- Annunciation System Definition: An annunciation system is a setup that uses devices to announce faults or unusual activities in an electrical or electronic process.
- Alarm Annunciator: An alarm annunciator is an audio-visual system that alerts operators to faults or potential issues, enhancing safety.
- Annunciator Relay: The annunciator relay changes over to activate alarms when faults are detected, ensuring timely warnings.
- Monitoring Faults: Connecting monitoring devices like overvoltage relays or PTC thermistor relays to an annunciator system helps detect and signal faults efficiently.
- Modern Annunciator Components: Modern annunciators use power supply units, programming units, and LED display units for efficient, low-power fault monitoring and indication.
In an electrical or electronic plant an Annunciator is a panel that announces a fault or an unusual process state so the operator can see which point has gone abnormal.
What is Alarm Annunciator?
An alarm annunciator is an audio-visual warning. A window flashes and a horn sounds when a field contact changes state. The operator can then act before the fault becomes an accident. ISA-18.1 defines the usual flash, horn and acknowledge sequence. The rest of this page describes one typical panel.
Operation of Alarm Annunciator
Alarm Annunciation System
Start from a simple monitor. An electromagnetic coil is energised from a supply. If overvoltage burns the coil, that process stops. Walking the plant to find which coil failed takes time, more so if you have fifty coils to watch.
Wire a lamp in series with each coil supply. The lamp glows while that coil is energised and intact. One lamp per coil then shows the state of fifty coils on a local board.
An alarm annunciator brings those points to one panel as flashing windows and a horn. Modern units use a microprocessor or microcontroller so sequences, first-out and grouping can be programmed.
Connection of Alarm Annunciator
Each system has two connection groups: input fault contacts and output relay change-over contacts. Each input is a normally-open contact, or a selectable NC, to a common C. Those inputs are usually potential-free (dry). When a fault contact shorts to C the matching fascia window flashes and the common output relay changes over at once. Acknowledge then silences the horn and holds the lamp steady until the process returns to normal, if the panel follows ISA-18.1 Sequence A.
Take an eight-window panel watching eight points. Assign F1 to an overvoltage alarm on motor 1 and F2 to armature overheating on motor 2. Wire an overvoltage relay on motor 1 and a PTC thermistor relay on motor 2. Their outputs (normally open, close on fault) go across F1 and C, and F2 and C, of the annunciator system. If motor 1 voltage rises past the relay setting, that relay closes F1 to common. Window F1 flashes to show overvoltage on motor 1. The common annunciator relay also changes over. A hooter already wired to those contacts then sounds.
If motor 2 armature temperature rises past the PTC setting, that relay closes F2 to common C. Window F2 flashes to show overheating. The same common output relay changes over and the hooter sounds. One output change-over and one hooter serve every window. The panel itself needs an auxiliary AC or DC supply. Modern units often add a window that watches that supply so a dead panel is visible.
A modern alarm annunciator has a power-supply unit SMPS, a programming unit (CPU) and the fault contacts plus fascia windows. The windows are usually acrylic, lit by an LED so each point draws little power. Commercial panels often start at four windows. When more than about 64 points are needed, makers commonly ship the CPU, PSU and fascia as separate modules so the rack can grow. That split is a packaging choice, not a guarantee of accuracy.
