From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Dyno Sheet
Date: Sun, 9 Aug 2020 13:31:46 +0800
References: <list-618571@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-618571@logan.com>
Message-Id: <FF2EFB81-B584-4856-BCD7-094E16E03A2A@gmail.com>

Hi Finn.

Thats what I came to when I looked at the temp compensation, just =
wasn=E2=80=99t confident.
Thanks for the critique and calcs Finn.
Much appreciated.

Steve

> On 8 Aug 2020, at 10:05 pm, Finn Lassen finn.lassen@verizon.net =
<flyrotary@lancaironline.net> wrote:
>=20
> If max from the pressure sensors is 35mV it should work very well =
directly with the EGT inputs. Yes, brilliant. If 1.45psi is 35mV then =
the Skyview should show something like 850C before you change the =
Skyview default EGT setting for an EGT channel. (41uV/C)
>=20
> Just be aware that the temperature around the Skyview may influence =
the numbers. But if you're only interested in the differences between =
the 5 sensors and not the absolute numbers from flight to flight, it may =
not be a factor.
>=20
> A temperature probe on the Skyview, logged to one of the channels, =
should let you correct the EGT-Pressure channel values in the =
spreadsheet for zero-offset.
>=20
> Actually if the difference in Skyview ambient temperature is only 10 =
to 20C, it may prove insignificant (0.41 to 0.82mV compared to the =
35mV). In other words, an 8C difference in ambient temperature should =
only give a 1% offset error in your pressure readings. Don't know if you =
can even calibrate the EGT-Pressure inputs with a manometer that =
accurately.
>=20
> Finn
>=20
> On 8/7/2020 9:50 PM, Stephen Izett stephen.izett@gmail.com wrote:
>> So Finn. The fuller story is.
>>=20
>> I???m thinking I need to make up a string of 5 amps for my 5 =
transducers that I have already, to condition the few millivolts to =
0-3.3v for a pic micro or the sort.
>> Then I???m thinking how do I read and log the data.
>> But I???d like it synced with the dynon log data which is brilliant.
>> Look at a graph with pressures along side temps and speeds and =
altitudes???..
>>=20
>> And then I think of the abundant excess EGT inputs that are used to =
that kind of millivolt input all connected and logged and displayable. =
Just a bit of configuration and basically no circuit and development =
time required.
>>=20
>> Is it to good to be true. Maybe, but indications are its too easy.
>>=20
>> Brilliant if it works.
>>=20
>> Steve
>>=20
>>=20
>>=20
>>=20
>>=20
>>=20
>>=20
>>> On 8 Aug 2020, at 9:39 am, Stephen Izett stephen.izett@gmail.com =
<flyrotary@lancaironline.net>
>>>  wrote:
>>>=20
>>> Hi Finn
>>> I input a polynomial based on the raw data from the transducer data =
sheet.
>>> Full scale output is 35mV for 1.45psi.
>>> Offset at 0 reading is on average 20mV.
>>>=20
>>> But I thought I???d create a polynomial based on a new set of data =
using the water manometer incase the 'junction flux capacitor' was =
throwing out the readings to far.
>>> To far would be pretty far, as I???m simply wanting rough numbers =
for comparison as I play with the cowl flaps etc.
>>>=20
>>> Does that make sense?
>>>=20
>>> Steve
>>>=20
>>>=20
>>>=20
>>>=20
>>>> On 8 Aug 2020, at 9:14 am, Finn Lassen finn.lassen@verizon.net =
<flyrotary@lancaironline.net>
>>>>  wrote:
>>>>=20
>>>> Oh, I thought you'd already worked out the polynonmial values.
>>>>=20
>>>>=20
>>>> =
http://www.mosaic-industries.com/embedded-systems/microcontroller-projects=
/temperature-measurement/thermocouple/calibration-table#computing-cold-jun=
ction-voltages
>>>>=20
>>>>=20
>>>> probably way overkill.
>>>>=20
>>>> Input from a  type K (EGT) thermocouple would expect  a maximum of =
55mV (1370C +).
>>>>=20
>>>> So you may need a voltage divider, depending on the max expected =
outputs from the pressure sensors.
>>>> Then the trick will be to come up with a formula to counteract the =
chip's calculation.
>>>>=20
>>>> For the MAX6675 used in the EM3, it appears fairly simple:
>>>> The MAX6675 includes signal-conditioning hardware to
>>>> convert the thermocouple???s signal into a voltage compatible
>>>> with the input channels of the ADC. The T+ and T-  inputs
>>>> connect to internal circuitry that reduces the introduction
>>>> of noise errors from the thermocouple wires.
>>>> Before converting the thermoelectric voltages into
>>>> equivalent temperature values, it is necessary to compensate
>>>> for the difference between the thermocouple
>>>> cold-junction side (MAX6675 ambient temperature) and
>>>> a 0??C virtual reference. For a type-K thermocouple, the
>>>> voltage changes by 41??V/??C, which approximates the
>>>> thermocouple characteristic with the following linear
>>>> equation:
>>>> VOUT =3D (41??V / ??C) ??? (TR - TAMB)
>>>> Where:
>>>> VOUT is the thermocouple output voltage (??V).
>>>> TR is the temperature of the remote thermocouple junction
>>>> (??C).
>>>> TAMB is the ambient temperature (??C).
>>>>=20
>>>> Fortunately one of the channels in my EM3 is the temp of the PCB =
where the chip is located (TAMB).
>>>>=20
>>>> Don't know what chips are used in the Dynon Skyview.
>>>>=20
>>>> Finn
>>>>=20
>>>>=20
>>>> On 8/7/2020 7:14 PM, Stephen Izett=20
>>>> stephen.izett@gmail.com
>>>>  wrote:
>>>>=20
>>>>> Hi Finn.
>>>>>=20
>>>>> The pressure transducers I have can measure from memory a =
differential pressure of about 40??? of water.
>>>>> They have a millivolt output and in the process of cooking up a =
set of amps and thinking about the fact that Ive used up all my Engine =
Monitor inputs I pondered all those unused EGT and CHT inputs with =
amplifiers for millivolt input.
>>>>> I thought about the thermocouple compensation, impedance matching =
and common mode currents from the egt amps (don't really have a handle =
on these) and decided I probably wouldn't damage them!
>>>>> So I just thought Id try it out.
>>>>> I wired one straight to an egt input and the Dynon 5v supplied, =
and applied some lung pressure and the dynon display showed some life.
>>>>> I reworked a new Polynomial and she seems to provide a linear =
output over my lung burst pressure which from memory is a little over 1 =
psi.
>>>>> I???m not after certifiable numbers but have built a manometer to =
hopefully roughly calibrate the output by playing with the Polynomial.
>>>>> So lots of ignorance as far as what???s happening with the =
electrons at the interface but the results look promising and could be =
so much more helpful and easier than rigging a manometer in the cockpit.
>>>>>=20
>>>>> Happy to have my party spoilt by someone with knowledge of the =
compensation circuit used in the EGT amps.
>>>>>=20
>>>>> Cheers
>>>>>=20
>>>>> Steve
>>>>>=20
>>>>>=20
>>>>>=20
>>>>>=20
>>>>>=20
>>>>>=20
>>>>>=20
>>>>>> On 7 Aug 2020, at 11:01 pm, Finn Lassen finn.lassen@verizon.net =
<flyrotary@lancaironline.net>
>>>>>>  wrote:
>>>>>>=20
>>>>>> On 8/7/2020 10:00 AM, Stephen Izett=20
>>>>>> stephen.izett@gmail.com
>>>>>>  wrote:
>>>>>>=20
>>>>>>> I worked out that they interface quite nicely without any other =
circuitry with the Dynon Skyview's surplus EGT inputs via a new =
Polynomial in the sensor config settings.
>>>>>>>=20
>>>>>> I'm thinking of using my unused?? EGT inputs for current (Hall) =
sensors.
>>>>>>=20
>>>>>> How did you compensate for the EGT compensation?
>>>>>>=20
>>>>>> Finn
>>>>>>=20
>>>>>>=20
>>>>>> ---
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