Combined Alarm And Analog Output Monitoring - GE Hydran 201i Instruction Manual

1.1.1.14 Method Drawbacks
Analog outputs have the following disadvantages:
• Analog outputs are generally sensitive to electric noise. Special software must
be used to compute the gas hourly and daily trends using "noisy" data.
• It is not possible to detect analog outputs that are out of calibration.
• An industrial-grade analog input and cables are necessary for each Hydran
201i System.
• Analog outputs carry only one type of information in only one direction: The
level of dissolved gases in oil.
• In the following cases, the trend computations are interrupted and cannot be
restarted before enough data are available again. For a 30-day trend, this
represents a long time.
- The analog output cable is broken.
- The host computer loses contact with the analog output signal.
- The host computer becomes "unavailable."
Because of the above considerations, it is difficult to implement a reliable gas-trend
alarm system based on the analog output signal.
1.1.1.15 Conclusion
Because of the above limitations and because it is not possible to change the Hydran
201i System's parameters from the control room, we can conclude that the analog
output monitoring method (gas level monitoring via the analog output) still requires that
a host computer be connected to the Hydran 201Ci Controller to retrieve the Hydran
201Ti's historic data and modify parameters.

12.1.4 Combined Alarm and Analog Output Monitoring

As the name implies, this method combines the two previous monitoring methods.
The major advantage of this method is its familiarity. Its limits become apparent when
one reads the text on the two previous methods:
• Although the gas level, the gas alarms (gas level, hourly trend and daily trend)
and fail alarm are now available at the same time, important information is
still confined to the Hydran 201Ti.
• Accessing the H201Ti is still required to modify operation parameters.
• The amount of cabling becomes an important issue. For each H201Ti, a
minimum of four pairs of wires is required to connect the analog output, the
two gas alarms and the fail alarm. To receive this information, three digital
inputs and one analog input must be available in the SCADA system.
Page 174
Hydran* 201i Instruction Manual
MA-033 Rev. 14.0, 12-Nov-18