HP 4262A User Manual

Model 4262A
Section VIII
This equation means that discharge period T2
(number of counts for fc) is directly equal to the
mantissa of a measured Cp value (note that Rr =
10™ ; and m is an integer).
For example, if a 1200pF capacitor is measured
at a measurement frequency of 1kHz, the
4262A automatically selects 10kS2 as the Rr and
constant k2 is 50. Therefore, equation 8-9 may
be written as:
C —3 n. 10.6 3 n- 10-6
P=D o oRr " 2x50x10x 103
Consequently,
=n-1012
n=Cp x 1012 = (1200 x 10-12) x 10 12=1200
The 4262A will display 1200 counts and the
“pF” unit lamp will light.
In a D measurement cycle, the integrator is
charged for period T3 by the E2 signal as detec-
ted by a detection phase in phase with E2, In-
tegrator output voltage rises to k1GpRrE1TS3.
During the discharge cycle T4, the detection -
phase is different by 90 degrees as referred to
- E2. The discharge voltage becomes
k1w CpRrE1T4. From these integrator voltage
changes in the D measurement cycle, the follow-
ing equation may be composed:
k1GpRrE1T3 = k1w CpRrE1T4 . ... eq. 8-10
Dissipation factor D is derived as follows:
-_Gp _T4 8-11
D
wCp
T3
eq.
1
The period T3 is constant and is equal to 1000 g¢
(fc = 31.83kHz). If n stands for number of
counts for fc during period T4, T4 is equal ton- -
Thus, equation 8-11 may be converted to:fc
n -
D= T4 _ fc n
T3 1000_1_ 1000
fc
Therefore, n = 1000D.
If D value for the unknown is 1.2, n will become
1200 which will be displayed at the front panel
with the decimal point. Figure 8-3 shows the ex-
panded forms of calculations for impedance
parameters.
As shown in Figure 8-3, two kinds of integrator
waveforms exist. These two distinctive inte-
grator operations may be examined with respect
to Cp and Cs measurement modes. For a Cs - D
measurement, a constant current drive is applied
to the unknown. Voltage E2 is a constant value
drop across Rr and E1 is a variable voltage pro-
. duced by DUT. The following equation shows
the relationship between voltages E1 and E2:
El =(%+Tw—c}s§¥)' E2
The reference phase for the phase detector is
now taken from E2 signal. During charging
cycle T1, the phase detector detects input volt-
age E1/10 by a detection phase in phase with
E2. The integrator output voltage becomes:
........
.....................
The integrator charges to a constant voltage re-
gardless the value of the DUT. During integrator
discharge cycle, the phase detector detects E1
signals with a detection signal that is different in
phase by 90 degrees with respect to the E2
signal. The resulting integrator output voltage
change is:
E2
-kl'mTz ................ eq. 8-14
Therefore,
E2 E2
k1 ET) Tl =kl ~SCsRr T2 ....... eq. 8-15
Cs is derived from equation 8-15 as follows:
10 T2
= P .81
Cs
ORr
TL
-
eq.
8-16
Substituting T1 in equation 8-6 produces:
- 10 .
Cs
=
o
koRr
T2
....ciiivienenn
eq.
8-17
Since T2 is counted by a 31.83kHz (its period is
107 x 10-6 sec) clock, equation 8-17 is:
00
1
Cs=n SioRr ™
where, n is number of clock counts.
106
............
If 4262A measurement frequency is 1kHz, Rr is
1k, and k2 is 5, equation 8-18 becomes:
Co = 100
ST N 5% 5x103
When the capacitance of the unknown is 10uF,
the 4262A displays 10.00 counts and the uF
unit lamp lights.
%10 =10n x 10°(F)
(Sheet 2 of 2)
8-

HP 4262A Specifications

General

Brand	HP
Model	4262A
Category	Measuring Instruments
Language	English