1 – 6
Getting Started
1.2.3.1
Output Overload
The SIM928 is specified to maintain its programmed voltage dif-
ference between the output terminals for load currents smaller than
±
10 mA. If an low-impedance load causes the output current to reach
around
±
15 mA, the output will go into current-limit mode, and the
red
OVLD
indicator will turn on. The SIM928 can remain in over-
load indefinitely, and will return to its programmed output voltage
as soon as the load current is reduced.
1.2.3.2
Overvoltage / TRIP
In addition to its current-limiting circuitry, the SIM928 has an over-
voltage sensing circuit that detects excessive voltage across the out-
put terminals. If the voltage across the outputs exceeds
∼ ±
30 V, this
protection circuitry disconnects the output driver from the output
terminals, and the red
Trip
indicator will turn on. Typically, an over-
voltage TRIP is generated by some external voltage applied to the
SIM928 across its output terminals.
To clear an overvoltage TRIP, press [On
/
O
ff
]. This will return the
SIM928 to the
O
ff
state; a second press of [On
/
O
ff
] will attempt to
switch the instrument back on. If the overvoltage condition still
exists, the output will again trip o
ff
.
1.3
SIM Interface
The primary connection to the SIM928 Isolated Voltage Source is the
rear-panel DB–15 SIM interface connector. Typically, the SIM928 is
mated to a SIM900 Mainframe via this connection, either through
one of the internal Mainframe slots, or the remote cable interface.
It is also possible to operate the SIM928 directly, without using the
SIM900 Mainframe. This section provides details on the interface.
The SIM928 has no internal protection against reverse polarity, missing
CAUTION
supply, or overvoltage on the power supply pins. Misapplication of power
may cause circuit damage. SRS recommends using the SIM928 together
with the SIM900 Mainframe for most applications.
1.3.1
SIM interface connector
The DB–15 SIM interface connector carries all the power and commu-
nications lines to the instrument. The connector signals are specified
in Table 1.1
SIM928
Isolated Voltage Source
