Stanford Research Systems SIM918, Руководство по эксплуатации и обслуживанию, Страница: 20 / 68

1 – 8 Getting Started
1.2.4.2 Bias shield
Successive presses of the [BIAS Shield] button float the outer
shell of the Bias BNC and connect it to ground. The state of the
bias shield connection is indicated by one of two LEDs: the yel-
low
BIAS Shield Float or the green BIAS Shield GND .
Note that it is the electric potential at the Bias terminal, not the po-
tential di
ff
erence across the Bias connector, that the autozero circuit
uses as the reference for the input voltage.
1.2.5 Output overload
An overload condition is recognized and the OUTPUT OVLD LED
is activated if the absolute value | i
in
× R
F
| exceeds certain limits. These
limits are typically
±
10
.
0 V
,
and are between
output overload limits
− 10
.
4 V ≤ V
min
≤ − 9
.
9 V
,
9
.
9 V ≤ V
max
≤ 10
.
4 V
.
The overloaded state is also recognized, and OUTPUT OVLD acti-
vated, if the raw output of the transimpedance stage, | V
bias
− i
in
× R
F
|
,
exceeds these limits. To distinguish between the two output over-
load possibilities, use the
OVLD? query. The overload LED stays on
for a minimum of 50 ms; after this time it turns o
ff
if the overload
condition has ceased.
1.3 Connections
There are five BNC connectors in the SIM918, three on the front panel
and two at the rear.
Panel BNC Terminal Signal Direction
Front Input Center Input current Input
Shield Shield program voltage, Output
bias voltage, signal ground
Bias Center Bias voltage Input
Shield Float, power ground
Output Center Output voltage Output
Shield Signal ground Output
Rear Shield Program Voltage Center Shield program voltage Input
Shield Chassis ground
Ref Clock Sync Center Reference clock Input, output
Shield Chassis ground Input, output
Table 1.1: BNC connections in the SIM918.
For a further discussion of grounding, see Section 2.2.1. The SIM
interface connector is discussed in Section 1.6.1.
SIM918 Precision Current Preamplifier