What is the resistor used for on the Alarm.com Flex IO sensor?
The Alarm.com Flex IO® sensor comes with an End-Of-Line (EOL) resistor. If there is a risk of breaking the wires, it is important to install the EOL resistor to avoid any false information coming from the sensor. The resistor allows Alarm.com to alert users if the wires running to the sensor are no longer intact.
Note: The Alarm.com Flex IO® sensor uses a 300 kΩ resistor.
Sensors can have two different configurations – normally closed zones or normally open zones. A normally closed zone triggers an alarm when the flow of electricity is reduced. This is the most commonly used configuration and is typically used for sensors like door and window contact sensors, motion sensors, glass break detectors, etc.
The Alarm.com Flex IO® sensor functions as a normally closed zone. The following sections explain how a normally closed zone works without and with a resistor.
Note: This is a resistor installed in parallel with the sensor, not in series.
A normally closed zone without a parallel EOL resistor
|
Sensor status |
Resistance value |
Behavior |
|---|---|---|
|
Closed |
0 ohms of resistance |
When a normally closed zone is closed, then the loop is complete, and the electricity will flow through the sensors and back to the panel. This results in the panel seeing zero ohms of resistance. |
|
Open |
Infinite ohms of resistance |
When a normally closed zone is opened, then the electricity stops at the sensor and does not make it back to the panel. This is the equivalent of seeing an infinite resistance or infinite ohms. This change in resistance will result in the panel triggering an alarm. |
|
Closed when the circuit has wire break |
Infinite ohms of resistance |
When the normally closed zone has a wire break, no electricity can flow through the sensor and will result in the system seeing infinite ohms. |
|
Open when the circuit has wire break |
Infinite ohms of resistance |
When the normally closed zone has a wire break, no electricity can flow through the sensor and will result in the system seeing infinite ohms. |
A normally closed zone with a parallel EOL resistor
|
Sensor status |
Resistance value |
Behavior |
|---|---|---|
|
Closed |
0 ohms of resistance | When a normally closed zone is closed, the electricity will flow through the loop taking the path of least resistance. The panel will see 0 ohms of resistance. |
|
Open |
EOL Resistor resistance | When a normally closed zone is opened, the electricity flows through the EOL resistor. The panel sees the EOL resistor resistance. This resistance change is sufficient to trigger an alarm. The panel will use the EOL resistor resistance to show that the wires are still intact |
|
Closed when the circuit has wire break |
Infinite ohms of resistance | When wires are broken, no electricity flows through the circuit as the path is broken. The panel will see infinite ohms of resistance. This will alert the panel that a tamper has occurred to the wire install. |
|
Open when the circuit has wire break |
Infinite ohms of resistance | When wires are broken, no electricity flows through the circuit as the path is broken. The panel will see infinite ohms of resistance. This will alert the panel that a tamper has occurred to the wire install. |