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take a number
of minutes
for the input current to
drop within specified limits. Input current can be
verified by placing
the protection
cap on the IN-
PUT jack and then connecting
a jumper between
the COM
and chassis
ground
terminals.
With
the instrument
on the 2pA range and zero check
disabled,
allow the reading
to settle until the in-
strument
is within
specifications.
Use the following
procedure
to measure
charge
with
the
Model 617.
1. Turn on the power and allow a two-hour
warm up period
for rated accuracy.
2. Place the instrument
in the coulombs
mode by pressing the
COUL button.
Set V, R GUARD
to OFF.
3. To achieve
rated accuracy,
place the instrument
on the
2COpC range
and zero the instrument
by enabling
zerc~
check and then pressing
the ZERO CORRECT
button.
4. Select the desired range, or use autoranging,
if desired.
5. Disable
zero check. A small amount
of zero check hop
(sudden change in the reading)
may be observed when zero
check is disabled.
If desired,
enable
suppress
to null out
any zero check hop, which
typically
will be in the lo-25
count
range.
'
6. Connect
the Model 6011 cable to the INPUT jack. Connect
the other end of the cable to the circuit being measured.
as
shown
in
Figure
2-11.
For
low-level
measurements,
shielding
may be required.
Note: Do not connect
the cir-
cuit to the instrument
with zero check enabled.
7. Read the charge value from the display. The exponent
may
be placed either in the alpha or numeric
modes as described
in paragraph
2.5.
A
0
\
RED
00
QS
MEASURED
IN;;;T
00
CHARGE
0
6011 CABLE
NOTE: LEAVE OS DISCONNECTED
"NTlL
ZERO CHECK DISABLED
r----i
00
cl
----
1
SHIELD ,OPTIONAL)
J
MODEL 617
INPUT AMPLlFlER
PREAMP OUT
TO A/D
CONVERTER
EQUIVALENT C,RCUIT
Figure 2-11. Coulombs Connections
2-14
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