Fluke 5520A Service Manual page 104

5520A
Service Manual
A technique for measuring capacitance is to apply a known current across the capacitor
and measure the voltage change over a known time interval.
Table 3-29. Test Equipment Required for High-value Capacitance Measurement
Quan.
1
1
1
Computer control of the instruments is highly recommended to eliminate manual timing uncertainties.
For this technique, the amplitude of the current is chosen to limit compliance
voltage across the capacitor under test to < 3 V over a charging interval of 10
seconds. Refer to Table 3-28 for the dc current required for each capacitance
value to be verified.
For proper timing, implementing this routine under computer control is highly
recommended. See Figure 3-19. for an example Visual Basic program. If you wish to
perform this verification under manual control, the HP 3458A DMM can be programmed
from its front panel to give the necessary timing and reading storage. Please refer to the
HP 3458A operator's documentation for more information.
Proceed as follows to measure high-end capacitance:
1. Connect the Fluke 5700A, 5520A, HP 3458A DMM and computer as shown in Figure 3-
18 below. See Table 3-29 for the equipment required.
2. Lock the HP 3458A in the 10 V dc range.
3. Program the meter to take 100 samples at 1 ms-aperture width and a 100 ms sweep for a
total of 10 seconds on a trigger command.
4. Enter the desired capacitance on the 5520A and place the 5520A into Operate mode.
5. Enter the predetermined DCI level on the 5700A.
6. Set the 5700A to Operate.
7. As soon as the calibrator's remote status indicates a settled condition, your computer
program should trigger the HP 3458A reading sequence. Voltage sensing is performed at
the 5520A output.
8. At the completion of the measurement, set the 5700A to Standby and then retrieve the
data from the HP 3458A.
If operating under manual control, and you do not activate the 5700A Standby
key in a timely manner, either the 5520A or 5700A will automatically trip into
Standby because of an overload condition. This is acceptable and should not
affect the readings over the 10 second measurement period.
9. The capacitance is computed as the product of the dc current and the ratio of the time
interval (10 seconds) divided by
3-48
Manufacturer
Fluke
Hewlett Packard
Fluke
Note
Note
( V V
final
Model
5500A/LEADS
3458A
5700A
)
.
initial
Equipment
Test lead set
DMM
Calibrator