A5366
Photoelectric Smoke Detector
with Interconnect and Timer
increased to one pulse every OSC CAP cycle and the STROBE
pin is always active. To exit this mode, the TEST pin should be
floated, or returned to V
SS
, for at least one OSC CAP cycle.
Alarm Indications
Alarm conditions include: local smoke detection, a remote alarm,
low battery, or degraded chamber sensitivity. These are indicated
by a combination of horn and LED signals, which continue until
the alarm condition is resolved. A local alarm always overrides
a remote alarm, and a local or remote alarm will inhibit warning
signals for low battery or degraded chamber.
During a local or a remote alarm condition, the horn output is a
continuous modulated tone (temporal horn pattern), nominally:
0.5 s on, 0.5 s off, 0.5 s on, 0.5 s off, 0.5 s on, and 1.5 s off. The
visible LED distinguishes a local alarm from a remote alarm.
During a local alarm, the LED blinks every 0.5 s (nominally), but
during a remote alarm, the LED is disabled and does not blink.
The degraded-chamber test occurs periodically (nominally every
43 s). During this test, the gain of the photoamplifier is switched
to the high (supervisory) level, set by C1. The device expects
that the photodiode will receive enough reflected background
light in the chamber to cause an alarm condition. If a faulty, dirty,
or obstructed chamber prevents this for two consecutive tests,
the device signals degraded chamber with one short (nominally
10 ms) horn chirp every 43 s, essentially halfway between LED
flashes. The condition is resolved when the chamber is either
cleared or cleaned.
The low-battery test also occurs periodically (also nominally
every 43 s, but offset from the degraded-chamber test). Dur-
ing this test, the load of the LED is applied to the battery, and
a resistive divider off V
DD
is compared to an internal band-gap
reference. If V
DD
is below the threshold, the device signals low
battery with one short (nominally 10 ms) horn chirp every 43 s,
occurring almost simultaneously with the visible LED flash. The
condition is resolved when the battery is replaced.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
SENSITRON [ SENSITRON ]
