Scanning Channels; Ieee-488 Bus Control; Closing And Opening Channels; Switching Considerations - Keithley 7017 Instruction Manual

Operation

3.3.2 Scanning channels

To scan through channels, first configure a scan list, and then
program the Model 7001/7002 to perform a scan sequence.
You can create a scan list in the same manner as you would a
channel list. First, however, press the SCAN LIST key to select
the SCAN CHANNEL mode, and then enter the desired chan-
nels to be included in the scan list. For example, the following
list scans channels 1, 3, and 5 through 8 of a Model 7017 in-
stalled in slot 2:
SCAN CHANNELS 2!1, 2!3, 2!5-2!8
Note that channels are scanned in the order they appear in the
scan list.
To perform a manual scan, select the RESET default condi-
tions in the SAVESETUP menu of the main MENU. Press
STEP to take the mainframe out of the idle state, and then
manually scan through channels by pressing the STEP key.
For information on more complex scan sequences, refer to the
Model 7001 or 7002 Instruction Manual.
3.4

IEEE-488 bus control

3.4.1 Closing and opening channels

Use the following SCPI commands to close and open channels:
:CLOS <list>
:OPEN <list> | ALL
For example, the following command will close channels 2
and 6 of a Model 7017 installed in slot 1:
:CLOS (@ 1!2,1!6)
Conversely, either of the commands below will open previous-
ly closed channels 2 and 6:
:OPEN (@ 1!2,1!6)
:OPEN ALL
Do not close more than one channel per multiplexer to main-
tain 50 Ω characteristic impedance.
3.4.2 Scanning channels
You can perform a simple scan using the following four com-
mands:
*RST
:TRIG:SEQ:COUN:AUT ON
:ROUT:SCAN <list>
:INIT
3-2
The *RST command selects the default scan configuration,
while the second command automatically sets the channel
count to the number of channels in the scan list. The
:ROUT:SCAN command programs the scan list, and the
:INIT command takes the mainframe out of the idle state.
For example, send the following commands to scan through
all eight channels of a Model 7017 installed in slot 1:
*RST
:TRIG:SEQ:COUN:AUT ON
:ROUT:SCAN (@ 1!1:1!8)
:INIT
3.5

Switching considerations

Signals passing through the Model 7017 Multiplexer Card
are subject to various effects that can influence their charac-
teristics. The following paragraphs discuss some of these ef-
fects and ways to minimize them.

3.5.1 Card characteristics

Insertion loss
Insertion loss indicates signal power lost while passing
through the card. This loss occurs in the various signal path
components through the card (connectors, PC board traces,
and relays). The amount of power lost depends on the partic-
ular insertion loss specification as well as the applied power.
For example, with an insertion loss of 1dB and a 10W source
signal applied to the card, about 2W will be dissipated in the
card, and approximately 8W will appear at the load. Note
that, as with most transmission lines, Model 7017 insertion
loss values increase with increasing frequency.
Capacitance
Model 7017 capacitance values are small enough to be of lit-
tle concern in most applications. In some applications, ca-
pacitance may be a factor (primarily with pulse signals
where capacitance can affect rise times).
Crosstalk
Crosstalk figures indicate the amount of signal leakage be-
tween channels or switches on the card. With similar power
levels applied to the various channels, crosstalk will be of lit-
tle consequence. With widely different power levels, howev-
er, crosstalk may produce undesired results. For example,
assume that 10W is applied to channel 1, and 1mW is applied
to channel 2. Assuming a -60dB crosstalk figure, the unwant-
ed signal coupled from channel 1 to channel 2 will only be
20dB below the desired channel 2 signal.