GE Hydran 201i, Инструкция по эксплуатации

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Operating Methods
Part 17997 Rev. 6, March 2011 11-3
11.1.3 Analog Output Monitoring
The analog output monitoring (gas level monitoring via the analog output) solves the disad-
vantages of the alarm monitoring method (Section 11.1.2 on page 11-2) as follows:
• Connecting the analog output to a SCADA system. The Hydran 201T i and the
Hydran 201C i -1 both have analog outputs that allow to monitor the gas level evolution.
• Using a SCADA system to generate alarms based on the collected data.
• Periodic, visual reading (weekly) of the gas level on the display of the H201T
i ’s or the
H201C i -1. For details on the various methods of data reading, see Section 11.2 on
page 11-5.
It is recommended to use a SCADA system that offers the following advantages:
• Gas level reading from the control room.
• Regular processing data analysis.
• Detection of gas and fail alarms when the specified alarm conditions are present. The
system’s response time must be short enough for the application’s needs.
• Safe storage of historic data in a format that allows easy analysis from a host computer.
11.1.3.1 Method Drawbacks
Analog outputs have the following disadvantages:
• Analog outputs are generally sensitive to electric noise. A 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 201
i 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.