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MODEL 615
CALIBRATION
NOTE*
To verify
the accuracy
on the 10w8A through
10-11~
ranges
a specially
calibrated
Keithley
Model 261
Picoampere
source
is required.
The "three
month"
accuracy
for
the Model 261 is +a.6% on lo-8A
to
Lo-11.4.
However,
a Model 261 may be calibrated
co within
50.4% when used with
a Model
515A
Megohm Bridge
and B set of 5155 Megohm Standards
(traceable
to the N.B.S.).
Since
the resisrars
exhibit
a temperature
coefficient
of approx.
-0.1%
per 'C it
may be necessary
to compensate
for
cemp-
erature
variarions
between
the calibration
area
and the measurement
area.
To minimize
the effects
of drift
in the value
of the resistors
it
is im-
parcant
to recalibrate
the Model 261 jusr
prior
to making a calibration
check on the Model 615.
Where it
may not be necessary
to verify
the Made1
615 current
ranges
f~ within
+4%, a standard
Model 261 Picoampere
source
may be used.
To ver-
ify
the accuracy
an the lO-lA
to LOm6A ranges , a
Made1 34LA should
be used with
preci&x
reeis-
tom
having
5.03%
accuracy.
b.
DC 818s Adjustment.
set
the front
panel
controls
88 above.
To set the dc bias,
monitor
the voltage
acro8e
resistor
R1249 (test
terminals
o and E as shown
in Figure
22).
Adjust
the dc bias
control
(R1268)
for
25 mV +3
mV using
voltmeter
(A).
C.
Power Supply
Check.
Set the Sensitivity
con-
trol
(51203)
t0 the 100.0 volt
range;
the range switch
to VOLTS; the Feedback
switch
to PAST.
With the line
voltage
set to 117 volts
measure
the power supply
voltages
*e follows:
TABLE 6-2.
Power Suonlv
Valtanes
C15"
-15"
+3.6V
+17ov
+12ov
-120"
+9.1v
-9.lV
250 mv
(Adjust
the +15V cal poc-
enriomerer
R115 as shwn
in Figure
22.)
+0.4"
Zl.lV
7170 to LSOV)
+12v
+12v
70.3v
3.3v
d.
Ohma Calibracian.
Measure
the voltage
across
resistors
R1213 + R1214 (test
terminals
B and D as
sham
in Figure
22).
Adjust
the OHMS CAL potentiometer
(R1216)
fo:
1 vole +L m" using
voltmeter
(A).
e.
Analog
Range Calibratian.
(Check zero before
each measurement.)
h.
Clock Frequency
Adjust.
Locate
the CLOCK test
point
on the oscillator
board PC-217 as shown in
Figure
26.
Connect
a digital
frequency
counter
be-
1.
Voltage
Range.
Set the franc
panel
centrals
as shown in Table
6-3.
Apply
an input
voltage
in
Ween the CLOCK test
point
and 1~.
Adjust
trimming
decade steps
from 1V to 1OOV +0.02X.
Measure the
capacitor
C503 so that
the frequency
reading
is 120 k"z
analog
weput
at 51207 for
fuiL
scale
indication
on
kl
Hz for
instrumenta
operated
at 60 Hz.
(The crystal
each range.
The 1 volt
output
should
be within
Y501 should
be a Keithley
CR-L for
60 Hz; CR-2 for
50.2%.
50 Hz.)
The frequency
reading
should
be set to 100 kHz
+L Hz for
instrumenfs
operated
at 50 Hz.
2.
Amperes Range.
See the front
panel
controls
BS shown in Table
6-4.
Apply
an input
current
in
decade steps
from lo-LA
ta 10-11~.
MC¶SUFS
the analag
wtput
at 51207 for
full
scale
indicaeian
an each range.
Ihe 1 volt
output
should
be within
+0.5X
on LO-L,
to LU-6~ ranges:
+2X on LO-7A and
iO-8.4 ranges;
24%
on lo-9A
to 1OqlA
ranges.
3.
Coulombs Range.
See the front
panel
cantrols
as shown in Table
6-5
Apply
an input
currenf
in
decade steps
from LOe8A to.lO-11~
+0.4%.
Measure
the analog
output
at 51207 for
full
scale
indication
oxeach
range.
The output
should
integrate
to 1
volt
within
e period
of 10 seconds +1/Z second
(+5%).
4.
Ohms Ranges.
See the front
panel
controls
as
shown in Table
6-6.
Apply
resistance
values
at the
input
in decade steps
from 1050 to 10120.~ Measure
the analog
wtput
af 51207 for'full
scale
indication
an each ran e.
s
The 1 volt
output
should
be within
5.5%
an 10 n to 106n
ranges;
24% on 107~
to
1012~
ranges.
f.
Offset
current.
Set the front
panel
centrals
88 fallara:
Zero Check Button
-
Lock
Sensitivity
Switch
-
0.0000
Range Switch
-
LO-l1 Amperes
Feedback
Switch
-
Fast
Place
B cap on the input
receptacle
and adjust
the
zer'o control
88 necessary
for
B zero display.
on-
Lock the zero check button.
The digital
display
should
indicate
less
than 0.0005
x LO-11 amperes
(5
x
lo-l5A).
g.
Drift
Check.
Set the front
panel
controls
as
follows:
Zero Check Button
-
Lock
Sensitivity
Switch
-
0.0000
Range Switch
-
10-6 ~mperee
Feedback
Switch
-
Fast
Connect
recorder
(B) to the analog
output
(51207)
end set for
1 V full
scale
sensitivity.
Readjust
the zero control
as necessary.
Cannect
a 10 kilahm
resistor
(LX talerance;
Keifhley
R88-10K)
~croes
the
input.
Unlock
the zero check button.
Monitor
the
1 V autput
on the recorder
far
B 24 hour period
at
constant
ambient
temperature.
The recorder
output
should
not vary
more than LOX 0f full
scale
during
the 24 hour period.
0372
49
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