Additional Oil Pressure Switch

Sean, I re-read your reply and think I have a better understanding.  The Rotax oil pressure sensor is a resistive device that is modulated by pressure.  The Dynon EMS reads this resistance and sends the info to the EFIS.  It generates the display that the user defines the color coded ranges.

For what we used to call an "idiot" light, we add a switch, so we either have oil pressure or not.  That's why I want to add another sensor.  I drive a Ford F-150 and I noticed the oil pressure gauge never changed, and as you know, the oil pressure is higher when the oil is cold so the pressure tends to drop somewhat as it heats up.  After a little investigation I realized that Ford was using an on-off oil sensor and driving a gauge with it.  Kind of dumb if you ask me, but that's what they do.

Hi John,

Random thaughts;

".....so we either have oil pressure or not"

I can see this being very simple but would it not be better,  to know that pressure is approaching (ie you select a safe minimum  pressure at which warning light goes on) a lower limit, rather than  "pressure or not"

Pressure "...not..." has sudden engine failure connotations.

Approaching may give you valuable time to decide on a life/engine/aircraft saving strategy.😈

Hi John,

If the aim is just to illuminate an "attention getter" warning light, the Dynon EMS has a built in external warning light output which can flash a warning light whenever any engine parameter enters a "red" range. See page 7-91 in revision AV of the SkyView Installation Guide.

Note that almost all failures of the oil pressure sensor would cause an out-of range signal level, which the Dynon would annunciate with a red X through the pressure gauge. Adding a separate pressure switch might gain a little bit of redundancy - but you're also adding more potential for leaks on the high pressure side of the oil system.

Here are my thoughts:

1. If the Dynon provides an audio/visual warning of parameters outside limits, I would go with that rather than a separate detection system.

2. During engine start it is possible to observe the oil pressure indicator to see the oil pressure increasing from zero to the normal operating pressure. This then confirms that the engine, pressure sensor and Dynon are all working correctly.

3. A genuine oil pressure problem in flight will be accompanied by other symptoms. If there are none, then it is more likely to be a measurement problem. You can live with this until you land and then get the fault fixed. Your time at risk is relatively low.

4. I would suggest that the Dynon uses an internally regulated supply that it uses as a current source for all of the various external sensors. Faults in the simple 2-terminal sensors are unlikely to drag the internal reference down whereas more complex sensors like the MAP sensor probably make a direct connection to the reference supply, so a fault here may well affect multiple sensors. That's just bad luck or bad design depending on your perspective.

5. From what I have seen, oil pressure failure in a Rotax 9xx engine is rare and most of the older installations like my 20 year old Eurostar just offer a single analogue pressure gauge. There is no warning light or anything else to draw your attention to it.

Tim,

I did not know about that feature in the Dynon, that might be the best solution.  My main concern has been the instance where my neighbor's MAP sensor failure caused the EFIS to not display the other two sensors.  They are all powered by a common, low-current output on the EMS.  I suspect the faulty MAP sensor perhaps pulled down the voltage on that output and the Dynon perceived it as all three sensors being bad.  Also, the MAP sensor doesn't seem to be the best quality of sensor.  I don't want to mention the country of origin but it's plainly printed on the outside.  Thanks for your comments.