Emerson NGA2000 Reference Manual page 111

NGA2000 Reference
RAW_SIGNAL
Direction
Binding
Type
Value range
Units
Description
Usage
See also
REF_DUTY_CYC
Direction
Binding
Type
Value range
Units
Description
Usage
See also
RNGHI
Direction
Binding
Type
Value range
Units
Description
Usage
See also
Rosemount Analytical Inc. A Division of Emerson Process Management
Output
None
Floating point
Between 0 and 220; typically around 550,000
None
The signal from the ADC, filtered by AFT90_ and the median filter if any.
The raw signal from the physical hardware, although filtered. Used to determine
whether the signal is making sense or not, since the user may have calibrated the
analyzer incorrectly. Analyzers with 20-bit ADC's have a typical value on zero gas
around 500,000, whereas the 16-bit ADC in the CLD has an output on zero gas of
around 32,000. A span gas of value close to the MAXRANGE should give a
RAW_SIGNAL of about 800,000 to 1,000,000. Anything else indicates some kind of
problem. At the least, the span gas should give a value significantly different from the
zero gas value, if it does not, there is probably an error in the choice of gases, or the
analyzer physics is inoperable, as for example in the case of a FID whose flame is
out.
DET_SIG
Bidirectional
None
Floating point
Typically 0.2785
None
CLD only; the temperature compensation offset term
The CLD uses the duty cycle of the sensor block controller to determine the
temperature of the analyzer as a whole. This is used to compensate the PVA value.
This variable is used to provide the offset term in this compensation.
Analyzer: bidirectional; I/0 module: input
RNGHI
4-element floating point array
Between 0 and MAXRANGE
ppm
The upper range end points, element 1 being the upper end point for range 1 etc.
The range definition, together with RNGLO. RNGHI cannot be edited higher than
MAXRANGE or lower than MINRANGE using the control module, and should not be
made so through a PC either. It is possible to set the higher ranges of lower value
than the lower ranges, but doing so will confuse any auto-range change algorithm.
The resolution of the analyzer is not directly affected by the choice of range in most
cases, except for the FED which changes a range resistor between certain settings.
However the output resolution is affected, as is the operation of a. linearizer
algorithm.
RNGLO
MAXRANGE
MINRANGE
Reference Manual
748384-C
September 2003
Analyzer Variables 2-49