CHT Probes

[DjAg5dosk2]

I just finished a set of engine runs minus cowl and top of plenum. I reused my Blue Mountain CHT bayonet probes. They are Aerosance p/n 11395-3 and I am seriously wondering if they are compatible with Skyview.

The CHTs never rose above 118 F and believe me they were at least 200 F or greater from past experience with engine and ambient conditions (94F+ oat).

I understood them to be J types, but am in doubt now. In you guys experience are these compatible? They apparently don't read until 230 F, but I am truly confused now. I double checked pins, grounds and connections. Any help is appreciated.  

Thank you
Howard Rhodes

 

[n223rv]

Hmmmm, so I have the same probes from my Blue Mountain and I assumed they would work as they read accurately at room temperature.... I read your note and was literally heading out to the hangar to rivet on my upper skin between my IP and firewall. I pulled a CHT probe and stuck a heat gun to it. I could only get it up to 126 degrees.... And it was BLAZING hot! I checked an EGT and it heated up to 400+ degrees really fast.....

So, I'm guessing it isn't currently supported... So do I need to swap out my CHT probes too?

 

[DjAg5dosk2]

After some research and input from Mike at Dynon, I discover they are thermistors, resistance signal with a voltage divider needed. You avionics pros and EE types can relate and correct me if I have goofed in my description. They are not compatible.

Solution, replace them with Lycoming bayonets from Dynon at $38/probe. Its always something. My car A/C went out the other day the first 92 F day with my wife driving. $811 later all is well with the car. In this case the airplane was cheaper. Victory. After the probes are on I can fly again.

Best
Howard

 

[n223rv]

Thanks for the feedback, I was litterally walking into the hangar to rivet on that top skin. Had I done so, it would have turned a 4 hour job into a 30 hour job..... I'll order up my new probes tomorrow.

Are my Blue Mountain EGT probes gonna be OK?

 

[dynonsupport]

If we knew more about the probes (resistances at temps) we can make them work on a SkyView system. They would need to plug in to general purpose inputs, not thermocouple inputs, but it's pretty easy beyond that.

It would use up 4 GP inputs (or 6 if you have a 6 cyl), so it matters if you are running out of those or not.

Never seen an EGT that isn't a K-type thermocouple so those should be fine.

 

[DjAg5dosk2]

The k type BMA EGTs work fine. Dynon would need one of my probes to get the calibration (resistance v temp) curve. This is the least painful way to do this. I also would have to change my inputs on the top side from thermocouple to GP, at the end of the day this is easier.

So the waiting for the FedEx/UPS truck begins.

Best
Howard

 

[Edwardoc]

I am converting from a BMA to Skyview.  Need to replace three CHT's as they are Aerosance Resistance type K Bayonets probes.  One cylinder has a type J dual output thermocouple probe which came with the LASAR system in order to provide an output to both the LASAR box and the engine instrument display.  I cannot find a part number or price for single CHT probes on the Dynon site.  Does Dynon sell individual probes and what is the price?  If not, any recommended sources to purchase them from?   I have the Dynon EGT/Cht wiring harness already to install.  And will the Westach oil temp sensor work?  I saw a post where someone said it would not.  Thanks

 

[trevpond]

It depends on the engine type. Rotax CHT are resistive sensors and I have used the standard Rotax supplied parts.

Trev

 

[dynonsupport]

The full price list, including individual prices for CHTs and other engine probes, are found on our home page under the PDF Price List link in the green box on the left.

 

[Edwardoc]

:-?I looked at all the LASAR posts concerning RPM and cannot determine if there was ever confirmation that the LASAR RPM output would drive the RPM circuit in the latest EMS since it puts out such a low voltage.
According to my LASAR install manual it outputs a square wave pulse from .5 volts minimum to 5 volts at the peak at 2 pulses per revolution. My intent is to hook the output to the low voltage input (Pin 34) on the EMS and see what happens. Is there any recent experience with the LASAR RPM hooked directly to the EMS on the low voltage pins in a Skyview system.

 

[dynonsupport]

On the low voltage RPM input, as long as it goes below 0.8V and above 2.1V, it should work. On the higher voltage pins the thresholds are 2.0V /5.1V.

 

[Edwardoc]

Thanks, I'll let you know in about two weeks if it works as I hope it will.

 

[Edwardoc]

:-[I was in error about the LASAR pulse output in my previous post.  Attached is a scan of what is in the install manual about the TACH output of the LASAR.  Please take a look at tell me if I will need to install some kind of pull down resistor or something or just give up and buy Vans GENTACH accessory.  I don't understand the diagram as it list the maximum voltage at the bottom of the pulse and the minimum at the top of the square wave pulse.  It is confusing to me.

 

[dynonsupport]

:-[I was in error about the LASAR pulse output in my previous post.  Attached is a scan of what is in the install manual about the TACH output of the LASAR.  Please take a look at tell me if I will need to install some kind of pull down resistor or something or just give up and buy Vans GENTACH accessory.  I don't understand the diagram as it list the maximum voltage at the bottom of the pulse and the minimum at the top of the square wave pulse.  It is confusing to me.

Edwardoc:

What I think the spec sheet is saying:
* The voltage level for a "low" will be no HIGHER than 1.5V
* The voltage level for a "high" will be no LOWER than 4.5V
(It would have been ideal if the spec sheet had stated what both the minimums and maximums were for each state.)

Restating from the previous response, for reliable pulse detection, the SV-EMS-220:
* Low Voltage RPM input(s) requires a low state to go below 0.8V and a high state to go above 2.1V
* RPM input(s) requires a low state to go below 2.0V and a high state to go above 5.1V.

So, bottom line, depending on the tolerances of your particular LASAR unit's output signal, it may work, it may not, on the SV-EMS-220 RPM input or the Low Voltage RPM input.

 

[dynonsupport]

Try hooking it to the low V input directly. It will probably just work. If it doesn't put a 22K or 27K resistor in series between the LASAR and the SkyView Low V input and then it should work.

--Dynon Engineering

 

[Edwardoc]

Did an engine run today. Have my LASAR RPM output hooked directly to Pin 34 (Low voltage input) on the EMS. I also have the EMS set for 2 pulses.revolution. My RPM is reading exactly double the actual. I have a tru-tack strobe Tach mounted and all readings were exactly double on the Skyview. So my question is shall I try 1 pulse per revolution or four pulses or install a drop down resistor in series to lower input voltage. Which would any of you EE majors or experienced installers recommend I try first. All other EMS reading were right on. Very happy with the results.

 

[dynonsupport]

Just increase it to 4 PPR. 1 PPR will make the reading double what it is now.

 

[Edwardoc]

Just an update on the Lasar RPM interface with the EMS 220. I have the laser RPM output hooked to Pin 34 on the EMS which is a low voltage input. I thought I had the EMS set up for 2 pulses/revolution on Pin 34. I really had it set for 1 pulse/revolution which is what caused it to read double the actual RPM. I corrected the setting to two pulses/revolution today and did an engine run. The RPM was dead on when compared to my strobe TACH up to an RPM of just under 1800 RPM. Above about 1800 RPM the displayed RPM began to fluctuate and any higher RPM would peg the display at 3000RPM. So at the higher RPMs the voltage must not drop long enough for the EMS to read. It reads correctly at any RPM below 1800. I'm thinking of putting a 22 ohm resistor in series to see what that does. When you say to install the resistor in series, do I just install in in line or do I connect the resistor to ground?

 

[dynonsupport]

Inline, but the resistor isn't going to be high enough to make a difference. Try something in the 20K-60K range.

 

[Edwardoc]

OK I meant a 22K resistor. I'll try that first and step it up if necessary. Thanks.