Annunciation

Some practitioners recognize that certain failures within equipment used in a safety instrumented function prevent the automatic diagnostics from correct operation. When reHabihty models are built, many account for the automatic diagnostics ability to reduce the probabihty of failure. When these diagnostics stop working, the probability of dangerous failure or false trip is increased. While these effects may not be significant, unless they are modeled, the effect is not known. 

An annunciation failure is therefore defined as a failure that prevents automatic diagnostics from detecting or annunciating that a failure has occurred inside the equipment. Note that the failure may be within the equipment that fails or inside an external piece of equipment designed for the purpose of automatic diagnostics. These failures would be classified as Fail-Safe in the definition provided in lEC 61508. 

---

The alarm occurs. This usually activates an audible annunciator. 

The alarm occurrence is acknowledged by the process operator. When all alarms have been acknowledged, the audible annunciator is silenced. 

Another serious distraction to a process operator is the multiple alarm event, where a single event within the process results in iTuuti-ple alarms. When the operator must individually acknowledge each alarm, considerable time can be lost in silencing the obnoxious annunciator before the real problem is addressed. Air-handling systems are especially vulnerable to this, where any fluctuation in pressure (for example, resulting from a blower trip) can cause a number of pressure alarms to occur. Point alarms (high alarms, low alarms, status alarms, etc.) are especially vulnerable to the multiple alarm event. This can be addressed in one of two ways ... 

ISA S18.1. 1989. Annunciator Sequences and Specifications. (ANSI approved.) Instrument Society of America, Research Triangle Park, N.C. 

Control wiring Wiring from supervisory or annunciator devices to the terminal blocks may be carried out with smaller wires, as may be recommended for such devices. However, they should run through separate wire bunches, and not through the bunches of control wires for easy identification and to remain unaffected by heat of control wires. 

Some oi all of the fallowing alarms and annunciations may be provided on the AMF panel, depending upon the size of the DG set and the type of load it has to feed to forewarn the operator, and prevent a trip ... 

Figure 16.11 illustrates a general arrangement of such an AMF panel and the above alarm and annunciation provision.s. 

Figure 16.10 Typical control and annunciation scheme for an AMF panel...

Annunciation control (for low pressure alarm, high pressure alarm and operation ot the safety valve etc.)... 

Safety systems are typically divided into emergency trip/shutdown functions, controlled (slow) shutdown, alarm activation, or startup annunciation of auxiliary equipment such as oil pumps. 

Breakdown maintenance means no preventive maintenance (i.e., failure is annunciated by the fact of failure). 

Annunciator panels should be in a central location with alarm annunciators and shutdown annunciators grouped separately. The first alarm and the first shut-down normally sound a horn and are annunciated. This is called first-out indication. Subsequent shutdown or alarm signals received by the panel are either not annunciated or are annunciated in a different manner so that the operator can determine the initiating cause of the process upset. 

Annunciators 1- Catastrophic a. Operates Spuriously b. Fails to Operate on Demand 2- Degraded a Operates at Low Intensity 3- Incipient a Arcing... 

RP18.1 Specifications and Guides for the Use of General Purpose Annunciators... 

My new friend gave me the names of establishments where the drinking was best. They included Eleven 79 on Annunciation Street, owned by a gentleman named Joe Segreto, who is also a sometime filmmaker. 

Alarms are used to alert operators of serious, and potentially hazardous, deviations in process conditions. Key instruments are fitted with switches and relays to operate audible and visual alarms on the control panels and annunciator panels. Where delay, or lack of response, by the operator is likely to lead to the rapid development of a hazardous situation, the instrument would be fitted with a trip system to take action automatically to avert the hazard such as shutting down pumps, closing valves, operating emergency systems. 

An alarm system consists of sensors that detect different types of events an arming station that is used to turn the system on and off a control panel that receives information, processes it, and transmits the alarm and an annunciator that generates a visual and/or audible response to the alarm. When a sensor is tripped it sends a signal to a control panel, which triggers a visual or audible alarm and/or notifies a central monitoring station. A more complete description of each of the components of an alarm system is provided below. 

An annunciator responds to the detection of an event by emitting a signal. This signal may be visual, audible, electronic, or a combination of these three. For example, fire alarm signals will always be connected to audible annunciators, whereas intrusion alarms may not be. 

Once a sensor in an alarm system detects an event, it must communicate an alarm signal. The two basic types of alarm communication systems are hardwired and wireless. Hardwired systems rely on wire that is run from the control panel to each of the detection devices and annunciators. Wireless systems transmit signals from a transmitter to a receiver through the air—primarily using radio or other waves. Hardwired... 

---