Theory of Operation—
DM 5010
EXTERNAL
CONNECTORS
2994-10
Fig. 4-2. Simplified overvoltage protection and function switching.
DCV SIGNAL CONDITIONER
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The
DCV Signal Conditioner provides range-dependent
gain
for the
various
de mode-dependent signals applied to it.
Figure
4-3
shows a simplified diagram of the buffer
amplifier
Table
4-1 shows the states of the buffer amplifier.
Table 4-1
DCV
SIGNAL CONDITIONER GAIN SETTINGS
FET
Gain
of
the Buffer Amplifier
Switch
10
1
0.1
Q1105
ON
OFF
OFF
Q1106
OFF
OFF
ON
Q1112
OFF
ON
ON
Q1114
ON
ON
OFF
gain
of the buffer amplifier is set depending on
which of the
FET
switches are turned on by a high at their gates.
Feedback
to
the inverting input of the operational amplifier
is through
either
Q1112 or Q1105
while forward attenuation
of the signal to the
A/D converter is determined
by Q1114
for
Q1106.
Diodes
CR1221 and CR1223 prevent
overdriving the buffer amplifier.
To ensure linear
response of the buffer amplifier over its
input
range,
a bootstrap buffer is used to make the buffer
amplifier supply voltages track its input. This has
the effect
of
making U1210 operate at the middle of its range, avoiding
the
linearity problems encountered when the output ap
proaches one of the supply
voltages. By making the gate
bias of
the
various
FET switches also track the input volt
age, proper
bias is maintained
and current leakage through
the FETs
(and thus the associated error) is minimized. A
simplified schematic of the
bootstrap buffer is shown
in Fig.
4-4.
The
Function Switch directs the mode-dependent de level
to the
noninverting input of U1210, the buffer amplifier. The
The input to the
bootstrap buffer, pin 3 of U1110, is
con
nected to the inverting input of U1210 and is therefore at the
4-6
ADD JAN 1982
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 337: ...63 REV JUN 1986...
Page 338: ...FIG 1 EXPLODED DM 5010...
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