Douglas Krantz - Technical Writer - Describing How It Works
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How do I Test Devices Using a Multimeter?

Only some conventional devices can be tested at all using a multimeter. However, in order to test whether a device can send an alarm, the device has to be wired into the fire alarm system, and then activated as if there was a real fire.

How do I Test Devices Using a Multimeter?


Greetings Douglas,

How do I test a device like a pull station or even a relay module to see if it is properly changing state with a multimeter?

Thank you, ML

Testing Pull Stations

A pull station is an input device for a fire alarm system. For a conventional fire alarm system, the pull station is a switch. It may look different from a light switch on the wall, but electrically, it is identical to a light switch. In a conventional fire alarm system, all it does is to electrically short-out the input zone to the panel. That is how it sends an alarm.

You can use an ohmmeter to see if it shorts out the wires when it's activated. However, to see if activating the pull station will send an alarm to the fire alarm panel and "sound the alarm", the only way to test it is to wire it into the fire alarm system, and by activating the pull station, use it to try and "sound the alarm". An ohmmeter doesn't show anyone whether or not the pull station sounds the alarm.

An addressable pull station is different. It does not short-out the circuit that it's attached to. Because there's a lot of circuitry inside the pull station, a multimeter can't be used to test anything with the addressable pull station. An addressable pull station has to be connected to a fire alarm system to test whether or not it will sound the alarm.

Testing Relay Modules

A relay module is an output device for the fire alarm system. A relay module is actually a regular relay, but uses added circuitry inside the module to turn on and off the relay. See: How Does a Relay Work?

Basically, the contacts on a relay are exactly like the contacts on a switch. It may not look like a switch, but using an electromagnet rather than a human hand, it is only a switch. In order for the relay module to be tested, though, the relay module has to be connected to the fire alarm panel so the panel can operate the relay.

When it isn't connected to another system, testing the relay module can be done using an ohmmeter. First, check the resistance of the common-to-normally open contacts and then the common-to-normally closed contacts. Write down the resistance that's measured in each case. Then activate the module. (Usually setting the fire alarm panel into alarm will activate the relay.)

With the panel in alarm, measure both resistances again. They will have changed states if the relay is activated.

Testing the Relay Module when Connected to Other Systems

Sometimes while testing, just disconnecting wires isn't a big issue, like when all the fire doors close while testing. Sometimes while testing, just disconnecting wires becomes a real big problem, like when the elevators shut down for a few hours in a 27-story apartment building (at least until the elevators can be reset).

Usually, the only way to test a relay module when it's wired to other systems is to set the fire alarm system into alarm and watch what happens to the other systems.

Douglas Krantz


Mr. Krantz

This is very helpful. Thank you. I had an issue the other day with an elevator recall module and another today with a duct detector shutting a unit down. I was able to resolve both issues. Appreciate the help. I did not realize you cannot see a change of state on an addressable pull station. That is good to know.

Keep up the great work and thank you for getting back to me.

Thank you, ML


facpdoug@douglaskrantz.com
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