Section 2. Power On
The LI-840A can be connected to a constant source of AC power using a transformer that
provides 12-30VDC (14 watt maximum) to the LI-840A. If the LI-840A is powered with a voltage
below 10.5 volts, the analyzer will not power up, and the Low Battery LED on the top panel will
illuminate. The LI-840A will continue to operate with a low battery; there will, however, be a cor-
responding reduction in performance.
Alarms
The LI-840A is equipped with high and low alarms, which can be configured as open collector
or 0-5V output (TTL levels) using jumpers on the main PC board ( above). The default con-
figuration is 0-5V output. Figure 2-2 on page2-3 shows the position of the jumpers for each of
the two alarm conditions.
Note: The alarms can be used for either CO
2
or H
2
O concentrations; only one can be chosen
at a time, however.
Section 2. Power On 2-1
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