From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Dyno Sheet
Date: Sat, 8 Aug 2020 09:39:12 +0800
References: <list-617363@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-617363@logan.com>
Message-Id: <6443E2E6-D14C-4F4B-8BD7-3749A75BB449@gmail.com>

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.

But I thought I=E2=80=99d 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=E2=80=99m simply wanting rough numbers =
for comparison as I play with the cowl flaps etc.

Does that make sense?

Steve

=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
> =
http://www.mosaic-industries.com/embedded-systems/microcontroller-projects=
/temperature-measurement/thermocouple/calibration-table#computing-cold-jun=
ction-voltages
>=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=E2=80=99s 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=C2=B0C virtual reference. For a type-K thermocouple, the
> voltage changes by 41=CE=BCV/=C2=B0C, which approximates the
> thermocouple characteristic with the following linear
> equation:
> VOUT =3D (41=CE=BCV / =C2=B0C) =E2=9C=95 (TR - TAMB)
> Where:
> VOUT is the thermocouple output voltage (=CE=BCV).
> TR is the temperature of the remote thermocouple junction
> (=C2=B0C).
> TAMB is the ambient temperature (=C2=B0C).
>=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 stephen.izett@gmail.com wrote:
>> Hi Finn.
>>=20
>> The pressure transducers I have can measure from memory a =
differential pressure of about 40=E2=80=9D 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=E2=80=99m 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=E2=80=99s 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
>>> 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 stephen.izett@gmail.com wrote:
>>>> 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.
>>> 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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>>>=20
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>=20
>=20
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