Campbell Scientific CR9000X Measurement and Control System - Manual (Page 69)

Section 1. Installation
1.2.5 Safety Precautions
There are inherent hazards associated with the use of sealed lead acid batteries.
Under normal operation, lead acid batteries generate a small amount of
hydrogen gas. This gaseous by-product is generally insignificant because the
hydrogen dissipates naturally before buildup to an explosive level (4%) occurs.
However, if the batteries are shorted or overcharging takes place, hydrogen gas
may be generated at a rate sufficient to create a hazard. Because the potential
for excessive hydrogen buildup does exist, CSI makes the following
recommendations:
1. A CR9000X equipped with standard lead acid batteries should NEVER
be used in environments requiring INTRINSICALLY SAFE
EQUIPMENT.
2. When attaching an external battery to the CR9000X, insulate the bare lead
ends to protect against accidental shorting while routing the power leads.
3. When the CR9000X is to be located in a gas-tight enclosure or used in a
gas-tight mode with the standard ENVIRONMENTALLY SEALED
FIBERGLASS CASE, the internal lead acid batteries SHOULD BE
REMOVED and an external battery substituted.
1.3 Humidity Effects and Control
The CR9000X system is designed to operate reliably under environmental
conditions where the relative humidity inside its enclosure does not exceed
90% (noncondensing). Condensing humidity may result in damage to IC
chips, microprocessor failure and/or measurement inaccuracies due to
condensation on the various PC board runners. Effective humidity control is
the responsibility of the user and is particularly important in environments
where the CR9000X is exposed to salty air.
Two humidity control methods are:
1. the use of desiccant
2. nitrogen
purging
1.3.1 Desiccant
As a minimal precaution, the packets of HUMI-SORB desiccant shipped with
the CR9000X should be placed inside the case. These packets should be
routinely replaced. Obviously, the desiccant requires more frequent attention
in environments where the relative humidity is high.
1.3.2 Nitrogen Purging
Several CSI customers have had success in preventing humidity-related
equipment malfunctions in harsh environments by allowing nitrogen gas to
slowly bleed into the datalogger enclosure. The sensor leads, power cables,
etc. are routed to the terminal blocks of the datalogger through simple,
inexpensive conduit elbows which are left unplugged. A nitrogen bottle is
then left at the field site with its regulator valve slightly open so that nitrogen is
allowed to escape slowly through a rubber tube which is routed along with the
sensor leads through the conduit elbows into the CR9000X enclosure.
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