Instruction manual

Instruction Manual
760006-A
September 2001
Rosemount Analytical Inc. A Division of Emerson Process Management Appendices 11-11
Model NGA 2000 Platform
Analog I/O Module Track and
Hold Feature
An I/O Module function critical to certain
applications (such as CEMS) is the track
and hold feature.
The three "Output hold..." selections on
the Analog output Parameters menu refer
to the I/O Module capacity to maintain or
hold the output of the gas concentration
value despite a change in the state of the
Analyzer module.
If Output hold on validity: is enabled and
the state of the Analyzer module becomes
invalid, the last gas concentration value
measured during the valid state is held
and output from the I/O Module. When the
Analyzer module state returns to valid, the
gas concentration value is updated in-
stead of held.
If Output hold on maintenance: is enabled
and the state of the Analyzer module is
either maintenance or standby, the last
gas concentration value measured during
the valid state is held and output from the
I/O Module. When the Analyzer module
state returns to valid, the gas concentra-
tion value is updated instead of held.
If Output hold on calibration: is enabled,
three selections are available; Disabled,
Enabled and CEMS. These selections
operate as follows:
If Disabled, the gas concentration value
is updated while the Analyzer module is in
the calibration state.
If Enabled, and when the Analyzer mod-
ule is in the calibration state or the QC
check state, the last gas concentration
value measured during the valid state is
held and output.
If CEMS, and when the Analyzer module
is in the calibration state, the gas con-
centration value is updated throughout the
zero and/or span cycles. The calibration
factors are held until the calibration cycle
is over. Therefore the output responds to
the reading of the calibration gases using
the factors from the previous calibration,
as if the Analyzer were simply measuring
them rather than calibrating itself. Only
when the calibration cycle is over does
the Analyzer use the new calibration fac-
tors. This allows the user to determine
how much drift has occurred.
IO module ID: