HP 4262A User Manual

Model 4262A
impedance of the unknown is usually low and Ro
is set to a value much greater than the impedance
of the unknown device to achieve a constant cur-
rent drive. On the other hand, for a parallel equiva-
lent circuit measurement (Lp, Cp or Rp), the
impedance of the unknown device is usually high
so Ro is set to a much smaller value than the
impedance of the unknown. Thus,a constant volt-
age drive is realized. The resistance values for Ro
and Rr are always equal.
8-15. Here is a brief discussion of Vector Volt-
age-Ratio Measurement Section operation. The €m
signal selected by S2 (from either E1 or E2) is de-
tected by a phase detector that outputs the rectan-
gular component or in-phase component to an inte-
grator. Phase detector drive signals €1 through
€4 are produced in the following manner: a 4f
signal is generated from an €ref signal (at a fre-
quency of f) as selected by switch S1. This creates
signals €1 through €4, each being different by 90
degrees in phase from one another (a 4 phase gen-
erator). As a PLL (Phase Lock Loop) circuit is used
for generating the reference phase signal to mini-
mize measurement error, the phase of signals E1
through E4 is very accurate. One of these signals,
as directed by the digital circuitry, detects the €m
measurement signal. Phase detector output is a vec-
tor component signal representing the capacitive,
reactive, or other characteristic of unknown to be
measured. R
\
8-16. This paragraph discusses the parallel capaci-
tance Cp measurement principle. To simplify the
explanation, the example used here is that of meas-
uring an ideal capacitor. See Figure 8-2, Cp Meas-
urement. During time T1, Switch S2 selects E2 and
the integrator is charged by that portion of the E2
sinusoidal waveform which is synchronously phase
detected by the €2 pulse train. Both S1 and S2
Section VIII
Paragraphs 8-15 to 8-18
switches select the E1 signal that is fed to discharge
the integrator after being phase-detected by the €1
signal. Since time period T2, for the integrator to
discharge to zero volts, is proportional to the value
of Cx, Cx can be directly obtained from the con-
tents of a counter if the values for Rr and T1 are
properly and accurately set. A zero detector signals
the digital section to establish a counted number
corresponding to Cx each time the integrator out-
put crosses the zero level. Other measurements are
done similar to the Cp measurement.
8-17. The analog section of the 4262A is control-
led by nanoprocessor centered control which
manages the various sequences required to perform
the desired measurements. Range control, selection
of measurement mode, and timing of the A-D con-
version processes are governed by the nanoproces-
sor. The nanoprocessor also acts as a computing de-
vice and calculates deviation ALCR and the quality
factor of sample (mathematical operation) as well
as counting the L, C, R and D values converted
into time periods.
8-18. The functions set by pushing front panel
pushbuttons are inputted to the nanoprocessor
through the keyboard control. The keyboard
switches are assigned individual addresses for dis-
crimination. When a panel control pushbutton is
depressed,
the
keyboard
control
identifies
the
ad-
dress of switch and causes the nanoprocessor to
treat the “interruption’ of the function it recog-
nizes by the address code. The nanoprocessor gives
priority to specific pushbutton functions so as to
be able to restrict improper control settings. Key-
board operation is monitored by and in-part
managed by nanoprocessor programming. This is
partly to assist the operator and partly to prevent
misoperation.
1 ]
A
/?\
/
Integrator
Sy
.
Er
(eref)
Sv
.
Ei(eref)
Ei
/
:
:
Output
S2
|
E2
(em)
Sz
.
Ei
(em)
' ' N . ' 1 \
i
'
\/:
'
\/
ez
(detected
er
(detected
!
|
[
!
V
'
i
phase)
phase)
\ N : ! 1 ' ! 1 '
' . . ' | i ' ' ' < &,
4
!
'
1
I
'
!
r
)
&
/
E2
4\3
!
':/;\:
'
/\
Ez
=(jwCx)RREI
OC"‘
N L NS
' i i ' . 1 ¥ '
R
T
T
R
0
:
!
.
:
!
!
.
)
'
Ti
T2
. ' ] i
o«
I
7
L
L
T
e2 ___]——L___i—— ) 1T
|
wCXRREITy
=
BTz
Cx
=
w_RE.T%
Cx
o=
T2
Figure 8-2. Cp Measurement.
8-3

HP 4262A Specifications

General

Brand	HP
Model	4262A
Category	Measuring Instruments
Language	English