Cabling And Grounding; Autocalibration; Remote Interface And Status - Stanford Research Systems SIM918 Operating And Service Manual

1.1 Introduction to the Instrument

1.1.3 Cabling and grounding

1.1.4 Autocalibration

1.1.5 Remote interface and status

remote interface
SIM918 Precision Current Preamplifier
a rear-panel connector. Alternatively, the same connector can be
used to input a clock signal at (1 0
synchronizing the switching to an external source.
The reference clock in the SIM918 operates independently of the oscil-
lator used to clock the digital control circuitry. The latter is designed
with a special clock-stopping architecture. The microcontroller is
turned on only in the following cases: when the settings are being
changed; autozero is turned on or o ; and during autocalibration, re-
mote communications, or when an overload condition or an external
reference clock event occurs. This guarantees that no digital noise
contaminates low-level analog signals.
With autozero o and in the absense of an external clock input,
the preamplifier enters a completely quiescent state: no reference
clock transitions are present that can disturb the measurement of a
low-level electric current.
The SIM918 provides maximum flexibility for cabling and ground-
ing. The input connection can be opened, and the bias voltage can
be connected to signal ground.
The shield of the Input BNC can be switched between signal ground,
the bias voltage, or the rear-panel Program input (which can be left
floating, if desired). With the Program input, a user can supply
an excitation potential to an experiment via the shield conductor of
the input cable, while the excited current flows through the center
conductor to the SIM918. The shield of the Bias BNC can be inde-
pendently grounded or floated.
The input and bias selections, and those of their shields, can be made
via the push of a front-panel button or remotely.
A user-commanded autocalibration procedure allows one to elimi-
nate the e ects of thermal drifts in the autozero circuit, and to reduce
output o set voltage.
A remote computer can access the module through the SIM900 Main-
frame, using RS–232 or GPIB. All instrument settings can be queried
via the remote interface. The SIM918 can be operated outside the
SIM900 Mainframe by powering it with its required DC voltages.
10%) pps (i.e. 1.10 Hz–0.90 Hz),
1 – 3