GAI-Tronics 12599-001 Hot Standby Amplifier Module - Manual (Page 8)

Pub. 42004-375A
Model 12599-001 Hot Standby Amplifier Module Page: 8 of 11
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Theory of Operation
The Amp-1 through Amp-6 fault inputs at TB3 on the Model 12599-001 Hot Standby Amplifier Module
provide a single connection point for each amplifier fault output. The OUT (output) terminal provides dc
common to the amplifier’s internal fault circuit and the RET (return) terminal ties to the output side of the
amplifier’s internal fault circuit.
When the connected power amplifier is functioning properly, the amplifier fault output control signal to
the RET terminal must be an active Low (below 6 volts; a dc level at or near zero volts is optimum).
When the amplifier’s internal fault circuitry detects a problem, such as a shorted or overloaded output,
excessive temperature, etc., or ac power is removed from the amplifier, the amplifier’s fault output floats
high to a positive (+) polarity. The associated RET input circuit detects this voltage change, and activates
the associated relay group to switch the standby amplifier in place of the faulty amplifier. The circuit will
remain active until the amplifier fault condition remedied.
Priority Switching
The 12599-001 Hot Standby Amplifier Module prioritizes the switching of the standby amplifier for two
reasons, which are:
1. To avoid excessive loading of the standby amplifier in the event of multiple amplifier failures, and
2. To ensure that critical facility areas receive alarm and voice audio broadcasts during emergencies.
The order of priority switching from highest to lowest is Amp-1 to Amp-6 respectively. This means that
Amp-1 has the highest priority and Amp-6 has lowest priority. This prioritization scheme applies if the
board is operated in either 1-channel or 2-channel modes. If cascaded with other modules, module 1 has a
higher priority than module 2, and module 2 has higher priority than module 3, etc.
While it is difficult to determine which area of a facility is the most critical (as in item 2 above), an
example is an offshore oil platform system with multiple amplifiers. In this case, the living quarters (LQ)
are usually considered such an area. In this type of system/cabinet design, the LQ amplifier should be
connected to the Amp-1 terminals to ensure that personnel (sleeping in the LQ) will be alerted during
emergencies.
Dry Contact Outputs
The Model 12599-001 Hot Standby Amplifier Module provides six, form “C” dry contact outputs (one
per amplifier circuit), which can be used for triggering either a remote status indicator, or an input at a
supervised system device for visual text display. Each output contact operates in conjunction with its
respective fault detection circuit so that the status of all connected amplifiers can be monitored at all
times, regardless of their priority assignment.
Cascading Modules
The Model 12599-001 Hot Standby Amplifier Module can be operated with a series of other modules in a
cascade. This feature is useful in cabinet/system applications when the following criteria must be met:
• A higher ratio of primary (active) amplifiers to a standby amplifier is needed, or
• In particular, when dual-channel amplifiers are employed.