5
Chapter 2
Theory of Operation
Alarm Response
When an alarm is triggered, the Bird Antenna & Cable Monitor turns on the
alarm LED and activates a Form C dry contact relay.
The alarm relay defaults to fail/safe. That is, the alarm activates when the relay
is not energized or power is lost. However, the PCTool software can configure
the alarm to either energize or de-energize in response to an alarm.
Alarm Reset
Alarms can be reset locally with the reset switch.
Alarms are reset when the reset pin on the Power/Alarm port is
activated by a TTL compatible logic low signal (0 to 0.8 VDC).
The PCTool can reset the unit through the RS-232 port by sending a
“Reset Alarm” command.
Alarm Latching
The alarm defaults to latching operation. In this mode, the alarm will stay active
until reset. In non-latching mode, the alarm will reset automatically about forty
seconds after the trigger condition is corrected.
VSWR Alarm
The ACM continuously monitors forward and reflected power. From the power
measurements, the VSWR is calculated and compared to the allowed maximum
(default of 1.5 to 1). Based on the results of the comparison, possible actions
include:
No alarm is activated if the VSWR is less than the maximum, or if the
VSWR alarm is disabled.
If the VSWR is equal to or slightly greater than the maximum,
additional measurements are accumulated to determine a trend. If
reverse power is increasing, an alarm is triggered. If the reverse power
is stable, measurements continue until a trend is established. An alarm
