35-20
~8-201~.
c22-. 02
RI&500
RIG-1,.67~
RI 2-51~
~1~~16.7~
R12-50K~
Rl,246-[K
Rx?-5OOK
~2-1.. 67~
lii2-5.OM
~3-1~6 .7M
RlIt-50.OM
Ri~JI~-l.OOM
R2O-109
R20-l,OLO
R:lL2-1K
RI 2-Z
Rl~2-2K
nl2-250
~12-250
WI. -7OK
H,ij-TOM
RIG-11:
RI -22K
171-33OK
lil -lM
R548K
RI 2-22K
RP3-51i

Circuit
Desig.
REPLACEABLEPARTS LIST - MODELklk or hlk!C
- - -
Part
Description No. --
R201 Resistor, camp. carbon, 100 ohm, lo%, 2w
R202 Resistor, wirewound, lOK, lo%, 10~
R203 Resistor, camp. carbon, 1.2K, lo%, '2~
R20)1 Resistor, wirewound, lOK, lo%,
5w
R205 Resistor, camp. carbon, L7 ohm, 108, &w
R206 Resistor, camp. carbon, lK, lo%, lw
~207
Resistor, camp. carbon, lM, lo%, ,&xv
R208
Same as R207.
RF1
RF2
RF3
RFL
RF5
SW1
SW2
Till
Selenium rectifier, 65 ma, 130 volt input
Same as RFl.
Same as RFl.
Same as RFl.
Same as RFl.
Meter reversing switch
Range switch, ceramic insulated
Transformer
Primary #l llsv, SO/60 cy
Primary #2 llSv, SO/60 cy
Secondary $1 325~, 6%LO ma
Secondary #2 22Ov, @ 20 mas
Secondary #3 6.3v@ 2 a
Secondary H3 6.3~ @ .6 a
Vl
v2
2
FUl
ME1
Electrometer tube, Raytheon CK5886-10
Vacuum tube, Type 6BH8
Vacuum tube, Type 6CM6
Vacuum tube, Type OB2
Fuse 1.5 amp, Type 3AG
Meter 0 - 200 Microamperes
Connectors On Chassis
Input
connect. Connector teflon insulated
Output
Termin.
Output
Connect.
Nylon (Two)
Microphone Type
Mating Plugs Furnished With Instruments
Input
Plug Plug, teflon insulated
output
Plug Microphone Type
R3-100
R5-10K
R3-1.2K
Rh-1OK
R147
R2-1K
Rl-1M
RFlR
SW70
SW18
m23
EV58f36-10
EV6BH8
EV6CM6
EVOB2
m-e
ME-19
cs-12
BP-13
cs-58
cs-L9
cs-33

REPLACEABLEPARTS LIST - MODELU&C ONLY
Circuit
Desig. Description Part
NO.
--__
Output
Connect.
c205
RX.1
ME1
RF6
SW3
output
Plug
Type AN3102A-18-1s cs-23
Capacitor, electrolytic, 1000 x 15 WV al-1000
SPDT 6 Volt AC Relay RL7 or RL8
O-200 ma Model h61-26, Assembly Products ME-20
Selenium Rectifier RF-7
Pushbutton reset switch
SW-35
Type AN3102A-18-15 CS-22

--

I r----F=
i

CHANGENOTICIZ
May 22, 1969 MODIX 414/i PICOA~7m?'ER
Page 19. Change to the following:
Circuit Mfg. Keithley I
Desl.g. Fig. : Description CO& Part NO. _ Ref. _
21850~ MOS PET Input Plug-in Card 80164 23734A 6 1
I
page 20. Change to the following:
Circuit Mfg. Mfg. Keithley Fig. 1,
Dosig. Value Rtiting Type COdf Part NO. Part No. Ref. :,
R123 2 kfi 20%, 0.2 w compv 71450 70 KP31- 211 I,7 j;
.) (.

CHANGE NOTICE
May 22, 1969
MODEL 41.4s PICOAMMlYl’CR
Page 31,. Change to the fol.lowing:
Circuit Mfg. Keithlcy Fig.
.pcsir,. Descri.ption code Part No.
- Ref.
21850~ MOS FET Input Plug-in Card .~
80164 2373m 7
af? 33. __ Change to the following:
Circuit
Desig.
RI.31
Valrvs
2 kfl
Mfg. ‘Mfg.. Kei.thley Fig.
Ril:ing TYPf Code Psrt No. Part N’o. Ref.
_-
20%, 0.2 w compv 71450 70
RP31.-2K
2,8