LI-COR LI-830, User Manual

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Section 2. Configuring the gas analyzer
Instrument settings
Under
Instrument > Settings
, you'll find the
DAC
(digital-to-analog)
Outputs
(0 to
2.5 V, 0 to 5 V, and 4 to 20 mA), and
Other Options
, including the heater controls,
pressure compensation control, pump control, and the digital signal filter.
Configuring the DAC outputs
This section describes how to configure the voltage and current outputs. Both
voltage and current outputs are configured at the same time, in the same place:
l
DAC 1
configures
V Out 1
(pin 9) and
4-20 mA 1
(pin 13) on the terminal strip
l
DAC 2
configures
V Out 2
(pin 7) and
4-20 mA 2
(pin 11) on the terminal strip
Optimizing the DAC resolution
When configuring the analog outputs, keep in mind that the selected ppm range
will affect the resolution of data that is sent over the analog outputs.
Think of it like this: The 16-bit DACs can output a fixed number of values (65,536
to be exact). If a DAC is configured to output 0 to 5000 mV, you will have res-
olution of 0.076 mV per count.
2-1
With the 0 to 5 volt output range corresponding with a 0 to 20,000 ppm CO
2
con-
centration range, the finest change in concentration that can be resolved is equal to
0.31 ppm.
2-2
2-4 Using the LI-830 and LI-850 Gas Analyzers