| This article describes the procedure for adding or replacing an internal sounder.
Introduction
An internal sounder is an extremely useful addition to any alarm system. Most importantly it immediately distracts any intruder in the protected area to such an extent that the intruder is unlikely to spend time on the premises while the sounder is activated. There are two types of internal sounder used - extension speakers and piezo sounders.
Extension Speakers
The majority of Stand-alone control panels and some blank end-stations are supplied with a speaker fitted inside the control panel. This speaker operates at two volume levels - low volume for signalling entry/exit tones and keypad acknowledgements, and a higher volume for alarm signalling. Also, on control panels which differentiate the alarm type as to whether to sound internal only or internal and external sounders, then the extension speaker is the sounder used for internal alarm. For example, some panels will indicate a tamper fault while the alarm is unset on the internal sounder only, whereas when the alarm is set both internal and external sounders are sounded. It should also be noted that Remote Keypads (RKPs) have a small low-volume internal sounder for signalling entry/exit tones and keypad acknowledgements.
More than one extension speaker can be fitted - refer to the particular control panel installation instructions for wiring instructions.
Piezo Sounders
Piezo sounders are small units which produce sound by using the piezoelectric effect. The piezoelectric effect is the property of some materials, typically crystals and some ceramics, to change sshape when a voltage is applied across them (and vice-versa). This change of shape can be used to produce sound. Piezo sounders connected to alarm systems should be wired in parallel with the external sounder. More than one piezo sounder can be connected but care must be taken to ensure that the available sounder output current is not exceeded.
Connecting Extension Speakers
When connecting extension speakers it is important that the resistive load on the circuit is adhered to. For example, the control panel specification may state that the total load must not be less than 16Ω such that one speaker would be connected as follows.
And two speakers as below.
Note: The 16Ω figure used above is only an example - always refer to the control panel specification.
By applying the rules for adding resistances, virtually any combination of speakers can be used to achieve the required load.
Series
The total resistance for resistances connected in series is simply the individual resistances added together Tot R = R1 + R2 + R3 + ...Rn
Parallel
The total resistance for resistances connected in parallel is the reciprocals of the resistances added together Tot R = 1/R1 + 1/R2 + 1/R3 + ...1/Rn
If the speaker is to be tamper protected then the tamper pair should be daisy-chained into the global tamper circuit.
Connecting Piezo Sounders
Piezo sounders are connected in parallel with the external sounder. They are connected across the +12v supply (12v Hold off) and the bell trigger.
Piezo sounders typically require 120mA in alarm condition. This figure needs to be added to the current required by any other sounders connected and the total must not exceed the total available.
If the speaker is to be tamper protected then the tamper pair should be daisy-chained into the global tamper circuit.
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