Operation Theorem • 15
Once the operation starts and has received a Trigger In signal, the switch
module updates the relay pattern to that specified in the first entry of scanlist.
T
S
is the default debounce time for a switch module, i.e. 8 ms for PXI-7901.
T
An
is the user specified scan delay time in the scanlist entry, indicating the time
between the relay being debounced and the exact moment that a measurement
device takes a new measurement. The actual delay time would be the greater
of the two times, to guarantee that measurement devices take measurements
after the signal path is fully settled, and the relays switch as close as possible to
their maximum operating speed.
As the scan delay time elapses, the switch module generates
Scanner
Advanced
signal to inform the measurement device to take a new
measurement.
After the measurement completes, the measurement device will generate
another
Trigger In
signal to have the switch module update the relay pattern to
that specified in the second entry of scanlist.
The handshaking process will continue, until it reaches the end of the scanlist
(if one-time scanning mode is selected), or when a software scan-abort
command is received.
Connecting, Trigger and Synchronize with External DMM
In this example, Agilent
®
33401A 6-1/2 Digital Multimeter (DMM) is used to
demonstrate signal connection for handshaking operation.
The DMM provides two terminals on the rear panel for the handshaking
operation process,
Trig In
and
VM Comp
. The
Trig In
connects to the
Scanner
Advanced
output on switch module, while the
VM Comp
to
Trigger In
. If the
terminal board is used, wire
Trig In
to
TRG_IN
on terminal board, and the
VM
Comp
to
S_ADV
.
Follow the instructions below to ensure the handshake functions properly:
1.
Configure ADLINK PXI switch module’s
Trigger In
to rising-edge
triggered,
Scanner Advanced
output in active-low pulsating
mode with pulse width of at least 2us.
2.
Configure the DMM to wait for external
Trig In
before a
measurement, and generate
VM Comp
after a measurement.
Arm the DMM to wait for the first trigger.
3.
Setup the scanlist and auto-scan mode. The first entry in the
scanlist should be set disable wait for the
Trigger In
, but enable
Scanner Advanced
output. Succeeding entries should enable
both
Trigger In
and
Scanner Advanced
output. Download the
scanlist to the switch module afterward.
