Keithley 708B Reference Manual page 109

Section 2: General operation
When the connection rule is set to make-before-break, the instrument ensures that all switch
channels close before any switch channels open. This behavior should be applied with
caution because it will connect two test devices together for the duration of the switch close
settle time. When switch channels are both opened and closed, the command executes not
less than the addition of both the open and close settle times of the indicated switch channels.
With no connection rule (set to channel.OFF), the instrument attempts to simultaneously
open and close switch channels in order to minimize the command execution time. This
results in faster performance at the expense of guaranteed switch position. During the
operation, multiple switch channels may simultaneously be in the close position. Make sure
your device under test can withstand this possible condition. When switch channels are both
opened and closed, the command executes not less than the greater of either the open or
close settle times of the indicated switch channels.
Cold switching is highly recommended.
Hot switching can dry weld reed relays such that they will always be on. Hot switching is
recommended only when external protection is provided.
The channel connect rule determines the order in which multiple channels are opened and closed on
the instrument. This attribute applies to electromechanical, reed, and solid state relay switching cards.
You can set the channel connect rule to be:
•
BBM (break before make): The instrument ensures that all switch channels open before any
switch channels close. It is used to avoid momentary shorting of two voltage sources. This is the
default.
•
MBB (make before break): The instrument ensures that all switch channels close before any
switch channels open. It is used to eliminate transients caused by switching between current
sources. MBB should be applied with caution because it connects two test devices together for
the duration of the switch close settle time.
OFF: Permits the instrument to initiate close and open operations simultaneously. This minimizes
settling time for the close operation.
You cannot guarantee the sequence of open and closure operations when the channel connect rule
set to OFF. It is highly recommended that you implement cold switching when the channel connect
rule is set to OFF.
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Models 707B and 708B Switching Matrix Reference Manual
CAUTION
NOTE
707B-901-01 Rev. A / August 2010