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Model 4277A
SECTION III
®DC BIAS SWITCH:
CABLE LENGTH Switch :
On instruments equipped with Option 001, DC
BIAS, this switch turns the internal DC bias
source on and off. When this switch is set to
ON and the DC BIAS Select Switch ((2) in
Figure 3-2) on the rear panel is set to INT,
the
DC
voltage
selected
by
the
FREQUENCY/DC BIAS Step Control Keys
(U)
is oir^ut from
the
Hcur
UNKNOWN
terminal
When set to OFF, this switch
turns off tFie internal DC bias source; no DC
voltage is output from the
Hcur
UNKNOWN
terminal
and
"OFF" will be briefly
displayed
on
the
FREQUENCY/DC
BIAS
Display (?) each time a new DC bias voltage
is set by the FREQUENCY/DC BIAS Step
Control Keys (0) or via the HP-IB.
Note
This switch
facilitates
balancing of the
measuring
bridge
circuit
and
minimizes
measurement errors when the standard 1
meter test leads are used.
Im: Set the switch to this position when
using the standard 1 meter test leads.
Appropriate compensation is made for
propagation
delay
and
phase
error
caused
by
the
test
leads
in
high
frequency measurements.
0 ;
Set the switch to this position when
using a direct attachment type test
fixture, such as the 16047A (connects
to the UNKNOWN terminals (||)).
Note
This switch controls the internal DC
bias source only. It does not control
external DC bias voltage applied to
the
EXT
INPUT/INT
MONITOR
connector @ in Figure 3-2) on the
rear panel. Also, this switch is not
HP-IB programmable.
@ ZERO Offset :
These
buttons
perform
ZERO
offset
compensation (OPEN and SHORT) for the
residuals of the test fixture, test leads, and
measurement
circuit.
ZERO
offset
is
performed at the following spot frequencies:
IMHz, 900kHz, 700kHz, 505kHz, 202kHz,
lOOkHz, 50.5kHz, 20.2kHz, and lOkHz.
This switch is not HP-IB programmable.
UNKNOWN Terminals :
These four BNC connectors provide the
means to connect DUT's in a four-terminal
pair configuration:
High current terminal
(Hcur),
High potential terminal
(Hpot),
Low
potential terminal
(Lpot),
and Low current
terminal
(Lcur).
Four-terminal
pair
test
fixtures attach directly to these terminals.
GUARD Terminal;
This terminal is tied to the instrument's
chassis and can be used in measurements
that require guarding.
OPEN :
If this button is pressed when the
test fixture or test leads are
terminated
open,
measured
values at this time are stored as
residual admittance data.
SHORT;
If this button is pressed when the
test
fixture or test leads are
shorted, measured values at this
time
are
stored
as
residual
impedance data.
Figure 3-1. Front Panel Features (Sheet 6 of 6).
3-7
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