Keithley 6521, Инструкция по эксплуатации, Страница: 39 / 65

Operation
3-11
When the Model 6517 is programmed for the current scan
mode, a ground relay contact shorts the HI and LO terminals
of each off channel, maintaining a true current path at all
times. For that reason, you should program the Model 6517
to operate in the current scan mode when switching currents.
See paragraphs 3.4.4 and 3.5.3 for more information on se-
lecting the voltage or current scan modes.
3.7 Typical applications
Typical applications for the Model 6521/22 are discussed in
the following paragraphs. For more information on these and
other scanner card applications, contact the Keithley Appli-
cations Department.
3.7.1 Capacitor leakage measurements
One of the more important test parameters associated with
capacitors is their leakage characteristics. Such leakage may
be specified as the “IR” (Insulation Resistance), or it may be
expressed as leakage current at a given voltage, usually the
operating voltage.
Since capacitor leakage characteristics are largely dependent
on the applied voltage, an ordinary ohmmeter is of little
value in making such tests. Instead a fi ed voltage is applied
to the capacitor, and the resulting leakage current is
measured. Leakage resistance can then be determined by
simple computation.
In many cases, a number of capacitors of a given type are
tested in order to obtain useful statistical data. In those cases,
an automated test system like the one shown in Figure 3-6
may be used to test a number of capacitors. The system in-
cludes a Model 6517 Electrometer to apply test voltages and
measure leakage currents, while the Model 6521/22 Scanner
card provides the necessary switching functions. The elec-
trometer ohms function can be used, of course, to measure
the leakage resistance directly. Resistors are connected in se-
ries with the capacitors under test to limit current and reduce
noise.
The test configuration shown in Figure 3-6 can be used only
where test speed is unimportant because of the capacitor
charging time caused by large RC time constants, particular-
ly with larger value capacitors. If shorter test times are re-
quired, external switching can be added to allow a voltage to
be applied to each capacitor for a “bias” time before each
test. (The bias time is the period required for the capacitor to
charge fully, or about fi e RC time constants.)
Figure 3-6
Capacitor leakage test system
Model 6517 Electrometer
HI
1
10
C
1
R
1
C
10
R
10
6521/22 Card
Capacitors under test
Note: Electrometer must be configured
for internal voltage source connection
Triax Cable
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
INPUT
250V PEAK
!
LINE RATING
50-60HZ
50VA MAX
AC ONLY
LINE FUSE
SLOWBLOW
1/2A 90-125V
1/4A 180-250V
IEEE-488
(CHANGE IEEE ADDRESS
WITH FRONT PANEL MENU)
DIGITAL
I/O
TRIG LINK
115V
Voltage source HI