Fuel Sump Sensor
Many of us have found, and the factory confirmed when I spoke to them, that the standard float style sump level switch is prone to issues. It can sink at high angle of attack and power settings, particularly at altitude. Folks have come up with a couple of solutions.
Gems Optical Sensor
Submitted by: Brett Ferrell
Submitted by:Ruben G. Creus
After some research, I found and ultrasonic sensor with is rated for liquid and includes gasoline. It is also NPT, so very easy to swap for the existing one. This is an epoxy device with a metal shield on it. Inside it has and ultrasound emitter and receiver. The presence of liquid (in this case fuel) creates a distortion in the ultrasound and that triggers the sensor. The sensor can be ordered as a NO (Normally open) relay, which closes when liquid is present. (MODEL LVU-A716)
I am glad to report that I have experienced no more flickering or false alarms. It works great on the ground while taxing, turning, at low RPM and high RPM, flying even with nose up or nose down attitudes. It stays green all the time. I guess that in the case of low fuel in the wings and in a nose down it might let some air in the tank and that could trigger the sensor, I will let you know if I see that, but it might take a while as I rarely fly with low fuel on the wings. I also checked with low fuel on the sump to confirm that it triggers the alarm when it supposed and it certainly does. Differently than the float sensor, the ultrasonic sensor has no moving parts. It sends an ultrasound. The ultrasound is not affected by vibrations, or movement. If there is fuel there, it will signal it, if not it will not. Simple and works.
Note that, this sensor requires power. I have fuel tank level sensors and I had power already in the back of the plane, Very easy to install and wire. In my case I have a Dynon EMS, so I had to change the configuration of the sensor to be NO–Green and Closed–Red.
In case you are interested on knowing more about the sensor here is the link to the manufacturer.