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Fire Alarm -- Maintenance

Common senses are more than just sight, sound, feeling, smelling, tasting, common sense includes the sense of time.
Time... It's one of the common senses that isn't talked about much, but needs to be taken into account when troubleshooting.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

Is the Sense of Time Important?

By Douglas Krantz

Sometimes, when servicing fire alarm systems to find the troubles, one has to use all the common senses available to observe more than just the wiring or electronics.

I was just on a troubleshooting call where intermittently, every half an hour or so, the system was going into trouble. It would stay in trouble only a few minutes each time. Because the monitoring company kept calling the building engineer day and night, he was getting annoyed.

On my arrival, he explained the troubles.

After talking to the building engineer, I went straight to the main fire alarm control panel (FACP) to observe the troubles and fix whatever was going wrong.

To see what was going on inside, I opened it. Nothing seemed out of the ordinary, no smoke to see or smell, the temperature seemed normal, no wires seemed loose.

Of course, at the exact moment I arrived, the panel wasn't showing any troubles. However, checking history, I could confirm the troubles -- about every half an hour, all four loop controllers would go into failure to communicate with the CPU, and then the CPU would restart. Not good.

I had observed that the common problem was with the CPU, but because the troubles never showed up while looking at the panel, I couldn't confirm.

Doing the usual things, I powered down the panel, re-seated all the cards, and tightened all the screws. This took a while.

After doing all this without the panel going into the trouble, I took about 10 minutes to close up the panel, clear the test with the monitoring company, and turn in the keys.

As I was leaving, though, the annunciator at the door sounded off with troubles. What was going on?

Here's where all senses come into play.

To the rest of my observations,I added the sense of time. During the time the door was open, so I could observe the troubles, the troubles never showed up, but they came back after the panel was closed -- for a while.

I'd encountered a thermal trouble in the CPU. The temperatures inside the panel had felt normal, but with the door open, and slightly cooler air flowing in, the CPU would cool down just enough to stay out of trouble.
Was this
Yes   No

To confirm, I left the door open and the troubles quit.

Of course I knew this is a progressive condition, those troubles would get worse quickly. In the time it took to obtain a new CPU, even though the door was left open, the panel went into trouble again. But, because I had determined the cause of the problem, the problem was quickly fixed.

This shows the power of observation, looking at more than wires, screws, and plugs, one has to include all their common sense, including sight, smell, hearing, (well maybe not too much tasting), touch, and sense of time.


Douglas Krantz

Describing How It Works

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Electrical Flow

On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at