HINT: This article explains how the Sensor-C2 works, but see the tables further down the page for a quick and easy guide to configuring Sensor-C2 proximity and float sensors.

The Sensor-C2 dual channel contact sensor comes with a float sensor for detecting floods in bilges or basements and a proximity sensor for detecting whether a door, hatch or window is open or closed. The latter can be confusing - because it is possible that the proximity sensor will read OPEN when the door to which it is attached is closed, and CLOSED when the door is open.

Why? Because the Sensor-C2 has no idea it is connected to a door (or a bilge). It is simply measuring whether the two circuits to which it is connected are electrically OPEN (i.e. will not pass a small test current) or electrically CLOSED (will pass a small test current). The proximity sensors that come with it switch between these states of electrical OPEN- and CLOSED-ness depending on whether their component pieces are positioned together or apart. Sometimes we supply proximity sensors that are electrically OPEN when the pieces are positioned together (e.g. when a door is closed), sometimes the opposite ... because it really doesn't matter.

Why doesn't it matter? Well, let's consider the non-obvious case: where the proximity sensor reads OPEN when the door is closed and the proximity components are together (if it read CLOSED then the sensor is behaving in an obvious fashion). When the door is open the proximity components will be apart but read CLOSED. The solution is simple: select the sensor on the Settings> Sensor screen of the MaxMon app and rename it to Door (NO), meaning Door-normally-reads-OPEN, and set its alert condition to CLOSED. Now you no longer have to worry about what OPEN or CLOSED means for that sensor, just look to see if it is showing an alert condition.

The float sensor is the same, except that when the float is up (i.e. in a flood) it will either read OPEN or CLOSED. Use the MaxMon app Settings> Sensors screen to check which type you have, then select the sensor to set its label and alert condition accordingly.

Suggested configuration for proximity (door, window, hatch) sensors

Go to the MaxMon app Settings> Sensors screen and move the proximity sensor components together and apart (simulating a door, window or hatch being closed or open) and see which "Contact-n" sensor changes state. Then depending upon the sensor readings follow the recommendations below for setting the sensor label and alert condition.

Proximity positionDoor, hatch or windowSensor readingSuggested sensor labelAlert condition
Together Closed CLOSED  Rename "Contact-n" to "Door (NC)" OPEN
Together Closed OPEN  Rename "Contact-n" to "Door (NO)" CLOSED
Apart Open OPEN Rename "Contact-n" to "Door (NC)" OPEN
Apart Open  CLOSED Rename "Contact-n" to "Door (NO)" CLOSED

Suggested configuration for float (liquid level) sensors

Go to the MaxMon app Settings> Sensors screen and move the float sensor up and down (simulating a flood) and see which "Contact-n" sensor changes state. Then depending upon the sensor readings follow the recommendations below for setting the sensor label and alert condition.

Float position Flood? Sensor reading Suggested sensor label Alert condition
Down No CLOSED  Rename "Contact-n" to "Bilge (NC)" OPEN
Down No OPEN  Rename "Contact-n" to "Bilge (NO)" CLOSED
Up Yes OPEN Rename "Contact-n" to "Bilge (NC)" OPEN
Up Yes CLOSED Rename "Contact-n" to "Bilge (NO)" CLOSED