GAI-Tronics 12599-002 Hot Standby Amplifier Module - Manual (Page 13)

Pub. 42004-412A
Model 12599-002 Hot Standby Amplifier Module Page: 13 of 17
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Theory of Operation
The Amp-1 through Amp-6 fault inputs at TB3 on the Model 12599-002 Hot Standby Amplifier Module
provide a single connection point for each amplifier fault output. The module’s fault inputs can be
configured to accept a range of amplifier fault output types, and each is described in the following text:
Wet Mode – Active Fault Output
When the input jumper clip pair is set to the wet position, the + (plus) terminal accepts a positive dc
voltage and the - (minus) terminal accepts negative (dc common) voltage from the amplifier’s internal
fault circuit. When the connected power amplifier is healthy, the amplifier fault output signal to these
terminals must be active.
If the amplifier’s internal fault circuits detect a problem (e.g., a shorted or overloaded output, excessive
temperature, etc.), or ac power is removed from the amplifier, the amplifier’s fault output is no longer
producing an active output voltage. The associated input circuit detects this 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.
Dry Mode – N.C. Fault Contact
When the input jumper clip pair is set to the dry position, the + (plus) and - (minus) terminals accept a
normally closed, dry contact from the amplifier’s internal fault circuit. If the amplifier’s internal fault
circuits detect a problem (e.g., a shorted or overloaded output, excessive temperature, etc.), or ac power is
removed from the amplifier, the amplifier’s fault output contact opens. The associated input circuit
detects this 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.
Dry Mode – Active Open Collector Fault Output
When the input jumper clip pair is set to the D RY position, the + (plus) terminal connects to the “input”
(or emitter) side of the amplifier’s fault terminals, and the - (minus) terminal connects to the output (or
Collector) side of the amplifier’s fault terminals. When the connected power amplifier is healthy, the
amplifier fault output must be actively low (sinking to dc common) to the – (minus) terminal, of this
module’s input.
If the amplifier’s internal fault circuits detect a problem (e.g., a shorted or overloaded output, excessive
temperature, etc.), or ac power is removed from the amplifier, the amplifier’s fault output floats high. The
associated input circuit detects this 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 12599-002 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 is from highest to lowest; Amp-1 has 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.