
Scans by ArtekMedia © 2007
latter method should be used when you want the current buffer contents or
setup conditions to be retained.
NOTE:
After entering or exiting the rotate function, always verify rotation
has occurred by checking the orientation of the default recording area
(press
ZERO
and/or
FULL
SCALE.)
•
Connecting Analog Input Signals
Signal-Illput
An'CI
Using the
Guard Switch
&
WARNING
The HP 7090 is designed for laboratory use by qualified personnel. The
operator must be aware of the hazards of any external voltages that are
being measured.
Careful selection of external cables and probes is important based on the
input signal voltage. Any voltage over 42 volts peak should be considered
hazardous.
The HP 7090 accepts three analog signal inputs, one for each measurement
channel. The input jacks are floating, guarded, and accept a dual banana
plug. A switch able guard terminal is also available for each channel, allow
ing connection of an internal guard shield to an external common mode
voltage source. Voltage overflow conditions are indicated by an overflow
indicator. An input jack, guard terminal jack, guard switch, and overflow
indicator are grouped for each channel as shown below.
GUARD TERMINAL JACK
{SINGLE
BANANAl
INPUT JACK
(DUAL BANANAl
Each channel input jack is floating to reject common mode voltages (a
potential source of error during sensitive measurements). When the guard
switch is closed ("in" position) the channel's internal guard shield is con
nected to the low terminal, providing internal guarding and improving
common mode rejection. The HP 7090 will reject common mode signals by
more than 140 dB at dc and 100 dB at 60-Hz line frequency when the
internal guard is used. The common mode rejection ratios are for l-kfl
unbalance at the
LOW
terminal, using the most sensitive range.
For measurement applications in which an external guard connection is
desired, the guard switch should be opened ("out" position). Opening the
switch connects the guard shield to the guard terminal jack (refer to the
following diagram). A single banana plug inserted into the guard jack may
then be connected to the external common mode voltage source (common
3-22 Measurement Setup Operations