Keithley Series 2600 Application Manual Download

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2-4

SeCTIon 2

Two-terminal Device Tests

For example, assume that you measured a leakage current of 25nA
with a test voltage of 100V . The leakage resistance is simply:

R =100/25nA = 4G

(4 × 10

)

2.4.3 Measurement Considerations

After the voltage is applied to the capacitor, the device must be
allowed to charge fully before the current measurement can be
made . Otherwise, an erroneous current, with a much higher
value, will be measured . The time period during which the capac-
itor charges is often termed the “soak” time . A typical soak time is
seven time constants, or 7RC, which would allow settling to less
than 0 .1% of final value . For example, if R is 1M

, and C is 1µF,

the recommended soak time is seven seconds . With small leakage
currents (<1nA), it may be necessary to use a fixed measurement
range instead of auto ranging .

2.4.4 example Program 2:

Capacitor Leakage Test

Program 2 performs the capacitor leakage test described above .
Follow the steps that follow to run the test using this program .

WARNING

Hazardous voltage may be present on the capacitor
leads after running this test. Discharge the capac-
itor before removing it from the test fixture.

With the power off, connect the instrument to the computer’s

1 .

IEEE-488 interface .
Connect the test fixture to the instrument using appropriate

2 .

cables .
Turn on the instrument, and allow the unit to warm up for

3 .

two hours for rated accuracy .
Turn on the computer and start Test Script Builder (TSB) . Once

4 .

the program has started, open a session by connecting to the
instrument . For details on how to use TSB, see the Series 2600
Reference Manual .
You can simply copy and paste the code from Appendix A in

5 .

this guide into the TSB script editing window (

Program 2

manually enter the code from the appendix, or import the TSP
file ‘

Cap_Leak.tsp

’ after downloading it to your PC .

If your computer is currently connected to the Internet, you
can click on this link to begin downloading:

http://www.

keithley.com/data?asset=50927

Discharge and install the capacitor being tested, along with

6 .

the series resistor, in the appropriate axial component sockets
of the test fixture .

WARNING

Care should be taken when discharging the capac-
itor, as the voltage present may represent a shock
hazard!

Now, we must send the code to the instrument . The simplest

7 .

method is to right-click in the open script window of TSB,
and select ‘

Run as TSP file

’ . This will compile the code and

place  it  in  the  volatile  run-time  memory  of  the  instrument .
To  store  the  program  in  non-volatile  memory,  see  the  “TSP
Programming Fundamentals” section of the Series 2600 Refer-
ence Manual .
Once  the  code  has  been  placed  in  the  instrument  run-time

8 .

memory, we can run it at any time simply by calling the func-
tion ‘

Cap _ Leak()

’ . This can be done by typing the text

‘

Cap _ Leak()

’ after the active prompt in the Instrument

Console line of TSB .
In the program ‘

9 .

Cap_Leak.tsp

’, the function

Cap _

Leak(vsrc)

is created . The variable

vsrc

represents the

test  voltage  value  applied  to  the  device-under-test  (DUT) .  If
it is left blank, the function will use the default value given
to  the  variable,  but  you  can  specify  what  voltage  is  applied
by  simply  sending  a  voltage  that  is  in-range  in  the  function
call . As an example, if you wanted to source 100V, simply send

Cap _ Leak(100)

to the instrument .

The instrument will then source the programmed voltage and

10 .

measure the respective current through the capacitor . The
measured current leakage and calculated resistance value will
then be displayed in the Instrument Console window of TSB .

NOTE

The capacitor should be fully discharged before run-
ning the test . This can be accomplished by sourcing 0V
on the device for the soak time or by shorting the leads
together . Care should be taken because some capacitors
can hold a charge for a significant period of time and
could pose an electrocution risk .

The soak time, denoted in the code as the variable

l _ soak

has a default value of 10s . When entering the soak time, choose
a value of at least 7RC to allow settling to within 0 .1% of final
value . At very low currents (<500fA), a longer settling time may
be required to compensate for dielectric absorption, especially at
high voltages .

2.4.5 Typical Program 2 Results

As pointed out earlier, the exact value of leakage current will
depend on the capacitor value as well as the dielectric . A typical
value obtained for 1µF aluminum electrolytic capacitor was about
80nA at 25V .