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Kavlico transducer units in Garmin G3X Glass?

Radioflyer

Well Known Member
In a recent Kitplanes article, the author mentioned replacing the standard engine transducers with Kavlico sender units. These are much smaller, piezo transducers and because they contain embedded electronics require 3 wires (2 for power and one for return signal). These are used for fuel and oil pressure, manifold pressure, and oil temperature. They look neat with their built-in "cam- loc" connectors and are reported to have smoother, more reliable outputs. I looked some up at Allied Electronics and was blown away by the $275 price for each. Until reading this article, I had not heard of these units. I was wondering if anybody knows more about their use in our planes? I'm having a tough time finding value in a $275 part replacing a $20 part.
 
Garmin G3X Engine Sensors

Radioflyer, I saw that article too and wondered if it would generate questions.

The accuracy and consistent sensor-to-sensor reproducibility of the Kavlico sensors is quite impressive when compared to automotive grade sensors. It is actually difficult to even get automotive grade sensor manufacturers to provide guaranteed performance specifications for their sensors.

When I first installed my G3X system I retained the VDO brand temperature and pressure sensors that had been in use for years with my old instrumentation. With the improved digital readout and data logging afforded by the G3X system, I started to study and question the data that sensors like the oil pressure transducer were providing.

I pulled these sensors from the engine and started testing them on a bench and confirmed my suspicions that they were poor quality sensors. Each time I pressure cycled the oil pressure transducer I received different readings. It was not uncommon for this resistance type oil pressure sensor to provide different resistance values for both 0 psi and 80 psi each time I cycled the pressure. I believe the diaphragm in these sensors pushes a linear pot and the pot wiper can wear with engine pulsations leading to performance problems.

I installed the solid state Kavlico pressure transducers and replaced the VDO thermistor style oil temperature sensor with an RTD sensor that is the preferred oil temperature sensor for a G3X system.

I pressure tested the Kavlico pressure sensors while connected to the G3X system for an end-to-end test and was very pleased with what I observed.

I really appreciate the improved performance of the RTD oil temperature sensor over the VDO resistance sensor since in the summer oil temperature can become my limiting engine parameter in some scenarios.

It is a good feeling to power up the G3X on a cold hangar-stored aircraft and see the RTD OAT, RTD oil temperature, and thermocouple CHT probes all reading within 1 deg F of each other. :)
 
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Howdie, fellow Canardian,

Hmmm. Interesting datapoints. I would be thoroughly sold on the Kavlicos, if it were not for their steep, steep price.

When you said you tested the VDO types, what kind of precision were you getting? Yeah, I can easily see how these mechanical, resistive transducers can be less than optimal, but if, for example, oil pressure is +/- 5psi, I guess I would still consider that acceptable utility.

By the way, I see another advantage for the Kavlicos. Since they are so small, with much less mass than the VDO type, it would seem to me that it would be safer to install directly on the engine and get rid of the extra lines and hardware typically used to remote the VDO type sensors.

Hey, any pis of your G3X install?
 
Garmin G3X Engine Sensors

You might want to shop around a bit for the Kavlico sensors. That Allied price of $275 looks really high compared to Garmin's published current list prices for the Kavlico sensors: http://www8.garmin.com/aviation/pdfs/G3X_sensor_kits_pricing.pdf

494-30004-00 oil pressure sensor: $85
494-30004-01 manifold pressure sensor: $85
494-30004-02 fuel pressure (injected): $106.25
494-30004-03 fuel pressure (carbureted): $106.25

It has been a while, but I recall my oil pressure errors with the VDO being on the order of 5 to 8 psi. What was most frustrating is that I couldn't characterize the response curve of even a single sensor due to the pressure cycle to pressure cycle variability I mentioned. Having a 5 to 8 psi error might not be a big deal with an analog gauge, but it starts to get annoying with a nice digital/analog readout on an EFIS.

Since you can end up paying $30 to $40 for the VDO sensors, perhaps $85 for the nice Kavlico oil pressure sensor isn't so bad.

You are probably right about the Kavlico sensors being small enough that you could mount them without the remote manifold or flexible hose, but I still wouldn't do that myself.

Here is a picture of the Kavlico manifold pressure sensor mounted on the hose I made for my installation: https://picasaweb.google.com/lh/photo/W7zEynbefBHe45MdaNna6GW5MgOOQpNkhVHEWiCJOQQ?feat=directlink

Here are some installation pics:
New G3X panel before painting showing fuse block behind GDU375 display
New G3X panel before installation in plane.
G3X panel with Aera in flight.
Another in-flight pic.
 
I've been sorta' salivating over my box of G3X sensors for a few months - there they sit in the storage locker, taunting me because we have to get the engine mounted before getting to play with them. very nice looking sensors compared to what everyone else uses. I was also a bit surprised at the price quoted by the OP, since I didn't recall them being that high when I got the system last fall.

The Garmin system is really top-notch when it comes to quality components. Yes, you'll pay a little more for the quality, but these little sensors are going to fit very nicely in the compact cowling of the RV-3.

Paul
 
Maybe, I was looking at the wrong Kavlico sensors in the Allied Electronics website. I did not have actual part numbers and went by what looked reasonable. At any rate, I'm glad that the prices are much less than 1/2 of what I thought. For $85, they seem to offer good value given the advantages discussed.

Now that I'm tempted to try them out, does anyone know if they can be a direct replacement for the VDO type sensors? That is, besides the power inputs, is the signal output voltage of the same level as the VDO types?
 
Not sure who makes the sensors for Electronics International but all of their sensors are the 3 wire type.
 
Radioflyer,

As shown by these specs, the Kavlico sensor outputs voltage over a range from 0.5 Vdc to 4.5 Vdc. For the oil pressure sensor it outputs 0.5 Vdc at 0 psi and 4.5 Vdc at 150 psi.

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The VDO oil pressure sensor is quite different. It is essentially a variable resistor that changes from approximately 10 ohms at 0 psi to 190 ohms at 150 psi. Note also that unlike the Kavlico which has a linear response, the response of this probe is somewhat non-linear.

Whether you choose a powered sensor like the Kavlico, or a non-powered resistive sensor like the VDO, your readout system would have to be able to accomodate the sensor type you wish to use.

BTW, notice the Kavlico error specs on the linked image. The total error is less than 2% of full span which corresponds to less than 3 psi error on a 150 psi oil pressure sensor.
 
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