Table of Contents
Advertisement
MODEL 616
OPERATING INSTRUCTIONS
mm
tmm tmm
mm mm
mm
rnmaa
mam"i
SOURCE
ELECTROMETER
V
« 1/C
/i
dt
FIGURE
11.
Operation
As A Coulombmeter
in
FAST Mode
.
3-9.
OPERATION AS A COULOMBMETER.
The
Model
616 can
be used
to
measure charge by means
of a
current inte-
gration technique.
When
the
Model
616 is
set
to
any-
one
of the
4
coulomb ranges, an accurately
known
capa-
citor
is
connected
in the
feedback loop
of
the volt-
age
amplifier
so that
the
voltage developed
is
pro-
portional
to the
integral
of
current where V « Q/C
or
V
= 1/c/idt. The
Model
616 can
also
be used with
accessory Models
2501
or
2503 for
measurement
of
static charge on
a
dielectric surface.
A discussion
of
static charge measurement
is
given in section 3-lOc.
To use the
Model
616
as
a
coulombmeter, set the front
panel controls
as
follows:
RANGE
—
10"^° COULOMB
SENSITIVITY
—
AUTO
FAST /NORMAL
—
FAST
Make connections
to
the
Model
616 using
a
shielded
triaxial
cable.
Keep cable length
as
short
as
possible
to
reduce
the
slowing effects
of
cable
capacitance.
.The
zero control may need
occasional
adjustment
to
reduce
any
voltage offset which may
occur due
to the
temperature variations
.
To rezero
the
Model
616, set the ZERO
CHECK Switch
to
CHECK
position
and adjust
the
front panel ZERO control
for a
0~0"0-0
display.
(The
recommended warmup
time
for
the
Model
616 is two
hours although It
is
useable Immediately
after power
is
turned on.)
The
Model
616 provides a
direct reading display
with automatic decimal
point position.
NOTE,
3-10.
ALTERNATE MEASUREMENTS.
The
Model
616
can
also be used
with Keithley
accessories which ex-
tend the
measuring capabilities
of the
electrometer.
a.
Null
Method
for
Current Measurements.
The
Model
616 can
be used with an accurate current
source such
as
Keithley Model
261:
to
measure
small variations
of
current.
When using
this
method,
the
Model
616 is
operated
as a
current null detector
in the
FAST mode.
The current source should
be
ad-
justed
to
obtain
a
null reading on
the Model 616
(the
electrometer should be
set to an
appropriate
range and sensitivity depending on
the
magnitude
of
current variation)
b.
Volt-Ammeter Resistance Measurements.
The
Model
616
can be used with an accurate voltage
source such
as
Keithley Models
240A, 244, 245, or
246.
When using
this method, the
Model
616 is
operated
as a picoairaneter so that the
current
through
the
unknown resistance
is
measured by
the
electrometer.
The resistance
is
then calculated in
terms
of the
known voltage
impressed and
the
re-
sultant current measured on
the
electrometer.
e.
Static
Charge
Measureiaents
The
Model
616
can be used
with Models
2501
or
2503 Static
Detector
Probes
for
measurement
of
static charge
on
a
dielec-
tric surface.
When
using
this
method,
the
Model
616
is
operated
as a
voltmeter with
a
reading directly
in volte.
(Do
not attempt
to
measure static charge
with
the
Model 616 in
the
COULOMB mode.)
NOTE
The input offset current
of the
Model
616
contributes
a charge of
5
x
10"15
coulomb
per second
and should be subtracted-
from
the
actual
reading.
For more information about Static Charge
Measurements, request
the
Keithley Product
Notes entitled "Electrometer Static Charge
Measurements".
0374
11
Advertisement
Table of Contents
