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38 User Connections
Analog Current Control (applies in Fixed mode only)
The setup shown in Figure 4-11 allows an external dc voltage to program the Agilent SAS output current in Fixed mode. A
voltage applied to the differential current programming input programs the output current. Note that depending on the
polarity of the external source, the external signal is either added to or subtracted from the front panel current setting.
Output current is internally limited to a maximum of
≈
112% of the output current rating. If you want to fully control the
output current through the analog input, you must first set the front panel current control to zero. A voltage of 0 to 4 volts
programs the output current from zero amperes to the rated output current.
For proper operation, the maximum common-mode voltage between either the +IP or -IP inputs and the +OUT terminal
should be kept to less than
±
18 volts. Note also that the input impedance of the analog input is 20 k
Ω
. If the output
impedance of your programming source is not negligible compared to 20 k
Ω
, the programmed current will be less than
expected.
Wiring Considerations
Be careful of capacitive coupling from the programming inputs to other lines wired to the analog connector. Such coupling
can cause output oscillations and noise. You can minimize coupling by bundling the +IP and -IP lines and keeping them
separated from other wires. Twisting these lines together is also recommended.
+-
+240 VDC MAX
-
-
I
1
-
IM
IP
IP
+
S
-
S
+
-
-
I
SAS
P
+IP
-IP
+
-
2
0 – 4V
Analog connector
k 0 to 4 volt voltage source programs from 0 to the
rated output current
Figure 4-11. Analog Current Programming Connections
Controller Connections
Figure 4-12 shows two basic ways of connecting your Agilent SAS to a controller. They are "linked" and "stand-alone
configurations.
Stand-Alone Connections
See Figure 4-12A. Each stand-alone Agilent SAS has its own GPIB bus address. Stand-alone units may be connected
to the bus in series configuration, star configuration, or a combination of the two. You may connect from 1 to 15
stand-alone units to a controller GPIB interface.
Linked Connections
See Figure 4-12B. Up to 16 units may be used at a single GPIB primary bus address by making linked connections.
■ The first Agilent SAS in a linked connection is a "direct unit" connected to the controller via a GPIB cable. The
direct unit is the only unit connected directly to the bus and has a unique primary bus address.
■ The remaining units are "linked supplies” connected to the direct unit via a serial-link cable. Each linked unit has a
unique secondary GPIB address and derives its primary address from the direct unit. You may connect from 1 to 15
linked supplies to each direct unit.