Alarm systems characteristics

In two of the eight criticality accidents that are known to have occurred in processing fissionable material, lives were saved because criticality accident alarm systems were installed. The American National Standard Criticality Accident Alarm System provides guidance regarding the need for alarm systems, characteristics of such systems, maintenance and test programs, alarm characteristics, and emergency planning. 

It is important to notice that H2S loses its characteristic smell at about 50 ppm, and, therefore, no direct possibility for its detection exists. The density of H2S is slightly higher than that of the atmosphere (relative density 34/29). Therefore, H2S has a tendency to accumulate in, for example, pumping stations and manholes. As it is typically not detected by its smell at those concentrations, where it is life threatening, instruments or alarm systems for its monitoring must generally be used when working in sewer systems. 

The basic characteristics of chemical sensors and biosensors—including high specificity and sensitivity, portability, real time output, cost effectiveness, and user friendliness—make them applicable to virtually every major product market. The immediate market targets for these sensors are in medical diagnostics, detection and alarm systems, environmental monitoring, and food processing. Future markets include application of chemical sensors and... 

Heat is the most obvious choice of a characteristic by which a fire can be automatically recognized. In the section on fire suppression systems, the fusible links in the sprinkler heads represented one type of heat detector. Alloys have been developed that will have reproducible melting points. When the temperature at the detector site exceeds the melting point of the alloy, contacts are allowed to move so that the device can either make or break a circuit, just as with a manual alarm system. There are plastics which can perform in the same manner. Fixed temperature systems are very stable and not prone to false alarms, but are relatively slow to respond. There are several other versions of these fixed temperature detectors, including bimetalhc strips, where the differential rate of expansion of two different metals causes the strip to flex or bend to either make or break the contact. Others depend upon the thermal erqransion of hquids. 

ABSTRACT Paper presents problems connected with reliability analysis of the electronic protection systems, with the special regard to the intruder alarm systems. It is presented division of the intruder alarm systems these systems with regard of their structure, and then the analysis for the system with mixed, three branches reliability structure with eventuality of the simultaneously damage of the parallel branches. Utilization of the analysis of reliability structures makes possible the enlargement of the values of the reliability coefficients of the designed systems by accomplishment of the analyses and simulations which allow to select the optimal system structure with regard to the user requirements as well as the characteristics of the protected object (e.g. location of the protected objects in terrain, distances between buildings, etc.). 

The criticality accident diat is expected to be signaled by the alarm system may have widely varying characteristics, depending bn the form and type of fissile material and oh the initiating mechanism. Solution accidents, clearly the most probable for process areas, have a rise time limited by the neutron lifetime, which is on the order of milliseconds. While accidents involving metal or dry compbunds are easier to avoid, the shorter neutron lifetime and faster rise time of the excursion lead to much... 

The alarm standard addresses the need for alarm systems and also characteristics of alarm signals, dependability, testing procedures, and emergency planning. Appendixes are concerned vdth supporting the selection of a minimum accident of concern and with calculations of the radius of coverage of a detector. 

The International Standards Organization has under development a document directed toward criticality alarm systems, while the International Electrotechnical Commission is preparing guidance for the characteristics of the equipment used in these systems. 

The basic characteristics of alarm systems have already been covered at length in Chapter IX. Since an alarm is one of the most fundamental issues in a control system, it will be discussed here again in this context. In this clause, focus will be on independent alarm systems that can be applied to critical applications independently of a programmable logic controller/distributed control system (PLC/DCS). In spite of so much technological developments and modem instrumentation and... 

Mallory also supply a mercury-cadmium battery in their Duracell range. This battery (No. 304116) is of 12.6 V with a capacity of 630 mA h to an end-point of 10.3 V, or 900MA h to an end-point of 7.0 V, both on 13 000 Q at 20°C. This cylindrical battery weighs 127 g and occupies a volume of 40.5 cm and is recommended for use in applications such as alarm systems using voltage-sensitive low-battery indicators. Typical two-step discharge characteristics for this battery are shown in Figure 8.3. 

The CED range is used for communications, telecommunications, security and fire alarm systems, and low power control loads with long time periods. The electrical characteristics of this range are presented in Tables 51.52 and 51.53. 

Using the system shown in Figure 11-24, draw the fault tree and determine the failure characteristics of the top event (vessel overflows). In this problem you have human intervention that is, when the alarm sounds, someone turns off valve 7. 

Generally, the performance characteristics of greatest interest for an explosives detection system are sensitivity, selectivity, and response time. As used here, sensitivity is the ability to detect the target analyte in extremely small concentrations, while selectivity is the ability to distinguish the target analyte from other materials that may be present. In combination, good sensitivity and selectivity mean a high probability of detection when the analyte is present and a low false alarm rate when the analyte is not present. 

In military operations, where CW attack is anticipated as a result of intelligence, detection systems are used which alarm when the presence of one or more identified hazards is detected. A number of physical characteristics of the agents may be used for this, such as ion drift, infrared spectroscopy and mass spectrometry (Box 1). 

The example shows, that a fault can be detected based on a fast detection of deviations of the characteristic features as well as the analysis of their values with heuristic rules. As soon as the value of a feature is not within its limits rules will produce a hypothesis that a certain disturbance has been detected (symptom recognition). The presence of a hypothesis activates additional rules to diagnose the cause of the disturbance and to verify or falsify the hypothesis. The recognition of symptoms caused by faults is the ultimate goal of the knowledge-based system, so it can alarm the operator immediately. However, the analysis of the symptoms and the identification of the specific faults is also of great importance. A fundamental problem is to distinguish between faults that reveal themselves in the same or in similar symptoms. 

The second approach focuses on typical situations involving different falsepositive system actions as well as a false-negative system action (i.e., missed alarm). These are the acceptance situations mentioned in the previous section. Key characteristics are subjective ratings on acceptance of the false alarm and perceived hazard of the situation. 

Alarms are provided as part of the "human engineered" control complex (see CESSAR-DC, Chapter 18) and are included in the plant computer annunciator systems. After passing through the alarm unit, the amplified accelerometer signals are multiplexed, filtered, digitized, and transmitted to a computer for further analyses. The computer maintains data storage, performs comparisons, develops trends, and performs analyses to enhance the signal characteristics. 

Table 5.5 lists the key characteristics of the fuel cell system. The RS232 communication port is used because this is the type of port used by telecommunications stations. Some warning actions had two sets of values one set for less-severe situations that triggers the warning alarm but does not shut down the fuel cell system the other set is for more severe situations that trigger the warning alarm and shut down the fuel cell system. If the fuel cell system is not able to shut down when the severe values are reached, the fuel cell system or the load it powers can be damaged. 

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