A/D Measurement Cycle - Fluke 8062A Instruction Manual

True-rms multimeter

Table of Contents

Waveform at

the Integ

Capacitor

As the read period begins, the INTEG switches open and the READ switches

close. This applies the known reference voltage from a "flying" capacitor

whose polarity is chosen by the a/d converter to be the opposite of the

polarity of the unknown input voltage. The INTEG capacitor begins

discharging at a fixed rate while a counter begins counting. The counting

stops counting when the INTEG capacitor voltage equals the initial autozero

voltage. The count is proportional to the unknown input voltage, and is

placed on the display by the microcomputer.

If during the read period the counter counts up to the maximum number of

counts for a full-scale reading (19999 counts) and the INTEG capacitor

charge has not yet reached the initial autozero voltage, the microcomputer

knows an overrange reading has been taken. The microcomputer places

"OL" on the display and commands the a/d converter to go into the overload

(OL) period which rapidly slews the integrator voltage back to the initial

autozero voltage.

The measurement cycle ends at the end of the read period for an on-scale

reading, or at the end of the overload period for an overrange reading. A new

measurement cycle then begins with the autozero period. The display update

rate for measurement functions that use the a/d converter is approximately

0.4s, or about 2-1/2 readings per second.