Trend alarm

A computer-based system for facility management, control, and data archiving is useful for identifying critical systems that may require maintenance, as well as trending alarms and environmental data for routine review. ... 

In the Fieldbus example, the Asset Management System converts the standard Fieldbus descriptor (in device descriptor language [DLL]) to a D-COM object. This is then passed to OCS where it is converted from D-COM into the OCS s own object model. This is so that the relevant parts of the Fieldbus device descriptor can be distributed to the various OCS nodes for display, trending, alarm purposes and so on. The OCS then uses its OMM to transfer the data to the OCS controller, where it is again converted to DLL format prior to sending across the Fieldbus link to the intelligent instrument. 

Systems sueh as the EDS use a dual mieroproeessor system. As ean be seen in Figure 4-93, eritieal parameters of memory, input/output, alarm/trips, and host eomputer eommunieation are handled in the main proeessor. To maintain fast response time, this proeessor is kept free of less eritieal tasks sueh as operator interfaeing, trending, and arehiv-ing. A seeond proeessor, an administrative CPU, is used for these less eritieal yet important tasks. 

The software employed for the eritieal elements (memory, alarming, tripping, and eommunieating with the host eomputer) uses a real-time operating system and resides in the main CPU. The administrative CPU employs multitasking software that performs important tasks sueh as modem eommunieation, trending, and arehiving. 

The only useful function of broadband analysis is longterm trending of the gross overall condition of machinery. Typically, sets of alert/alarm limits are established to monitor the overall condition of the machine-trains in a predictive maintenance program. However, this approach has limited value and, when used exclusively, severely limits the ability to achieve the full benefit of a comprehensive program. 

Unlike broadband data, narrowband data provide the ability to directly monitor, trend, and alarm specific machine-train components automatically by the use of a microprocessor for a window of frequencies unique to specific machine components. For example, a narrowband window can be established to directly monitor the energy of a gear set that consists of the primary gear mesh frequency and corresponding side bands. 

The system should be able to establish the norm based on trends developed over time. However, the analyst must establish the level of deviation that triggers the alarm. The level of deviation in rate depends on the mechanical condition of each machine-train. For a new machine in good operating condition, the limit is typically set at two... 

The added capability of calculating unknown values based on measured inputs will greatly enhance the system capabilities. For example, the neither fouling factor nor efficiency of a heat exchanger can be directly measured. A predictive maintenance system that can automatically calculate these values based on the measured flow, pressure and temperature data would enable the program to automatically trend, log and alarm deviations in these unknown, critical parameters. 

The method of establishing and using alert/alarm limits varies depending on the particular vibration monitoring system that you select. Normally these systems will use either static or dynamic limits to monitor, trend and alarm measured vibration. We will not attempt to define the different dynamic methods of monitoring vibration severity in this book. We will however provide a guideline for the maximum limits that should be considered acceptable for most plant mechanical equipment. 

Data is recorded in two disk files. All measured process variables are periodically recorded in a trend table. A historical log records the beginning and end of execution of each command, alarms, and notations entered by the operator. 

Stand alone fire or gas detection and alarm panels are normally provided in the main control facility for the installation. Recent trends also incorporate the transmittal of fire and gas alarms through the DCS into the main process alarm real time control panel. When alarm panels are located within a protected building, they should be located for easy access for emergency response personnel and proximity to manual electrical power shut off facilities. 

The most alarming trend with regard to cocaine has been its rapid rise in Europe over the last few years. For the year 2005, 16 countries reported rising levels of cocaine use, 24 a stabilization and only four countries reported a decline. 

Fig. 7.108. Typical DCCS video displays (Kent P4000 system) (a) overview of data highway (b) plant overview as mimic diagram (c) alarm summary (d) unit (group) display (e) historic and current trends...

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