All new Gill level sensors come with a secondary output function which operates as a high or low level switch. So what is it and how do I use an Open Collector switch output?

Essentially the level sensor has an on board electronic switch (a Metal–Oxide–Semiconductor Field-Effect Transistor or MOSFET, if you are interested) that can be set-up to open or close at given liquid level conditions. Its exact switch point can be configured by the GS Level configuration tool available for download from their website www.gillsc.com/support

When combined with other components, the Open Collector Output can drive an LED to indicate reserve fuel level, a relay to switch on a pump or an Opto-Isolator to drive any number of other devices.

How do I choose the right value for ‘R’? 

Resistor Value – R

R = (Vindicator- V_LED) / I_LED

V_LED = Voltage drop across LED (Volts)

I_LED = Current flowing through LED (Amps)

V_indicator = Supply Voltage (Volts)

Resistor Power Rating 

W = (V_indicator – V_LED)² / R