Specifications

g.
Verify that both the +INPUT and-INPUT of
the 1820/1822 are set to DC.
h.
Remove the output cable of the sine wave
generator from the oscilloscope input and
reconnect the cable to the female to female
input of the BNC adapter and cables attached
to the inputs of the 1820/1822.
i. Set the + Input Coupling of the oscilloscope
preamplifier to AC, GAIN to X100, Offset
Off, any bandwidth limiting controls to Off or
Full Bandwidth.
j. Set the oscilloscope to display channel 1 and
the vertical as necessary to measure the
amplitude of the displayed waveform.
Autozero the oscilloscope preamplifier if
necessary to keep the displayed trace on
screen.
k. The displayed signal is the Common Mode
Feedthrough multiplied by 100 by the
preamplifier.
I. Record the displayed Common Mode
Feedthrough amplitude to two digit resolution
in the Test Record as ’Common Mode
Feedthrough X100 at 70 Hz’.
m. Divide the result recorded in step 7-1 by 100
to determine the Common Mode feedthrough
at the output of the 1820/1822 under test.
n. Record this as ’Common Mode Feedthrough
at 70 Hz’ to two digit resolution in the Test
record. Keep all leading zeros or use
scientific notation.
o.
Calculate the Common Mode Gain by
dividing the Common Mode Feedthrough (in
laV) by 30,000,000 ~V. Record the result to
two significant places in the Test record as
’Common Mode Gain at 70 Hz’. (Keep all of
the leading zeros or use scientific notation.)
p.
Calculate the Common Mode rejection Ratio
(CMRR) at 70 Hz by dividing the Differential
Mode Gain at 70 Hz (I .0) by the Common
Mode Gain recorded in step 7-0.
q. Record the result as ’Common Mode rejection
ratio at 70 Hz’ to two significant places in the
Test Record. (Keep all of the leading zeros.)
r. CHECK -- That the CMRR at 70 Hz is
greater than 100,000:1 (I 00 dB).
s. Remove the sine wave generator output cable
from the female to female BNC adapter
t.
Reconnect the cable to the channel 2 input of
the oscilloscope.
4-9
1820/1822 Operator’s Manual
u. Set the oscilloscope to display channel 2, the
vertical scale to 5 mV/div and the horizontal
to 5 laV/div. If necessary, adjust the trigger
level for a stable display.
v. Set the sine wave generator to 100 kHz.
w. Adjust the output amplitude of the sine wave
generator to 30 Vp-p (6 divisions). Readjust
the oscilloscope trigger level if necessary to
maintain a stable display.
x. Remove the sine wave generator output cable
and reconnect it to the female to female BNC
adapter and cables attached to the 1820/1822.\
inputs.
y. Set the oscilloscope to display channel 1 (the
output of the 100X preamplifier driven by the
1820/1822 output signal), and the vertical
scale as necessary to measure the amplitude
of the displayed signal. Autozero the
oscilloscope preamplifier if necessary to keep
the displayed signal on screen.
z. The displayed signal is the Common Mode
Feedthrough multiplied by 100 by the
preamplifier.
aa. Record the displayed Common Mode
Feedthrough amplitude to two digit resolution
in the Test Record as ’Common Mode
feedthrough X 100 at 100 kHz’.
bb. Divide the result recorded in step 7-aa by 100
to determine the Common Mode Feedthrough
at the output of the 1820/1822 under test.
cc. Record the Common Mode Feedthrough
amplitude to two digit resolution as ’Common
Mode Feedthrough at 100 kHz’ in the Test
Record. Keep all leading zeros or use
scientific notation.
dd. Calculate the Common Mode Gain by
dividing the Common Mode Feedthrough (in
laV) by 30,000,000 InV. Record the result to
two significant places as ’Common Mode
Gain at 100 kHz’ in the Test Record. (Keep
all leading zeros or use scientific notation.)
ee. Calculate the Common Mode Rejection Ratio
(CMRR) at 100 kHz by dividing the
Differential Mode Gain at 70 Hz (1.0) by the
Common Mode Gain recorded in step 7-dd.
ff. Record the result as ’Common Mode rejection
ratio at 100 kHz’ to two significant places in
the Test Record. Keep all of the trailing
zeros.)
gg. CHECK -- That the CMRR at 100 kHz is
greater than 100,000:1 (100 dB).