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Operating Instructions Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 90
6.8.1. Physical Range versus Analog Output Reporting Ranges
Functionally, the Gas Filter Correlation CO
2
Analyzer has one hardware Physical Range that is capable of
determining CO
2
concentrations between 50 ppm and 2,000 ppm. This architecture improves reliability
and accuracy by avoiding the need for extra, switchable, gain-amplification circuitry. Once properly
calibrated, the analyzer’s front panel will accurately report concentrations along the entire span of its 50
ppm and 2,000 ppm physical range.
Because, most applications use only a small part of the analyzer’s physical range, the width of the Model
GFC 7000TA’s physical range can create data resolution problems for most analog recording devices.
For example, in an application where the expected concentration of CO
2
is typically less than 500 ppm,
the full scale of expected values is only 25% of the instrument’s 2,000 ppm physical range. Unmodified,
the corresponding output signal would also be recorded across only 25% of the range of the recording
device.
The GFC 7000TA solves this problem by allowing the user to select a scaled reporting range for the
analog outputs that only includes that portion of the physical range relevant to the specific application.
Only the reporting range of the analog outputs is scaled, the physical range of the analyzer and the
readings displayed on the front panel remain unaltered.
6.8.2. Reporting Range Modes
The GFC 7000TA provides three analog output range modes to choose from.
Single range (SNGL) mode sets a single maximum range for the analog output. If single range is
selected (See Section 6.78.3) both outputs are slaved together and will represent the same
measurement span (e.g. 0-50 ppm), however their electronic signal levels may be configured for
different ranges (e.g. 0-10 VDC vs. 0-.1 VDC – See Section 6.9.4.1).
Dual range (DUAL) allows the A1 and A2 outputs to be configured with different measurement
spans (See Section 6.8.4) as well as separate electronic signal levels (See Section 6.9.4.1).
Auto range (AUTO) mode gives the analyzer to ability to output data via a low range and high range.
When this mode is selected (See Section 6.8.5) the GFC 7000TA will automatically switch between
the two ranges dynamically as the concentration value fluctuates.
Range status is also output via the external digital I/O status outputs (See Section 6.15.1.1).