Chris,

In addition to the capacitive fuel probes, which are connected to analog gauges, I installed one optical sensor in each wing tank on my Lancair ES in a location which will provide a 30-minute low fuel warning.  While not yet flying, they appear to be working as intended.  The only area that I feel it could be improved is to provide for a time-delay circuit to prevent the sensor from flashing on and off as the fuel sloshes in the tanks.  Other than that, I’m happy with them.        

 

Mark S.

 

 

Al Wick said:

Those appear to be discrete sensors. Meaning they are either off or ON. A very important concept in reducing risk is to use analog sensors whenever possible. Your understanding of your fluid level is better with analog sensors. Less apt to discount the readings, you can see the gradual change in fluid level.

You want as many factors in your favor as possible.

 

Al, you’re right, these sensors are either on or off, as in a switch, and I agree with your perspective on analog sensors for continuous sensing. 

 

The value in these sensors (that I see) is that they have no moving parts (usually higher reliability) and can provide low-level sensing of fuel or water (as in a fuel header tank or radiator overflow bottle).  Because they can only switch low currents, about 40 mA at 5V or 12V, they can either power an LED for the low-level sensing task, or switch something like a solid-state relay.  An example of the relay is Crydom’s D1D20, that requires a controlling amperage of 1.6 mA at between 3.5 to 32 VDC, providing up to 20 amps of DC current at 100V on the other end.  The picture on the left is a DC controlling DC relay, the one on the right is DC controlling AC. 

 

 

If I’m not mistaken Rusty’s tried the low level sensors.  Rusty, any experiences to offer? … or good applications?

 

Regards, Chris