Features and Functions
3
Keysight 34980A Mainframe User’s Guide
149
– Each time you start a new scan, the instrument clears all readings (including
alarm data) stored in reading memory from the previous scan. Therefore, the
contents of memory are always from the most recent scan.
– The Analog Bus relays are automatically opened and closed as required during
the scan to connect to the internal DMM for the measurement. For example,
all 2-wire measurements use the ABus1 (MEAS) relays; for 4-wire
measurements, the ABus2 (SENS) relays are used in addition to the ABus1
relays.
– When the scan is initiated, the instrument will open all channels in banks that
contain one or more channels in the scan list.
– In order to guarantee that no signals are connected to the Analog Buses prior
to the scan, the instrument will open all ABus1 relays (applies to all banks in all
slots). In banks that contain channels in the scan list, the instrument will also
open all ABus2 relays (regardless of whether 4-wire measurements are
involved). If no channels configured for 4-wire measurements are included in
the scan list, the state of the ABus2 relays in the non-scanned banks is not
altered.
– The state of the ABus3 and ABus4 relays is not altered and these relays remain
available for use during the scan. However, be sure to use
CAUTION
when
closing these relays on banks involved in the scan. While the scan is running,
any signals present on ABus3 and/or ABus4 will be joined with the scanned
measurement on ABus1 and ABus2.
– While the scan is running, the instrument prevents use of all channels in banks
that contain one or more channels in the specified scan list (these channels are
dedicated to the scan). In addition, the instrument prevents use of all ABus1
and ABus2 relays on banks containing channels in the scan list. If one or more
channels configured for 4-wire measurements are included in the scan list,
then the rules for ABus2 relay operations are extended to the non-scanned
banks as well.
– If the ABus1 relay used for current measurements (channel 931 on 34921A
only) is not closed prior to the initiation of the scan, the four current channels
(channels 41 through 44) are not affected by the scan. However, if the ABus1
relay is closed, the instrument will open the ABus1 relay as well as the four
associated current channels in a
make-before-break
fashion.
– When you add a digital read (digital modules) to a scan list, the corresponding
channel is dedicated to the scan. The instrument issues a Card Reset to make
that channel an input channel (the other channel is not affected).
