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:. ,. - .I


Section Psq:e

SpEClFIC*TIfJNS -___--__-___-____-__---------------------------- i"

1. GENEp&, DESCRIPTION--_-____------_------------------------- 1

2. OPWTlON --------------------__________I_________--------------- 3

3. Cl&-"lT DESCRIPTpJX--------------------______I_____________--- 10

`. *C(-ESSORlES -__------------------_----------I-------------------------- 25

5, CUp,UTION __-____----____----____________________I__------------ 27

lj. F\EP,dCEBLE pa?s ---------------------------------------------------- 32

SCHyJJICS -__--___-_---_-----_----------------------------- 53



Fip. NO. Title Page
1 Franc Panel. 1
2 Franc Panel Controls. 2
3 Rear Panel CmlfTOlS and Terminals. 2
4 Prinrer/Canerol Connector. 8
5 Timing Diagram. 9
6 Simplified Diagram of Feedback Ammeter. 10
7 Gain Calibration of Amplifier. 10
8 Damping for Anmeter. 11
9 Zero Check Operarion. 11
10 Block Diagram of AID Converter. 12
11 Delay Hold Circuit. 13
12 Incegratar Circuit. 13
13 Zero Crossing Decxtar. 13
14 "ode1 4401 Buffer Stage. 15
15 Chassis Top View, Showing Cal. Adjustments. 17
lb Location of Printed Circuit Boards. 18
17 Component Layout, K-207. 19
18 componenr layout, PC-208. 19
19 component Layour, PC-210. 21
20 Componene Layout, PC-217. 20
21 component Layout, PC-219. 20
22 component Layout, PC-222. 23
23 Componenr Layour, PC-223. 23
24 Componenf Layout, PC-229. 23
25 component I.ayouc, PC-209. 24
26 component Layout, PC-218. 24
27 Test Equipment Set-up far A/D Calibration. 30
28 AID Con~erfer Zero Adjusrmenrs. 31
29 Elechanical Assembly. 33
30 Template, Test Cover, Tap 51
31 Ternplace. Tesf cover, Bottom 52

0874 iii


RANGE: 100 picoamperes full scale (0.1 picoampere. DISPLAY RATE: 24 readings per second maximum
least signdicant digIt) to 10 milliamperes in nine (20 per second with 50.M units) adjustable to
decade ranges with 100% overrangingonall ranges. approximately two readings per manute.
DISPLAY: Four digits tram 000 to 1999; polarity and INPUT VOLTAGE DROP: Less than 1 millivolt for lull.
overload indicabon. scale display on all ranges when properly zeroed.
RANGE SELECTION: Manual with automatic decimal to-peak current of power line frequency or mul*lple
point positmn,ng. which will cause less than 1 digit of error. to that
error,. 100 dB on 100.p,coampere to 100."ano.
ACCURACY AND RESPONSE TIME: ampere ranges with mawmum damping. Peak input
current should not exceed 20 milliamperes.
Transient: 1000 volts for up to 3 seconds.
Continuous: 600 V using a Keithley or other current
limited (up to 20 mA) Hugh Voltage Supply.
ANALOG OUTPUT: % 1 volt from a 500.ohm sourcefor
full~scale display. Maximum output, 1 millismpere.
Output polanty 3s oppxite input polarity.
4401 accessory provides BCD OUtput and external
CONNECTORS: Input: Teflon-insulated UHF-type. Ana.
DAMPING: Varies rise time from minimum value to log output: Amphenol 8O.PCZF. Case ground: Bind.
approximately 1 second on the lOO.nanoampere to ,ng post.
100.picoampere ranges. POWER: 105.125 or 210-250 volts (switch selected).
ZERO DRIFT: Less than 0.5% of full Scale per week: 60 Hr. 50.Hz models available. 30 watts.
less than O.O54a/"C. after %-hour warmup with DIMENSIONS, WEIGHT: 51,`~" high x 19" wide x 10"
source voltages greater than 2 volts. deep: "et weight. 15 pounds.

I - . _. t

iv 0874
Safety Precautions

The following safely precautions should be observed before using Users of this producl muzl bc protected from elcclnc hhock a, nil
this product and any associated instrumentation. Although some iw times. The responsible body musk enwrc Ihal users arc prcvenied
strume"f~ and accessoties would normally be used with non-ha/- access andhr insulawd from every connection poini. In some cw5s.
ardous voltages, there are situarions where hazardous conditions ~onneckms mw be expored to potential human contact. Producl
may be present. users in these circumslances must be trained to protect thanselves
from the risk of elearic shock. If the circuit is capable of operating
This product is intended for use by qualified personnel who recog- at or abwe 1000 volts. no conductive part of the circuit may be
nize shock hazards and arc familiar with the safely prccaurions re- exposed.
quired to avoid possible injury Read the operating information
carefully before using rhe product. As described in the lnternaiional Electrorcchmcal Commissmn
(EC) Standard IEC 664, dtgiral muldmcler measuring cmam
The types of product users are:
(e.g.. Keithicy Mod& 175A. 199. 2000, 2001, 2002, and 2010~ arc
Responsible body is the individual or group responsible for the use Installation Category II. All other inwuments agnai rcrminals are
and maintenance of equipment, for ensuring that the equipment is lnsraliation Category I and mw no1 be connccxd 10 mani
operated within its specifications and operating limits. and lor ens
swing that operators are adequately trained. Donotconnect switchingcards directly to unlimited powcrcircults,
They are intended to be used with impedance limited sources,
Operators use the product for its intended funcrion. They must be NEVER connect switching cards directly to AC mains. When cons
trained in electrical safety procedures and proper use of the insrru- netting sources to switching cards, install prorective dcwces to llm-
ment. They must be protected from electric shock and contact with it fault current and vollage to the card.
hazardous live circuits.
Before operating an instrument. make sure the line cord is connecr-
Maintenancepersonnelperform routine procedures on the product ed to a properly grounded power recepraclc. Inspea the connecring
to keep it operating. for example, setting the line voltage or replac- cables, test leads. and jumpers for possible war. cracks, or breaks
ing consumable materials. Maintenance procedures are described in before each use.
the manual. The procedures explicitly state if the operator may per-
form them. Otherwise, they should be performed only by service For maximum safety, do not touch lbe product. iest cables. or any
personnel. other instruments while power is appiicd to rhe circuit under [es!
ALWAYS remove power from the entire lesl system and discharge
Service personnel are trained to work on live circuits, and perform my capacitors before: conneaing or disconnecrmg cables or jump-
safe installations and repairs of products. Only properly trained ser- us. installing or removing switching cards. or making internal
vice personnel may perform installation and service procedures. changes. such as installing or removing jumpers.

Exercise extreme caution when a shock hazard is present. Lethal Do nor touch any ObJecr that could provide a conem path to Ihc
voltage may be present on cable connector jacks or test fixtures. The common side of the circuit under test or power line (earth) ground.
American National Standards Institute (ANSI) states that a shock Always make measurements with dry hands while standing on a
hazard exists when voltage levels greater than 30V RMS. 42.4V dry, insulated surface capable of withstanding the voltage being
peak, or 60VDC are present. A good safety practice is to expect measured.
that hazardous voltage is present in any unknown circuit before
The instrument and accessories must be used in accordance with its The WARNING heading in a manual explains dangers that might
specifications and operating instructions or the safety of the equip- result in personal injury or death. Always read the associated infor-
ment may be impaired. maflon very carefully before performing the indicated procedure.

Do not exceed the maxjmum signal levels of the instruments and ac- The CAUTION heading in a manual explains hazards that could
cessories, as defined in the specifications and operating informa- damage the instrument. Such damage may invalidate the warranty.
tion, and as shown on the instrument or test fixture panels, or
switching card. Instrumentation and accessories shall not be connected to humans.

When fuses are used in a product, replace with same type and rating Before performing any maintenance, disconnect the line cord and
for continued protection against fire hazard. all test cables.

To maintain protection from electric shock and fire, replacement
Chassis connections must only be used as shield connections for
components m mains circuits. including the power transformer, test
measuting circuits, NOT as safety earth ground connections.
leads, and input jacks, must be purchased from Keirhley Instru-
merits. Standard fuses, with applicable national safety approvals,
If you are using a test fixture, keep the lid closed while power is ap-
may be used if the rating and type are the same. Other components
plied to the device under test. Safe operation requires the use of a
that are not safety related may be purchased from other suppliers as
lid interlock.
long as they are equivalent to the original component. (Note that se-
lected pans should he purchased only through Keithley Instruments
[email protected] SCI~W is present, connect il to safety earth ground using the
to maintain accuracy and functionality of the product.) If you are
wire recommended in the user documentation.
unsure about the applicability of a replacement component, call a
Keirhley Instruments office for information.
Then symbol on an instrumenr indicates that the user should re-
fer to the operating instructions located in the manual.
To clean an instrument, use a damp cloth or mild, wafer based
cleaner Clean the exterior of the instrument only. Do not apply
Then symbol on an instrument shows that it can source or mea-
cleaner directly to the instrument or allow liquids IO enter or spill
sure 1000 volts or more, including the combined effect of normal
on the instrument. Products that consist of a circuit board with no
and common mode voltages. Use standard safety precautions to
case or chassis (e.g., data acquisition board ior installation into a
avoid personal contact with these voltages.
computer) should never require cleaning if handled according to in-
structions. If the board becomes contaminated and operation is af-
fected, the board should be returned to the factory for proper

Rev. 2J99


Cancrol Functional Description Paragraph

RANGE Switch (S1202) Sees full rangesensitiviq. 2-3 a
POWER SWifCh (S102) Controls power instrument.
to 2-l b
ZERO CHECK (SL201) Selects Zero Check Mode. 2-3 c
ZERO ADJUST (R1211) Adjusts the zero offset. 2-3 e
D.424PINC conrro1 (R1221) Adjusts damping. 2-l d
DISPLAY RATE (R1201) Adjusts the A/D Conversion rate. 2-l f

0874 1


Suicch Switch S1203 Switch concro1 POSe Receptacle
s102 51203 It1211 51211 n210

FIGURE 3. Rear Panel Controls and Terminals.

TABLE 1-2.
Rear Panel.

I Control or Terminal Functional Description Paragraph

117-234V Swirch (SlOl) set* 117 or 234V operation.
FUSE (FlOl) Type 3AG Slow Blow: 117V-3fSA
ANALOG OLTPVI (51213) Provides a recorder ourput. 2-5
FRI>lTEI(/CONTKOL (31212) Provides SCD Ourputs from a 50-pin connector. 2-6
S?.uE Cover plate for mounting a" additional SO- 2-6
pin Connector.



2-l. INPM CONNECTIONS. 1. Thermal EMUS. ThemaeLectric potentials
(thermal emfs)
are generated by thermal gradients
a. Inp,,t Rece,,w.cle. The Input connecfor (51210) between two junctions of dissimilar metals. These
is a Teflon-insulated UHF t.,w (Keithlev Part No. CS- can often be large compared to the signal to be
64). A mating (CS-49) conniCtor is supblied far mak- measured. To minimize the drift caused by therma!
ing custom cables. The center terminal of the connec- emfs, use pure copper leads "herever possible in
tor is in the Input High terminal while the outer the source circuit. Drift can also be minimized by
shield is case ground. A separate grounding past "6" mainmining constant junction temperatures espec-
is provided for system ground connections. ially by using a large hear sink near the connec-
tions. The Keifhley accessory Model 1483 Lou Ther-
b. IDPUC Cables. Input connections should be made mal Connection Kit contains ali necessary materials
using coaxial cables which are low-noise types with far making very low rhemal copper crimp connections
graphite coaring beeween dielectric and shield braid. far minimizing Chermal effects.
Far eu~eom length cables Keithley Part No. SC-9 Low
Noise Coaxial Cable should be used. 2. AC Electric Fields. The presence of electric
fields generated by paver lines or ocher sources
1. Model 2611 Coaxial Cable. This cable is a can have an effect on instrument operacion. AC
pre-assembled cable 24 inches long having a IMF male voltages which are very large with respect co the
connector on each end. full-scale range sensitivity could drive the ac
amplifier into sacuracion, thus producing an erron-
2. Part No. 19072C Coaxial Test Cable. This eous dc output. Proper shielding as described in
cable is a pre-assembled cable 30 inches long having paragraph 2-1, d can minimize noise picl-up when
a UHF male connecmr an one end with alligator clips the instrument is in the presence of large ac fields
on the ocher. or when very sensitive measurements are being made.

C. Insulaeio". Use high resisrance, low-loss mafe-
rials such as sapphire, reflan, polyethylene or poly-
scyrene for insulation of the input circuit. 3. Magnetic Fields. The presence of scrang nag-
neck fields can be a potential source of ac noise.
NOTE Magnetic flux lines which CUL a conductor can pro-
duce large ac noise especially at power line fre-
The input terminal should be protected from con- quencies. The voltage induced due co magnetic flux
raminacion $0 chat the insulation will not be is prnpor~ional co ehe area enclosed by the circuit
degraded, Clean, dry connections and cables are as well as the rate of change of magnetic flux. For
very important to maincain the value of all in- example, the motion of a l-inch diameter loop in the
sulation materials. Even the best insulation earth's magnetic field will induce a signal of sev-
can be compromised by due, dirt, solder flux, era1 tenths of a microvolt. One way to minimize
films of oil or water vapor. A good cleaning magneric pickup is to arrange all wiring so that the
agent is methyl alcohol, which dissolves most loop area enclosed is as small as possible (such as
comon dirt without chemically atracking the rwiscing input leads). A second way to minimize
insulation. magnetic pickup is co use shielding as described in
paragraph 2-1, b.

b. ShieldinK.
1.` Electric Fields. Shielding is usually neces-
a. Noise. The limit of resolurion in voltage and sary'when instrumnt
the is in the presence of very
current measuremen?.s is determined largely by rhe large ac fields or when very sensitive measurements
noise penerared in rhe source. stray law-level noise are being made. The shields of the measurement cir-
is presene in some form in nearly all electrical cir- cuit and leads should be connected together co ground
cuirs. The instrumenr does nor distinguish between a~ only one point. This provides a "tree" config-
stray and signal currents since it measures the net uration, which minimizes ground loops.
current. When using the picoampere ranges, consider
the presence of low-level electrical phenomena such 2. Magnetic Fields. Magnetic shielding is useful
as thermocouples (thermoelectric effete), flexing of where very large magnetic fields are present. Shield-
coaxial cables (triboelecrric effect), apparent re- ing, which is available in the farm of plates. foil
sidual charges on capacitors (die-leccric absorption), or cables, can be used to shield the measuring cir-
and baCCery action of two terminals (galvanic action). cuir,, the lead wires, or the instrmenr itself.

0874 3

C. Damping. The amount of high frequency ooise f. Overloads. A unique input circuit provides
which will be observed on the picoammerer is deter- complete overload protection with fast recovery. The
mined by: I) the noise pickup ae the input, and 2) maximum transiene overload is 1000 voles for up co
the bandwidth of the amplifier circuir. The front 3 seconds. The maximum continuous overload is 600
panel DAMPING Confrol (R1221) controls the amount of volts using a current limited supply (up to 20 mA)
filtering from a minimum (NW) value (as stated in such as Keichley Models 240A, 245, or 246.
the rise time specification) fo a maximum value
(approximately 1 second on PICOAMP range) when see
fully clockwise. 2-3. FRONT PANEL CONTROLS.

d. Accuracy. The accuracy is specified in terme a. RANGE Switch (51202). This switch selects the
of a percent of reading on eech range. An additional full scale displsy range in nine decade steps. The
fl digit is specified since the A/D conversion has an dial is designated in engineering units, that is,
&herenc +I digir uncertainty. Noise and source re- PICO AMPS, NAN0 AMPS, MICRO AMPS, and MILL1 AMPS.
sistance conditions should be evaluated as additional
measurement considerations. b. POWERSwitch (SlOZ). This swirch controls the
line power to the instrument.
e. Source Resistance. The value of source resisf-
ante em affect the measurement if the loading effect C. OPERATE/ZERO CHECK Swifch (51201). This swirch
of the picoammecer is significant. To avoid a degrad- selects either normal operation or zero check opera-
ation of zero drift. rhe picoammeter range should be tion.
selected so that the range feedback resistor is much
less than the source resistance. The zero drift d. DAMPING Control (R1221). This control varies
specification is valid only for source voltages greac- the response time of the picoanrmeter on the PICO AMP
er than 2 volts. The suggested minimum source resisc- and NAN0 AMP ranges.
ante for each range is given in Table 2-l. The amounf
of degradation of the drift specification is given by e. ZERO Control (R1211). This control adjusrs the
the following equation. zero display. The ZERO Control should be used when
in ZERO CHECK mode.

Drift = %/week x Nominal Gain = f. DISPIAY RATS Control (R1201). *his control ad-
Effective Gain justs the A/D converter conversion rate from 24 reed-
ingslsec. (MAX) to 2 readingslmin (appron).
where Nominal Gain = K
Effective Gain = (w)(q

Example: If RANGE = 1 NICROAMP
RF = 1.02 x 106

Then Rs I' RF = 3 = 1.5 a. Preliminary Procedure.
RS 1. Check the 117-234V Switch (SlOl) dit the rear
panel for proper line voltage.

2. Check for proper rated fuse.

3. Connecr the power cord, place the POWERswitch
TABLE 2-l. ON, and allow a 30 minure warmup for critical meas-
Suggested Minimum Source Resistances. urements.

4. Adjust the ZERO Control (R1211) as necessary.
Zero is indicated by alternately flashing + polarity
RANGE RANGE Source Resistance lights.
Selected Resistance (ohms)

5. Connect the source es described in paragraph
100 PICO-AMPS 1010 2 x 1010 2-l.
1 NANO-AMP 109 2 x 109
10 NANO-AMPS 108 2 x 108 b. Measurements. The Model 440 measures current
100 t&NO-AMPS 107 2 x 107 over a full-scale range from 10 milliamperes (10m2 A)
1 MICRO-AMP 1.02 x 106 2 x 106 fo 10C1 picoampere (lo-10 A) with resolution to 0.1
10 MICRO-AMPS 1.05 x 105 2 x 105 picoarhpere (lo-l3 A). The display will indicate either
100 MICRO-AMPS 1.05 x 104 2 x 104 a positive or negative input current automatically.
1 MILLI-AMP 1050 2 x 103 (A positive curreot is defined as a positive "conveo-
10 MILLI-AMPS 105 2 x 102 rional current" applied ac Input High with respect co
case ground.)

4 0874
1 x 10-4 A 100 MTCKO-AMPS 100.0 x 10-6

LI xlo-? 10
1 x m-3 A
10.001 +llLLIlAME 1.000

2-5. ANALOG OUTPUT. The analog output on the rear

CO""eCrOr: so-pin Amphenol xicro-Ribbon mounted on
Model 440. "ueput mating connector supplied with


a. cenera1.

1. The Model 440 has provision for the installa-
tion of OUtpUt buffer printed circuit boards co
&rain Binary Coded Decimal (NO) outputs. Two 44-
pin card-edge cOn*eCeOrS are installed and complete-
ly wired on Che main PC board.

1. Full Scale Magnitude. The magnitude of the TABLE 2-7.
reading is indicated by BCD outputs which correspond PolariCy Output
to the three front panel display lights as shown in
Table 2-5.

TABLE 2-5.
Full Scale Magnitude

:onneccar Dee ima 1
Pin No. OUCp"t Digits

1 1 x 100
2 2 x 100
26 4 Y 100
4. ~ 27 8 x 100
exponent has a corresponding BCD oufpue as shown in
3 Table 2-8. The print-auf of the RANGE Swifch ex-
1 x 101
4 ponent uses 2 coiumns to represent information far
2 x 101
exponents from 00 thr" 10.
28 4 x 10'
29 `- a x 101 TABLE 2-8.
Range or Exponent Indication.
5 1 x 102
6 2 I 102 CO""eCCOC Decimal
30 4 x 102 Pin No. OUtpUt Digits
31 8 x 102
9 1 x 100 Range 1
10 2 x 100 Range 2
34 4 x 100 Range 4
35 8 x 100 Range 8
2. overrange Indicarian. Overrange is indicated i
by the faurrh (from the right) display light and
corresponding BCO output as shown in ~ahle 2-6.
Overload is indicated by a blanked display and d. External cancro1.
corresponding BCD output. The output at pi" 33
will he a logic "1" when the magnitude of ehe digital 1. General. To obtain optimum *ystem p%ffbrm-
display exceeds 1999. ante, if is often desirable CO operate Che~Nodel
440 synchronously with other digital equipment,
such as printers, paper tape punches, computers and
TABLE 2-6. other daea handling devices. The Model 440 with
Overrange and Overload Oucpurs. 4401 Printer Cards installed provides several print-
er control connnands for the purpose of synchronizing
external equipment to achieve maximum conversion

2. Applications. Several alrernate approaches
may he used in designing the overall system control

a) The Model 440 can be used to provide master
conerol of external devices so that the maximum
possible conversion race* can be obtained.

h) An external device can also he used for
master control such as a high speed printer.

3. Polarify Indication. The polariey is indicated c) A completely independent "master clock" can
automatically by ehe Polarity Indicator and corres- be used for system control far maximum flexibiliry.
ponding BCO output as shown in Table 2-7. Addition-
al BCO levels are available at pins 14 and 39 for 3. Description of external controls.
use with some printers. The zero check made is in-
dicaced by a BCD output from pin 38. Four pins may =I `71OI.C 1". This control inhibits A to D
be used to obcain BCD polarity codes for external conversion at the instant a closure to ground is
printers, where 1010 = + and 1011 = - prineer chsr- made. The conv'rsion cycle will resume immediate-
acters. ly when the "HO:D 1" line is opened.

1. Standard Outpue Codes and Levels. The stand-
ard o rpue code for Hodel 4401 Printer Output Cards
is l-2-4-8 Binary Coded Decimal (BCD). A binary
coded decimal digit is represented by a four-bit
binary code as show,, in Table 2-12. refer to figure
for a circuit diagram oI the Model 4401 Stand=,rd
Prineer outpue buffer stage.

2. PKpmx/CONTROL connector. nie PKINTEK/CONTROL
Connector used o,, the Model 440 provides for connec-
tions to 50 pins as shown in Table z-11. The mating
connecfor supplied with Model 4401 is an hmphcnoi
Part Number 57-,050o or Keithley Part Number cs-220.
available on special order.

3. Analog-fo-Digicai Conversion Cycle.

a) The analog-Co-digital conversion cycle can
be inifiafed in any one of three ways.

1.) DISPUY RATE concro1 set at MAX. With the
DISPLAY RATE Control set at MAX, the end of one
compleLe COnverSion triggers a second conversion
to obrain the maximum co""ersio" rate of ZL read-
ings per second.

2.) DISPLAY RATE ConLrol SeC at Other man EWY.
WiCh etle DISPLAY RATE Control set at soale psi-
tion other than MAX, (uncalibrated control set-
ting) the end of one complete conversion rriggers
a second conversion which is delayed by a speci-
fic time interval (DELAY). The time delay is a
funceio" of he position ai a continuously vari-
able control to provide a co""ersio" rate from
24 readings per second to 2 readings per minute.

3.) `HOLD 2" with TRIGGER Control. With the
"HOLD 2" command grounded, a ciosure to ground
of the "TRIGGER" command initiates one complete
5. Nigh and Low Keference. The PRINTEKICONTROL conversion cycle. A second conversion viii
connecror pro"ide* f"0 reference voltages, High foilow only if the TRIGGER cormand is removed
(t8") and Low (+ZV). These levels may be used to and m-applied a second time. The maximum con-
define the `~HICII" and "LOW" digital output states version rate using an external trigger is 24
1ar exeerna1 printing or computer devices. readings per second.

Typical Digital Outputs.

Front Panel RANGE Significant Range
Digital Display Sefting Polarity Digif & Overload Nag. EXP. InrerprelJrio"

-093.6 PICO-AMP 0 936 -0.936 x 10`10
+0.275 NANO-AMP + 0 275 09 +0.275 x ld
-17.31 NAN"-AMP 1 731 08 -1.731 x 10-a
c122.3 NANO-AMP + 1 223 07 +1.223 x 10-7
10.096 MICRO-AMP + 0 096 06 to.096 Y 10-6
-07.81 MICRO-AMP 0 781 05 -0.781 x 10-5
+165.2 MICRO-AMP + 1 652 04 hL.652 x 1V4
-L.921 MILLI-AMP i 92, 03 -1.921 7. 10-3
-06.17 MILLI-AMP 0 637 02 -0.637 x lo-*
+(bk*k) MICRO-AMP + 8 000 OS positive overloac

0874 7

TABLE 2-11.
PRINTER/CONTROL Connector Pin Identification.

Pin No. output Function Pin NO. O"tp"r Funcrion

13 1 x 100 Polarity 38 1 x 10 Zero Check
14 + 15" _-_ 39 + 15" ---

15 Blank --_ LO Blank ---
lb ELIkInk ___ 41 Blank ---

17 b 15" -__ 42 - 15" ---
18 + 3.6V --- 43 Common __-

19 Blank --- 44 Grounded
20 Blank --- 45 Grounded

21 Blank --- 46 Grounded Trigger
22 Blank ___ 47 Blank ___

23 i lb" Pulse Print Command 48 Blank ---

24 + av Hi Reference 49 Blank ---
25 /' 2v LO" Reference 50 Blank --_

FICURF. 4. Printer/Control Connector.


b) Conversion Cycle Timing. The Conversion 4.) PRINT COMMAND. The PRINT COEPWNO signal
Cycle is composed Of three timing periods, namely. is used to trigger external
printers or paper
Integrator zero, Integrator Sampling, and A-D tape punches. The PRINT CObDL\ND signal is de-
Counting period. Refer to Timing Diagram Figure layed 10 microseconds to allow the Storage Reg-
isters to settle. The PRlNT COMMAND pulse width
1.) Integrator Zero Period (ZERO). "hen a is approximately 100 microseconds with a I volt/
trigger pulse initiates a new conversion cycle, microsecond rise time into a 1 kilohm load. The
the Inregracar circuit is zeroed for a period pulse smplitude is approximated by ehe follow-
not to exceed 8.33 milliseconds for 60 Hz aper- ing equation:
ation. The Integrator Zero Period is 10.00
milliseconds for 50 Hz operarim. % = 14R/(R + 2200~

2.) Integrator Sampling(INTEGRATE).
Period where R is the output load resistor.
The Ineegraeor follows
Sampling automat--
ically the Integrator Zero Period and lasts for The "OFF" state is less ihan co.4 volt with
a duration of 16.67 milliseconds for 60 Hz op- approximately 1 milliampere sink current.
eration. The Integrator Sampling Period lasrs
for a duration of 20.00 milliseconds for 50 Hz

3.) A-D Counting Period (COUNT). The A-D
Gunring Period is initiated immediately follow-
ing the Integrator Sampling Period. The actual
counring rime durarion vi11 depend on the actual NOTE
incegraror voltage up to a maximum of 2000 clock
pulses or 16.67 milliseconds. Following the The data stared in the Output Registers will not
counting period a Buffer/Storage cormand is change for at leasr 25 milliseconds for 60 Hz op-
automatically generated in order to store the eration. If the front panel controls are charmed.
new reading in the output registers. the Zero Check BCD o"tput vi11 be changed only.

FIGURE 5. Timing Diagram.

0874 9


3-l. GENERAL. The Model 440 Digifal Picoamerer con- b. Circuitry. The amplifier input stage is a pair
sisfs of two separate sections packaged together in of insulated-gate, field-effect transistors (IGFET)
one chassis for optimum performance and convenience: designated Q1201 and Q1202 connected in a differential
a sensitive picoammerer and an analog-to-digital con- configurarion. The circuit designared 218508 is a
verrer. special overload protection circuit on the Input FET
board (which connects to 51201). The gate of Q1201 is
a. Picoameeer. The picoameter is a linear dc connected;to the input through 10M ohms. The gate of
amplifier connected as a feedback ammeter with nine Q1202 is referenced to ground. Poteneiometer RI205 is
CUrrent ranges. an internal COARSE ZERO adjusment. Potentiometer
R1206 is an internal Balance control. Transistors
b. A/D Converter. The analog-to-digital converter Q1203-Q1204 form a second differential amplifier stage.
is a dual slope, integrating type converrer with med- Potentiometer R1211 is a fronr panel ZERO adjustment.
ium conversion race. cold cathode readout tubes, BCD Transistor Q1205 and emitter follower transistor Q1206
output options and external control. provide sufficient gain for the analog output and A/D
converter. The analog output is connected through
R614 (499n) fo the dc amplifier output (the junction
of R1220 and D1203). The full scale current sensitiv-
ity is determined by ehe range resistor connected
across the feedback. The range resistance RF is com-
posed of a fixed resistance Rl plus a calibrarion ad-
3-2. PICOAMMETER justment resistance R2 as shown in Figure 7. Potent-
iomerer Rl221 controls the amount of damping on rhe
a. Ooerarion. The picoamerer consists of a sms- PICO AMP and NAN0 AMP ranges only. Switch S1203 de-
itive, linear dc amplifier with a 1 volt full scale feats the damping feature when set to 'WIN" or open
sensitiviey. The amplifier provides an analog output position. The damping circuir is shown in Figure 8.
up to 2 volts for*a 100% overrange display. The When switch S1201 is ser fo ZERO CHECK the picoamerer
RANGE resistors are connected across the feedback of is connected as shown in Figure 9. Ie should be noted
the amplifier. A simplified diagram of a feedback that the feedback resistor RF is shorted out & the
anmeter is shown in Figure 6. inpur High terminal is shorted to ground.



FIGURE 6. Simplified Diagram of Feedback &meter. FIGURE 7. Gain Calibration of Amplifier.




cu.-,- I