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SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The Model 261 Picoampere
Source is a secondary
standard
for use in calibrating
picoammeters
and electrometers.
The
output
of the Model 261 can be adjusted
between
10-'4A and
1.1 x 10.4A in eight decade
ranges.
The source has 3 digit
resolution
for current outputs
b#etween 10~12 and 10~4A.
The current
output
of the Mlodel 261 is derived
from
a
variable voltage source and a selectable
range resistance.
The
voltage
supply is highly ragulatled for stability
and uses high-
quality components
throughoul
for reliability.
The low side of
the output
can be floated to avoid possible ground
loop pro-
blems.
1.2 MODEL
261 FEATURES
Important
Model 261 features
iixlude:
1. 11V Internal Source. The internal voltage source can be set
to a value between
0 and 1'lV in O.OlV increments.
This
permits
accurate
calibration
of picoammeters
and elec-
trometers
with
input voltagt!
drops
up to 1OmV without
calibration
correction.
2. Stable
High-Meg
Resistance
Standards.
The
high-
megohm
resistance
standards
are selected
for maximum
stability.
Individual
temperature
coefficients
and resistance
values are supplied
with each instrument.
3. Line Operation.
The Model 261 is line operated
from either
105.125V
or 210.250V
power sources.
Voltage
selection
is
easily accomplished
with the rear panel line voltage
selec-
tion switch.
4. Eight Current Ranges. Eight current ranges are user select-
able with a single front panel control.
5. Shielded
Output
Connector.
The UHF output
connector
on the front panel is Teflon@
insulated
to minimize
possi-
ble leakage problems.
6. Floating
Low Connection.
The low side of the output
con-
nection
can be floated
to miinimize the effects
of ground
IOOPS.
1.3 WARRANTY
INFORMATION
Warranty
information
may be found inside the front cover of
this
manual.
If warranty
service
is required,
contact
the
Keithley
representative
in your area or the factory
to deter-
mine the correct course of action.
Keithley
Instruments,
Inc.,
maintains
service
facilities
in the United
States,
West Ger-
many,
Great
Britain,
the
Netherlands,
Switzerland
and
Austria.
Information
concerning
the application,
operation,
or setvice of your instrument
may be directed
to the applica-
tions engineer
at any of these locations.
Addresses
can be
found inside the front cover of this manual.
1.4 MANUAL
ADDENDA
Changes
pertaining
to the instrument
that occur after the
printing
of this manual will be found in an addendum
included
with this manual.
Be sure to note any changes before attemp-
ting to operate or service the instrument.
1.5 SAFETY
TERMS
The
WARNING
heading
used
in this
manual
explains
dangers that could result in personal injury or death.
The CAUTION
heading used in this manual explains hazards
that could damage
the instrument.
1.6 UNPACKING
AND
INSPECTION
The Model
261 was carefully
inspected
before
shipment.
Upon receiving
the unit, carefully
unpack
all items from the
shipping
canon and check for any damage
that might have
occurred
during transit.
Report any damage
to the shipping
agent
at once.
Save the original
packing
material
in case
reshipment
becomes
necessary.
Contact
the nearest Keithley
representative
or the factory
if the unit fails to function
pro-
perly.
The following
items are included
in every Model 261 ship-
ment:
1. Model 261 Picoampere
Source
2. Model 261 Instruction
Manual
3. Model 2611 Test Lead Cable
4. Additional
accessories
as ordered.
1.7 USING
THE MODEL
261 INSTRUCTION
MANUAL
This manual is intended
to familiarize
the operator
with the
operating
controls
and features of the Model 261 Picoampere
Source.
Also
included
is information
on
calibration,
maintenance
and spare parts. The manual is divided into the
following
sections:
1. Sections
2 and 3 contains
pertinent
operating
information,
including
applications
and possible
pitfalls to avoid when
using the source.
2. Section
4 covers performance
verification
and calibration
procedures.
3. A complete
description
of operating
theory is contained
in
Section
5.
4. Troubleshooting
and maintenance
procedures
are covered
in Section 6.
5. Parts ordering
information
can be found in Section
7.
1.8 SPECIFICATIONS
A complete
list of Model 261 specifications
can be found im-
mediately
preceding
this section.
1-l
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