SIGMA AM-255 - Manual (Page 15)

4. THEORY OF OPERATION page 12
Model AM-255
4. THEORY OF OPERATION
The alarm monitor model AM-255 is a battery powered, remote monitor unit used with TSA’s
pedestrian and vehicle portal monitors. The AM-255 provides both audible and visual alarm
indications for radiation alarms, low and high background alarms, and tamper conditions.
Parallel relay outputs are provided to permit interfacing with existing alarm systems.
Please reference the wiring/signal flow diagram drawings package provided with the instrument
as they are noted in this manual. The Drawings list can be found in the APPENDIX F. Drawings
section in this manual.
4.1. UNIT OPERATION
The relays in the portal monitor are continuously monitored by the AM-255. Whenever the
relays change state, the AM-255 reads the change and turns on the correct lamp and relay, and
sounds the audio alarm. The alarm will follow the system. The green ready LED will go out
when the alarm condition occurs, and re-illuminate when the alarm condition clears.
NOTE:
Multiple alarms can occur and more than one alarm lamp be illuminated simultaneously.
The monitor operates from the 12 volt, lead acid battery. If ac power is lost, the battery provides
power to permit continued operation without interruption. Should the battery get too low for
reliable operation (approximately 10.5 volts), the monitor will turn itself off. Normal operation
will resume when the battery has been recharged to approximately 12.5 volts.