Advertisement
SECTION m
Model 4277A
When the ZERO OPEN button is pressed, the
instrument will be automatically set to C-G
measurement mode.
It will then measure the
test fixture's stray admittance at each of the
previously
mentioned
test
frequencies.
The
measured values are stored in the instrument's
internal memory.
When offset adjustment is
completed, DISPLAY A and DISPLAY B will be
blank for 1 or 2 seconds, after which the front
panel controls will be reset to the settings that
existed
when
the
ZERO
OPEN
button
was
pressed.
The purpose of OPEN Zero Offset Adjustment is
to measure the test fixture's stray admittance,
which, as shown in Figure 3-12 (a), consists of
Go and Co. (This stray admittance is equivalent
to a high impedance, which will "swamp out" a
high impedance
DUT connected to
the
test
fixture.)
The residual impedance of the test
fixture--Ro
and
Lo
in
Figure
3-12
(a)—is
negligibly low and therefore does not affect the
accuracy of OPEN Zero Offset Adjustments.
ZERO SHORT:
The
procedure
for
performing
SHORT
Zero
Offset Adjustment is as follows:
(1)
Connect the test fixture or test leads to the
instrument's UNKNOWN terminals.
Note
If test leads are used, you
must
convert
the
four-
terminal configuration to a
two-term inal
configuration.
Refer to paragraph 3-45 and
Figure 3-8.
(2)
Connect a low impedance shorting-bar to
the test fixture. If you're using test leads,
simply
connect
the
ends
of
the
leads
together.
(3)
Press the ZERO SHORT button.
When the ZERO SHORT button is pressed, the
instrument will be automatically set to L-ESR
measurement mode.
It will then measure the
test fixture's residual impedance at each of the
previously
mentioned
test
frequencies.
The
measured values are stored in the instrument's
internal memory.
When offset adjustment is
completed, DISPLAY A and DISPLAY B will be
blank for 1 or 2 seconds, after which the front
panel controls will be reset to the settings that
existed
when the ZERO SHORT button was
pressed.
The purpose of SHORT Zero Offset
Adjustment is to measure the test fixture's (or
test lead's) residual impedance, which, as shown
in Figure 3-12 (b), consists of Ro and Lo. This
residual impedance, although small, degrades the
accuracy of low impedance measurements. The
stray admittance of the test fixture—Go and Co
in
Figure
3-12 (b)— is shunted
by the low
impedance shorting-bar
and therefore is not
measured.
Once
OPEN
and
SHORT
Zero
Offset
Adjustments have been made, the instrument
automatically
compensates
all
subsequent
measurements for the residuals and strays of the
test fixture or test leads. The values displayed
on the front panel are the actual values of the
DUT.
Also, because the Zero Offset data is
maintained
by
the
instrument's
continuous
memory function, OPEN and SHORT Zero Offset
Adjustments do not have to be repeated each
time the instrument is turned on.
You need to
repeat Zero Offset Adjustments only when you
change test fixtures (the residuals and strays of
one test fixture are different from those of
another).
Maximum values that can be offset
are listed below.
'-II-'
Co
-o
o-
OPEN
(a)
3-40
Figure 3-12.
Equivalent
Circuits
for
Zero
Offset Adjustment.
Advertisement
