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OPERATION
MODEL 615 ELECTROMETER
tars
remain
lighted
during
an overload
condition
indicating
the correct
polarity.
Thus the Electrom-
eter
display
will
indicate
correctly
within
specifi-
cations
with
no ambFguous overload
display.
4.
To remove the overload
condition,
change the
SENSITIVITY
Switch
setting
or decrease
the input
signal
magnitude.
b.
Ammeter Digital
Readout
1.
When the RANGE Switch
is placed
in the AMMETER
position,
the Electrometer
digital
readout
desig-
nates
the voltage
across
an accurately
known self-
contained
resistor.
The RANGE Switch
selects
the
calibrated
range resistor
for current
measurements
from 10-l
to lo-11
amperes.
The range resistor
is
the reciprocal
value
of the Range setting.
The
readout
indicates
the voltage
across
the Range re-
sismr.
2.
The full
scale
current
range is determined
by
multiplying
the Range setting
times
the digital
readout
display.
The SENSITIVITY
Switch
operates
in the same fashion
aa for voltmeter
measurements.
(Refer
to preceding
paragraph
2-3,
a).
3.
The full
scale
current
range
far various
front
panel
control
settings
is shown in Table
6.
TABLE 6.
Full
Scale
RANGE
SENSITIVITY
I
Switch
C.
Ohmmeter Readout.
1.
When the RANGE Switch
is placed
in the OHMS
position,
the Electromerer
digital
readout
desig-
nates
the actual
voltage
across
the unknown resis-
tor
as an accurately
known current
(internal
to the
Electrometer)
is applied
to the unknown.
2.
The RANGE Switch
selects
the current
for Olw
lll~ClS"C~lU~"t~.
The current
is the reciprocal
value
of the OHMS range setting
from 105 to lo12 ohms.
The SENSITIVITY
Switch
operates
in the same fashion
aa for voltmeter
measurements.
3,
The actual
resistance
measurement
is deter-
mined by multiplying
the RANGE Switch
setting
tFmes
the digital
readout
display.
d.
Coulombmeter
Readout.
1.
When the RANGE Switch
is placed
in the CO"-
LO"BS position,
the Electrometer
digital
readout
designates
the actual
voltage
across
a self-contained
ac~rately
knovn capacitor
since
the Electrometer
is sensitive
to the integral
of the current
applied
from the external
unknown source.
2.
The coulomb measurement
is determined
by mul-
tiplying
the RANGE Switch
setting
times
the digital
readout
display.
e.
DISPLAY RATE Control.
(This
control
is a con-
tinuously
variable
control
that
permits
the user to
select
the rate
of analog-to-digital
conversion).
That is,
the control
determines
the number of times
a new reading
will
be recomputed
per unit
of time.
Thts
is useful
for
sampling
a continuously
varying
in-
pllt current
as well
as for controlling
slower
external
devices
such as paper
tape punches and printers.
With
the DISPIAY Control
in the MAX Position
the display
rate
is 24 times
per second (20 for 50 HZ models).
When the control
is varied
clockwise,
the rate
de-
creases
to a minimum of about
2 per minute
in the ex-
treme clockwise
position.
The front
panel
DISPLAY
SATE Control
applies
to the digital
circuitry
only.
2-4.
VOLTAGE MEASUREMENTS.
a.
The Model 615 can meas,,re an unknown voltage
when the low impedance
terminal
is up to 100 volts
off
case ground.
Safe operation
of the Electrometer
is insured
by grounding
the case.
To use the Model
615 for
off
ground voltage
measurements,
disconnect
the shorting
link
between LO and CASE GND Terminals
on rhe rear
panel.
(Refer
t.3 Figure
2).
CAUTION
Operating
the Model 615 at more than 100
volts
off
ground may permanently
damage
the instrument.
The isolation
between
circuit
low and ground could
break
dawn
making the instrument
unusable
far safe
off
ground measurements.
Refer
to Paragraph
2-6 far complete
instructions
for
making off
ground measurements.
b.
The Model 615 has been designed
to meas"re
valt-
ages up to 100 volts
from very
high
resistance
sources.
However,
the Model 615 can also
be used for meaaure-
ments from low sr,urce
resistance
and voltages
up to 30
kilovolts
with
high voltage
divider
probe.
1,
The input
resistance
can be decreased
in or-
der to reduce
the effects
of stray
pickup
with
low
sou*ce resistances.
Refer
to Paragraph
2-4,
f for
complete
instructions.
2.
ear measurements
of voltage
up to 30 kilovolts
refer
to Paragraph
2-4,
g which describes
various
divider
probes
available
from Keithley.
c.
The Model 615 can measure voltages
in two modes:
Normal Mode and Fast Mode.
1.
Normal Mode.
In the Normal Mode -
FEEDBACK
Switch
at NOWAL -
the unknown voltage
is connected
to the INPW Receptacle.
Input
impedance with
th
RANGE Switch
in VOLTS position
is greater
than 10 84
ohms shunted
by 35 picofarsds,
0570
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