General Information 1-3
January 2008
A Typical Application Heavy-duty electricity generators are typically cooled with hydrogen
gas to maximize generator efficiency. The hydrogen gas level is
continuously monitored, at both ends of the generator. An XDP
system with a remote transmitter is ideally suited for this service.
During normal operation, the hydrogen gas must be monitored for the
presence of air, which would create an explosion hazard. Then, in
preparation for a maintenance shutdown, the hydrogen gas is purged
with carbon dioxide gas before the chamber is opened up and exposed
to air. At the conclusion of the maintenance work, the chamber is
resealed and the air is purged with carbon dioxide. Finally, the carbon
dioxide is purged with hydrogen prior to resuming operation. Thus, at
various times, the following gas mixtures must be monitored:
• 70-100% hydrogen in air
• 0-100% hydrogen in carbon dioxide
• 0-100% air in carbon dioxide
GE Sensing offers several transmitters that are well suited for
operation in all of these environments, and the XDP has been
designed to permit quick and easy switching between the analysis and
display of these three gas mixture inputs.
Alarm Settings When factory-configured for this typical application, the XDP’s built-
in alarms are set up as follows:
• XDP Normal Alarm: failsafe, tripped if:
a. active curve is not H2/AIR
b. field calibration is in progress
c. any built-in error condition occurs
d. power to the XDP is interrupted
• XDP Fault Alarm: failsafe, tripped if:
while in measurement mode:
a. any error condition, except Low H2 or Low-Low H2, occurs
b. power to the XDP is interrupted
or
while in calibration mode:
a. ADC is out of range, mA input under/over range error occurs
b. power to the XDP is interrupted
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