Oil Temp Sensor - which one?

[PhantomPholly]

After a long restoration I am flying, and getting information that my oil temps are running high.

Can someone verify the correct sensor setting (Type 1 or Type 2) for a Dynon sensor with the value 07-23 stamped on the side?

Thanks,

Bill

 

[dynonsupport]

If it's the 5/8" fitting it's type 1.

 

[PhantomPholly]

Thanks.

I suspect a poor ground issue - would that cause it to read high or low, and would the discrepancy vary more at high temp or would it be linear?

In other words, is there an easy way to test if the probe is accurate?

 

[dynonsupport]

A simple bad ground on the sensor would make it read low. The temp goes up as the resistance goes down, so extra resistance with a bad ground would lower the temp.

A bad ground between the sensor ground and the EMS (ie between the engine and the battery) can make the sensor read high, since this causes a voltage drop across the wire, which is the same as a lower resistance.

With a voltage drop, the sensor gets much more inaccurate at higher temps. It only takes a few mV at 220F to cause a 10-20 degree error.

The easiest way to test for this is to turn off your alternator. This will stop the ground current and will show you if it's causing an issue.

 

[PhantomPholly]

Ok so clarify a bit for me. I have a Lancair 320 where the engine / alternator is in front; avionics bus in the middle; and battery at the back.

So, if there is a less-than-perfect ground between the engine and the rest of the plane, are you saying that the temp will read high while the alternator is on and low when it is off? THAT would be an easy test...

 

[dynonsupport]

It takes a lot less of a bad ground to mess you up when the alternator is on. I'd guess you'll find it to be reading high with the alternator on and dead on with the alternator off.

 

[PhantomPholly]

Ok, thanks.

How high (degrees Fahrenheit) will the probe accurately read temperature?

 

[dynonsupport]

About 275F, assuming less than 1 ohms of resistance error in the wires and everything.

 

[PhantomPholly]

Follow-up: Is there another type of Oil Sensor that I can use? Currently using type 1.

I have verified that there is in fact a small amount of resistance between the engine ground and instrument bus ground. It is very small, but at high temperature and high current load it creates up to 70 degrees of temperature difference (alternator On/Off). I am concerned that even if I run a brand new ground strap there will still be some slight resistance that would report higher-than-actual temperatures.

The EGTs and CHTs all seem to be fine.

Help?

 

[PhantomPholly]

Bump - Dynon, is there an alternative sensor not dependent on the engine block ground?

Thanks,

Bill

 

[dynonsupport]

We do support the GRT oil temp sender which has an alternate ground.

Be aware that while the oil temp sensor is sensitive to this, everything in your aircraft is going to have some sensitivity, and having a resistive connection between your alternator ground and the rest of the aircraft isn't a great situation. Remember that all your 100-300 amps of starter current go through the same resistance. In most "bad ground" cases we only see 20-30 degrees of error, so 70 is pretty extreme.

 

[PhantomPholly]

Yep - I'm going to fix the ground situation.

It just made me consider that even if the ground is "better" than it is I might still be seeing erroneous oil temps. Since my oil temps seem to frequently border on the caution zone, I really want the most accurate reading possible.

 

[PhantomPholly]

Follow-up. New ground strap absolutely fixed the temperature discrepancy.

Still have higher than desirable oil temps, but that is common to Lancairs. Now have to do the cooling mods to get it back down...

 

[pbennett]

I have ordered the Dynon oil temp sensor with the D10, but I would prefer to use a two lead sensor and ground it at the EMS. My old EMS used an AD590 sensor that I had to assemble and pot in the brass plug. I understand from this thread that Dynon uses a NTC resistor grounded to the plug, and GRT uses the same or similar resistor isolated from the plug. Using a GRT sensor would be an option.

Can Dynon point me to the resistor make and part so I can pot it in my existing plug, or alternatively advise the nominal resistance and temperature/resistance gradient?

 

[dynonsupport]

We don't publish the full characterizations of the sensors - we consider that proprietary data - but here are a few points that should help you along:

49.4F 1540 Ohms
103.5F 390 Ohms
150F 155 Ohms
220F 45 Ohms
280F 22.1 Ohms

 

[pbennett]

For the record, those points indicate a nominal resistance at 25C of about 750 ohm and a beta of about 3900K. I can't find anything close enough with the required temperature range from the usual sources. Looks like it's going to be the GRT probe for me.

To make it easier to convert from another supplier's EMS to Dynon, it would seem relatively straightforward for Dynon to include a "generic" sensor type in the setup for all the non-thermocouple temperature sensors. The EMS would read calibration values at zero and 100 deg C, and would then calculate and use the beta for the sensor. It should work for both linear and logarithmic resistive sensors, and could be used for pressure sensors where a water manometer was able to provide sufficient range for calibration.

Am I dreaming......?

Peter

 

[dynonsupport]

If you saw the curves on some of these sensors you'd be surprised at how bendy they are. SkyView will offer the ability to build your own characterizations, but on the D10/D100 series, there are too many back-end limitations to offer that capability.