HP 5501A Operating And Service Manual page 180

b. The system electronics can become very sensitive to external noise (such a s power line
switching transients) due to undesirable currents flowing through ground wiring. These
currents cause a voltage potential other than zero volts to exist at points in the ground-
ing system. (See Figure 5-2).
Notes:
I f the power supply
requirements
to Unlt B fluctuate due t o lead
switching, for example, a changlng current will be present n o t only
in the path of I*, b u t also i n the path o f I, and 13. I f the signal
l ~ n e associated wlth path I, is sensitive t o the resulting voltage
fluctuations. system troubles can result. The remedy is to break
the loop, probably at the path of 13.
UNITS ELECTRICALLY CONNECTED BY
VIRTUE OF COMMON MOUNTING (SUCH
AS IN A CONDUCTIVE RACK)
Figure 5-2. Grounding to Avoid Ground Loops
UNIT
A
1 3
-
In general, try to avoid unnecessary ground or common return connections while wiring the
system. Ensure, however, that all units are grounded. The best approach is to have one com-
mon earth ground connection in the system with
all
system components connected at the
single ground. Also, avoid connecting both ends of
a
signal cable shield to a ground point.
This would allow currents to flow through the shield and possibly cause interference with the
signal lines within the cable. The shields from the 10780A receiver, for example, should be
grounded at one end only, and the receivers should be mounted in such a fashion that they
form no electrical connection with the mounting surface. A typical distribution of the +15V
power and the reference and measurement signals is shown in Figure 5-3. The correct wiring
of the individual units to the terminal strip on the rear of the 10740A coupler is shown in
Figure 5-4.
-
UNIT
B
For further information on the subject of system grounding, refer to "Grounding and Shielding
Techniques in Instrumentation" by Ralph Morrison. Published by John Wiley and Sons, Inc.
SIGNAL
LINE
COMMON
RETURN
1
I,
1 2
POWER
SUPPLY
COMMON
RETURN