www.tek.com/keithley
Model 3761
10-Channel Low Current Multiplexer Card
User’s Manual
3761-900-01 Rev. B / January 2018
*P3761-900-01B*
3761-900-01B
Model 3761
10-Channel Low Current Multiplexer Card
User's Manual
© 2018, Keithley Instruments
Cleveland, Ohio, U.S.A.
All rights reserved.
Any unauthorized reproduction, photocopy, or use of the information herein, in whole or in part,
without the prior written approval of Keithley Instruments is strictly prohibited.
These are the original instructions in English.
All Keithley Instruments product names are trademarks or registered trademarks of Keithley
Instruments. Other brand names are trademarks or registered trademarks of their respective
holders.
Microsoft, Visual C++, Excel, and Windows are either registered trademarks or trademarks of
Microsoft Corporation in the United States and/or other countries.
Document number: 3761-900-01 Rev. B / January 2018
Safety precautions
The following safety precautions should be observed before using this product and any associated instrumentation. Although
some instruments and accessories would normally be used with nonhazardous voltages, there are situations where hazardous
conditions may be present.
This product is intended for use by personnel who recognize shock hazards and are familiar with the safety precautions required
to avoid possible injury. Read and follow all installation, operation, and maintenance information carefully before using the
product. Refer to the user documentation for complete product specifications.
If the product is used in a manner not specified, the protection provided by the product warranty may be impaired.
The types of product users are:
Responsible body is the individual or group responsible for the use and maintenance of equipment, for ensuring that the
equipment is operated within its specifications and operating limits, and for ensuring that operators are adequately trained.
Operators use the product for its intended function. They must be trained in electrical safety procedures and proper use of the
instrument. They must be protected from electric shock and contact with hazardous live circuits.
Maintenance personnel perform routine procedures on the product to keep it operating properly, for example, setting the line
voltage or replacing consumable materials. Maintenance procedures are described in the user documentation. The procedures
explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.
Service personnel are trained to work on live circuits, perform safe installations, and repair products. Only properly trained
service personnel may perform installation and service procedures.
Keithley products are designed for use with electrical signals that are measurement, control, and data I/O connections, with low
transient overvoltages, and must not be directly connected to mains voltage or to voltage sources with high transient
overvoltages. Measurement Category II (as referenced in IEC 60664) connections require protection for high transient
overvoltages often associated with local AC mains connections. Certain Keithley measuring instruments may be connected to
mains. These instruments will be marked as category II or higher.
Unless explicitly allowed in the specifications, operating manual, and instrument labels, do not connect any instrument to mains.
Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or test
fixtures. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than
30 V RMS, 42.4 V peak, or 60 VDC are present. A good safety practice is to expect that hazardous voltage is present in any
unknown circuit before measuring.
Operators of this product must be protected from electric shock at all times. The responsible body must ensure that operators
are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential
human contact. Product operators in these circumstances must be trained to protect themselves from the risk of electric shock. If
the circuit is capable of operating at or above 1000 V, no conductive part of the circuit may be exposed.
Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance-limited
sources. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective
devices to limit fault current and voltage to the card.
Before operating an instrument, ensure that the line cord is connected to a properly-grounded power receptacle. Inspect the
connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.
When installing equipment where access to the main power cord is restricted, such as rack mounting, a separate main input
power disconnect device must be provided in close proximity to the equipment and within easy reach of the operator.
For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under
test. ALWAYS remove power from the entire test system and discharge any capacitors before: connecting or disconnecting
cables or jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.
Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth)
ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the
voltage being measured.
For safety, instruments and accessories must be used in accordance with the operating instructions. If the instruments or
accessories are used in a manner not specified in the operating instructions, the protection provided by the equipment may be
impaired.
Do not exceed the maximum signal levels of the instruments and accessories. Maximum signal levels are defined in the
specifications and operating information and shown on the instrument panels, test fixture panels, and switching cards.
When fuses are used in a product, replace with the same type and rating for continued protection against fire hazard.
Chassis connections must only be used as shield connections for measuring circuits, NOT as protective earth (safety ground)
connections.
If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use
of a lid interlock.
screw is present, connect it to protective earth (safety ground) using the wire recommended in the user documentation.
If a
The
symbol on an instrument means caution, risk of hazard. The user must refer to the operating instructions located in the
user documentation in all cases where the symbol is marked on the instrument.
The
symbol on an instrument means warning, risk of electric shock. Use standard safety precautions to avoid personal
contact with these voltages.
The
The
If this
symbol on an instrument shows that the surface may be hot. Avoid personal contact to prevent burns.
symbol indicates a connection terminal to the equipment frame.
symbol is on a product, it indicates that mercury is present in the display lamp. Please note that the lamp must be
properly disposed of according to federal, state, and local laws.
The WARNING heading in the user documentation explains hazards that might result in personal injury or death. Always read
the associated information very carefully before performing the indicated procedure.
The CAUTION heading in the user documentation explains hazards that could damage the instrument. Such damage may
invalidate the warranty.
The CAUTION heading with the
symbol in the user documentation explains hazards that could result in moderate or minor
injury or damage the instrument. Always read the associated information very carefully before performing the indicated
procedure. Damage to the instrument may invalidate the warranty.
Instrumentation and accessories shall not be connected to humans.
Before performing any maintenance, disconnect the line cord and all test cables.
To maintain protection from electric shock and fire, replacement components in mains circuits — including the power
transformer, test leads, and input jacks — must be purchased from Keithley. Standard fuses with applicable national safety
approvals may be used if the rating and type are the same. The detachable mains power cord provided with the instrument may
only be replaced with a similarly rated power cord. Other components that are not safety-related may be purchased from other
suppliers as long as they are equivalent to the original component (note that selected parts should be purchased only through
Keithley to maintain accuracy and functionality of the product). If you are unsure about the applicability of a replacement
component, call a Keithley office for information.
Unless otherwise noted in product-specific literature, Keithley instruments are designed to operate indoors only, in the following
environment: Altitude at or below 2,000 m (6,562 ft); temperature 0 °C to 50 °C (32 °F to 122 °F); and pollution degree 1 or 2.
To clean an instrument, use a cloth dampened with deionized water or mild, water-based cleaner. Clean the exterior of the
instrument only. Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that
consist of a circuit board with no case or chassis (e.g., a data acquisition board for installation into a computer) should never
require cleaning if handled according to instructions. If the board becomes contaminated and operation is affected, the board
should be returned to the factory for proper cleaning/servicing.
Safety precaution revision as of June 2017.
Table of contents
Introduction ............................................................................................................... 1-1
Your multiplexer card ........................................................................................................... 1-1
System switch / multimeter card compatibility ..................................................................... 1-2
Extended warranty ............................................................................................................... 1-2
Series 3700A documentation ............................................................................................... 1-2
Contact information .............................................................................................................. 1-3
General information .............................................................................................................. 1-3
Specifications ....................................................................................................................... 1-3
Installation and connections .................................................................................... 2-1
Handling precautions ........................................................................................................... 2-1
Unpack and inspect .............................................................................................................. 2-1
Card connectors ................................................................................................................... 2-2
Card installation ................................................................................................................... 2-2
Web browser support ........................................................................................................... 2-3
General operation ..................................................................................................... 3-1
General operation ................................................................................................................ 3-1
Safety hazards .......................................................................................................................... 3-1
Current and voltage switching applications ............................................................................... 3-2
Operation considerations ......................................................................................... 4-1
Cables .................................................................................................................................. 4-1
External factors .................................................................................................................... 4-1
High impedance measurements .......................................................................................... 4-2
Typical applications .................................................................................................. 5-1
Introduction .......................................................................................................................... 5-1
Application considerations......................................................................................................... 5-2
Direct measurement of capacitor leakage or insulation resistance ..................................... 5-2
Indirect measurement of capacitor leakage or insulation resistance ................................... 5-4
Connecting multiple 3761 cards ........................................................................................... 5-5
Index ........................................................................................................................... I-1
In this section:
Specifications ........................................................................... 1-3
Your multiplexer card ............................................................... 1-1
System switch / multimeter card compatibility .......................... 1-2
Extended warranty ................................................................... 1-2
Series 3700A documentation ................................................... 1-2
Contact information .................................................................. 1-3
General information .................................................................. 1-3
Your multiplexer card
Thank you for choosing a Keithley Instruments product. The Model 3761 10-channel Low Current
Multiplexer Card is a single-pole, single-throw, low-leakage multiplexer designed for use in the Model
3706A System Switch/Multimeter. The 3761 is ideal for switching either current or voltage into a
picoammeter or an electrometer voltmeter.
Section 1
Introduction
Figure 1: Model 3761 10-channel Low Current Multiplexer Card
The 3761 has two output connectors which allow you to add additional cards. Each additional card
increases the capacity of the multiplexer by ten channels. High-speed, low-leakage reed relays with
actuation times as low as 1 ms let you use the 3761 to make accurate, low-current measurements.
The 3706A supports up to six 3761 cards, for a maximum of 60 low-current channels in a single
mainframe system.
An automatically-configured software relay isolates all circuitry on the card from the outputs when all
channels are open, and it closes when any channel closes. You will use this relay when configuring
multiple 3761 cards. See the Typical applications (on page 5-1
) topic for more information.
Section
User's Manual
Model 3706
3720, 3721, 3722, 3723, 3724, 3730, 3731, 3732, 3740,
3750
Model 3706A
3760, 3761, 3762, 3765
and remote interface operation
3700AS-900-01
Series 3700A System
Manual
Information about scanning, reading,
Series 3700A System
Manual
Information about controlling the
1: Introduction Model 3761 10-Channel Low Current Multiplexer Card
When an interlock is required for safety, a separate circuit should be provided that meets the
requirements of the application to reliably protect the operator from exposed voltages. The
digital I/O port of the 3761 is not suitable for control of safety circuits and should not be used
to control a safety interlock. Bypassing the interlock can result in personal injury or death
from electric shock.
System switch / multimeter card compatibility
The following table lists the cards that are compatible with the 3706 and 3706A.
Mainframe System Switch / Multimeter Compatible plug-in cards
The 3761 is designed for use only with the Model 3706A System Switch / Multimeter. Using
the 3761 with the Model 3706 mainframe can cause unpredictable behavior.
Extended warranty
Additional years of warranty coverage are available on many products. These valuable contracts
protect you from unbudgeted service expenses and provide additional years of protection at a fraction
of the price of a repair. Extended warranties are available on new and existing products. Contact your
local Keithley Instruments office, sales partner, or distributor for details.
Series 3700A documentation
Complete documentation for the Series 3700A System Switch/Multimeter instruments is available at
the Keithley Instruments website (http://www.tek.com/keithley
documentation.
Document
number
3700AS-903-01 Series 3700A System
3700AS-901-01
Document name Content description
Switch/Multimeter Quick Start
Guide
Switch/Multimeter User's
Switch/Multimeter Reference
). The following is a list of available
Hardware and software requirements,
switching card installation instructions,
and a brief description of front-panel
writing, and controlling channels
Series 3700A from a remote interface
1-2 3761-900-01 Rev. B / January 2018
Model 3761
10-Channel Low Current Multiplexer Card User's Manual Section 1:
Introduction
Voltage rating*
30 V
Current rating
100 mA
Input and output connections
Ten sample inputs for female SMA cables
Two measurement outputs for female SMA cables
Environmental conditions
Indoor use only
Contact information
If you have any questions after you review the information in this documentation, please contact your
local Keithley Instruments office, sales partner, or distributor. You can also call the corporate
headquarters of Keithley Instruments (toll-free inside the U.S. and Canada only) at 1-800-935-5595,
or from outside the U.S. at +1-440-248-0400. For worldwide contact numbers, visit the
Instruments website (http://www.tek.com/keithley).
General information
General ratings for the 3761 are listed in the following table.
Category Specification
Keithley
Operating: 0 °C to 50 °C (32 °F to 122 °F), 70% relative humidity up to
35 °C (95 °F); derate 3% relative humidity per °C, 35 °C to 50 °C,
noncondensing
Storage: −25 °C to 65 °C (-13 °F to 149 °F)
Altitude: 0 to 2000 m (0 to 6562 ft) above sea level
Pollution degree: 2
Specifications
*Input voltage operating range ±8 V
For the most recent instrument specifications, search for the 3761 on the Keithley Instruments
website (http://www.tek.com/keithley).
3761-900-01 Rev. B / January 2018 1-3
In this section:
Web browser support ............................................................... 2-3
Handling precautions ............................................................... 2-1
Unpack and inspect .................................................................. 2-1
Card connectors ....................................................................... 2-2
Card installation ....................................................................... 2-2
Handling precautions
Make sure to handle the 3761 carefully. Always grasp the multiplexer card by the side edges or
covers. Do not touch board surfaces, components, or areas adjacent to electrical contacts.
Contamination from foreign materials such as dirt, dust, and body oils can substantially lower leakage
resistances, degrading card performance.
Section 2
Installation and connections
The information in this section is intended only for qualified personnel. Do not perform these
procedures unless you are qualified. Failure to recognize and observe standard safety
precautions could result in personal injury or death due to electric shock.
Unpack and inspect
To unpack and inspect your instrument:
1. Inspect the box for damage.
2. Open the top of the box.
3. Remove the contents accessories and verify that all items are included. You should hav
eceived:
r
• One 3761 card
• One Model 3761-BNC-SMA 1.2 m (4 ft) Low Noise SMA Male to BNC SMU cable
• 12 CAP-47 SMA male protective caps
• One CS-573 BNC to triaxial adapter (optional)
4. Inspect the 3761 card for any obvious signs of physical damage.
5. Report any damage to the shipping agent immediately.
e
Section
User's Manual
2: Installation and connections Model 3761 10-Channel Low Current Multiplexer Card
Card connectors
You can make signal input and output connections with the SMA connectors on the card. The
locations for each channel input and its outputs are located on the front of the card.
While SMA connectors are not typically used in low-current applications, the connectors on the 3761
are compact, Teflon-insulated, and exhibit low-leakage characteristics.
Card installation
Figure 2: Model 3761 card connectors
Slot covers must be installed on unused slots to prevent personal contact with high voltage
circuits. Failure to recognize and observe standard safety precautions could result in
personal injury or death due to electric shock.
2-2 3761-900-01 Rev. B / January 2018
Model 3761
10-Channel Low Current Multiplexer Card User's Manual Section 2:
Installation and connections
Item
Description
1
Card guide (part of the mainframe)
2
Card edge (part of the card)
4
Mounting screws (part of the card)
Perform the following steps to install a switching card into the instrument mainframe:
1. Turn the instrument off and disconnect the power line cord and any other cables connected to t
r
ear panel.
he
2. Position the instrument so that you are facing the rear panel.
3. Remove the slot cover plate from the desired mainframe slot. Retain the plate and screws for
future use.
4. With the top cover of the switching card facing up, align the card's edge into the slot's card guide
and slide in the card. For the last ¼ inch or so, press in firmly to mate the card connector to the
m
ainframe connector.
5. On each side of the card, there is a mounting screw. Tighten these two screws to secure the card
t
o the mainframe. Do not overtighten.
6. Reconnect the power line cable and any other cables to the rear panel, then turn the instrument
on.
7. Press the SLOT key to see the model numbers, description, and the firmware revision of th
e
installed switching cards, along with the mainframe firmware and DMM (if present).
Item shipped may vary from model pictured here.
Figure 3: 3761 card installation
3 Card
Web browser support
Web browser support for the 3761 10-Channel Low Current Multiplexer Card is not supported with the
3706A Switch System/DMM.
3761-900-01 Rev. B / January 2018 2-3
In this section:
General operation .................................................................... 3-1
General operation
This section provides information needed to use the 3761 Model 3706A system switch mainframe.
Once the card is installed in the mainframe, refer to the Series 3700A System Switch/Multimeter
Reference Manual for complete operating instructions.
Safety hazards
To prevent electrical shock that could cause injury or death, never make or break
connections while the equipment is powered on. User supplied lethal voltages may be
present on the PC board or the connections. Turn off the equipment from the front panel,
disconnect the main power cord, and discharge stored energy in external circuitry before
making or breaking cable connections. Putting the mainframe equipment into an output-off
state does not guarantee that the outputs are powered off if a hardware or software fault
occurs. Precautions must be taken to prevent a shock hazard by surrounding the test device
and any unprotected leads (wiring) with double insulation for 500 volts, Category I.
Section 3
General operation
Follow these recommendations before and after applying power to the equipment:
1. Do not exceed the 3761 maximum allowable signal level as defined in the specifications.
2. Do not exceed the 3761 maximum common mode voltage of 30 V as defined in th
spe
cifications.
3. Make sure the system switch mainframe is grounded through an earth grounded receptacle
bef
ore operation.
4. Turn off all power supplies and discharge any residual energy before installing or removing the
3761
from the system switch mainframe or changing the 3761 SMA connections.
5. Inspect all cables for wear and defects such as cracks and exposed wires. Make sure that you
c
orrect any defects found before operating the instrument.
6. Use only low noise coaxial cables.
7. Ensure that the mounting screws for the card are securely connected to the system switc
ainframe chassis in order to provide the proper chassis protective grounding.
m
8. Read this manual carefully and adhere to all of the safety precautions listed before operating t
nstrument.
i
e
h
he
Section
User's Manual
3: General operation Model 3761 10-Channel Low Current Multiplexer Card
Current and voltage switching applications
For current switching applications, each channel on the 3761 has a pair of single-pole single-throw
(SPST), normally open (NO) relays. The relay pair switches signal HI between signal LO (analog
ground) and output HI. Signal LO (the outside shell of the SMA connector) is common to all channels
and outputs in the test system.
Figure 4: 3761 current switching schematic
3-2 3761-900-01 Rev. B / January 2018
Model 3761
10-Channel Low Current Multiplexer Card User's Manual Section 3:
General operation
The 3761 is designed for scanning low-ampere currents into a low-impedance picoammeter. When a
channel is not selected for measurement, the current path is maintained through that channel's
analog grounding relay, which is automatically updated with the channel selection.
You can also configure the 3761 for voltage switching. See the next figure for a schematic of the 3761
card configured for voltage mode.
Figure 5: 3761 voltage switching schematic
3761-900-01 Rev. B / January 2018 3-3
Section
User's Manual
3: General operation Model 3761 10-Channel Low Current Multiplexer Card
You can use the following 3706A commands with the 3761 card for voltage and current mode
applications.
-- set slot numbers
slot_3761 = 1
slot_not_3761 = 2
slot_empty = 3
-- 0=Amps-mode=default; 1=Volts-mode
-- get the present mode of a 3761 card
print(slot[slot_3761].voltsampsmode)
-- set the mode of a 3761 card to Amps-mode
slot[slot_3761].voltsampsmode = 0
-- set the mode of a 3761 card to Volts-mode
slot[slot_3761].voltsampsmode = 1
-- setting voltsampsmode to any value other than 0 or 1 will result in the
following error
-- "-222, Parameter data out of range"
slot[slot_3761].voltsampsmode = 2
-- setting voltsampsmode on a card that does not support it will result in the
following error
-- "1114, Settings conflict with VoltAmps-mode not supported for this slot"
slot[slot_not_3761].voltsampsmode = 1
-- setting voltsampsmode on an empty slot will result in the following error
-- "1114, Settings conflict with VoltAmps-mode not supported for empty slot"
slot[slot_empty].voltsampsmode = 1
The isolation impedance of the 3761 in voltage mode is high enough to use with an
9
electrometer voltmeter to switch devices with impedances greater than 10
Ω. This
configuration minimizes voltage loading on the device under test.
3-4 3761-900-01 Rev. B / January 2018
High impedance measurements ............................................... 4-2
Cables
Section 4
Operation considerations
In this section:
Cables ...................................................................................... 4-1
External factors ........................................................................ 4-1
Shielded cables should be used with the 3761. The shield should be connected to circuit guard,
analog LO. This helps prevent excessive radiation from the cables from interfering with any
equipment. The cable rating must not exceed the maximum allowable signal levels as defined in the
3761 card specifications. For more information on cable requirements, go to the
website (http://www.tek.com/keithley) and search for Switching Handbook or Low Current
Measurements Application Note.
Keithley Instruments
The test system response is affected by cable capacitance. This should be considered when the
sources are connected to the 3761. Use a feedback ammeter for currents below 10
measurement speed and decrease the effects of cable capacitance measurement.
External factors
The 3761 is specified for a resistive load. However, external circuit capacitances and inductances can
cause excessive currents and voltages across the relay contacts. The currents and voltages must be
limited to within the maximum allowable signal levels.
• Capacitance: Charged capacitances in the circuit can cause excessive currents (surge currents)
to flow through the relay contacts if the source is shorted out or if the output is switched to
c
apacitive loads. This excessive current can weld the relay contacts together. Therefore, us
s
eries resistors, where needed, to limit the maximum current to within the contact ratings. T
ma
ximum signal levels are stated in the specifications.
• Inductance: The inductance of cables can produce high voltage and arcing across relay
contacts when switching. The peak transients must be limited to within the maximum signal levels
as defined in the 3761 specifications.
When a channel is opened or closed, there is a charge transfer in the picocoulomb range. This is due
to the mechanical release or closure of the contacts, the contact-to-coil capacitance, and the stray
capacitance between the signal and relay drive lines. The charge transfer causes a current pulse, and
the effect on the signal depends on the magnitude of the source being measured.
Extreme environmental conditions can cause the offset current to exceed the 1 pA specification. If the
card has been exposed to high humidity or temperature (for example, during shipping), stabilize the
board within the specified environmental limits for 24 hours.
-5
A to increase
e
he
Section
User's Manual
4: Operation considerations Model 3761 10-Channel Low Current Multiplexer Card
High impedance measurements
Because of the high impedance circuits on the 3761, this card contains no user-serviceable
components and should only be opened by a Tektronix factory service technician.
4-2 3761-900-01 Rev. B / January 2018
In this section:
Connecting multiple 3761 cards ............................................... 5-5
Introduction .............................................................................. 5-1
Direct measurement of capacitor leakage or insulation resistance5-2
Indirect measurement of capacitor leakage or insulation resistance 5-4
Introduction
The 3761 card has ten channels of paired, single-pole, single-throw (SPST), normally open (NO)
relays. The card will switch one or more of ten signals to one output or signal LO.
Signal HI is connected to signal LO (analog ground) when the scanner mainframe channel is open
(current mode), and to output HI when the channel is closed. Signal LO is common to all ten channels
and the output. An additional relay isolates all circuitry on the card from the output when none of the
channels are closed.
Section 5
Typical applications
Features of the scanner card include:
• Low offset current error (< 1 pA specified, < 30 fA typical)
• Switching of AC or DC signals up to 100 mA
• SMA input and output connectors
• Two outputs for connecting multiple 3761 cards
• Low current or low voltage switching
The 3761 is field-installable in the 3706A scanner mainframe, and can be used in a variety of
applications to switch low current levels. Typical applications include those where sourcing voltage
and measuring current are required, such as:
• Leakage currents (e.g. capacitor, FET gate)
• PCB test coupons
• Materials research and characterization
• Semiconductor sub-threshold current
The following applications focus on:
• Capacitor leakage / insulation resistance measurements using the direct and indirect methods of
measurement using the Model 3761 and 3762 cards, and a Model 6517B Electrometer.
• Connecting multiple 3761 cards to expand your multiplexer system.
Section
User's Manual
5: Typical applications Model 3761 10-Channel Low Current Multiplexer Card
Application considerations
Voltage applications include those where the 3761 can be used to switch a single pole of low voltage
sources. When measuring low currents, consider the following sources of noise:
• Triboelectric currents are caused by friction between a conductor and insulator when a coax
cable flexes due to vibration or temperature fluctuation. To minimize noise, use cables such as
the Keithley Instruments Model 3761-BNC-SMA. This low-noise cable is ideal for low-level
measurements of voltage and current.
• Piezoelectric currents are caused by mechanical stress to the insulating materials of
connectors. Minimize stress on the insulators and use a connecting cable such as t
3761
-BNC-SMA. This cable features BNC and SMA connectors with low piezoelectric effects.
• Electrochemical effects generate current between PCB conductors due to contamination of t
ard surface. To minimize card contamination, handle the card by the edges only.
c
To prevent overheating or damage to the relay contacts, do not exceed the signal level
specifications of the 3761 card. Maximum switched and carry current and voltage levels are
100 mA and 30 V in voltage mode. The card can switch low power AC (typical bandwidth up to
1 MHz). Maximum switched and carry current and voltage levels are 100 mA and 30 V peak
using resistive loads.
he
he
Direct measurement of capacitor leakage or insulation resistance
If you want to measure the leakage current or insulation resistance of a capacitor, the direct method
of measurement lets you apply almost any test voltage to the capacitor under test. The direct method
uses the 3761 in current mode, operating the card at zero volts even though the capacitor test voltage
is large.
The leakage current measurement depends on the capacitor dielectric and the applied voltage. A
direct measurement of the insulation resistance is shown in the next figure for three channels of the
3761. In this test configuration, a picoammeter (IM) is connected to one of the two output connectors
of the 3761 card, a shielded test fixture is used to contain the capacitors under test, and a 3762 is
used to route the test and soak voltages for the capacitors under test.
To avoid inaccurate capacitor leakage measurements, do not enable the 3761 channels until
you verify that the capacitors under test are fully charged.
Make sure that each capacitor under test has a series resistance and an individual discharge resistor.
The discharge resistors are used to drain the electric charge on the capacitors when the test
completes.
If you are making measurements with capacitor values greater than 1 µF, use the indirect
method (on page 5-4) with a voltmeter measuring the voltage drop across a resistor
connected in series with the capacitor under test.
5-2 3761-900-01 Rev. B / January 2018
Model 3761
10-Channel Low Current Multiplexer Card User's Manual Section 5:
Typical applications
Figure 6: Direct capacitor insulation leakage measurement
To make a measurement using the direct method:
1. Make sure that your Model 3761 is in ampere mode.
2. Close the correct channels on the 3762 to charge the capacitor under test.
3. When the capacitor is charged, close the applicable channel of the 3761 to start t
easurement.
m
he
The current is measured at IM, as shown in the previous figure. To maintain the voltage
applied to the capacitor under test, be sure to keep the applicable channel of the 3762 closed
when making the measurement.
4. When the test is complete, open the channels on the 3761 and 3762. The charge on the
c
apacitor under test is released automatically through the discharge resistor.
5. Repeat the previous steps for each capacitor under test.
3761-900-01 Rev. B / January 2018 5-3
Section
User's Manual
5: Typical applications Model 3761 10-Channel Low Current Multiplexer Card
Indirect measurement of capacitor leakage or insulation
resistance
You can also make an indirect measurement of the capacitor's insulation resistance by using the
3761 in voltage mode (VM). Use this method if you are making measurements with capacitor values
greater than 1 µF. This configuration maintains stability and improves noise performance for large
capacitor values.
Make sure that each capacitor under test has a series resistance and an individual discharge resistor.
The discharge resistors are used to drain the electric charge from the capacitors when the test
completes.
Using the indirect method, the Model 3762 can be used to switch the soak voltage to each capacitor
under test for specific capacitor soak times with the 3761 in current mode. When the capacitors are
charged and settled, the 3761 is switched to voltage mode and a new source voltage (V
+ VEQ) is applied to the capacitors through the 3762. A Model 6517B is used to make the
V
SOAK
measurement.
To avoid inaccurate capacitor leakage measurements, do not enable the 3761 channels until
you verify that the capacitors under test are fully charged.
TEST
equal to
Figure 7: Indirect capacitor insulation leakage measurement
5-4 3761-900-01 Rev. B / January 2018
Model 3761
10-Channel Low Current Multiplexer Card User's Manual Section 5:
Typical applications
The capacitor insulation resistance is calculated using the following formula:
Where:
• R
• V
• V
• R
= Insulation resistance of the capacitor under test
INSL
= The test voltage
TEST
= Voltage measurement at the output of the 3761
MEAS
= Value of the discharge resistor
DCHG
Be sure to select a series resistor value that maintains the 3761 test voltage specifications,
and select a V
value that minimizes the settling time of the indirect measurement.
EQ
Connecting multiple 3761 cards
Two output connectors on each 3761 card let you add multiple cards to expand the size of the
multiplexer by ten for each additional 3761. An additional relay isolates all circuitry on the card from
the outputs when all channels are open and closes when any channel closes. This isolation relay
configures itself automatically when assembling a test system using multiple 3761 cards.
The 3706A supports up to six 3761 cards, for a maximum of 60 low-current channels in a single
mainframe system. Up to sixty-four 3706A systems can be configured to provide 3,840 low-current
channels. See the Series 3706A System Switch/Multimeter Reference Manual, available on the
Keithley Instruments website (http://www.tek.com/keithley
Leakage current specifications increase for each additional card enabled in a test system.
), for multiple 3706A system configurations.
A 20-channel scanner system is shown in the next figure. In this configuration, you will connect one
output connector of the 3761 to a picoammeter, and the second output connector to an output
connector of a second 3761 card.
Use a SMA-male to SMA-male cable to connect the cards, such as a Cinch Connectors part
number 415-0038-012.
3761-900-01 Rev. B / January 2018 5-5
Section
User's Manual
5: Typical applications Model 3761 10-Channel Low Current Multiplexer Card
Figure 8: 20-channel scanner system with two 3761 cards in ampere mode
5-6 3761-900-01 Rev. B / January 2018
Index
A
Application considerations • 5-2
C
Cables • 4-1
Card connectors • 2-2
Card installation • 2-2
Connecting multiple 3761 cards • 5-5
contact information • 1-3
Contact information • 1-3
Current and voltage switching applications • 3-2
D
Direct measurement of capacitor leakage or
insulation resistance • 5-2
E
extended warranty • 1-2
Extended warranty • 1-2
External factors • 4-1
G
General information • 1-3
General operation • 3-1
T
Typical applications • 1-1, 5-1
U
Unpack and inspect • 2-1
W
warranty • 1-2
Web browser support • 2-3
Y
Your multiplexer card • 1-1
H
Handling precautions • 2-1
High impedance measurements • 4-2
I
Indirect measurement of capacitor leakage or
insulation resistance • 5-2, 5-4
Installation and connections • 2-1
Introduction • 1-1, 5-1
O
Operation considerations • 4-1
S
Safety hazards • 3-1
Series 3700A documentation • 1-2
Specifications • 1-3
System switch / multimeter card compatibility • 1-2
All Keithley trademarks and trade names are the property of Keithley Instruments.
All other trademarks and trade names are the property of their respective companies.
Specifications are subject to change without notice.
Corporate Headquarters • 28775 Aurora Road • Cleveland, Ohio 44139 • 440-248-0400 • Fax: 440-248-6168 • 1-800-935-5595 • www.tek.com/keithley
Keithley Instruments
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