Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 67)

Model 9110E Instruction Manual Operating Instructions
M9110E Rev B 53
A2 OUTPUT (NO): Output Signal = 4-20 mA (with current loop option)
A3 OUTPUT(NO
2
): Output Signal = 0 - 1 V
Output A4 can be set by the user to report one of many of the parameters accessible
through the keys of the unit’s SAMPLE mode display. A4 is not available for the
current loop option.
6.5.1. Physical and Analog Output Ranges
Functionally, the model 9110E NO
x
analyzer has two physical ranges for determining NO
x
,
NO and NO
2
concentrations. The difference between the two physical ranges is the
resolution of the output signals from the preamplifier board. Internally, the analyzer’s signal
resolution is about 16-bit or 72000 counts per 5 V PMT signal. The low range spans 0 to
2000 ppb NO
X
(2000 ppb = 5 V) whereas the high range spans 0-20000 ppb NO
X
(20000
ppb = 5 V). Both ranges need to be calibrated independently to the same span gases in
order to allow switching back and forth between high and low ranges. Once properly
calibrated, the analyzer’s front panel will accurately report concentrations between 0 and
20000 ppb, regardless of the selected analog range. To switch between physical ranges, the
user has to specify an appropriate analog output range from the front panel. Any analog
range between 0 and 2000 ppb will cause the analyzer to remain in the low physical range.
Any upper analog range limit between 2001 and 20000 ppb will cause the instrument to
operate in its high physical range.
For applications using chart recorders or other analog recording devices, such a wide range
can usually not be resolved on the output. For example, in an application where the
expected concentrations of NO, NO
2
and NO
x
are typically less than 500 ppb, the full scale
of expected values is only 0.25% of the instrument’s 20000 ppb physical range. The
corresponding output signal would then only be recorded across 0.25% of the range of the
recording device.
The M9110E solves this problem by allowing the user to select a reporting range for the
analog outputs that only includes that portion of the physical range that covers the specific
application. Note that only the reporting range of the analog outputs is scaled, the physical
ranges of the analyzer remain unaltered with the exception of the 2000/2001 ppb split. This
increases the reliability and accuracy of the analyzer by avoiding additional gain-amplifica-
tion circuitry. If properly calibrated, both the iDAS values and the concentration values on
the front panel are also unaffected by any change in analog output ranges.
6.5.2. Reporting Range Modes
The M9110E provides three analog output range modes to choose from.
• Single range mode (SNGL) sets all measured gases to the same output reporting
range.
• Independent range mode (IND) allows the reporting ranges for all gases to be
different.
• Automatic range mode (AUTO) gives the analyzer the ability to report data through
a low range and high range by automatically switching into the appropriate range as
the concentrations change.
Only one of the above range modes can be active at any time. To select output range types,
use the following key sequences.