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PPA55xx “KinetiQ” user manual
5.3
Zero compensation
There are 2 levels of zero compensation:
Trim out the dc offset in the input amplifier chain.
Measure any remaining offset and compensate.
The trim of the dc offset in the input amplifier chain can be
manually invoked with the ZERO key, or over the RS232
with the REZERO command. This dc offset trim measures
the dc present while the autozero switch is active and
applies an equal and opposite offset via a D/A converter so
that the input range to the A/D is optimised.
The measurement of the remaining offset also happens
when the offset is trimmed but is also repeated at regular
intervals. This is to compensate for any thermal drift in the
amplifier chain. The remaining DC offset is precisely
measured and stored so that the measurements can be
compensated by an appropriate algorithm in the
instrument firmware.
Real time measurement is not possible while the autozero
measurement is in progress so this repeated autozero
function can be disabled via the SYSTEM OPTIONS menu.
5-4