Fluke 8062A, Instruction Manual

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8062A
Instruction Manual
3-6
Read
2V dc
9R R
C
AZ
C
Integ
200 mV
dc
Integ
AZ
+
+
+
+
Reference
Voltage
Integrator Gain
Integrator Comparators
AZ
Integ or Read
To Digital
Control Logic
Buffer Amp
±
Unkown
Input Voltage
Internal to the MAC
dy26f.eps
Figure 3-2. Analog Portion of the A/D Converter
The measurement cycle begins with the autozero period. The AZ switches
close, applying a ground reference as the input to the converter. Under ideal
conditions the output of the comparator would also go to zero. However,
input-offset voltage errors accumulate in the buffer amplifier loop, and
appear at the comparator output as an error voltage. To compensate for this
error, the error is impressed across the AZ capacitor where it is stored for the
remainder of the measurement cycle. The stored level is used to provide
offset voltage correction during the integrate and read periods.
The integrate period begins at the end of the autozero period. As the period
begins, the AZ switches open and the INTEG switches close. This applies
the unknown input voltage to the input of the converter. The voltage is
buffered and then begins charging the INTEG capacitor. The waveform at
the INTEG capacitor is a ramp from near zero to some maximum value
determined by the amplitude and polarity of the unknown input voltage.