How To Write a Technical Specification for an Alarm Annunciator

Before writing a specification for a generic alarm annunciator to apply to a specific application certain technical aspects must be considered. They are as follows:

1. How many alarms need to be monitored?
2. What is the Voltage of the power source supplying the Annunciator?
3. Are the alarm inputs dry contacts or will they supply a separate Voltage upon alarm?
4. How is the unit to be mounted?
5. How large a display is required? A single LED per alarm point or a backlight window.
6. What is the “Sequence of Operation” when an alarm is received?

Depending on how complex the application, the specifications need to become more detailed.

An example of a simple eight-point alarm annunciator specification would read as follows:

The annunciator should be capable of:

1. Monitoring (8) Eight Alarm points
2. The unit will be powered by 115Vac
3. All eight of the alarm inputs will be Normally Closed, dry contacts and will open upon alarm.
4. The unit should be capable of being desk or 19” rack mounted.
5. Each alarm point should be a backlight window approximately 1” square in size the legends for each should be definable on site by the user and printed by a standard computer printer using software provided with the Annunciator by the Annunciator manufacturer.
6. The Sequence of operation should be as follows:

The Three Most Popular Sequences of Operation

The Instrument Society of America or ISA has defined a multitude of sequences of operation, which prescribes how the lights on the front panel of the annunciator will flash when the inputs to the Annunciator go into the alarm condition. Different industries have adopted different sequences as their own.

As control room instrumentation becomes more sophisticated, three sequences of operation among Annunciators have become most prevalent throughout all industries.
These sequences are as follows:

Sequence #1 This sequence always shows the current status of each of the alarm inputs and requires Acknowledgement when a transition has taken place.

Sequence #2 This sequence is used when only one color is available to illuminate the window. The window will flash when the point is in the alarm state as well as when the point returns to the normal state. A reset button is used to darken the window after the point has “Returned to Normal”

Sequence #3 This Sequence uses one red LED per alarm point and will flash when the alarm input is in the alarm state and will continue until acknowledged. When Acknowledged it will remain lit steady. Upon return to normal it will just darken without operations personnel required to press Acknowledge or Reset.

The preceding was a simple overview of the considerations required when an annunciator system is specified. Please continue to check this site as we expand upon this discussion.