Alarm Stays On

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Here's a weird one. I have an old Ademco hard-wired alarm panel which
has been running well since 1985. Recently it went into alarm
condition but would not shut off. (For a momentary opening of the
closed loop, it's supposed to shut off after 12 minutes.
     The closed loop contains a Dual Tec PIR/microwave combo unit
which has a very low false alarm rate. When it false alarmed recently,
I forgave it, but the alarm stayed on so I assumed it was "latching"
due to some failure and not shutting off. I replaced it with a second
unit, and watched the LED's carefully. The new one was clearly working
      On testing the system, I simulated an alarm condition and
watched the LEDs turn on and off, so I knew the OC was momentary. I
even checked the output with a meter. The alarm did not turn off after
12 minutes!!!!!
      I then did a manual open and reclose of the loop with the Dual
Tec out of the circuit. The alarm cut off after 12 minutes.
      What is going on here? The Ademco recognizes the opening of the
loop but does not recognize the closing, but *only* when the closing
is done by the Dual Tec and not manually.
      Ideas? I'd say the relay on the DT is not re-closing properly
but the other unit apparently did the same thing. The panel must think
it sees something other than a closed loop!
      A real hair tearer. (Thanks for help.)
     P.S. The loop has a 2000 ohm terminating resistor.

Re: Alarm Stays On

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  Is it wired backwards, by chance? Removing the sensor and just
opening/closing the circuit makes the alarm work properly? Almost has
to be a sensoe related problem.

Re: Alarm Stays On
On Jun 7, 9:30=A0pm, wrote:
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You think after 25 years it re-wired itself to be backwards?

For the OP, it might be time to consider a new
system.  Anything electronic that is approaching 30
years of service is bound to have issues.  Just simple
things like electolytic caps for example.  Another
problem with a system of that vintage is that it's
probably going to be impossible to program if you
want to change anything, even
if you have the codes.  My old one of that vintage
was programmed by blowing PROMS to set the
thing up.  You can get a whole new panel kit for

Re: Alarm Stays On
On Fri, 8 Jun 2012 06:41:26 -0700 (PDT), ""

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Being obtuse again, eh??
The unit was replaced. Always possible the first one was defective and
the new one reversed, no??

Stranger things have happened.

By his description and basic analysis it would APPEAR to be a sensor
related problem - either function or installation, or interference.
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Re: Alarm Stays On
On Jun 8, 1:22=A0pm, wrote:
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How can you say that with such certainty
our Canadian know-it-all ?

It could have more to do with changes in
the resistance of the loop and how the old
SOLID STATE electronics are dealing with
that...  Hence it is more pertinent to check
for out of spec EOL resistors and components
on that circuitry which is effecting the way
the central controller is reacting to the
sensor devices wired to it...

Re: Alarm Stays On
On Fri, 8 Jun 2012 12:34:07 -0700 (PDT), Evan

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  Hey, I'm not saying NOT to check the resistors - but it APPEARS it
is only the one sensor causing a problem, and if the sensor is removed
from the circuit and a switch substituted, the system works as it is
supposed to.  This would lead ME to suspect it is an issue with the

Now,I don't pretend to know it all.
However, many times, particularly with older tech solid state devices,
reverse connections can have strange results, and unlike a simple
switch type "sensor" like a door or window sensor, the microwave and
PIR units ARE polarity sensitive.


On any Honeywell Dual Tec I've seen there is a separate 7-16 (usually
12) volt power supply  which is polarity sensitive, as well as the
alarm contacts - which have 4 different programmable resistor values
across the NC contacts if connected C to NC. and another 4 resistors
across the NC tamper switch connections. On some you can connect C to
EOL - I don't know what the rammifications would be if connected C to

Being Normally Closed contacts, if there is more than one sensor or
switch on the loop, they are wired in series, with the EOL resistor
across the terminals at the panel (generally) so with the whole string
closed the resistance across the circuit is nominally ZERO ohms, and
as soon as any contact is opened the panel sees the EOL resistance (in
the OP's case, 2.2K ohms. If the sensor is installed jumpered to 2.2K
ohms, the panel will see 4.4 k ohms with the sensor tripped - and the
panel could "fault".

If he is using an external EOL resistor he needs to remove all of the

If he has not removed the jumpers, it would very likely malfunction
with the sensor connected, and work fine with it removed and replaced
with a switch or jumper.

You can look for zebras and unicorns all day, but when you hear
hoofbeats, it's much smarter to look for horses, ponies, or jack-asses

Re: Alarm Stays On wrote:

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LMFAO -- I don't think you have ever seen one based on this
explanation of alarm system workings.

x-posted to ASA for a good laugh.

Re: Alarm Stays On wrote:

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Why did you remove my x-post?

Re: Alarm Stays On
On Fri, 08 Jun 2012 20:56:37 -0500, G. Morgan

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 I've installed a few. Some over 30 years ago, The last ones about 15
years ago - wired and wireless - and I've worked on one of the new
ones within the last 2 years - a whole lot more complex - a whole
computer packed into the box, with complex programming up the ying
yang. Other than moving the control panel (keypad) and a few sensors,
I said "get the alarm company - it'll be cheaper than paying my time
to figure out how to program it".

 There's more than just open and closed switches and resistors in the
new digital jobs.  The old analog or "2 bit digital" systems WERE
simple.  The 30 year old ones were a lot simpler than the 15 year old
ones - which were not "leading edge" at the time.

But (at least most of) the sensors from the 30 year old system still
work on the new systems, and many of the new sensors work on the 30
year old ones as well.

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