Annunciation System Alarm AnnunciatorPublished on 24/2/2012 & updated on 30/8/2018
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What is Alarm Annunciator?It is basically an audio visual warning system, which highlights the fault or mishap which is going on, or even before it happens. This is very necessary for safety concern also, and sometimes the warning comes before improper procedure which warns the operator to avoid unwanted accident etc. This is the basic concept of Alarm Annunciator, and the alarm annunciation system. Let us look at the operation of a typical alarm annunciator device.
Operation of Alarm Annunciator
Alarm Annunciation SystemIn order to understand the fundamental operation and connections of alarm Annunciator, we have to understand the basic concept of alarming system in process monitoring. Suppose, an electromagnetic coil is energized by power supply and acts as an electromagnet for certain application. Now, because of over voltage a portion of the coil has been burnt. As a consequence, the entire process associated with it gets hampered. So, when finding the very cause of this mishap, you have to check each and every part of the system in order to find and recognize the actual fault. Now think you have 50 such coils, which you have to monitor. In this case finding the actual faulty coil becomes very difficult and time consuming too.
But if you connect a bulb in series with the power supply of each coil, it glows if and only if the coil is energized and healthy. In this way, for 50 such electromagnetic coils you need to use 50 bulbs each of them connected in series with each of the individual coil through which you can monitor the processes by viewing the glow status of those bulbs. This is the basic and easiest model of process monitoring. Alarm Annunciator is a centralized model, which gives audio visual signals for the faulty processes. Latest models of annunciators are based upon microprocessor or microcontroller circuitry, which ensures the maximum reliability as well as enhanced wide ranges of features and functionalities.
Connection of Alarm AnnunciatorThere are two types of connections for each annunciation system; they are input fault contacts and output relay changeover contacts. Input fault contacts are simple connection normally open (or NC Selectable) with respect to a common C contact. Usually these input fault contacts are potential free contacts. The logic is, if any fault contacts and the common contact C becomes short circuited by any means, the respective fascia or fault window will start blinking, and the output relay contact will changeover instantly.
Suppose, you are using 8 windows annunciation system, which means you are monitoring 8 operations at a time, by the annunciation system. Let us think your fault 1 (F1) is assigned as over voltage alarm of motor 1 and your fault 2 (F2) is assigned as overheating of a motor 2 armature. You will connect an over voltage relay with motor 1 and a PTC thermistor relay with Motor 2, and the respective outputs (Normally open output, changes to close when faulty) of those relays will be connected across F1 (fault input) and C (common), and F2 (fault input) and C (common) of the annunciator system. Therefore, if the voltage of motor 1, is increased beyond the predefined safe level, the over voltage relay will operate and will make a closed loop between F1 and Common. So, the F1 window will start blinking which indicates the motor 1 is getting over voltage. At the same time, the annunciator relay will changeover, and if you connect a hooter previously with its output contacts, then the hooter will start alarming.
Similarly, if the armature temperature of motor 2 is increased beyond the predefined safe level, then the PTC thermistor relay will changeover and will make a loop path between F2 and Common C of annunciation system. So, the F2 window will start blinking which indicates the motor 2 is getting over heated. At the same time, the annunciator relay will changeover, and the hooter connected with its contacts, it will start alarming. Basically, the annunciator output relay changeover is common, irrespective of any faults. A single hooter is used for all fault windows. An auxiliary AC/DC supply is necessary to operate the annunciator and in modern annunciators, there is also a window and connection provided for monitoring its own auxiliary supply. Modern Alarm Annunciators consist of a power supply unit SMPS, a programming unit CPU and other connections including fault contacts and facial display units. The blinking windows are generally acrylics, which are enlightened by LED with very low power consumption. Typically, annunciation effectively starts from 4 faults that is 4 windows, if the number of faults to be monitored is more than 64, it is preferable to install the programming unit CPU, power supply unit PSU and the display facial unit individually, which ensures the maximum accuracy and effectiveness.
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