Theory of Operation—DM
5010
input
BUFFER
2994-13
Fig. 4-5. Simplified charge-balancing converter.
Figure
4-7
illustrates the currents at the summing
node
when
the
zero-reference is being set.
The node current from
the
Converter Input buffer, U1
120, may be ignored since it is
very small during the Auto-Zero period.
As the
Auto-Zero period
begins,
a
counter in the Timing
Logic
is
set to zero.
The
Reference Buffer input is then
toggled by TO
and T8 with a 50% duty cycle between
and
ground, injecting an average current l^ in equal to
+
V<ef/ (2 X R1231)
into the summing node. The Integrator
produces
a
voltage output to the Auto-Zero Buffer.
The
Auto-Zero Buffer
sinks
current, via R1233, of opposite po
larity to
the current
injected by the Reference Buffer until
the
current removed
from the node balances the current being
injected.
This is the
equilibrium state,
and the voltage
waveform
at the input of the Auto-Zero Buffer is that re
quired
to
precisely track the injected current input. Resistors
R1139,
R1227,
and
capacitor C1139 at the Auto-Zero Buff
ers
input integrate the integrator output waveform over a
preset
number of
measure intervals.
The negative Auto
Zero
Buffer output voltage across
R1233 generates a cur
rent equal
in magnitude but of
opposite polarity to the
average injected reference current.
The averaged voltage at
the
input of the
Auto-Zero Buffer is the zero-reference volt-
ADD
JAN
1982
4-9
Summary of Contents for DM 5010
Page 14: ...DM 5010 2994 00 DM 5010 Programmable Digital Multimeter xii ADD JUL 1986...
Page 27: ...Operating Instructions DM 5010 2994 03 Fig 2 3 DM 5010 front panel controls and connectors 2 3...
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Page 251: ...Section 8 DM 5010 OPTIONS No options are available 8 1...
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Page 272: ...DM 5010 2994 37 Fig 10 2 Location of DM 5010 adjustments and test points...
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Page 276: ...DM 5010 2994 112 DM 5010 BLOCK DIAGRAM...
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Page 337: ...63 REV JUN 1986...
Page 338: ...FIG 1 EXPLODED DM 5010...
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